Dipankar Saha

• Ghosh, Rupam; Dutta, Shrestha; Joseph, Irin Mary; Roy, Ushita; Rathod, Radha & Saha, Dipankar [Show all 9 contributors for this article] (2026). Local Atomic Structure of Molybdenum-Based Vacancy-Ordered Perovskites: A Direct Evidence of Oxyhalide Formation and Selective Doping. ACS Applied Energy Materials. 9(11), p. 7366–7376. doi: 10.1021/acsaem.6c01186. Full text in Research Archive
• 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), p. 11887–11894. doi: 10.1039/d5dt01111f. Full text in Research Archive Show summary

  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.

• Brennhagen, Anders; Saha, Dipankar; Berdiell, Izar Capel; Jr, Andrew Pastusic; Koposova, Marta & Wragg, David S. [Show all 10 contributors for this article] (2025). Mechanical deformations in battery current collectors observed by operando X-ray diffraction on Si/graphite anodes. Chemical Communications. ISSN 1359-7345. 61(98), p. 19485–19488. doi: 10.1039/d5cc04995d. Full text in Research Archive Show summary

  Current collectors in Li-ion batteries are often considered passive components with minimal influence on performance. However, materials with large expansion during lithiation may influence the current collector. Herein, we demonstrate mechanical deformations of the Cu current collector in Si/graphite electrodes using operando X-ray diffraction.

• Fjellvåg, Øystein Slagtern; Saha, Dipankar; Chernyshov, Dmitry; Bernal, Fabian Leonardo Martinez; Fjellvåg, Helmer & Hauback, Bjørn Christian [Show all 7 contributors for this article] (2025). On the low temperature crystal structure of KCrF3. Journal of Solid State Chemistry. ISSN 0022-4596. 352. doi: 10.1016/j.jssc.2025.125558. Full text in Research Archive Show summary

  We report on the low-temperature phase transition and crystal structure of KCrF3, revisiting the previously reported reentrant tetragonal transition at 5 K. Using high-resolution X-ray powder diffraction across a temperature range of 5–300 K in two independent experiments, we study the structural developments and apply symmetry-mode analysis to describe the transition from tetragonal to monoclinic. A tilt of the CrF6-octahedra drives the symmetry reduction. Evaluation of the bond lengths and angles shows no sign of a reentrant or incipient transition. Our findings confirm that the low-temperature phase of KCrF3 is monoclinic.

• Mondal, Shekhar; Sharma, Gauri; Bhoi, Sunanda; Wadepalli, Sadashiv; Santra, Pralay K. & Saha, Dipankar [Show all 7 contributors for this article] (2024). A-site composition tuning in methylammonium-based metal halide perovskite colloidal nanocrystals. Nanoscale. ISSN 2040-3364. doi: 10.1039/d4nr03422h. Full text in Research Archive Show summary

  Utilizing the soft-lattice nature of metal halide perovskites, we employ post-synthetic cross-ion exchange to synthesize a series of narrow band-gap colloidal nanocrystals of methylammonium-based lead iodide solid solutions of composition FAxMA1−xPbI3, as well as those of triple-cation composition CsxFAyMA1−x−yPbI3 (TCPbI3). The ability to finely tune the compositions not only helps in tailoring the optical properties in the near-infrared region, but also improves the stability of these colloidal nanocrystals towards moisture, which has been demonstrated as compared to their bulk counterparts. The thermal stability of these solid solutions is also comparable to that of the bulk, as evidenced by thermogravimetric studies. This study helps in expanding the composition space of stable 3D lead halide perovskites with band gaps suitable and relevant for photovoltaic applications.

• Gayathri, Sampath; Arunkumar, Paulraj; Saha, Dipankar; Acharya, Dolan; Karthikeyan, Jeyakumar & Han, Jong Hun (2024). Modulating Coordination-Driven Metal-Oxygen Interaction Triggers Oxygen Evolution in Polymorphic and High-Entropy Phosphate Electrocatalyst. Advanced Functional Materials. ISSN 1616-301X. doi: 10.1002/adfm.202416834. Full text in Research Archive
• Saha, Dipankar; Sławiński, Wojciech A.; Kumar, Susmit & Fjellvåg, Helmer (2024). Local Symmetry Deviation from the Average Structure of MnAs Revealed by Pair Distribution Function. Inorganic Chemistry. ISSN 0020-1669. 63, p. 15503–15509. doi: 10.1021/acs.inorgchem.4c02667. Full text in Research Archive Show summary

  MnAs is an interesting material due to its magnetocaloric properties, which can be utilized in magnetic refrigeration. However, despite major efforts, its magnetic refrigeration performances in the substituted forms could not be improved compared to the parent MnAs phase. Both small and big box modeling of the pair distribution function of MnAs for the local structure description and powder X-ray diffraction for the average structure reveal an inherent local orthorhombic distortion in the hexagonal structure of MnAs. As a result of this distortion, any modification to the hexagonal structure results in an orthorhombic structure and a weaker magnetocaloric performance. This study highlights the importance of studying local distortion in magnetic materials. This is achieved by combining X-ray absorption spectroscopy with total scattering X-ray diffraction.

• Saha, Dipankar; Kumar, Susmit; Gonano, Bruno Raymond Gino; Sjåstad, Anja Olafsen & Fjellvåg, Helmer (2021). Total Scattering Study of Local Structural Changes in MnAs1-xPx Influenced by Magnetic Interactions. Chemistry of Materials. ISSN 0897-4756. 33, p. 2576–2584. doi: 10.1021/acs.chemmater.1c00128. Full text in Research Archive Show summary

  The interplay between fluctuations of the local structure and magnetic interactions is of great importance for phenomena like superconductivity, colossal magnetoresistance, and frustrated magnetism. Such local distortions are often subtle and difficult to probe. The metallic MnAs1–xPx (x = 0.06, 0.12, 0.18) solid solution represents a sensitive model system, currently analyzed by variable-temperature X-ray total scattering (TS). A second-order transition (Pnma to P63/mmc) occurs on heating, intimately coupled to magnetic ordering at low temperatures and a temperature-induced low- to high-spin transition for manganese. Intrinsic compositional fluctuations along with a particular magneto-volumetric coupling to low- and high-spin like states triggers formation of local high-symmetry nanosized domains in an orthorhombically deformed matrix that eventually converts globally into a high-temperature hexagonal arrangement. These features are only traced by TS analyses, whereas diffraction provides a regular second-order transition with, e.g., cationic displacements defined by Rietveld analysis acting as order parameter. The coexistence model provides good fits of the TS data and, on average, translates nicely into a continuous V(T) thermal expansion relation with maximum expansivity in the range where the TS data shows the largest difference between local (<20 Å) and intermediate-range (20–80 Å) structures. The degree of local distortions, Mn(As, P)6 octahedra inclusive, is a result of volume-dependent electronic properties as well as magnetic interactions. This study demonstrates how X-ray TS can conveniently give essential insights into the local symmetry fluctuations from the perspective of strong magnetic interactions.

• Gayathri, Sampath; Arunkumar, Paulraj; Saha, Dipankar & Han, Jong Hun (2021). Composition engineering of ZIF-derived cobalt phosphide/cobalt monoxide heterostructures for high-performance asymmetric supercapacitors. Journal of Colloid and Interface Science. ISSN 0021-9797. 588, p. 557–570. doi: 10.1016/j.jcis.2020.11.129. Full text in Research Archive Show summary

  The fabrication of interpenetrated heterostructures from desirable energy materials for the development of efficient supercapacitors is promising yet challenging. Herein, a leaf-shaped cobalt phosphide/cobalt oxide heterostructure, (CoPx)1-y/CoOy (0.44 > y > 0.06), was synthesized from 2D-zeolitic-imidazolate-framework (ZIF-Co-L) molecular precursor via phosphidation of the Co3O4 intermediate. The efficient construction of heterostructure through the variation of surface/bulk composition significantly alters the interfacial properties and electronic structure, yielding enhanced supercapacitor performance. Further, gas-phase phosphidation entails a core–shell formation mechanism via gas diffusion, regulated by the Kirkendall effect. The optimized heterostructure (y = 0.10) exhibits remarkable interfacial properties derived from the CoO/Co0/CoP interface, thus facilitating a high specific capacitance (467 F g−1 at 5 A g−1) and excellent cycling stability (~91% after 10000 cycles) at 30 A g−1. A further increase in the cyclability (~107%) was achieved by employing a graphene hybrid. Further, an asymmetric supercapacitor device was fabricated, that delivers reasonably high energy density of 12.7 Wh kg−1 at a power density of 370 W kg−1 and cycling stability of ~93% after 10000 cycles. This study reports on the modulation of interfacial properties of CoPx/CoO heterostructure to enhance energy storage performance via bulk/surface compositional variation, thereby providing a strategy to develop heterostructure electrodes for high-performance supercapacitor.

• Gonano, Bruno Raymond Gino; Fjellvåg, Øystein; Steciuk, Gwladys; Guillou, Francois; Saha, Dipankar & Pelloquin, Denis [Show all 7 contributors for this article] (2021). Tuning the Magnetically Segregated Nanolayering in Mn–Ni–As Intermetallics. Chemistry of Materials. ISSN 0897-4756. 33(8), p. 3002–3010. doi: 10.1021/acs.chemmater.1c00760. Full text in Research Archive Show summary

  2D materials exhibiting alternating ferro- and non-ferromagnetic layers are highly sought due to their potential for applications. In this work, we demonstrate, through the use of robust methodology, the existence of single-phase, Mn1–xNixAs (0.25 ≤ x ≤ 0.50), with a unique intrinsic nanostructuring where the thickness of MnAs and NiAs nanolayers can be tuned via the composition, x. We describe a periodic variation of nanolayers of edge-sharing MnAs6 and NiAs6 octahedra layers with thicknesses ranging from 1 to 6 octahedra, 2–16 Å. These crystalline structures are modulated and fully described based on 3D electron diffraction and neutron diffraction. Moreover, by X-ray magnetic circular dichroism, an elemental and orbital-specific technique, we probe the 3d magnetic moments of Mn and Ni. We unveil that the nanosegregated MnAs and NiAs layers behave very differently, with the magnetic moment of manganese being one order of magnitude greater than that of nickel. This study opens the path to a completely new class of materials with intrinsic layers of high and low magnetization with potential applications within spintronics.

• Gonano, Bruno Raymond Gino; Fjellvåg, Øystein; Steciuk, Gwladys; Saha, Dipankar; Pelloquin, Denis & Fjellvåg, Helmer (2020). Exotic Compositional Ordering in Manganese–Nickel–Arsenic (Mn-Ni-As) Intermetallics. Angewandte Chemie International Edition. ISSN 1433-7851. 132(50), p. 22568–22573. doi: 10.1002/anie.202006135. Full text in Research Archive Show summary

  In this work we benefited from recent advances in tools for crystal‐structure analysis that enabled us to describe an exotic nanoscale phenomenon in structural chemistry. The Mn0.60Ni0.40As sample of the Mn1−xNixAs solid solution, exhibits an incommensurate compositional modulation intimately coupled with positional modulations. The average structure is of the simple NiAs type, but in contrast to a normal solid solution, we observe that manganese and nickel segregate periodically at the nano‐level into ordered MnAs and NiAs layers with thickness of 2–4 face‐shared octahedra. The detailed description was obtained by combination of 3D electron diffraction, scanning transmission electron microscopy, and neutron diffraction. The distribution of the manganese and nickel layers is perfectly described by a modulation vector q=0.360(3) c*. Displacive modulations are observed for all elements as a consequence of the occupational modulation, and as a means to achieve acceptable Ni–As and Mn–As distances. This modulated evolution of magnetic MnAs and non‐magnetic NiAs‐layers with periodicity at approximately 10 Å level, may provide an avenue for spintronics.

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