High-pressure stability and compressibility ofAPO4(A=La, Nd, Eu, Gd, Er, and Y) orthophosphates: An x-ray diffraction study using synchrotron r

Abstract

Room temperature angle-dispersive x-ray diffraction measurements on zircon-type YPO 4 and ErPO 4 , and monazite-type GdPO 4 , EuPO 4 , NdPO 4 , and LaPO 4 were performed in a diamond-anvil cell up to 30 GPa using neon as pressure-transmitting † Corresponding author; email: daniel.errandonea@uv.es 2 medium. In the zircon-structured oxides we found evidence of a reversible pressureinduced structural phase transformation from zircon to a monazite-type structure. The onset of the transition is near 17 -20 GPa. In LaPO 4 a non-reversible transition is found around 26 GPa, being a barite-type structure proposed for the high-pressure phase. In the other three monazites, this structure is found to be stable up to the highest pressure reached in the experiments. No additional phase transitions or evidences of chemical decomposition are found in the experiments. The equations of state and axial compressibility for the different phases are also determined. In particular, we found that in a given compound the monazite structure is less compressible than the zircon structure.This fact is attributed to the larger packing efficiency of monazite than that of zircon. The differential bond compressibility of different polyhedra is also reported and related to the anisotropic compressibility of both structures. Finally, the sequence of structural transitions and compressibilities are discussed in comparison with other orthophosphates.

In situhigh-pressure synchrotron x-ray diffraction study of CeVO4and TbVO4up to 50 GPa

“…In particular, a LeBail analysis allows indexing the pattern measured at 14.7 GPa with a CaSeO 4 -type structure (a = 6.88 Å , b = 5.88 Å, and c = 6.76 Å space group: P2 1 2 1 2 1 , Z = 4) similar to the high-pressure structure recently found in BaSO 4 [31]. The orthorhombic structure is a distortion of barite and its appearance as post-monazite phase in CeVO 4 is consistent with the fact that bariterelated structures have been found as HP phases in different monazites [13]. Barite and post-barite structures have been reported for high-pressure phases of CaSO 4 [32], BaSO 4 [31].…”

“…In contrast under non-hydrostatic conditions the zircon-to-scheelite transition has been detected. Both, non-hydrostatic effects and the change of the trivalent cation have been shown to play a role also in the structural behavior of zircontype arsenates, chromates, and phosphates [12,13]. Both factors deserve to be further studied into detail.…”

High-pressure powder x-ray diffraction study of EuVO4

“…5� 10 -3 GPa -1 and κ c =1.3 � 10 -3 GPa -1 . The fact that the a-axis of zircon EuVO 4 is more compressible that the c-axis, is a typical behavior of zircon-structured oxides [47], in particular vanadates [7,14]. The origin of this behavior is related with the packing of EuO 8 and VO 4 polyhedral units in the zircon structure.…”

“…In this case, the most compressible axis is the c-axis. Since the scheelite and zircon structure are made of similar polyhedral units [47], the anisotropic behavior of scheelite can be explained using a similar argument which is used to explain the anisotropic compressibility of the zircon structure [45].…”

High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4

“…1,4,7,8 During the last decade, intensive investigations have been carried out on the structural evolution of MTO 4 -type ternary oxides under high-pressure (HP). They showed that compression is an efficient tool to improve the understanding of the main physical properties of vanadates, 9 phosphates, 10 chromates, 11 tungstates, 12 molydbates, 13 arsenates, 14 and many other MTO 4 compounds. 15 However, to the best our knowledge, an investigation of BiSbO 4 under pressure is still lacking in literature.…”