Elastic anomalies associated with transformation sequences in perovskites: I. Strontium zirconate, SrZrO3

Elastic behaviour associated with the hierarchy of tilting transitions in SrZrO3 has been examined using resonant ultrasound spectroscopy on a ceramic sample at temperatures between 153 and 1531 K. Changes in slope of the evolution of resonance frequencies with temperature indicate that phase transitions occur at 1038 K (Pnma <-> Imma), 1122 K (Imma <-> 14/mcm), and 1367 K (14/mcm <-> Pm (3) over barm). Strain analysis of previously recorded neutron diffraction data shows that the 14/mcm <-> Pm (3) over barm and Pnma <-> Imma transitions are close to tricritical in character, and that Imma <-> 14/mcm is first order. Deviations from the form of the elastic behaviour predicted by Landau theory are found. In particular, elastic softening in the vicinity of the Imma <-> 14/mcm transition suggests that local dynamical fluctuations between individual tilt systems occur, rather than a discontinuous switch from one phase to another. Determinations of the mechanical quality factor, Q, show that SrZrO3 in the Pm (3) over barm phase is a classically high-Q (i.e. non-dissipating) cubic material. 14/mcm and Imma phases both have much greater dissipation (low Q), which is tentatively attributed to the mobility of twin walls. The room temperature Pnma phase is unexpectedly much stiffer than both 14/mcm and Imma phases and has high Q. It appears that when two separate tilt systems operate, as in Pnma, they can interact to reduce strain/order parameter relaxations.