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The effect of pressure and composition on Cu-bearing hydroxide perovskite

DOI: 10.1007/s00269-019-01047-9 DOI Help

Authors: Jens Najorka (The Natural History Museum) , Annette K. Kleppe (Diamond Light Source) , Mark D. Welch (Natural History Museum)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physics And Chemistry Of Minerals , VOL 36

State: Published (Approved)
Published: July 2019
Diamond Proposal Number(s): 9903 , 11121

Open Access Open Access

Abstract: Hydroxide perovskite solid solutions along the CuxZn1−xSn(OH)6 join have been investigated at ambient conditions. Two compositions, Cu0.4Zn0.6Sn(OH)6 (cubic) and CuSn(OH)6 (tetragonal), have also been studied at pressures up to 17 GPa. In both ambient and high-pressure experiments, samples were characterised using powder X-ray diffraction. Bulk compositions between 0 ≤ XCu ≤ 0.4 are metrically cubic (space group Pn 3 ¯ 3¯ ), whereas those with XCu = 0.9 and 1 produced single-phase tetragonal Cu0.9Zn0.1Sn(OH)6 and CuSn(OH)6 (space group P42/n). The products of syntheses with 0.5 ≤ XCu ≤ 0.8 contain coexisting cubic and tetragonal phases. The cubic → tetragonal transformation is rationalised in terms of being driven by local strain associated with the accumulation of Cu-rich domains in the cubic phase. The high-pressure studies of cubic Cu0.4Zn0.6Sn(OH)6 and tetragonal CuSn(OH)6 phases showed contrasting behaviour. The compression curve of the cubic phase is smooth without inflexion or discontinuity to 17 GPa. The derived bulk modulus of Cu0.4Zn0.6Sn(OH)6 is K0 = 75.8(4) GPa (K′ = 4). For CuSn(OH)6, compression data cannot be fitted by a single equation-of-state over the entire pressure range to 17 GPa, as there is a clear discontinuity between 7 and 10 GPa that corresponds to an increase in compressibility at higher pressures. Compression data for CuSn(OH)6 to 7 GPa are: K0 = 59.7(9) GPa, Ka0 = 79(2) GPa, and Kc0 = 38.0(3) GPa (K′ = 4 for all). It is shown that the strong Jahn–Teller distortion associated with the Cu(OH)6 octahedron is primarily responsible for the discontinuous and highly anisotropic compressional behaviour of the unit cell of CuSn(OH)6 hydroxide perovskite.

Journal Keywords: Hydroxide perovskite; Vismirnovite; Mushistonite; Jahn–Teller distortion; High pressure; Diamond-anvil cell; X-ray diffraction

Subject Areas: Chemistry

Instruments: I15-Extreme Conditions