Thermal expansion of the perovskite-type NdGaO3

Abstract

The structure of NdGaO3 was investigated by means of powder diffraction using synchrotron radiation in the temperature range 12–1173K. The NdGaO3 structure can be assigned to the GdFeO3-type (space group Pbnm) in the whole temperature range investigated. The thermal behaviour of the cell parameters was measured and found to be highly anisotropic. NdGaO3 shows practically the same thermal expansion along [100] and [001] directions, whereas the expansion along [010] is about 40% lower. In order to calculate the NdGaO3 thermal expansion three independent simulation techniques were applied: lattice dynamics, molecular dynamics and the Debye model. Using the GULP code and interatomic potentials described in the Buckingham form the Nd–O and Ga–O interactions have been derived. The total phonon DOS, its projections onto atomic species, the heat capacity Cv, the Grüneisen parameter γ and the thermal expansion coefficient α were determined using quasiharmonic lattice dynamics. Molecular dynamic simulations were applied to model the thermal expansion at different pressures and temperatures. The structure, its elastic properties and melting temperature are close to the experimentally observed values, which indicate the correct choice of the interatomic potential form and parameters. Comparison between the total DOS and its projections with the Debye DOS and Grüneisen parameter values calculated for different approaches allows to conclude that NdGaO3 cannot be considered as a good Debye-like solid.