Search

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 ¯ ), 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. [ABSTRACT FROM AUTHOR]

The isothermal equation of state of silicon has been determined by synchrotron x-ray diffraction experiments up to 105.2 GPa at room temperature using diamond anvil cells. A He-pressure medium was used to minimize the effect of uniaxial stress on the sample volume and ruby, gold and tungsten pressure gauges were used. Seven different phases of silicon have been observed along the experimental conditions covered in the present study. [ABSTRACT FROM AUTHOR]

The atomic-scale structure, melting curve, and equation of state of liquid gallium has been measured to high pressure (p) and high temperature (T) up to 26 GPa and 900 K by in situ synchrotron x-ray diffraction. Ab initio molecular dynamics simulations up to 33.4 GPa and 1000 K are in excellent agreement with the experimental measurements, providing detailed insight at the level of pair distribution functions. The results reveal an absence of dimeric bonding in the liquid state and a continuous increase in average coordination number n̅GaGa from 10.4(2) at 0.1 GPa approaching ~12 by 25 GPa. Topological cluster analysis of the simulation trajectories finds increasing fractions of fivefold symmetric and crystalline motifs at high p-T. Although the liquid progressively resembles a hard-sphere structure towards the melting curve, the deviation from this simple description remains large (=40%) across all p-T space, with specific motifs of different geometries strongly correlating with low local two-body excess entropy at high p-T. [ABSTRACT FROM AUTHOR]