Study Of Acoustical Properties In Crystals And Ceramics

Along with the development of the technology and industry, people require more and more characteristics of the materials, and the environmental protection requirements are increasingly high. People are not satisfied with single component crystals. Multi-component crystals can take advantage of various single component crystals, in addition, multi-component crystals can develop some new properties, so people do a lot of research on them. This paper studies on the sound propagation characteristics of the single crystal, multi-component crystals and ceramics. The physical properties of the crystals and ceramics and guidance of the corresponding design have a prospect of application.In order to study the pure modes of PMN-PT with different content of PT, this paper introduce a method to study the pure mode of the crystals through the slowness surface. Different contents of PT will lead to the differences of crystalline structure.With the increment of PT, PMN-PT will turn into ferroelectric, tetragonal phase symmetry from the rhombohedral phase symmetry, and there is a MPB. The slowness surfaces of PMN-0.30PT,PMN-0.33PT and PMN-0.42PT on different planes are analyzed in detail. This paper summarizes the pure modes of PMN-PT, showing the differences of the velocity of the transverse wave and the longitudinal wave and the diversity of anisotropy. Analysis results show that PMN-PT crystals nearby MPB have stronger anisotropy characteristics, more pure modes and great variation of velocity of elastic wave.This paper also studies the interaction of the sound waves, and we derive the evolution equations for the wave amplitudes and find analytical formulas for all interaction coefficients of quadratically non-linear interacting waves. We derive general formulas for the interaction coefficients of plane waves in medium including cubic, trigonal, tetragonal, hexagonal crystals. The formulas are expressed in terms of the derivatives of the strain energy. We use our formulas to calculate the interaction coefficients in the general anisotropic medium emphasizing the influence of nonlinearities.There already has theories and experiments on the linear and nonlinear characteristics of the LiNbO3crystals. It shows the velocity and the attenuation has abnormal change at75℃. But there is still no report on the nonlinear acoustics characteristics of the LiTaO3crystals. Based on the technique of second harmonic generation, the sound velocity, the amplitude of fundamental frequency, second harmonic changing with the temperature are studied.PIN-PMN-PT is one of the important materials for transducers, particularly for ultrabroad-band medical ultrasonic imaging transducers. This paper deeply studies the linear and nonlinear acoustics properties of PIN-PMN-PT. The samples are poled in [001] and [111] respectively. We have experiments to show the relationship of the velocity, the attenuation and the nonlinear parameters with the temperature. It shows the acoustic properties of PIN-PMN-PT poled in [001] change drably. But those of PIN-PMN-PT poled in [111] are different, it has inflexion point.High-order nonlinear behaviors in PZT ceramics were studied using the harmonic generation technique, both before and after poling. It was found that the amplitude of the third harmonic is smaller than that of the second harmonic before poling, but the situation is reversed after poling with a substantial increase of the third harmonic amplitude. Noticeable time dependence of nonlinearities was observed in poled ceramics, which gradually decreased and saturated after about two days. These facts confirmed the generation of microcracks during poling.At the same time, we study the NBT ceramics and the BZT ceramics. In this paper, we study the relationship of the phase transition temperature and the mutation temperature of the sound velocity in the ceramics. The NBT ceramics has phase transition at a higher temperature, and in the100℃scope, there was little change in velocity. While the velocities of the BZT-7and BZT-15ceramics as a function of the temperature show differently. At70℃, the velocity of BZT-7have significantly change, range up to12.5%. that matches the facts that BZT-7has the phase transition at70℃. At60℃nearby, the velocity of the BZT-15ceramics also has a significant change, which is more apparent than BZT-7, range up to34.6%. While BZT-15has the phase transition at58℃. These facts show that the phase transition temperature can be measured by measuring the relationship of sound velocity with the temperature in the ceramics.