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2013.12.009

42 Piezoelectric Materials

2014.04.026

4. doi:10.1088/0022-3727/41/4/045402

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/62711

#### **Abstract**

Sound velocities were measured in relaxor single-crystal plates and piezoelectric ceramics including lead free using an ultrasonic precision thickness gauge with high-frequency pulse generation. Estimating the difference in the sound velocities and elastic constants in the single crystals and ceramics, it was possible to evaluate effects of domain and grain boundaries on elastic constants. Existence of domain boundaries in single crystal affected the decrease in Young's modulus, rigidity, Poisson's ratio, and bulk modulus. While existence of grain boundaries affected the decrease in Young's modulus and rigidity, Poisson's ratio and bulk modulus increased. It was thought these phenomena come from domain alignment by DC poling and both the boundaries act as to absorb mechanical stress by defects due to the boundaries. In addition, the origin of piezoelectricity in single crystals is caused by low bulk modulus and Poisson's ratio, and high Young's modulus and rigidity in comparison with ceramics. On the contrary, the origin of piezoelectricity in ceramics is caused by high Poisson's ratio by high bulk modulus, and furthermore, low Young's modulus and rigidity due to domain alignment.

**Keywords:** relaxor single crystals, sound velocities, elastic constants, domain boun‐ dary, grain boundary, piezoelectric ceramics
