Pseudoproper ferroelastic softening behaviour and dynamic microstructure of monoclinic PrAlO₃ perovskite

Abstract

Elastic and anelastic properties of single crystal PrAlO₃ have been investigated by resonant ultrasound spectroscopy at 0.2–1.2 MHz. Non-linear (pseudoproper) softening with falling temperature in the stability field below ∼690 K is related to the elastic stability limit . Before this instability point is reached, the first order Imma transition intervenes and is marked by a steep minimum in shear elastic constants. Further pseudoproper ferroelastic softening then occurs, consistent with at ∼151 K for the second-order Imma ↔ C2/m transition. Superattenuation of acoustic resonances within the stability field of the C2/m structure implies that the monoclinic twin walls are highly mobile, apart from in a narrow temperature interval near 100 K where the structure becomes metrically tetragonal. PrAlO₃ appears to represent a general class of Jahn–Teller phase transitions in perovskites for which the predominant order parameter transforms according to symmetry and which displays an unusual anelastic dissipation.

Keywords:

• PrAlO₃
• elastic softening
• pseudoproper ferroelastic
• Jahn–Teller
• superattenuation

Acknowledgements

The authors thank Andy Buckley and Paul Taylor for their help in establishing and maintaining RUS facilities in Cambridge, which were set up with a grant from the Natural Environment Research Council (NE/B505738/1) to MAC.