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The quasi-transverse ultrasound absorption in cubic crystals with positive and negative anisotropies of the second-order elastic moduli is analyzed. The scattering of the ultrasound by point defects and during anharmonic scattering processes is considered. The quasi-transverse ultrasound absorption is analyzed as a function of the wavevector direction in terms of the anisotropic continuum model. The Landau-Rumer mechanism is considered for anharmonic scattering processes. Known values of the second- and third-order elastic moduli are used to calculate parameters determining the ultrasound absorption. It is shown that the angular dependences of the quasi-transverse ultrasound absorption differ qualitatively if the anharmonic scattering processes dominate in cubic crystals with positive and negative anisotropies of the second-order elastic moduli. For the scattering by point defects and the anharmonic scattering processes, the angular dependences of the quasi-transverse ultrasound absorption exhibit the inverse behavior, making it possible to determine the dominating mechanism of the ultrasound relaxation in the crystals under study.

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A comparative analysis of 6,7 Li NMR spectra is performed for the samples of monoclinic lithium titanate obtained at different synthesis temperatures. In the 7 Li NMR spectra three lines are found, which differ in quadrupole splitting frequencies Q Q and according to ab initio EFG calculations are assigned to three crystallographic sites of lithium: Li1 (Q Q a 27 kHz); Li2 (Q Q a 59 kHz); Li3 (Q Q a 6 kHz). The dynamics of lithium ions is studied in a wide temperature range from 300 K to 900 K. It is found that the narrowing of 7 Li NMR spectra as a result of thermally activated diffusion of lithium ions in the low-temperature Li 2 TiO 3 sample is observed at a higher temperature in comparison with a sample of high-temperature lithium titanate. Based on the analysis of 6 Li NMR spectra it is assumed that there is mixed occupancy of lithium and titanium sites in the corresponding layers of the crystal structure of low-temperature lithium titanate, which hinders lithium ion transfer over regular crystallographic sites.

The quasi-transverse ultrasound absorption during anharmonic processes of the scattering in cubic crystals with positive (Ge, Si, diamond and InSb) and negative (KCl and NaCl) anisotropies of the second-order elastic moduli is studied. Mechanisms underlying the relaxation of the slow quasi-transverse mode by two slow (the SSS mechanism) or two fast (the SFF) modes are discussed in the long-wavelength approximation. Angular dependences of the ultrasound absorption for the SSS, SFF and Landau-Rumer relaxation mechanisms are analyzed in terms of the anisotropic continuum model. The full absorption of the slow quasi-transverse mode is determined. It is shown that the SSS and SFF relaxation mechanisms are due to the cubic anisotropy of the crystals, leading to the interaction between noncollinear phonons. Two most important cases-the wavevectors of phonons are in the cube face plane or the diagonal planes-are considered. In crystals with a considerable anisotropy of the elastic energy (Ge, Si, InSb, KCl and NaCl) the total contribution of the SSS and SFF relaxation mechanisms to the full absorption is either several times or one to two orders of magnitude larger than the contribution from the Landau-Rumer mechanism depending on the direction. Much of the dominance of the former relaxation mechanisms over the Landau-Rumer mechanism is explained by second-order elastic moduli.