Pressure-induced Hexagonal to Monoclinic Phase Transition of Partially Hydrated CePO 4

SERGIO FERRARI; S. NAGABHUSAN ACHARY; ENRICO BANDIELLO; JULIO PELLICER-PORRES; AVESH K. TYAGI; D. ERRANDONEA; DOMINGO MARTÍNEZ-GARCÍA; C. POPESCU

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2019 vol. 58 p. 4480 - 4490

0020-1669

We present a study of the pressure dependence of the structure of partially hydrated-hexagonal CePO 4up to 21 GPa using synchrotron powder x-ray diffraction. At a pressure of 10 GPa a second-orderstructural phase transition is observed, associated with a novel polymorph. The previously unknownhigh-pressure phase has a monoclinic structure with a similar atomic arrangement as the low-pressurephase, but with reduced symmetry, belonging to space group C2. Group-subgroup relations hold for thespace symmetry groups of both structures. There is no detectable volume discontinuity at the phasetransition. Here we provide structural information on the new phase and determine the axial compressibility and bulk modulus for both phases. They are found to have an anisotropic behavior and to be much more compressible than the denser monazite-like polymorph of CePO 4 . In addition, the isothermal compressibility tensor for the high-pressure structure is reported at 10 GPa and the direction of maximum compressibility described. Finally, the possible role of water and the pressure medium in the high-pressure behavior is discussed. The results are compared with those from anhydrous rare-earth orthophosphates.