Björn Martin Valldor

• Dai, Tian; Ahmed, Razan M. N.; North, Eira Tiberg; Valldor, Björn Martin & Koposov, Alexey Y. (2026). Exploring Antiperovskite Cathodes for Na‐Ion Batteries. ChemSusChem. ISSN 1864-5631. 19(10). doi: 10.1002/cssc.70723. Fulltekst i vitenarkiv Vis sammendrag

  Recently discovered cathode materials with antiperovskite (AP) structure have shown a promising performance in Li‐ion batteries. However, their applicability in other battery chemistries have not been well explored. In this work, an AP‐based cathode material, Li 2 FeSeO, was systematically studied for application in Na‐ion batteries (NIBs). Delithiated Li 0.8 FeSeO was used as a precursor for preparing an Na‐ion analog. The electrochemical characterization of Na‐based AP cathode revealed a reversible galvanostatic cycling behavior with an initial capacity of 129 mA g −1 and a capacity retention of 57% after 200 cycles when cycled at a current density of 10 mA g −1 . Up to 0.75 Na + can be reversibly inserted into the AP framework. Synchrotron operando and ex situ X‐ray studies revealed a working mechanism based on a dual redox behavior including both Fe and Se, with Se being the main redox actor. The (de)sodiation capacity below expected value is possibly attributed to the formation of a core–shell structure formed due to kinetic limitation of Na + diffusion into bulk structure, thus preventing a full utilization of the available redox activity. These findings establish AP cathodes as viable candidates for NIBs and provide mechanistic insights that can guide their future structural optimization.

• Mohn, Chris Erik; Fjellvåg, Helmer; Ponniah, Vajeeston; Valldor, Björn Martin & Bergum, Kristin (2026). Benchmarking Density Functional Theory for Accurate Calculation of Nitride Band Gaps. Journal of Chemical Theory and Computation. ISSN 1549-9618. 22(3), s. 1321–1337. doi: 10.1021/acs.jctc.5c01703. Fulltekst i vitenarkiv Vis sammendrag

  We benchmark exchange-correlation functionals for the calculation of fundamental band gaps of inorganic nitrides. These include conventional functionals such as the local density approximation (LDA), the generalized-gradient (Perdew–Burke–Ernzerhof) approximation (PBE), simple Slater exchange functionals (SLOC), specialized LDA/GGA-derived high local exchange (HLE16) and Armiento–Kümmel semilocal (AK13) functionals, meta-GGA functionals including TASK, the modified Becke–Johnson functional (mBJ), and Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional, as well as quasiparticle GW theory. Since inorganic nitrides remain strongly under-represented in previous extensive benchmark studies, the current subdatabase contributes towards building a future large-scale balanced materials compilation of band gaps to benchmark theory. From a literature survey, we carefully collect 25 binary and 11 ternary nitrides with a focus on semiconductors spanning the periodic table, including ionic Li3N, antibixbyite-structured X3N2 (X = Be, Mg, Ca), early transition metals and lanthanides (e.g., ScN, YN, and LaN), ultrahard Th3P4-type structured M3N4 (M = Zr, Hf) compounds, promising photocatalysts Ta3N5, different polymorphs of III–V reference covalent nitrides (BN, AlN, GaN), and many M3N4 polymorphs (M = C, Si, and Ge) such as spinel-structured phases. Consistent with previous extensive benchmark tests, conventional LDA/PBE unsystematically largely underestimate band gaps with mean absolute errors (MAE) of >1.0 eV and mean absolute percentage errors (MAPE) of about 50%. Simple Slater exchange functional, SLOC, the GGA-derived AK13LDA and HLE16 functionals show improvement over LDA/PBE with MAE of 0.5–0.6 eV (MAPE ∼ 20–25%) with mBJ and HSE06 being the most accurate, with MAE = 0.30 and 0.28 eV (MAPE 12.1% and 11.1%), respectively. Strategies for the development of machine learning and the choice of appropriate exchange-correlation functionals for high-throughput large-scale material screening are discussed in light of these results.

• Bråtalien, Lars Botolv; Nilsen, Ola; Saha, Dipankar; Mohn, Chris Erik; Chatzitakis, Athanasios & Valldor, Björn Martin (2025). Layered anion ordering in oxide chloride Ca2TlO3Cl. Dalton Transactions. ISSN 1477-9226. 54(31), s. 11887–11894. doi: 10.1039/d5dt01111f. Fulltekst i vitenarkiv Vis sammendrag

  Single crystals and polycrystals of the novel compound Ca2TlO3Cl can be obtained by gas-phase and solid-state reactions, respectively. The title compound's crystal structure is hexagonal (a = 3.8806(2) Å, c = 18.6168(7) Å, P63/mmc) as measured by single crystal X-ray diffraction. A Rietveld refinement on powder X-ray diffraction data confirms this crystal structure. The atomic arrangement can be described as a cation ordered anti-structure of ScAl3C3, with a homoleptically, five-fold oxygen coordinated Tl3+ that consitutes corner-sharing trigonal bipyramids. Between these Tl–O sheets, a Cl-layer is found, making the whole structure quasi-2D. Thermal expansion coefficients in the range 15–290 K, as estimated from X-ray powder diffraction data, reveal that the relative length of the crystallographic c-axis (α33) is more temperature dependent than that of the a-axis (α11) lengths. The brown color of the polycrystalline title compound was investigated by spectroscopic reflectometry measurements. These data suggest an optical band gap of either 1.4 eV (indirect) or about 2.4–2.7 eV (direct), depending on interpretation model. However, density funciton theory calculations deliver a band structure that indicates that indirect band gaps are most likely, but with a size of about 2.7 eV. This discrepancy is discussed as a result of further local excitation phenomena, like charge-transfers and crystal defects. Photo-electrochemical investigations suggest that the title compound has an n-type character and is electrochemically activated by solar light.

• Dai, Tian; Park, Heesoo; Brennhagen, Anders; Andersen, Niels Højmark; Giorgetti, Marco & Valldor, Björn Martin [Vis alle 7 forfattere av denne artikkelen] (2025). Role of Dual-Redox Couples in Antiperovskite Li2FeSeO Cathodes. Chemistry of Materials. ISSN 0897-4756. 37(22), s. 9091–9104. doi: 10.1021/acs.chemmater.5c01341. Fulltekst i vitenarkiv Vis sammendrag

  In recent years, cathode materials for Li-ion batteries with antiperovskite (AP) structure have attracted growing interest due to their high capacity, chemical flexibility, low cost, and relatively simple synthesis. Among AP cathodes, Li2FeSeO has emerged as a promising candidate, demonstrating high capacity and good cycling stability. However, the lack of fundamental knowledge of the operating mechanism of AP cathodes significantly impedes efforts for further improvement. In this work, the redox mechanism and structural evolution of Li2FeSeO cathode material during electrochemical cycling are revealed through a combination of operando and ex situ X-ray diffraction, X-ray absorption spectroscopy, and Raman spectroscopy coupled with density functional theory calculations. Within the voltage range of 1–3 V vs Li/Li+, two stages in the (de)lithiation process during the initial cycle are determined, involving simultaneous redox activity of Se2– and Fe2+ with strong local structural distortion, leading to the formation of Se22– and Fe3+ species in the delithiated state and possible formation of Fe0 in the lithiated state. While the dual-redox activity of Se2– and Fe2+ ions is the key to high capacity, the −O–Fe–O– framework serves as a crucial element for reversibility during cycling. The study highlights the potential for optimizing the structural frameworks of AP cathodes.

• Gonano, Bruno; Fjellvåg, Øystein Slagtern; Steciuk, Gwladys; Marshall, Kenneth; Fjellvåg, Helmer & Valldor, Björn Martin (2025). PVDF fluorination of La₄Co₃O₁₀: Synthesis, structure and physical properties of La₄Co₃O₁₀F₂. Scripta Materialia. ISSN 1359-6462. 255. doi: 10.1016/j.scriptamat.2024.116379. Fulltekst i vitenarkiv Vis sammendrag

  Topochemical fluorination of oxides recently gained interest as it opens the way to substantial structural modifications and drastic changes in physical properties. We present a study of La4Co3O10F2, synthesized via low-temperature topochemical methods using polyvinylidene difluoride (PVDF). Using synchrotron X-ray powder diffraction, we find the compound to crystallize in a monoclinic cell (A2/a, with a = 5.32969(9) Å, b = 5.37555(1) Å, c = 30.5958(6) Å and β = 90.994(1) °), where the fluoride anions occupy the rock-salt layer's interstitial sites, inducing a tilting of the CoO6 octahedra. The physical properties of this novel compound are compared with those of the parent compound La4Co3O10, evidencing changes in resistivity and magnetism, highlighting the possibility of tuning magnetic interactions and electronic correlations through PVDF fluorination.

• Andersen, Eline Haug; Sannes, Johnny Andreas; Frøen, Emil Herman; Nilsen, Ola & Valldor, Björn Martin (2025). Diamagnetic sulfide Ba3Sc2S6 – With infinite [ScS6/2] chains as structural element. Journal of Solid State Chemistry. ISSN 0022-4596. 342. doi: 10.1016/j.jssc.2024.125105. Fulltekst i vitenarkiv Vis sammendrag

  The sulfide Ba3Sc2S6 was synthesized by the conventional high-temperature solid-state technique in an inert atmosphere, utilizing sealed silica ampules with low internal pressure of Ar gas. The crystal structure was determined by single crystal X-ray diffraction and can be described by a trigonal crystal lattice with rhombohedral symmetry, R 3‾ c (No. 167), with powder diffraction unit cell parameters a = 12.0402(1) Å and c = 13.3893(2) Å. The compound crystallizes with the K4CdCl6-type structure, which has been used to describe homologous sulfides. This crystal structure shares features with the 2H-perovskites but contains infinite 1D chains, Niggli notation [ScS6/2]∞1, consisting of alternating, distorted octahedra and trigonal prisms connected by face-sharing. Ba3Sc2S6 is diamagnetic, as determined from magnetic susceptibility measurements. UV–Vis spectroscopy data suggest a direct bandgap of about 2.88 eV. Further, DFT calculations reveal a band gap of about 1.8 eV and 2.9 eV using the PBE and the HSE06 functional, respectively, of which the latter agrees perfectly with UV–Vis observations.

• Havemann, R.; Hammerath, F.; Lepucki, P.; Fritsch, P.; Dioguardi, A.P. & Grönke, M. [Vis alle 14 forfattere av denne artikkelen] (2024). Comparison of local structure of CrCl3 bulk and nanocrystals above and below the structural phase transition. Physical review B (PRB). ISSN 2469-9950. 110(2). doi: 10.1103/PhysRevB.110.024202. Fulltekst i vitenarkiv
• Frøen, Emil Herman; Nowak, Domenic; Adler, Peter & Valldor, Björn Martin (2024). Synthesis and Properties of BaMTeS (M = Fe, Mn, Zn) and the Disordered Structural Analog BaGe<inf>0.5</inf>TeS. Inorganic Chemistry. ISSN 0020-1669. doi: 10.1021/acs.inorgchem.4c00146. Fulltekst i vitenarkiv Vis sammendrag

  A series of tertiary sulfide-tellurides, BaMxTeS (M = Fe, Mn, Zn, Ge), has been synthesized by solid-state synthesis. The compounds assume an orthorhombic crystal structure, described by the Cmcm (No. 63) space group, and are structural analogs of the BaMSO (M = Co, Zn) phases. The properties of all four analogs are investigated by DFT analysis. As only the BaFeTeS analog was prepared as a relatively pure phase, this homologue was subject to further experimental investigations, including heat capacity, magnetometry, and Mössbauer spectroscopy. BaFeTeS exhibits no obvious phase transition between 2 and 300 K, has no paramagnetic behavior, and lacks long-range magnetic ordering. However, the Mössbauer spectra, as well as electrical resistance data, indicate a hidden transition near 200 K that is tentatively explained by a dynamic charge-density-wave mechanism, based on a resonating valence bond (RVB) model.

• Dai, Tian; Kouoi, Xavier; Reynaud, Marine; Wagemaker, Marnix; Valldor, Björn Martin & Famprikis, Theodosios [Vis alle 7 forfattere av denne artikkelen] (2024). Antiperovskite active materials for metal-ion batteries: Expected advantages, limitations, and perspectives. Energy Storage Materials. ISSN 2405-8297. 68. doi: 10.1016/j.ensm.2024.103363. Fulltekst i vitenarkiv Vis sammendrag

  Metal-ion batteries, particularly lithium-ion (Li-ion) and sodium-ion (Na-ion) batteries, are currently among the most compelling technologies for energy storage. However, the growing demands driven by wide implementation of batteries in multiple applications call for further improvements of energy and power densities. Despite the incredible developments in this field observed over the past decades, the innovation of new active materials for metal-ion batteries has seen only modest progress, with primary focus on the optimization of already existing materials. The recent discovery of cathode materials with antiperovskite structure signals a promising direction for the creation of relatively simple materials geared towards electrochemical energy storage. These materials can be synthesized through relatively simple chemical processes using abundant elements and could offer stable electrochemical performance. Even though the number of reported examples is still limited, the structural flexibility of these materials offers multiple possibilities for tuning the chemical stability, operating voltage and capacity. This perspective provides a summary of the latest advancements in the field of antiperovskite active materials, highlighting both the advantages and the challenges associated with their integration into metal-ion batteries, and suggests possible future research directions towards practical implementation of this promising yet underexplored class of materials.

• Nowak, Domenic; Käppler, Erik; Knupfer, Martin; Subakti, Subakti; Lubk, Axel & Efremov, Dmitriy [Vis alle 14 forfattere av denne artikkelen] (2024). Exploring the heteroanionic 2D materials RhSeCl and RhTeCl as promising semiconductor materials. Dalton Transactions. ISSN 1477-9226. doi: 10.1039/d4dt01487a. Fulltekst i vitenarkiv Vis sammendrag

  Heteroanionic materials show promising potential as 2D semiconductors due to their tunable band gaps, making them excellent candidates for photocatalytic water splitting applications. We conducted detailed theoretical and experimental analysis of two selected materials by synthesizing crystals through chemical vapor transport and investigating the impact of anion variation on crystal structure and properties. Using powder X-ray diffraction and convergent beam electron diffraction, we elucidated the non-centrosymmetric space groups of these compounds. Thermochemical studies revealed the influence of the crystal structure on the decomposition points of both compounds. Theoretical investigations predict that both materials are indirect bandgap semiconductors, which is confirmed by electron energy loss spectroscopy and photoluminescence studies.

• Frøen, Emil Herman & Valldor, Björn Martin (2024). Synthesis and Properties of La<inf>14</inf>TME<inf>6</inf>CuS<inf>24</inf>O<inf>4</inf>, Exhibiting Multivalent Spin Chains (TME = Cr, Fe). ACS Omega. doi: 10.1021/acsomega.4c00564. Fulltekst i vitenarkiv Vis sammendrag

  Two homologues in a series of quinary oxysulfides, La14TME6CuS24O4 (TME = Cr or Fe), have been synthesized by solid-state synthesis in sealed ampules, and their structures are homologue to assume a novel crystal structure. X-ray diffraction analyses of single crystal and powder samples give a monoclinic lattice, described in the C2/m (No. 12) space group, with lattice parameters a = 15.3853(5) Å, b = 13.9729(5) Å, c = 10.5074(4) Å, and β = 116.227(3)° for the Cr analogue and a = 15.4303(2) Å, b = 14.0033(2) Å, c = 10.4909(2) Å, and β = 116.261(2)° for Fe. The crystal structure contains one-dimensional (1D) chains consisting of interconnected transition metal element (TME) trimers, which are further arranged into two-dimensional (2D) layers. These spin-chain planes are interspaced with 1D chains of lanthanum–oxygen coordinations and an apparent disordered occupation of copper sites. Alternating current (AC) and direct current (DC) magnetic susceptibility measurements show that the Cr and Fe analogues exhibit what is best described as spin-domain formation. Density functional theory (DFT) calculations suggest the formal oxidation state of the species is best represented in the form La14TME52+TME3+Cu+S24O4.

• Fjellvåg, Øystein Slagtern; Gonano, Bruno; Bernal, Fabian Leonardo Martinez; Amedi, Salah Bra; Lyu, Jike & Pomjakushin, Vladimir [Vis alle 12 forfattere av denne artikkelen] (2024). Order-to-Disorder Transition and Hydrogen Bonding in the Jahn-Teller Active NH4CrF3 Fluoroperovskite. Inorganic Chemistry. ISSN 0020-1669. 63(23), s. 10594–10602. doi: 10.1021/acs.inorgchem.4c00931. Fulltekst i vitenarkiv Vis sammendrag

  Large quantities of high-purity NH4CrF3 have been synthesized using a wet-chemical method, and its structural chemistry and magnetic properties are investigated in detail for the first time. NH4CrF3 is a tetragonal fluoroperovskite that displays an ordering of the ammonium (NH4+) groups at room temperature and C-type orbital ordering. The ammonium groups order and display distinct signs of hydrogen bonds to nearby fluoride anions by buckling the Cr–F–Cr angle away from 180°. The ammonium ordering remains up to 405 K, much higher than in other ammonium fluoroperovskites, indicating a correlation between the flexibility of the Jahn–Teller ion, the hydrogen bond formation, and the ammonium ordering. At 405 K, an order-to-disorder transition occurs, where the ammonium groups disorder, corresponding to a transition to higher symmetry. This is accompanied by a contraction of the unit cell from breaking hydrogen bonds, similar to the phenomenon observed in water ice melting. The compound orders antiferromagnetically with a Neél temperature of 60 K, an effective paramagnetic moment of 4.3 μB, and a Weiss temperature of −33 K. An A-type antiferromagnetic structure is identified by neutron diffraction, with an ordered moment of 3.72(2) μB.

• Frøen, Emil Herman; Adler, Peter & Valldor, Björn Martin (2024). Synthesis and properties of La<inf>18</inf>Fe<inf>5</inf>Cu<inf>4</inf>S<inf>26</inf>O<inf>8</inf>, a compound containing large magnetic clusters. Journal of Materials Chemistry C. ISSN 2050-7526. doi: 10.1039/d4tc03067b. Fulltekst i vitenarkiv Vis sammendrag

  A new quinary oxysulfide, La18Fe5Cu4S26O8, was synthesized by solid-state reaction, and is found to crystallize in a novel type structure. X-Ray diffraction on powder and single crystal samples reveal an orthorhombic lattice, which can be described with the Cmcm (no. 63) space group, with lattice constants a = 9.7999(2) Å, b = 26.1186(3) Å and c = 9.7767(1) Å. The matrix of the crystal structure is built up of layers of [La9O4]-units connected by sulfur ions and interspaced with transition metal arrangements. The structure exhibits a guest-in-host arrangement where the guest constitutes 1D chains of transition metal ions with substantial static disorder, which can be simulated using several split positions with partial occupancies. AC and DC magnetic susceptibility (χ) measurements reveal the formation of magnetic spin domains below ∼15 K; AC data indicate that the domain wall motions are thermally activated because Arrhenius-like frequency dependencies on both the real and imaginary parts of χ(T) are observed. However, the spin domains should have relatively large sizes because there is a significant entropy release during the domain formation, as indicated by specific heat measurements. Temperature-dependent 57Fe-Mössbauer spectroscopy data reveal that the compound lacks magnetic order down to 20 K, but exhibits signatures of spin-freezing at 6 K. Hence, it is suggested that the title compound exhibits large magnetic clusters with significant spin dynamics at high temperatures, which freeze into a disordered state at low temperatures.

• Sannes, Johnny Andreas; Chatzitakis, Athanasios; Andersen, Niels Højmark; Nilsen, Ola; Frøen, Emil Herman & Valldor, Björn Martin (2024). Characterization and Solid-State UV-Vis Investigations of Photoelectrocatalytically Active La5Cl7[TeO3]4, a Mixed Anion Compound with Alternating 2D Layers of Oxygen and Chlorine. Inorganic Chemistry. ISSN 0020-1669. 63(40), s. 18632–18641. doi: 10.1021/acs.inorgchem.4c02392. Fulltekst i vitenarkiv Vis sammendrag

  An oxide chloride, La5Cl7[TeO3]4, was synthesized using the conventional high-temperature solid-state synthesis technique in an inert atmosphere. This compound possesses a novel crystal structure that can be described with the triclinic space group P1̅ (No. 2) and unit cell parameters: a = 7.2634(3) Å, b = 8.1241(3) Å, c = 9.1993(3) Å, α = 79.373(1)°, β = 83.599(1)°, and γ = 82.511(1)°. The preference of Te(IV) to coordinate to oxygen and direct its lone pair toward the lower charged chlorine results in 2D layers of both oxygen and chlorine, alternating along the crystallographic b-direction. Homoleptic coordination, solely to oxygen, and heteroleptic coordination to oxygen and chlorine are observed for lanthanum, forming layers connected through edge-sharing polyhedra. In the crystal structure, two distinct tellurium positions are observed, with three close Te–O distances, emphasizing an active lone pair. The compound has been investigated by solid-state UV–vis measurements, and a band gap of 3.44 eV has been determined by DFT calculations. Detailed photoelectrochemical measurements clearly indicate that the title compound is photoelectrocatalytically active, showing an n-type behavior. Raman spectroscopy confirms that complex tellurite ions are present in the crystal structure; several observed bands can be assigned to Te–O stretching, reflecting the relatively low crystallographic symmetry of the title compound.

• Qureshi, Navid; Morrow, Ryan; Eltoukhy, Samar; Grinenko, Vadim; Buzanich, Ana Guilherme & Onykiienko, Yevhen A. [Vis alle 10 forfattere av denne artikkelen] (2024). Noncollinear Magnetic Structures in the Chiral Antiperovskite β-Fe<inf>2</inf>SeO. Inorganic Chemistry. ISSN 0020-1669. 63(48), s. 22712–22720. doi: 10.1021/acs.inorgchem.4c02916. Fulltekst i vitenarkiv
• Sharma, Rohit; Valldor, Björn Martin & Lorenz, Thomas (2024). Phonon thermal Hall effect in nonmagnetic Y2Ti2 O7. Physical review B (PRB). ISSN 2469-9950. 110(10). doi: 10.1103/PhysRevB.110.L100301. Fulltekst i vitenarkiv
• Nowak, Domenic; Valldor, Björn Martin; Rubrecht, Bastian; Froeschke, Samuel; Eltoukhy, Samar & Büchner, Bernd [Vis alle 8 forfattere av denne artikkelen] (2023). Crystal growth of the 2D Janus rhodium chalcohalide RhSeCl. Inorganic Chemistry Frontiers. ISSN 2052-1545. 10(10), s. 2911–2916. doi: 10.1039/d2qi02699f. Fulltekst i vitenarkiv Vis sammendrag

  Here, we report the discovery of the novel 2D Janus material RhSeCl.

• Sannes, Johnny Andreas & Valldor, Björn Martin (2023). Sr<inf>2</inf>Te<inf>4</inf>V<inf>2</inf>O<inf>13</inf>Cl<inf>2</inf>, a Layered Structure Forming a Canted Antiferromagnetic Ground State. Chemistry of Materials. ISSN 0897-4756. 35(5), s. 2355–2362. doi: 10.1021/acs.chemmater.3c02961. Fulltekst i vitenarkiv
• Sannes, Johnny Andreas; Gonano, Bruno; Fjellvåg, Øystein Slagtern; Kumar, Susmit; Nilsen, Ola & Valldor, Björn Martin (2023). X-ray and Neutron Diffraction Studies of SrTe<inf>2</inf>FeO<inf>6</inf>Cl, an Oxide Chloride with Rare Anion Ordering. Inorganic Chemistry. ISSN 0020-1669. 62(32), s. 13081–13088. doi: 10.1021/acs.inorgchem.3c01951. Fulltekst i vitenarkiv Vis sammendrag

  The oxychloride SrTe2FeO6Cl is obtained by high-temperature solid-state synthesis under inert conditions in closed reaction vessels. The compound crystallizes in a novel monoclinic crystal structure that is described in the space group P121/n1 (No. 14). The unit cell parameters, a = 10.2604(1) Å, b = 5.34556(5) Å, c = 26.6851(3) Å, and β = 93.6853(4)°, and atomic parameters were determined from synchrotron diffraction data, starting from a model that was obtained from single-crystal X-ray diffraction data. The anion lattice exhibits a rare ordering of oxide and chloride ions: one-dimensional zig-zag ladders of chlorine (squarelike motif) are surrounded by an oxygen matrix. Two different iron sites coordinated solely to oxygen are present in the structure, one octahedral and one square pyramidal, both distorted. Similarly, two different strontium coordinations are present; the first homoleptic coordinated to eight oxygen atoms and the second heteroleptic coordinated to four oxygen and four chlorine atoms in a fac-like manner. The lone pair of Te(IV) is directed toward the larger chlorine atoms. Magnetic susceptibility measurements confirm that Fe is +3 (d5) in the high-spin electronic configuration, exhibiting an almost ideal spin-only moment, μeff = 5.65 μB Fe–1. The slightly negative Weiss constant (θCW = −39 K) suggests dominating antiparallel spin-to-spin coupling in the paramagnetic temperature range, agreeing with an observed long-range antiferromagnetic spin ordering below Néel temperature, TN ∼ 13 K, and a broad second order-like anomaly in the specific heat measurement data. Low-temperature neutron diffraction data reveal that the antiferromagnetic ordered phase is C-type, with a k-vector (1/2, 1/2, 0) and ordered moment of 4.14(7) μB. The spin structure can be described as antiferromagnetic ordered layers stacked along the a-axis, forming layers of squares that alternate along the c-axis.

• Mohamed, M.A.A.; Saadallah, H.A.A.; Gonzalez-Martinez, I.G.; Hantusch, M.; Valldor, Björn Martin & Büchner, B. [Vis alle 8 forfattere av denne artikkelen] (2023). Mechanochemical synthesis of Li-rich (Li<inf>2</inf>Fe)SO cathode for Li-ion batteries. Green Chemistry. ISSN 1463-9262. 25(10), s. 3878–3887. doi: 10.1039/d3gc00861d. Fulltekst i vitenarkiv Vis sammendrag

  Li-rich antiperovskite (Li2Fe)SO with its high specific capacity is an attractive cathode material for Li-ion battery applications. While many battery materials depend on hazardous substances and their production is also rarely sustainable, we present an environmentally friendly and sustainable approach for the synthesis of Li-rich (Li2Fe)SO using mechanochemistry based on ball milling. This one step process enables preparing a large quantity of phase-pure (Li2Fe)SO using low-cost and non-toxic precursors, making it a viable alternative to current solid state synthetic method in terms of simplicity, laboratory safety and scalability. The obtained micro-sized particles are nearly spherical and have a small size distribution. To control the crystallinity and reduce the intrinsic defects of the ball-milled (Li2Fe)SO material, a post-heat treatment procedure was tested. Thermodynamic measurements confirmed the high thermal stability of the ball-milled (Li2Fe)SO material. Increasing the ball to powder weight ratio was found to be an effective strategy to decrease the milling time required for the synthesis, thus promoting energy saving. Overall, this work provides a practical guide for the green and scalable production of (Li2Fe)SO cathode material, as well as a method for particle modification for improved electrochemical properties.

• Frøen, Emil Herman; Adler, Peter & Valldor, Björn Martin (2023). Synthesis and Properties of Ba<inf>6</inf>Fe<inf>2</inf>Te<inf>3</inf>S<inf>7</inf>, with an Fe Dimer in a Magnetic Singlet State. Inorganic Chemistry. ISSN 0020-1669. 62(31), s. 12548–12556. doi: 10.1021/acs.inorgchem.3c01775. Fulltekst i vitenarkiv Vis sammendrag

  A new quaternary sulfide telluride, Ba6Fe2Te3S7, was synthesized by a solid-state reaction, and its crystal structure is novel. X-ray diffraction data on powder and single crystals reveal an orthorhombic lattice with a = 9.7543(3) Å, b = 18.2766(6) Å, and c = 12.0549(4) Å, and the noncentrosymmetric space group Cmc21 (No. 36). The properties of the compound were studied by magnetic susceptibility investigations, specific heat measurements, Mössbauer spectroscopy, and density functional theory calculations. Assuming Ba2+ and, as verified by the Mössbauer spectra, Fe3+, the charge balance requires the presence of a polytelluride, suggested to be a straight-chain [Te34–] polyanion. Further, the crystal structure contains [Fe2S7]8– dimers of two vertex-sharing tetrahedra, with a nearly linear Fe–S–Fe atom arrangement. The dimer exhibits antiferromagnetic coupling, with a coupling constant J = −10.5 meV (H = −2JS1S2) and S = 5/2, resulting in a spin singlet ground state. The interdimer magnetic interaction is so weak that the magnetic dimers can be treated as individuals.

• Sannes, Johnny Andreas; Malayil, Ranjith K. Kizhake; Corredor, Laura T.; Wolter, Anja U. B.; Grafe, Hans-Joachim & Valldor, Björn Martin (2023). Synthesis and Characterization of Oxide Chloride Sr<inf>2</inf>VO<inf>3</inf>Cl, a Layered S = 1 Compound. ACS Omega. 8(15), s. 14233–14239. doi: 10.1021/acsomega.3c01151. Fulltekst i vitenarkiv Vis sammendrag

  The mixed-anion compound with composition Sr2VO3Cl has been synthesized for the first time, using the conventional high-temperature solid-state synthesis technique in a closed silica ampule under inert conditions. This compound belongs to the known Sr2TmO3Cl (Tm = Sc, Mn, Fe, Co, Ni) family, but with Tm = V. All homologues within this family can be described with the tetragonal space group P4/nmm (No. 129); from a Rietveld refinement of powder X-ray diffraction data on the Tm = V homologue, the unit cell parameters were determined to a = 3.95974(8) and c = 14.0660(4) Å, and the atomic parameters in the crystal structure could be estimated. The synthesized powder is black, implying that the compound is a semiconductor. The magnetic investigations suggest that Sr2VO3Cl is a paramagnet at high temperatures, exhibiting a μeff = 2.0 μB V–1 and antiferromagnetic (AFM) interactions between the magnetic vanadium spins (θCW = −50 K), in line with the V–O–V advantageous super-exchange paths in the V–O layers. Specific heat capacity studies indicate two small anomalies around 5 and 35 K, which however are not associated with long-range magnetic ordering. 35Cl ss-NMR investigations suggest a slow spin freezing below 4.2 K resulting in a glassy-like spin ground state.

• Wang, Guangmei; Dorn, Katharina V.; Siebeneichler, Stefanie; Valldor, Björn Martin; Smetana, Volodymyr & Mudring, Anja-Verena (2022). The missing link between zeolites and polyoxometalates. Science Advances. 8(46), s. eadd9320–eadd9320. doi: 10.1126/sciadv.add9320. Fulltekst i vitenarkiv
• Siribbal, Shifaa M.; Ilyas, Shaista; Renner, Alexander M.; Iqbal, Sumiya; Vázquez, Sergio Muñoz & Moawia, Abubakar [Vis alle 10 forfattere av denne artikkelen] (2022). Click functionalized biocompatible gadolinium oxide core-shell nanocarriers for imaging of breast cancer cells. RSC Advances. 12(49), s. 31830–31845. doi: 10.1039/d2ra00347c. Fulltekst i vitenarkiv Vis sammendrag

  Site-specific delivery using functionalized nanocarriers is in high demand in imaging applications of modern clinical research. To improve the imaging capabilities of conventionally used contrast agents and expand the targeting accuracy, functional gadolinium oxide based nanocarriers originated from homogeneous core shells structures (Gd2O3@SiO2@Fe3O4) were developed using a multilayer formation approach. The synthesis and chemical configuration for the covalent binding of macrocyclic chelating agents and estrogen targeting molecules on these nanocarriers were designed by a two-step chemical synthesis method. Initially, SiO2@Fe3O4 structures were prepared and encapsulated with a homogenous thin Gd2O3 overlayer. The exterior surface of the as-prepared carriers offered chemical binding with a breast cancer specific estrogen molecule, covalently grafted through a Click-Chemistry protocol. In the next step, to enhance the diagnostic imaging capabilities of these carriers, thiocyanate-linked chelator molecule, DOTA, was attached to the surface of estrogen bound Gd2O3@SiO2@Fe3O4 using basic reaction conditions. The active amino groups before and after conjugation of estrogen molecules on the surface were quantified using a fluorescamine based approach. Due to the covalent binding of the macrocyclic chelator to the Gd2O3@SiO2@Fe3O4 surface, core shell carriers showed potential radiolabeling efficiency using positron emitter radionuclide, gallium-68 (68Ga). Intracellular uptake of estrogen-conjugated carriers was evaluated with MCF7 breast cancer cell lines using confocal laser scanning microscopy and fluorescent flow cytometry. In addition, in vitro cytotoxicity studies of functional nanocarriers as compared to bare nanoparticles showed reduced toxicity to HEK-293 cells demonstrating the role of surface attached molecules in preventing direct exposure of the Gd2O3 surface to the cells. The as-developed gadolinium based nanocarriers presented excellent capabilities as biocompatible target-specific imaging probes which indicates great potential in the field of dual-mode contrast agents.

• Schweika, W.; Valldor, Björn Martin; Reim, J.D. & Rößler, U.K. (2022). Chiral Spin Liquid Ground State in YBaCo3FeO7. Physical Review X. 12(2). doi: 10.1103/PhysRevX.12.021029. Fulltekst i vitenarkiv Vis sammendrag

  A chiral spin liquid state is discovered in the highly frustrated, noncentrosymmetric swedenborgite compound YBaCo3FeO7, a layered kagome system of hexagonal symmetry, by advanced polarized neutron scattering from a single domain crystalline sample. The observed diffuse magnetic neutron scattering has an antisymmetric property that relates to its specific chirality, which consists of three cycloidal waves perpendicular to the c axis, forming an entity of cylindrical symmetry. Chirality and symmetry agree with relevant antisymmetric exchanges arising from broken spatial parity. Applying a Fourier analysis to the chiral interference pattern, with distinction between kagome sites and the connecting trigonal interlayer sites of threefold symmetry, the chiral spin correlation function is determined. Characteristic chiral waves originate from the trigonal sites and extend over several periods in the kagome planes. The chiral spin liquid is remarkably stable at low temperatures despite strong antiferromagnetic spin exchange. The observation raises a challenge, since the commonly accepted ground states in condensed matter either have crystalline long-range order or form a quantum liquid. We show that, within the classical theory of magnetic order, a disordered ground state may arise from chirality. The present scenario, with antisymmetric exchange acting as a frustrating gauge background that stabilizes local spin lumps, is similar to the avoided phase transition in coupled gauge and matter fields for subnuclear particles.

• Vogl, Michael; Valldor, Björn Martin; Piening, Roman Boy; Efremov, Dmitri V.; Büchner, Bernd & Aswartham, Saicharan (2022). Synthesis and Physical Properties of Iridium-Based Sulfide Ca1−xIr4S6(S2) [x = 0.23–0.33]. Electronic Materials. 3(1), s. 41–52. doi: 10.3390/electronicmat3010004. Fulltekst i vitenarkiv
• Qureshi, Navid; Ouladdiaf, Bachir; Senyshyn, Anatoliy; Caignaert, Vincent & Valldor, Björn Martin (2022). Non-collinear magnetic structures in the magnetoelectric Swedenborgite CaBaFe4O7 derived by powder and single-crystal neutron diffraction. SciPost Physics Core. 5(1). doi: 10.21468/SciPostPhysCore.5.1.007. Fulltekst i vitenarkiv Vis sammendrag

  We have investigated the magnetic structures of the Swedenborgite compound CaBaFe4O7 using magnetic susceptibility and neutron diffraction experiments on powder and single-crystal samples. Below TN1 = 274 K the system orders in a ferrimagnetic structure with spins along the c axis and an additional antiferromagnetic component within the kagome plane which obviously cannot satisfy all exchange interactions. Competing single-ion anisotropy and exchange interactions lead to a transition into a multi-q conical structure at TN2 = 202 K. The derivation of the complex ordering scheme below TN2 is an important step towards the understanding of the magnetoelectric effect under magnetic fields in this polar ferrimagnet.

• Qureshi, N.; Morrow, R.; Valldor, Björn Martin; Puente-Orench, I. & Adler, P. (2022). Magnetic structure of the swedenborgite compound CaBaMn2Fe2 O7 derived by powder neutron diffraction and Mössbauer spectroscopy. Physical review B (PRB). ISSN 2469-9950. 106(14). doi: 10.1103/PhysRevB.106.144428. Fulltekst i vitenarkiv
• Mohamed, M.A.A.; Gorbunov, Mikhail V.; Valldor, Björn Martin; Hampel, Silke; Gräßler, Nico & Mikhailova, Daria (2021). Tuning the electrochemical properties by anionic substitution of Li-rich antiperovskite (Li2Fe)S1−xSexO cathodes for Li-ion batteries. Journal of Materials Chemistry A. ISSN 2050-7488. 9(40), s. 23095–23105. doi: 10.1039/d1ta05130j. Fulltekst i vitenarkiv Vis sammendrag

  The development of electrode materials with multielectron redox functionality is imperative for next-generation Li-ion batteries with a high gravimetric capacity. Within this context, a Li-rich (Li2Fe)SO antiperovskite cathode is a promising candidate exhibiting such multielectron cationic and anionic redox features, resulting in a reversible extraction/insertion of about 1.2 Li+ per formula unit. However, it suffers from poor structural and cycling stabilities which hinder its practical application. Herein, we systematically investigate the effect of anionic substitution of S with Se on the structural, thermal and electrochemical properties of the (Li2Fe)SO cathode. With increasing the Se content, higher thermal stability and lower sensitivity to moist air were obtained. Multi-stage cationic and anionic redox processes characterized the electrochemical activity of all the prepared (Li2Fe)S1−xSexO solid solutions. The cationic redox process was shifted to higher potentials while the anionic redox process was shifted to lower potentials upon the increase of the Se content. Among the various synthesized compositions, (Li2Fe)S0.7Se0.3O exhibited the best electrochemical performance with a high discharge capacity of ∼245 mA h g−1 and an outstanding cycling stability at 0.1C current rate as well as nearly 100% capacity recovery after rate capability tests of 50 cycles. To deeply characterize (Li2Fe)S0.7Se0.3O, various ex situ and in situ techniques were applied. In contrast to (Li2Fe)SO, the substituted (Li2Fe)S0.7Se0.3O material remains crystalline without the evolution of secondary phases or superstructures after the first charge/discharge cycle highlighting its enhanced structural stability. Similar to (Li2Fe)SO, both the cation (Fe) and anions (S/Se) from (Li2Fe)S0.7Se0.3O participate in the redox process.

• Kim, J.K.; Ranjith, K.M.; Burkhardt, U.; Prots, Yu; Baenitz, M. & Valldor, Björn Martin (2020). Impact of inversion symmetry on a quasi-1D S = 1 system. Journal of Physics: Condensed Matter. ISSN 0953-8984. 32(22), s. 1–9. doi: 10.1088/1361-648X/ab7134. Fulltekst i vitenarkiv Vis sammendrag

  Here, we report the synthesis and magnetic properties of a novel, centrosymmetric, quasi-1D spin chain system La3VWS3O6, with hexagonal crystal structure (P63/m, a  =  9.460 76(3), c  =  5.518 09(2) Å). Pure powders were obtained by solid-state reactions from La2O3, WO3 and metal powders of V and W. X-ray powder diffraction, specific heat, magnetization, 139La-nuclear magnetic resonance (NMR), and electric resistivity measurements indicate that the compound is a low dimensional magnet with an S  =  1 spin chain that exhibits no sign of magnetic ordering above 2 K. A single ion anisotropy (D/kB ~ 10 K), caused by magneto-crystalline effects, is probably responsible for a thermodynamic entropy release at lower temperatures, which concurs with 139La-NMR data. By detailed comparison with non-centrosymmetric Ba3V2S4O3, having a very similar magnetic lattice, it is obvious that the presence of crystallographic inversion symmetry has an effect on the behaviour of the magnetic chains.

• Schütz, Markus B.; Ilyas, Shaista; Lê, Khan; Valldor, Björn Martin & Mathur, Sanjay (2020). Nanoparticle Arrays Having Directed Hybrid Topology via Covalent Self-Assembly of Iron Oxide and Silica Nanoparticles. ACS Applied Nano Materials. 3(6), s. 5936–5943. doi: 10.1021/acsanm.0c01097. Fulltekst i vitenarkiv
• Adler, Peter; Medvedev, Sergey A.; Valldor, Björn Martin; Naumov, Pavel G.; Elghazali, Moaz A. & Rüffer, Rudolf (2020). Pressure-induced collapse of large-moment magnetic order and localized-to-itinerant electronic transition in the host-guest compound [C s6Cl] [F e24 S e26]. Physical review B (PRB). ISSN 2469-9950. 101(9). doi: 10.1103/PhysRevB.101.094433. Fulltekst i vitenarkiv Vis sammendrag

  The magnetic properties of iron chalcogenides and pnictides have found much interest as magnetic fluctuations are suggested to drive the formation of Cooper pairs in iron-based superconductors. Here, we have studied the pressure dependence of the magnetic and electrical properties of the iron-selenide compound [Cs6Cl][Fe24Se26] by energy-domain synchrotron Mössbauer spectroscopy up to 17 GPa and by resistivity measurements up to 45 GPa. Similar to the binary superconductor Fe1+xSe, the host-guest-type crystal structure of [Cs6Cl][Fe24Se26] contains edge-sharing FeSe4 units, but its ground state is antiferromagnetically ordered. A complex hyperfine pattern suggests a nontrivial spin structure like a spin spiral with large magnetic moments in the range 2 to 3μB at ambient pressure. High pressure drastically suppresses the Néel temperature from 220 K at ambient pressure to below 30 K at 12 GPa. Between 5 and 10 GPa the complex magnetic hyperfine pattern collapses and a low-moment magnetic ground state emerges at higher pressures. A concomitant decrease of the resistivity by several orders of magnitude indicates that the electronic system becomes more itinerant. Full metallization occurs near 25 GPa, but no sign of superconductivity down to 1.5 K was found at any pressure. It is suggested that the insulating ground state of [Cs6Cl][Fe24Se26] corresponds to an orbitally selective Mott phase, which due to an increased bandwidth, is transformed into a Hund's metal state under pressure.

• Siebeneichler, Stefanie; Dorn, Katharina V.; Smetana, Volodymyr; Valldor, Björn Martin & Mudring, Anja-Verena (2020). A soft chemistry approach to the synthesis of single crystalline and highly pure (NH4)CoF3 for optical and magnetic investigations. Journal of Chemical Physics. ISSN 0021-9606. 153(10). doi: 10.1063/5.0023343. Fulltekst i vitenarkiv
• Gorbunov, Mikhail V.; Carrocci, Salvatore; Maletti, Sebastian; Valldor, Björn Martin; Doert, Thomas & Hampel, Silke [Vis alle 9 forfattere av denne artikkelen] (2020). Synthesis of (Li2Fe1–yMny)SO Antiperovskites with Comprehensive Investigations of (Li2Fe0.5Mn0.5)SO as Cathode in Li-ion Batteries. Inorganic Chemistry. ISSN 0020-1669. 59(21), s. 15626–15635. doi: 10.1021/acs.inorgchem.0c01753. Fulltekst i vitenarkiv
• Valldor, Björn Martin; Galle, Lydia; Eichler, Franziska; Wolf, Andre & Morrow, Ryan (2019). Synthesis, Crystal Structure, and Optical Characterization of the Sulfide Chloride Oxide CsBa6V4S12ClO4 with a Near-Infrared Fluorescence. Inorganic Chemistry. ISSN 0020-1669. 58(21), s. 14728–14733. doi: 10.1021/acs.inorgchem.9b02393. Fulltekst i vitenarkiv

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• Kjeldby, Snorre Braathen; Olsen, Vegard Skiftestad; Frodason, Ymir Kalmann; Zacharaki, Eirini; Cooil, Simon Phillip & Vines, Lasse [Vis alle 12 forfattere av denne artikkelen] (2025). Thin film top cell absorbers for multijunction solar cells. Fulltekst i vitenarkiv
• Dinesh, Dharsana Pulikkottil; Valldor, Björn Martin; Nilsen, Ola & Sønsteby, Henrik Hovde (2024). Ozone based Atomic Layer Deposition of Titanium Dioxide (TiO2 ) using TTIP. Fulltekst i vitenarkiv
• Dinesh, Dharsana Pulikkottil; Nilsen, Ola; Valldor, Björn Martin & Sønsteby, Henrik Hovde (2024). Barium Titanate Thin Films with Ozone Assisted ALD: Binary Oxides Deposition. Fulltekst i vitenarkiv
• Frøen, Emil Herman; Adler, Peter & Valldor, Björn Martin (2023). The Absence of Expected Paramagnetic Behaviour in Ba6Fe2Te3S7. Fulltekst i vitenarkiv
• Qureshi, Navid; Morrow, Ryan; Eltoukhy, Samar; Grinenko, Vadim; Onykiienko, Yevhen & Inosov, Dmytro [Vis alle 8 forfattere av denne artikkelen] (2023). Morin transition in beta-Fe2SeO? Fulltekst i vitenarkiv
• Sannes, Johnny Andreas; Gonano, Bruno; Fjellvåg, Øystein Slagtern; Kumar, Susmit; Nilsen, Ola & Valldor, Björn Martin (2023). X-ray and neutron diffraction studies of SrTe2FeO6Cl, an oxide chloride with rare ordering of anions. Fulltekst i vitenarkiv
• Valldor, Björn Martin (2023). Magnetic order and disorder in Swedenborgites. Fulltekst i vitenarkiv
• Siribbal, Shifaa M.; Ilyas, Shaista; Renner, Alexander M.; Iqbal, Sumiya; Vázquez, Sergio Muñoz & Moawia, Abubakar [Vis alle 10 forfattere av denne artikkelen] (2022). Erratum: Click functionalized biocompatible gadolinium oxide core-shell nanocarriers for imaging of breast cancer cells (RSC Adv. (2022) 12 (31830–31845) DOI: 10.1039/D2RA00347C). RSC Advances. 12(53), s. 34639–34639. doi: 10.1039/d2ra90119f. Fulltekst i vitenarkiv
• Valldor, Björn Martin (2022). Neumann’s principle applied on magnetic chains. Fulltekst i vitenarkiv
• Valldor, Björn Martin (2021). Two-anion chemistry and its possibilities. Fulltekst i vitenarkiv

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