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1. X-ray-diffraction and electrical-transport imaging of superconducting superhydride (La,Y)H10

   https://doi.org/10.1038/s41467-025-66262-1  

   Manayil_Marathamkottil, Abdul Haseeb; Wang, Kui; Salke, Nilesh P; Ahart, Muhtar; Mark, Alexander C; Hrubiak, Rostislav; Chariton, Stella; Smith, Dean; Prakapenka, Vitali B; Somayazulu, Maddury; et al (December 2025, Nature Communications)

   Abstract Understanding how microscopic structural domains govern macroscopic electronic properties is central to advancing hydride superconductors, yet such correlations remain poorly resolved under pressure. We report the synthesis and characterization of (La_0.9Y_0.1)H₁₀superhydrides exhibiting coexisting cubic$${Fm}\bar{3}m$$ $Fm\overline{3}m$ and hexagonal$$P{6}_{3}/{mmc}$$ $P{6}_3/mmc$ clathrate phases observed over the pressure range from 168 GPa down to 136 GPa. Using synchrotron-based X-ray diffraction imaging at the upgraded Advanced Photon Source, we spatially resolved μm-scale distributions of these phases, revealing structural inhomogeneity across the sample. Four-probe resistance measurements confirmed superconductivity with two distinct transitions: an onset at 244 K associated with the cubic phase and a second near 220 K linked to the hexagonal phase. Notably, resistance profiles collected from multiple current and voltage permutations showed variations in transition width and onset temperature that correlated with the spatial phase distribution. These findings demonstrate a direct connection between local structural domains and superconducting behavior. 

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2. Structural phase purification of bulk HfO ₂ :Y through pressure cycling

   https://doi.org/10.1073/pnas.2312571121  

   Musfeldt, J. L.; Singh, Sobhit; Fan, Shiyu; Gu, Yanhong; Xu, Xianghan; Cheong, S.-W.; Liu, Z.; Vanderbilt, David; Rabe, Karin M. (January 2024, Proceedings of the National Academy of Sciences)

   We combine synchrotron-based infrared absorption and Raman scattering spectroscopies with diamond anvil cell techniques and first-principles calculations to explore the properties of hafnia under compression. We find that pressure drives HfO ${}_2$ :7%Y from the mixed monoclinic ( $P{2}_1/c$ ) $+$ antipolar orthorhombic ( $\mathit{Pbca}$ ) phase to pure antipolar orthorhombic ( $\mathit{Pbca}$ ) phase at approximately 6.3 GPa. This transformation is irreversible, meaning that upon release, the material is kinetically trapped in the $\mathit{Pbca}$ metastable state at 300 K. Compression also drives polar orthorhombic ( $Pca{2}_1$ ) hafnia into the tetragonal ( $P{4}_2/nmc$ ) phase, although the latter is not metastable upon release. These results are unified by an analysis of the energy landscape. The fact that pressure allows us to stabilize targeted metastable structures with less Y stabilizer is important to preserving the flat phonon band physics of pure HfO ${}_2$ . 

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3. High Pressure Synthesis of Rubidium Superhydrides

   https://doi.org/10.1103/PhysRevLett.134.196102  

   Kuzovnikov, Mikhail A; Wang, Busheng; Wang, Xiaoyu; Marqueño, Tomas; Shuttleworth, Hannah A; Strain, Calum; Gregoryanz, Eugene; Zurek, Eva; Peña-Alvarez, Miriam; Howie, Ross T (May 2025, Physical Review Letters)

   Through laser-heated diamond anvil cell experiments, we synthesize a series of rubidium superhydrides and explore their properties with synchrotron x-ray powder diffraction and Raman spectroscopy measurements, combined with density functional theory calculations. Upon heating rubidium monohydride embedded in ${\mathrm{H}}_2$ at a pressure of 18 GPa, we form ${\mathrm{RbH}}_9\text{−}\mathrm{I}$ , which is stable upon decompression down to 8.7 GPa, the lowest stability pressure of any known superhydride. At 22 GPa, another polymorph, ${\mathrm{RbH}}_9\text{−}\mathrm{II}$ is synthesised at high temperature. Unique to the Rb-H system among binary metal hydrides is that further compression does not promote the formation of polyhydrides with higher hydrogen content. Instead, heating above 87 GPa yields ${\mathrm{RbH}}_5$ , which exhibits two polymorphs ( ${\mathrm{RbH}}_5\text{−}\mathrm{I}$ and ${\mathrm{RbH}}_5\text{−}\mathrm{II}$ ). All of the crystal structures comprise a complex network of quasimolecular ${\mathrm{H}}_2$ units and ${\mathrm{H}}^{-}$ anions, with ${\mathrm{RbH}}_5$ providing the first experimental evidence of linear ${\mathrm{H}}_3^{-}$ anions. Published by the American Physical Society2025 

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4. Heterogeneous Microstructure in Laser-Processed Metastable Ti25Nb Alloy

   https://doi.org/10.1007/s40830-025-00540-1  

   Lin, Wenhao; Akinwande, Abayomi Adewale; Hoglund, Eric; Heinrich, Helge; Ma, Ji (June 2025, Shape Memory and Superelasticity)

   Abstract The high thermal gradient and solidification velocity associated with the laser powder bed fusion process spurs formation of diverse microstructures in additively manufactured materials. This study focused on the phase composition observed in the microstructure of a laser-processed metastable titanium–niobium alloy. Through transmission electron microscopy experiments, we reveal the microstructures with several metastable phase, among which is a novel orthorhombic phase found in Nb-lean regions that is fundamentally different from the expected$${\alpha }^{{\prime}{\prime}}$$ ${\alpha }^{\prime \prime }$ orthorhombic phase. Second is the$${O}{\prime}$$ $O\prime$ phase and the$${O}{\prime}$$ $O\prime$ variant selection phenomenon in laser-processed metastable β-Ti alloys. Microstructural features were found to be highly sensitive to the processing history. We further examine the mechanisms behind these phase formations and discuss how these features can influence the properties of the alloy. 

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5. High pressure raman spectroscopy and X-ray diffraction of K2Ca(CO3)2 bütschliite: multiple pressure-induced phase transitions in a double carbonate

   https://doi.org/10.1007/s00269-023-01262-5  

   Zeff, G; Kalkan, B; Armstrong, K; Kunz, M; Williams, Q (March 2024, Physics and Chemistry of Minerals)

   Abstract The crystal structure and bonding environment of K₂Ca(CO₃)₂bütschliite were probed under isothermal compression via Raman spectroscopy to 95 GPa and single crystal and powder X-ray diffraction to 12 and 68 GPa, respectively. A second order Birch-Murnaghan equation of state fit to the X-ray data yields a bulk modulus,$${K}_{0}=46.9$$ $K_0=46.9$ GPa with an imposed value of$${K}_{0}^{\prime}= 4$$ $K_0^{\prime }=4$ for the ambient pressure phase. Compression of bütschliite is highly anisotropic, with contraction along thec-axis accounting for most of the volume change. Bütschliite undergoes a phase transition to a monoclinicC2/mstructure at around 6 GPa, mirroring polymorphism within isostructural borates. A fit to the compression data of the monoclinic phase yields$${V}_{0}=322.2$$ $V_0=322.2$  Å³$$,$$ $,$ $${K}_{0}=24.8$$ $K_0=24.8$ GPa and$${K}_{0}^{\prime}=4.0$$ $K_0^{\prime }=4.0$ using a third order fit; the ability to access different compression mechanisms gives rise to a more compressible material than the low-pressure phase. In particular, compression of theC2/mphase involves interlayer displacement and twisting of the [CO₃] units, and an increase in coordination number of the K⁺ion. Three more phase transitions, at ~ 28, 34, and 37 GPa occur based on the Raman spectra and powder diffraction data: these give rise to new [CO₃] bonding environments within the structure. 

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