High-pressure properties of TiP₂O₇, ZrP₂O₇and ZrV₂O₇

Abstract

High‐pressure synchrotron X‐ray powder diffraction studies of TiP2O7, ZrP2O7 and ZrV2O7 have been performed. The ZrV2O7 structure undergoes a reversible transition at 1.38–1.58 GPa from cubic α‐ to pseudo‐tetragonal β‐ZrV2O7 that displays an orthorhombic 2 × 3 × 3 supercell. At pressures above 4 GPa, ZrV2O7 becomes irreversibly X‐ray amorphous. No such transformations are observed for TiP2O7 and ZrP2O7, which compress smoothly up to the highest investigated pressures (40.3 and 20.5 GPa, respectively). These differences in high‐pressure properties are discussed in terms of the negative thermal expansion of ZrV2O7. The bulk moduli at ambient pressure (B0) for TiP2O7, ZrP2O7, α‐ZrV2O7 and β‐ZrV2O7 were estimated to be 42 (3), 39 (1), 17.0 (7) and 20.8 (10) GPa, respectively.

Pressure-enhanced decomposition of Ag3[Co(CN)6]

“…The possible correlation between these phenomena in framework structured materials is a controversial issue in the literature. Especially, several studies have been published dealing with the possible relationship between PIA and the anomalous thermal behavior observed for some framework structured materials [4][5][6][7][8][9][10][11]. These studies, which followed a first report on PIA of zirconium tungstate [6], have been mainly focused on oxide compounds.…”

Structural phase transitions in Zn(CN)2 under high pressures

“…On the other hand, cubic ZrV 2 O 7 , wherein only the rotation of the VO 4 contributes to NTE, transforms from cubic to an orthorhombic phase over $1.4-1.7 GPa [9]. A large number of anisotropic compounds (Sc 2 (WO 4 ) 3 , Lu 2 (WO 4 ) 3 , Al 2 (WO 4 ) 3 , and molybdates) [4,7,8] have also been studied under pressure with the help of X-ray diffraction as well as Raman and IR measurements and these too undergo transitions to crystalline phases before leading to pressure-induced amorphization (PIA) [10].…”

“…where the librational motion of both the constituent polyhedra contribute to NTE [9], transform to other crystalline phases at 0.2, 0.6 GPa and over 0.7-2.5 GPa, respectively ([4] and reference therein). On the other hand, cubic ZrV 2 O 7 , wherein only the rotation of the VO 4 contributes to NTE, transforms from cubic to an orthorhombic phase over $1.4-1.7 GPa [9].…”

Entropy increase in the amorphous-to-crystalline phase transition in zirconium tungstate

“…In fact, this trend has indeed been verified for several other NTE materials (see, for instance, Refs. [15][16][17][18]). As previously shown, the amorphous phase of zirconium tungstate reverts to a-ZrW 2 O 8 upon annealing at about 900 K at ambient pressure [8].…”