Issue 20, 2009

Structural transitions and conductivity of BaPrO3 and BaPr0.9Y0.1O3−δ

Abstract

The temperature dependence of the crystal structures of the perovskites BaPrO3 and BaPr0.9Y0.1O3−δ has been determined between room temperature and 900 °C using time-of-flight neutron powder diffraction data. The orthorhombic room temperature structures evolve to a primitive cubic cellvia three changes of symmetry PnmaImmaR[3 with combining macron]cPm[3 with combining macron]m which occur at T ≈ 240, ≈ 375, and ≈ 860 °C for BaPrO3. The stability fields of the Pnma and Pm[3 with combining macron]m structures are lowered markedly by the presence of yttrium on the B-site. The first and last structural transitions are assigned as continuous events, and analysis of the octahedral tilt angle order parameter suggests the latter is tricritical in nature. The ImmaR[3 with combining macron]c transition is expected to be discontinuous first order and hysteresis effects in dilatometry data support this assignment although no discontinuity is found in the refined structural parameters. Conductivity data collected under dry, oxidising conditions reveal significantly higher conductivity levels in 10% acceptor (Y or Gd) substituted samples compared to undoped BaPrO3. For the acceptor substituted samples electron holes are the dominant charge carriers and the conductivity is weakly influenced by the changing crystal structure. In the undoped BaPrO3, a crossover, probably between extrinsic (impurity-derived) and intrinsic electronic conductivity, coincides with the high temperature rhombohedral to cubic transition.

Graphical abstract: Structural transitions and conductivity of BaPrO3 and BaPr0.9Y0.1O3−δ

Supplementary files

Article information

Article type
Paper
Submitted
02 Dec 2008
Accepted
02 Mar 2009
First published
26 Mar 2009

J. Mater. Chem., 2009,19, 3238-3247

Structural transitions and conductivity of BaPrO3 and BaPr0.9Y0.1O3−δ

C. S. Knee, A. Magrasó, T. Norby and R. I. Smith, J. Mater. Chem., 2009, 19, 3238 DOI: 10.1039/B820976F

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