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arXiv · 2610.25913

A Stress-Induced Tetragonal Distortion in K2OsCl6 under Pressure

Neha Bura·Peije Zhang·Ganesh Bera·Catalin Popescu·Caleb J. Bennett·Brendan J. Kennedy·Daniel Errandonea
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Abstract

The structural behaviour of cubic (Fm-3m) K2OsCl6 under compression was investigated to 35.4 GPa using angle-dispersive synchrotron powder X-ray diffraction. Upon increasing pressure, K2OsCl6 undergoes a sequence of structural transformations from the ambient-pressure cubic phase to a tetragonal (P4/mnc) phase above 9.5(3) GPa, followed by a transition to a monoclinic (P21/n) phase beginning at approximately 14.2 GPa. The tetragonal and monoclinic phases coexist over the pressure range 14.2-17.2 GPa, while the monoclinic phase is observed as the sole phase at 17.9 GPa and remains stable up to the maximum pressure investigated. Analysis of the diffraction profiles and unit-cell parameters indicates that the intermediate tetragonal structure is likely associated with stress-induced symmetry lowering rather than a distinct thermodynamic phase. This distortion, which is adequately described by the tetragonal P4/mnc space group, is attributed to non-hydrostatic deviatoric stresses arising from the pressure-transmitting medium. Equation-of-state analysis reveals a pronounced reduction in compressibility across the structural transitions, with the bulk modulus increasing from 26(2) GPa for the cubic phase to 71(3) GPa for the monoclinic phase. The pressure-induced structural sequence is analogous to that reported for related compounds such as K2IrCl6, although the transitions in K2OsCl6 occur at lower pressures. All structural transformations are reversible upon decompression.

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Neha Bura, Peije Zhang, Ganesh Bera, Catalin Popescu, Caleb J. Bennett, Brendan J. Kennedy, Daniel Errandonea. 2026-10-19. A Stress-Induced Tetragonal Distortion in K2OsCl6 under Pressure. https://arxiv.org/abs/2610.25913

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