The complex elastic compliance and dielectric susceptibility of (Na0.5Bi0.5)1$-${}xBaxTiO3 (NBT-BT) have been measured in the composition range between pure NBT and the morphotropic phase boundary included, 0$\le${}x$\le${}0.08. The compliance of NBT presents sharp peaks at the rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the determination of the tetragonal region of the phase diagram, up to now impossible due to the strong lattice disorder and small distortions and polarizations involved. In spite of ample evidence of disorder and structural heterogeneity, the R-T transition remains sharp up to x=0.06, whereas the T-C transition merges into the diffuse and relaxorlike transition associated with broad maxima of the dielectric and elastic susceptibilities. An attempt is made at relating the different features in the anelastic and dielectric curves to different modes of octahedral rotations and polar cation shifts. The possibility is also considered that the cation displacements locally have monoclinic symmetry, as for PZT near the morphotropic phase boundary.

The complex elastic compliance $s_{11}(\omega ,T)$ of $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3-\delta }$ has been measured as a function of the O deficiency $\delta <0.01$. The two main relaxation peaks in the absorption are identified with hopping of isolated O vacancies over a barrier of $0.60\mathrm{eV}$ and reorientation of pairs of vacancies involving a barrier of $1\mathrm{eV}$. The pair binding energy is $\simeq 0.2\mathrm{eV}$, and indications for additional clustering, possibly into chains, is found already at $\delta \sim 0.004$. The anisotropic component of the elastic dipole of an O vacancy is $\Delta \lambda =0.026$. The possible role of electrostatic repulsion between vacancies in slowing the kinetics for their aggregation is discussed.

The elastic response of (Ba,Ca)(Ti,Zr)O₃ at compositions where the piezoelectric effect is maximized has been measured by different methods between 1 Hz and 250 kHz and compared with that of PZT at the middle of its morphotropic phase boundary. In all cases, the compliance is peaked at the border between the tetragonal (T) and the orthorhombic (O) phases, intermediate between the T and the low-temperature rhombohedral phase. The anomalies do not exhibit dependence on frequency and their relative amplitude is 200–300 times larger than the losses, demonstrating that they are intrinsic rather than due to the domain wall motion. This also demonstrates the role of an intermediate O or monoclinic phase in enhancing the transverse instability and piezoelectric coupling at a (morphotropic) phase boundary between R and T phases.

Internal friction and resonant frequency measurements have been carried out in $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$; after oxygen outgassing the material becomes semiconducting Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_6$ and the anelastic processes observed in the superconducting samples are suppressed. Instead, a new intense effect appears: The process is thermally activated (shifting from 56 to 75 K when the frequency changes from 1.1 to 17.4 kHz) with an activation energy $E_s=0.11\mathrm{}$ eV, and is only 25% broader than a single relaxation time process. It is attributed to the stress-induced hopping of residual free oxygen and the derived diffusion coefficient is $D=4\mathrm{}\times {10}^{-4\mathrm{}}\exp (-0.11\mathrm{} \frac{\mathrm{eV}}{\mathrm{kT}})$ ${\mathrm{cm}}^2$/sec, which extrapolated to room temperature is comparable with that of hydrogen in transition metals.