The ferroelastic domain processes responsible for low-frequency anelasticity in ${\mathrm{LaAlO}}_3$ have been investigated using dynamical mechanical analysis in three-point bend geometry combined with in situ optical observations under dynamic stress at high temperature. Transformations in the types of collective motion of domain walls have been observed optically. For low temperatures and small forces, the anelastic response is dominated by rapid advancement/retraction of combs of $\{100{\}}_{\mathrm{pc}}$ needle domains. At higher temperatures, lateral translation/rotation of $\{110{\}}_{\mathrm{pc}}$ twins also contributes to the response. Needle tips are pinned by a broad range of potentials, such that the ratio of mobile to static needle tips increases steadily with increasing temperature. For large forces, three distinct peaks in the relaxation spectrum can be resolved. A small low-temperature peak in the mechanical loss is attributed to the rapid saturation of weakly pinned needles. The dominant intermediate-temperature loss peak is attributed to the gradual relaxation of the comb as a whole. A third high-temperature loss peak occurs at the end of the domain-freezing regime and the beginning of the saturation regime. Activation energies for domain-wall motion of 95, 85, and 86 kJ/mol were determined for samples subjected to low, intermediate, and high forces, respectively. Cole-Cole plots of the response at small forces show a linear section at intermediate frequency and a depressed semicircle at low frequency. The semicircular portion is very well described by the Cole-Cole equation with a broadening exponent μ. Physically, this model corresponds to a Debye-like relaxation process with a distribution of activation energies (domain-sliding regime). The broadening of the relaxation peak is a function of temperature, with μ decreasing from 0.7 at 130 °C to 0.5 at 205 °C. This corresponds to an increase in the full width at half maximum of the activation-energy distribution from 9 to 21 kJ/mol. Fits to the entire data set suggest a parabolic temperature dependence of μ with maximum at ∼120 °C. A number of physical processes are suggested to explain this phenomenon. The linear portion of the Cole-Cole plots provides evidence for a dynamic “transition” between the domain-sliding and thermally activated creep regimes with increasing frequency.

• Received 16 September 2003

DOI:https://doi.org/10.1103/PhysRevB.69.144101