Thermal expansion and atomic displacement parameters of cubic KMgF₃perovskite determined by high-resolution neutron powder diffraction

Abstract

The structure of KMgF 3 has been determined by high-resolution neutron powder diffraction at 4.2 K, room temperature and at 10 K intervals from 373 K to 1223 K. The material remains cubic at all temperatures. The average volumetric coef®cient of thermal expansion in the range 373±1223 K was found to be 7.11 (3) Â 10 À5 K À1. For temperatures between 4.2 and 1223 K, a secondorder Gru È neisen approximation to the zero-pressure equation of state, with the internal energy calculated via a Debye model, was found to ®t well, with the following parameters: D = 536 (9) K, V o = 62.876 (6) A Ê 3 , K H is a Gru È neisen parameter. The atomic displacement parameters were found to increase smoothly with T and could be ®tted using Debye models with D in the range 305±581 K. At 1223 K, the displacement of the F ions was found to be much less anisotropic than that in NaMgF 3 at this temperature.

Thermal expansion of CaIrO3 determined by X-ray powder diffraction

“…In particular, the neglect of anharmonicity can lead to an underestimate of the thermal expansion coefficient at high temperatures (see e.g. Wood et al 2002), but there is little indication of this in the present case.…”

Thermal expansion and crystal structure of cementite, Fe3C, between 4 and 600 K determined by time-of-flight neutron powder diffraction

“…Two very recent studies of the ambient-temperature equation of state of this material (Scott et al, 2001;Li et al, 2002) have been made using high-pressure X-ray powder diffraction with diamond-anvil cells. The results obtained for the incompressibility, K o , and its ®rst derivative with respect to pressure, K Wood (1993). At ®rst sight, it might, therefore, be concluded that the case for Fe 3 C as a major component of the inner core has been signi®cantly strengthened by these measurements.…”

“…The physical properties of the cementite phase of Fe 3 C have been of interest to Earth and planetary scientists since it was suggested (Wood, 1993) that they were consistent with those of the Earth's inner core. Two very recent studies of the ambient-temperature equation of state of this material (Scott et al, 2001;Li et al, 2002) have been made using high-pressure X-ray powder diffraction with diamond-anvil cells.…”

High-resolution structure studies and magnetoelectric coupling of relaxor multiferroicPb(Fe0.5Nb0.5)Sim1, Peets2, Lee3 et al. 2014Phys. Rev. B15060View full textAdd to dashboardCite

“…In order to further analyze the temperature dependence of the unit-cell volume, the Debye-Grüneisen formula [23] was used…”

“…D is related to zero-point energy of the atoms concerned with atomic mass M i [23]. However, it was necessary to add constant offsets to A to achieve better agreement.…”