The features of acoustic property investigations carried out in different classes of ferroelastic crystals are considered. The special attention is given to elastic and anelastic properties of ferroelastics at low frequencies: the nonlinear hysteretic dependence of a strain on an external mechanical stress, a mechanical relaxation, a spontaneous twisting of samples below a Curie point, etc. Mechanisms of mechanical losses and nonlinear shear elasticity considering a rearrangement of lattice defects and their interactions are discussed.

Low-Frequency Shear Elasticity and Mechanical Losses in Ferroelastics

Effect of domain structure on the damping properties of LiNbO3/Al composites

Low-frequency internal friction (IF) of SrBi2Ta2O9 (SBT) ceramics has been measured at temperatures ranging from 293 to 623 K. Two IF peaks, with their locations around 393 K (P1) and 569 K (P2) (f ≈ 1.58 Hz), respectively, are observed. P1 is found to be associated with a relaxation process with activation energy of 0.97 eV and pre-exponential factor of 3.58 × 10-14 s. Peak shape analyses reveal that P1 can be well described by a broadened Debye peak with the width parameter β from 2.70 to 2.92. The mechanism responsible for P1 is proposed to be relaxation of oxygen vacancies near domain walls (DWs). P2 is considered to arise from viscous motion of DWs since it shows characteristics of static hysteresis type. Comparisons for the IF behavior between SBT and Pb(Zr, Ti)O3(PZT) suggest that in SBT oxygen vacancies are much less localized near DWs than that in PZT. This result provides a possible explanation for the weak DW pinning due to oxygen vacancies in SBT.

Low-frequency internal friction study for SrBi2Ta2O9 ferroelectric ceramics

The anelastic relaxation of lithium tantalate crystal is studied by using a multifunction inverted torsion pendulum. A relaxation internal friction (IF) peak is observed in the temperature range 100 degrees C to 350 degrees C and the orientation, domain and oxygen-deficiency effects on the IF peak are studied. The activation energy of this process is determined to be 1.26+or-0.02 eV and the IF peak is shown to be associated with the stress-induced anelastic motion of the electric domain boundaries.

Low-frequency mechanical relaxation in lithium tantalate

The internal friction Q−1 in LiNbO3 single-domain and poly-domain crystals is investigated It is found that the Q−1 maximum in the vicinity of 300°C is the supperposition of two peaks Q−1 maxima at −30 and 300°C are discussed in terms of the interaction model between domain boundaries and two types of charged point defects having different mobilities



[Russian Text Ignored]

S. A. Gridnev

Papers

Specific features of low‐frequency sound attenuation in LiNbO3 poly‐ and single‐domain crystals