Structures, Phase Stability, Amorphization, and Decomposition of V₆O₁₃ at High Pressures and Temperatures: Synthesis of Rutile-Related V_0.92O₂

Abstract

The stability of mixed-valence V 6 O 13 at high pressures and high temperatures is studied experimentally in multianvil presses both ex situ and in situ using synchrotron energy-dispersive powder diffraction. V 6 O 13 starts to amorphize and decomposes above 18.5 GPa at room temperature. It transforms to rutile-related V 0.92 O 2 above 500 K in the pressure range up to about 15−17.5 GPa. The crystal structure of this new phase (C12/m1, Z = 4) was determined from laboratory single-crystal and powder X-ray diffraction data measured on single crystals grown at 10 GPa and 1373 K. The characteristic feature is the presence of two zigzag V− V chains. One of them has equidistant V atoms, while the other is with short and long V−V distances. In the average-ordered structure (P2/m, Z = 2), both V−V chains are linear and equidistant. The M2 polymorph of VO 2 is considered to be the ordered (though distorted) variant of V 0.92 O 2 . The experiments are complemented by density functional theory calculations and global explorations of the energy landscape of V 6 O 13 and V 0.92 O 2 compounds at high pressures using a multimethodological approach to construct and predict feasible structures.