High‐pressure behavior of (Cs,K)Al₄Be₅B₁₁O₂₈ (londonite): A single‐crystal synchrotron diffraction study up to 26 GPa

Abstract

The compressional behavior and the P-induced deformation mechanisms at the atomic scale of (Cs,K)Al 4 Be 5 B 11 O 28 (londonite, a~7.31 A and space group P43m) were investigated by in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell up to 26 GPa. No phase transition was observed within the P-range investigated: this material exhibits isotropic compression (i.e., with cubic symmetry) in response to the applied pressure. Fitting the P-V data with a Birch-Murnaghan isothermal equation of state, we obtained:) and K 0 =4.6(6). A series of structural refinements, based on the high-pressure intensity data, were performed. The stiffness of londonite (similar to that of carbides) is governed by its close-packing structure, and in particular by the very low compressibility of B-and Be-tetrahedra and the modest compressibility of the Al-octahedra. The Cs-polyhedra are the most compressible units of the structure. The effects of pressure can be accommodated by intrapolyhedral compression or deformation, leading to a modest bulk compression. The high amount of boron in londonite (B 2 O 3~5 0 wt%) makes its synthetic counterpart a potential neutron absorber. In addition, the high content of Cs makes londonite-type materials as potential hosts for nuclear waste. K E Y W O R D Sborates, cesium/cesium compounds, elastic constants, single crystals, structure

Hydroxylherderite (Ca2Be2P2O8(OH)2) stability under extreme conditions (up to 750°C/100 GPa)

“…Besides, this information could help to explain beryllium deposit formation. 18 As far as we know, less than 10 Be-containing minerals were studied under high-pressure conditions, among them are beryl Be 3 Al 2 Si 6 O 18 , 19,20 chrysoberyl BeAl 2 O 4 , 21,22 phenakite Be 2 SiO 4 and bertrandite Be 4 Si 2 O 7 (OH) 2 , 23 behoite Be(OH) 2 , 24 londonite CsBe 4 Al 4 (B 11 Be)O 28 , 25 hurlbutite CaBe 2 P 2 O 8 , 26 and hingganite-(Y) Y 2 □Be 2 Si 2 O 8 (OH) 2 . 27 Of these, only hurlbutite was studied up to the amorphization (above 90 GPa), whereas all other minerals were studied up to 5-50 GPa, and these pressures are not their whole stability range.…”

Phase transition and high-pressure behavior of ulexite, a potential aggregate in radiation-shielding concretes

“…Recently, the behavior at non-ambient conditions of a series of natural borates has been studied, with the aim of improving the thermodynamic database of these minerals [32][33][34][35][36][37][38][39][40]. Overall, phase transitions occurring at different pressures were discovered in kernite, colemanite, kurnakovite and meyerhofferrite, which have structural homologies with ulexite.…”

High-pressure behaviour and phase stability of Ca2B6O6(OH)10·2(H2O) (meyerhofferite)

“…To the best of our knowledge, no in-situ X-ray diffraction experiments were devoted to unveil the highpressure behaviour mechanisms that govern the structure deformation at the atomic scale of meyerhofferite. Our research group investigated the behaviour of a series of natural anhydrous and hydrous borates at non-ambient conditions, with the aim to provide accurately determined thermoelastic parameters, description of the deformation mechanisms at the atomic scale and of their P-T phase stability ranges (e.g., Gatta et al 2010Gatta et al , 2011Gatta et al , 2013Gatta et al , 2017Gatta et al , 2020Lotti et al 2017, 2018, 2019. Overall, we bracketed phase transitions occurring at relatively low pressure in kernite, colemanite and kurnakovite, which have some structural similarities with meyerhoferrite.…”