1 Department of Energy Conversion and Storage, Technical University of Denmark 2 Mixed Conductors, Department of Energy Conversion and Storage, Technical University of Denmark 3 Rutherford Appleton Laboratory 4 Risø National Laboratory for Sustainable Energy, Technical University of Denmark 5 Rutherford Appleton Laboratory
The thermoelastic and structural properties of BaCeO3 perovskite in the Pbnm phase field have been studied using high resolution neutron diffractometry at 37 temperatures between 2 K and 350 K. From a simultaneous fit of the isochoric heat capacity and unit cell volume, the vibrational density of states in the Pbnm phase is shown to be approximated by a two-term modified Debye model with characteristic temperatures 176(1) K and 543(2) K. Vibrational Debye temperatures, determined from the temperature-variation of the atomic displacement parameters, suggest the cations to be more associated with the lower characteristic temperature, whilst those for the anions, are closer to the higher characteristic temperature. The weighted average of the Grüneisen constants associated with the two characteristic temperatures is in good agreement with the experimentally determined thermodynamic Grüneisen parameter. Structural parameters are presented as the amplitudes of the seven symmetry-adapted basis-vectors of the aristotype phase, and a structural basis for the temperature-dependence of the bond lengths is outlined. The critical exponent associated with the temperature variation of the primary order parameter in the phase transition from Pbnm to Ibnn at 563 K is consistent with this transition being tricritical in nature.©Copyright 2012 Published by Elsevier B.V. All rights reserved.
Solid State Ionics, 2013, Vol 232, p. 112-122
Crystal structure; Debye temperature; Neutron diffraction; Structural properties; Temperature distribution; Thermoelasticity; Perovskite
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