http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11043 Resonant ultrasound spectroscopy has been used on single-crystal samples to observe pseudoproper ferroelastic softening across the (La,Pr)AlO₃ solid solution. It is suggested that softening is due to the presence of an intrinsic zone-center instability in addition to the small Jahn-Teller stabilization expected for Pr³⁺. Softening increases as smaller Pr³⁺ ions are substituted for larger La³⁺ which is attributed to a simple size effect as well as the possibility of bilinear coupling of the intrinsic instability with the weak Jahn-Teller effect. Superattenuation is observed above 600 K for all samples, which is consistent with twin wall related dissipation behavior seen in other perovskites with octahedral tilting. Superattenuation is also observed in the lowtemperature monoclinic phase, implying a high mobility also for the monoclinic twin walls. 2012-07-03T04:36:40.717Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7709 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 ↔ I4/mcm), and 1367 K (I4/mcm ↔ Pm3m). Strain analysis of previously recorded neutron diffraction data shows that the I4/mcm ↔ Pm3m and Pnma ↔ Imma transitions are close to tricritical in character, and that Imma ↔ I4/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 ↔ I4/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 Pm3m phase is a classically high-Q (i.e. non-dissipating) cubic material. I4/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 I4/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. 2011-09-13T00:41:06.701Z ]]>