Prediction of cell variations with pressure of ionic layered crystal Application to the matlockite family

Abstract

Compounds belonging to the matlockite family are ionic layered crystals. Some previous experimental studies on these compounds demonstrated the correlation between the difference in bond strength translating the layered properties and the anisotropic coordination of the highly polarizable halogen anion. In the present paper, we present a model to estimate the anisotropic compressibilities of matlockites which could be generalized to other ionic layered compounds. The compressibilities of each individual polyhedron which built the sheet of an ionic layered crystal are determined from a simple relation based on a semiempirical relation obtained by Hazen et al., involving the electrical charge of the ions and the interatomic distances. The electrical charge of the anions are taken to be direction-dependent and are modulated by the anion polarizability value. Finally, to validate the model, the calculated compressibilities are compared with previously published data, but also with new high pressure experimental data obtained by X-ray absorption spectroscopy up to 20 GPa on SrFCl and SrFBr at the K edge of the strontium and by X-ray diffraction up to 30 GPa on SrFBr and PbFBr. Present estimations give results which differ from the experimental values by less than 15%. PACS. 64.30.+t Equations of state of specific substances -62.20.-x Mechanical properties of solids -61.10.Ht X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Sm2+ as a probe of crystal field in fluorides and fluorohalides: Effect of pressure and temperature

“…The pressure was measured using the ruby (present with the sample) luminescence. (28 × 10 −3 GPa −1 ) than for SrFCl, SrFBr and BaFCl (18.6, 19.8 and 22.2 × 10 −3 GPa −1 ), respectively [8]. Qualitatively, this can be explained by the layer-type crystal structure.…”

“…Qualitatively, this can be explained by the layer-type crystal structure. In the case of BaFI, the compressibility along the c-axis is much larger than along the a-axis, while it is close to isotropic in BaFCl and SrFCl [8]. The local compression of the emitting Sm ion with its first coordination sphere of four fluorides and 4 + 1 iodides appears thus to be smaller than the compression of the entire crystal.…”

Ionic layered PbFCl-type compounds under high pressure

“…11) describes the evolution of the intrinsic anisotropic bonding of these compounds. 27 The evolution of c/a for the three compounds contrasts with the V/V0( P) curves (see Fig. 8) that are the same whatever the crystal, and therefore whatever their layer character.…”

Pressure-Induced Martensitic Phase Transition and Low Lattice Thermal Conductivity of SrClF

“…Moreover, high-pressure research on PbClF-type materials has received tremendous interest owing to their quasi-2D layered structure, , which can provide an avenue for exploring pressure-induced layered to nonlayered structural phase transformations. Several high-pressure X-ray diffraction (HP-XRD) − and theoretical − studies were focused on understanding the high-pressure behavior of layered PbClF-type compounds. A HP-XRD study on MClF (M = Ca, Sr, Ba) and BaFBr compounds using a diamond anvil cell and synchrotron radiation revealed that CaClF and SrClF are stable up to 27 and 42 GPa, respectively.…”