HR: 1340h
AN: NG33A-0171    [Abstracts]
TI: Phase transitions, domain wall relaxation, and anelastic response in perovskite.
AU: * Redfern, S A
EM: satr@cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences Downing Street, Cambridge, CB2 3EQ United Kingdom
AU: Daraktchiev, M
EM: mdar04@esc.cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences Downing Street, Cambridge, CB2 3EQ United Kingdom
AU: Harrison, R J
EM: rjh40@esc.cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences Downing Street, Cambridge, CB2 3EQ United Kingdom
AB: The mechanical loss behaviour of a number of oxide perovskites (selected as structural analogues of MgSiO₃) has been studied below ferroelastic phase transitions occuring between room temperature and 1000°C by dynamical mechanical analysis. The loss spectrum (measured as a function of temperature, frequency and magnitude of applied dynamic stress) of perovskite typically shows an anelastic relaxation peak in the tetragonal phase and close to zero mechanical losses in the cubic and orthorhombic phases. The relaxation times of such microstructural features are typically in the range of seismic waves. The peak and the softening of the storage modulus around the peak temperature is associated with a motion of transformation twin domain walls which are formed through the phase transitions from the twin-free cubic phase. We find a small value of internal friction in the orthorhombic phase of oxide perosvksites when the spontaneous volume strain associated with the phase transition is negative. The volume strain correlates with the domain wall width and the effectiveness of pinning of walls by lattice defects. The volume changes and mechanical loss in Ca_1-xSr_xTiO₃ were compared with those in Sr_xBa_1-xSnO₃, a system which shows a positive volume strain. In contrast to Ca_1-xSr_xTiO₃, the Sr_xBa_1-xSnO₃ spectrum shows a thermally activated peak in the orthorhombic phase. A frequency-independent peak attributed to the tetragonal-orthorhombic transition is also detected. The positive volume strain in Sr_xBa_1-xSnO₃ is associated with thick domain walls, which are insensitive to defect distribution and lattice singularities at low temperature. The patterns of domain wall relaxation in these microstrcutured solids themselves show phase transitions between different modes of relaxation as a function of applied force. The results indicate that domain wall relaxation must be considered as a potential source of anelasticity in ferroelastic microstructured silicates such as MgSiO₃ perovskite.
UR: http://www.esc.cam.ac.uk/astaff/redfern/domains.html
DE: 3909 Elasticity and anelasticity
DE: 4425 Critical phenomena
DE: 4460 Pattern formation
DE: 4465 Phase transitions
DE: 5144 Wave attenuation
SC: Nonlinear Geophysics [NG]
MN: Fall Meeting 2005