Journal
SOLID STATE SCIENCES
Volume 43, Issue -, Pages 15-21Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.solidstatesciences.2015.03.016
Keywords
NaTaO3; Crystal structure; Neutron diffraction; Phase transitions
Funding
- Australian Research Council
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Room temperature high resolution neutron powder diffraction data, measured in time-of-flight, from two independent samples of NaTaO3 shows the presence of phase coexistence of two orthorhombic structures with space groups Pbnm, and Cmcm. The failure of earlier work to recognise the extent of the hysteresis associated with the high temperature (similar to 763 K on heating) Cmcm - Pbnm phase transition, that extends down to room temperature, and probably to 0 K, is due to data having been collected at too low a real-space resolution to characterise the diagnostic pseudocubic fundamental and superlattice reflection multiplicities. The phase fraction of the Cmcm phase increases with increasing temperature from 45 weight % at 298 K, to 74 weight % at 758 K. Throughout the whole temperature interval 298 K-758 K, the volume per formula unit of the Cmcm phase exceeds that of the Pbnm phase by an almost constant similar to 0.01 angstrom(3) suggesting the addition of pressure would supress the volume fraction of the higher temperature phase. The crystal structure of both phases, determined from data collected at 298 K, are reported, with the atomic displacement parameters of the Cmcm phase being significantly larger than those associated with the Pbnm phase, probably reflecting a high degree of thermal and static disorder. (C) 2015 Elsevier Masson SAS. All rights reserved.
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