Structures, Phase Stability, Amorphization, and Decomposition of V6O13 at High Pressures and Temperatures: Synthesis of Rutile-Related V0.92O2

Abstract

The stability of mixed-valence V₆O₁₃ at high pressures and high temperatures is studied experimentally in multianvil presses both ex situ and in situ using synchrotron energy-dispersive powder diffraction. V₆O₁₃ starts to amorphize and decomposes above 18.5 GPa at room temperature. It transforms to rutile-related V_0.92O₂ 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 VO₂ is considered to be the ordered (though distorted) variant of V_0.92O₂. The experiments are complemented by density functional theory calculations and global explorations of the energy landscape of V₆O₁₃ and V_0.92O₂ compounds at high pressures using a multimethodological approach to construct and predict feasible structures.