High pressure phase transitions and compressibilities of Er2Zr2O7 and Ho2Zr2O7

Abstract

Phase stability and compressibility of rare earth zirconates with the defect-fluorite structure were investigated by in situ synchrotron x-ray diffraction. A sluggish defect-fluorite to a cotunnitelike phase transformation occurred at pressures of ∼22 and ∼30GPa for Er2Zr2O7 and Ho2Zr2O7, respectively. Enhanced compressibility was found for the high pressure phase as a result of increasing cation coordination number and cation-anion bond length.

Stability of fluorite-type La2Ce2O7 under extreme conditions

“…The high-pressure phase has nanometer scale grain size, which was observed before in quenched pyrochlores [33] by TEM analysis. Previous research revealed that pressure-induced phase transition in RE 2 Zr 2 O 7 pyrochlore or distorted-fluorite structure is reversible [30]. Quick unloading of pressurized sample with He pressure medium may easily break the diamond anvils because of the strain generated by the penetration of He across the diamond surface layer at high pressure conditions.…”

Structural Transformations and Disordering in Zirconolite (CaZrTi2O7) at High Pressure

“…45 The dioxides UO 2 , ThO 2 , ZrO 2 and HfO 2 undergo a transition into the cotunnite structure at high pressure, and Li 2 O transforms to an anti-cottunite structure. [46][47][48] Analysis of our results for zirconolite-III using a Pnma cell with a = 5.357(5) Å, b = 3.128(1) Å and c = 6.372(9) Å provides an excellent fit to the diffraction data, and a full Reitveld refinement using this structure model also led to a good fit (Figure 12 (d)).…”

New high-pressure phase and equation of state of Ce2Zr2O8

“…3,7,8 The high radiation and chemical stability and low neutron absorption coefficients of Zr make zirconate pyrochlores extremely useful for these purposes, but recent studies have found pressure-driven instabilities. 9 Structural transitions were reported for Sm 2 [10][11][12] Studies on related Y 2 Zr 2 O 7 indicated the formation of a defect-cotunnite structure at 18 GPa. 13 HP x-ray diffraction (XRD) and Raman studies of La 2 Hf 2 O 7 revealed no phase transition and instead showed decomposition to the constituent oxides.…”