Andreas Rosnes

• Andreassen, Magnus; Rosnes, Andreas; Petersen, Clemens; Schenk, Richard Justin; Both, Kevin Gregor & Bergum, Kristin [Show all 7 contributors for this article] (2026). Combinatorial Synthesis and Characterization of Lattice-Matched Ga2O3–Cr2O3 and Ga2O3–V2O3 Sesquioxide Alloys for Ultrawide-Bandgap Semiconductor Applications. Physica Status Solidi (a) applications and materials science. ISSN 1862-6300. 223(15). doi: 10.1002/pssa.70437. Full text in Research Archive Show summary

  Gallium sesquioxide is a wide‐bandgap semiconductor of high interest for power electronics and deep UV‐sensing applications. The α‐phase ( E g  = 5.6 eV) can be synthesized with excellent crystal quality on isostructural Al 2 O 3 substrates, removing the need for expensive homoepitaxial growth that is required for the thermodynamically stable β‐phase ( E g  = 4.9 eV). Here, continuous composition spread material libraries of (Ga 1‐ x V x ) 2 O 3 and (Ga 1‐ x Cr x ) 2 O 3 with 0.05 <  x  < 0.45 are synthesized by pulsed laser deposition, and characterized structurally and optically with the aim of decreasing the optical absorption edge of α‐Ga 2 O 3 to expand the range of potential optoelectronic applications. The (Cr x Ga 1‐ x ) 2 O 3 material library remained stable in the rhombohedral α‐phase throughout the investigated compositional range, exhibiting high crystal quality with minimal changes to the unit cell parameters. A systematic shift in optical absorption edge from 5.5 to 3.9 eV is observed, as determined by spectrophotometry. The (Ga 1‐ x V x ) 2 O 3 material library exhibits a systematic shift from 5.2 to 2.9 eV with increasing x V , but a region of decreased crystal quality is observed for 0.11 ≤  x V  ≤ 0.20. Additionally, a secondary V 2 O 5 phase is observed for x V  > 0.23. Overall, bandgap engineering of α‐(Ga 1‐ x V x ) 2 O 3 and α‐(Ga 1‐ x Cr x ) 2 O 3 is demonstrated, and chromium substitution is identified as especially promising due to high crystallinity and systematic change of optical absorption edge.

• Rosnes, Andreas; Jiang, Bo; Nguyen, Phuong D.; Wang, Luyang; Wenckstern, Holger Von & Prytz, Øystein [Show all 7 contributors for this article] (2026). Multiple Stages of Metal Exsolution from Nonstoichiometric Perovskites. Journal of the American Chemical Society. ISSN 0002-7863. 148(31), p. 33486–33495. doi: 10.1021/jacs.6c08762. Full text in Research Archive Show summary

  Exsolution enables controlled solid-state precipitation of metal nanoparticles from metal oxides, resulting in materials that exhibit excellent catalytic properties for electrochemical energy conversion. The diverse characteristics of particles exsolved at different temperatures indicate complex mechanisms that remain unresolved. Through a series of in situ electron microscopy, synchrotron X-ray diffraction, and thermogravimetry experiments on La0.2Ca0.7Ti0.9Sc0.05Cu0.05O3−δ across nanoscale wedges to μm-sized powders, multiple stages of exsolution are deconvoluted with increasing thermal activation: (1) minor exsolution of anchored surface nanoparticles, (2) exsolution of endoparticles within the bulk, and (3) diffusion and coalescing in the bulk and at the surfaces. Reconstruction of the perovskite surface by formation of nanoscopic steps and terraces proceeds concurrently with endoparticle growth. Moreover, distinct exsolution characteristics are observed in the near-surface region and deeper within the bulk, resulting in spherically and orthorhombically shaped endoparticles, respectively.

• Larsen, Aleksander Amble; Gorantla, Sandeep; Nguyen, Phuong Dan; Rosnes, Andreas; Xu, Yijiang & Iordanidou, Konstantina [Show all 10 contributors for this article] (2026). Atomic-Resolution EDS Characterization of Ordering in a β–Cu–Zn–Al Alloy. Metallurgical and Materials Transactions A. ISSN 1073-5623. doi: 10.1007/s11661-025-08093-9. Full text in Research Archive Show summary

  Abstract Atomic ordering in single-crystal β –Cu–Zn–Al, relevant to the martensitic transformation and functional properties, is investigated using analytical STEM. Atomic-resolution EDS along the [110] zone axis, where all Wyckoff positions are spatially resolved, reveals three chemically distinct site occupancies. Correlation with HAADF-STEM contrast provides real-space evidence consistent with L2 1 ordering. In agreement with experiments, first-principles calculations show a slight energetic preference for L2 1 over D0 3 , with finite-temperature free-energy calculations indicating that this preference persists at elevated temperatures.

• Wen, Yabing; Rosnes, Andreas; Jiang, Bo; Prytz, Øystein; Norby, Truls & Haugsrud, Reidar [Show all 7 contributors for this article] (2025). Nickel-Induced Lattice Defects Limit Proton Uptake in Barium Zirconate Electrolytes. Journal of the American Chemical Society. ISSN 0002-7863. 148. doi: 10.1021/jacs.5c13935. Full text in Research Archive Show summary

  Nickel provides essential catalytic properties for hydrogen electrodes in proton-conducting ceramic electrochemical cells. However, Ni diminishes the hydration capability and proton conductivity when incorporated into electrolyte materials including BaZr0.8Yb0.2O3−δ studied here. Through semiquantitative atomic-resolution scanning transmission electron microscopy, density functional theory simulations, X-ray total scattering, and absorption spectroscopy, we reveal that Ni forms point defect clusters with the Yb acceptors wherein oxygen vacancies are trapped and resist hydration. The resulting effective acceptor concentration is described by point defect reactions in quantitative agreement with thermogravimetric measurements of hydration for samples substituted with 2–5 mol % Ni by BaNiO2 addition. Moreover, excess B-site cations due to NiO addition induce the formation of antiphase boundaries (APBs) that are enriched in Yb and thereby deplete the bulk of acceptors, further suppressing hydration. The adverse effects of Ni are thereby resolved into two novel mechanisms, opening new avenues in point defect engineering for high-performance electrolytes.

• Rosnes, Andreas; Wenckstern, Holger Von; Polfus, Jonathan & Prytz, Øystein (2024). Identifying transient defects in exsolution of nanoparticles by semi-quantitative ABF STEM imaging. BIO Web of Conferences. ISSN 2273-1709. doi: 10.1051/bioconf/202412925030. Full text in Research Archive

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• Amedjkouh, Yani Leo; Jiang, Bo; Rosnes, Andreas; Wenckstern, Holger Von & Polfus, Jonathan M. (2025). Combinatoral PLD of proton ceramic electrode materials with exsolved nanoparticles. Full text in Research Archive Show summary

  Protonic ceramic electrochemical cells (PCECs) are poised to be a critical technology for the electrification of energy and chemical industry using hydrogen. One of the main bottlenecks hodling their widespread adoption back is the sluggish oxygen evolution/reduction reactions (OER/ORR) at the positrode. Wang et al. reported that Ba0.875Fe0.875Zr0.125O3-"δ" (D-BFZ) exhibits remarkable performance as a triple conducting PCFC positrode (Wang 2022). Here, we investigate further improvement of this system by exsolving nanoparticles of Co3O4 or noble metals such as Pt, Ir, Rh and Ru for improved OER/ORR kinetics. Combinatorial pulsed-laser deposition (c-PLD) is a novel thin film deposition technique for obtaining thin films with a continuous composition spread (CCS) (von Wenckstern 2020). D-BFZ doped with the cation species to be exsolved is deposited with a gradient in Ba-deficiency across the film. Spatially resolved synchrotron X-ray diffraction (XRD) and absorption spectroscopy (XAS) is utilized to study the impact of Ba-deficiency on the exsolution process and the resulting nanoparticle characteristics. Further studies involve oxygen exchange kinetics of pristine and exsolved materails using pulsed isotope exchange (PIE). Thus, the impact of the transition metal on the oxygen exchange kinetics can be directly compared between it being exsolved as nanoparticles and incorporated in the perovskite lattice.

• Rosnes, Andreas (2024). Anchored Nanoparticles for Energy Conversion. Full text in Research Archive
• Rosnes, Andreas; Lysne, Hogne; Christiansen, Emil; Reenaas, Turid Dory & Holmestad, Randi (2022). Differentiating Polyamorphous SiO2 by SPED, PDF and Blind Source Separation Algorithm. Full text in Research Archive
• Rosnes, Andreas (2026). Microscopic insights into metal exsolution and defects in non-stoichiometric perovskite oxides. Universitetet i Oslo. Full text in Research Archive Show summary

  A sustainable future requires thoughtful use of nature’s resources. Resilient catalysts are essential for efficient chemical production and for managing intermittency of renewable energy sources. Metal exsolution – precipitation of anchored metal nanoparticles from a metal oxide host – has emerged as an attractive approach to engineer nanostructures with durable and highly active catalysts. However, implementation in commercial devices is limited in part by the complexity of the process and the lack of a microscopic description. This dissertation therefore investigates metal exsolution and defects in state-of-the-art non-stoichiometric perovskite oxides. The main finding is a description of exsolution, which reveals that additional acceptor substitution in non-stoichiometric perovskite oxides can facilitate the reaction. In La0.2Ca0.7Ti0.95Cu0.05O2.95−δ, copper exsolution exhibits increased metal yield, higher particle nucleation density, and an enhanced rate of the reaction upon addition of aluminum or gallium acceptors. The addition of acceptors holds potential as a simple cost-effective strategy for better use of scarce transition metals as exsolved catalysts and to optimize the nanoparticle populations in the bulk and at the surface. Additionally, scandium acceptors promote growth of orthorhombic shaped nanoparticles in the bulk that induce extensive lattice strain in the perovskite. This may be leveraged to tailor functional properties of the substrate.

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