Structural and thermoelastic study of the protonic conducting perovskite SrCe0.95Yb0.05Oξ (ξ ∼ 3) between 373 K and 1273 K

Abstract

The temperature dependence of the crystal structure of the protonic conducting perovskite SrCe0.95Yb0.05Oξ (ξ ∼ 3) has been determined from Rietveld refinement of neutron time-of-flight powder diffraction data in 25 K steps from 373 K to 1273 K. In contrast to most SrBIVO3 perovskites which show a sequence of structural phase transitions from Pmcn – Incn – I4/mcm - \( Pm\overline 3 m \) with increasing temperature, SrCe0.95Yb0.05Oξ remains orthorhombic with space group Pmcn from 4.2 K to the highest temperature measured. Crystallographic results are presented graphically in the form of the magnitude of the seven unique symmetry adapted basis vectors of a hypothetical aristotype perovskite phase. Thermoelastic properties of SrCe0.95Yb0.05Oξ deduced from the temperature variation of the unit cell volume and Debye-Waller factors are compared with literature values derived from independent calorimetric, Raman and elastic measurements. Thermodynamically, SrCe0.95Yb0.05Oξ behaves as a Debye-like solid with an average Gruneisen parameter in the range 1.4–1.5, but with two characteristic temperatures, ∼200 K and ∼600 K, the lower temperature being more related to the cation vibrations, the higher to the anion vibrations.