High-pressure elastic behavior of Ca4La6(SiO4)6(OH)2 a synthetic rare-earth silicate apatite: a powder X-ray diffraction study up to 9.33 GPa

Abstract

The compression behavior of a synthetic Ca4La6(SiO4)6(OH)2 has been investigated to about 9.33 GPa at 300 K using in situ angle-dispersive X-ray diffraction and a diamond anvil cell. No phase transition has been observed within the pressure range investigated. The values of zero-pressure volume V0, K0, and \(K_{0}^{'}\) refined with a third-order Birch–Murnaghan equation of state are V0 = 579.2 ± 0.1 A3, K0 = 89 ± 2 GPa, and \(K_{0}^{'} = 10.9 \pm 0.8\). If \(K_{0}^{'}\) is fixed at 4, K0 is obtained as 110 ± 2 GPa. Analysis of axial compressible modulus shows that the a-axis (Ka0 = 79 ± 2 GPa) is more compressible than the c-axis (Kc0 = 121 ± 7 GPa). A comparison between the high-pressure elastic response of Ca4La6(SiO4)6(OH)2 and the iso-structural calcium apatites is made. The possible reasons of the different elastic behavior between Ca4La6(SiO4)6(OH)2 and calcium apatites are discussed.