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We describe the capability to measure high-resolution neutron powder diffraction data to a pressure of at least 8 kbar. We have used the HRPD instrument at the ISIS neutron source and a piston-cylinder design of pressure cell machined from a null-scattering titanium zirconium alloy. Data were collected under hydrostatic conditions from an elpasolite perovskite LaNiMnO; by virtue of a thinner cell wall on the incident-beam side of the cell, it was possible to obtain data in the instrument's highest resolution back-scattering detector banks up to a maximum pressure of 8.5 kbar. [ABSTRACT FROM PUBLISHER]

Detailed neutron powder diffraction measurements have been carried out on two polymorphs of anhydrous magnesium sulfate, α-MgSO4 and β-MgSO4. α-MgSO4 is orthorhombic, space group Cmcm ( Z = 4); at 4.2 K the unit-cell dimensions are a = 5.16863 (3), b = 7.86781 (5), c = 6.46674 (5) Å, V = 262.975 (2) Å3 [ρcalc = 3040.16 (2) kg m−3], and at 300 K, a = 5.17471 (3), b = 7.87563 (5), c = 6.49517 (5) Å, V = 264.705 (2) Å3 [ρcalc = 3020.29 (2) kg m−3]. The axial and volumetric thermal expansion coefficients are positive at all temperatures and exhibit no unusual behaviour. Structures were refined at 4.2 and 300 K to RP < 3%; less precise structural parameters were determined during warming from 4.2 to 300 K. β-MgSO4 has a more complex structure, crystallizing in space group Pbnm ( Z = 4); the unit-cell dimensions at 4.2 K are a = 4.73431 (8), b = 8.58170 (12), c = 6.67266 (11) Å, V = 271.100 (5) Å3 [ρcalc = 2949.04 (5) kg m−3], and at 300 K, a = 4.74598 (7), b = 8.58310 (10), c = 6.70933 (10) Å, V = 273.306 (4) Å3 [ρcalc = 2925.42 (4) kg m−3]. The thermal expansivities of the a and c axes, and the volumetric thermal expansion coefficient, are positive at all temperatures and normally behaved. However, the thermal expansion of the b axis is both very small and negative below ∼125 K. Structural and thermal motion parameters for β-MgSO4 as a function of temperature are also reported. [ABSTRACT FROM AUTHOR]

Using high-resolution neutron powder diffraction, the molar volume of a pure sample of D2O ice II has been measured, within its stability field, at 225 K, over the pressure range 0.25 < P < 0.45 GPa. Ar gas was used as the pressure medium, to avoid the formation of `stuffed ice' gas hydrates encountered when using He. The third-order Birch–Murnaghan equation of state parameters of helium-free D2O ice II, referenced to 225 K, are: V0,225 = 306.95 ± 0.04 Å3 (1299.7 ± 0.2 kg m−3), K0,225 = 12.13 ± 0.07 GPa, with fixed at 6.0. The thermal expansivity of metastable D2O ice II samples recovered to ambient pressure has also been measured, over the range 4.2 < T < 160 K; above 160 K an irreversible transition to ice I c was observed. The volumetric expansion coefficient, αV, at P = 0 and T = 225 K, is predicted to be 2.48 × 10−4 K−1. [ABSTRACT FROM AUTHOR]