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arXiv · 2401.13818

Experimental and theoretical confirmation of an orthorhombic phase transition in niobium at high pressure and temperature

Daniel Errandonea·Leonid Burakovsky·Dean L. Preston·Simon G. MacLeod·David Santamaria-Perez·Shaoping Chen·Hyunchae Cynn·Sergey I. Simak·Malcolm I. McMahon·John E. Proctor·Mohamed Mezouar
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Abstract

Compared to other body-centered cubic (bcc) transition metals Nb has been the subject of fewer compression studies and there are still aspects of its phase diagram which are unclear. Here, we report a combined theoretical and experimental study of Nb under high pressure and temperature. We present the results of static laser-heated diamond anvil cell experiments up to 120 GPa using synchrotron-based fast x-ray diffraction combined with ab initio quantum molecular dynamics simulations. The melting curve of Nb is determined, and evidence for a solid-solid phase transformation in Nb with increasing temperature is found. The high-temperature phase of Nb is orthorhombic Pnma. The bcc-Pnma transition is clearly seen in the experimental data on the Nb principal Hugoniot. The bcc-Pnma coexistence observed in our experiments is explained. Agreement between the measured and calculated melting curves is very good except at 40-60 GPa where three experimental points lie below the theoretical melting curve by 250 K (or 7%); a possible explanation is given.

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Daniel Errandonea, Leonid Burakovsky, Dean L. Preston, Simon G. MacLeod, David Santamaria-Perez, Shaoping Chen, Hyunchae Cynn, Sergey I. Simak, Malcolm I. McMahon, John E. Proctor, Mohamed Mezouar. 2024-01-24. Experimental and theoretical confirmation of an orthorhombic phase transition in niobium at high pressure and temperature. https://doi.org/10.1038/s43246-020-00058-2

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