Characterization of aliovalent substituted relaxor piezocrystals for high-power applications

Oriented piezocrystals in system Pb(BNb2/3)O3 - PbTiO3 (B = Zn,Mg) of near and at the morphotropic phase boundary (MPB) composition, are known to exhibit high dielectric and piezoelectric constants. Previous investigations have focused on off-resonance and low power resonance properties. However, investigation under high power resonance conditions has still not been addressed. Further, there is no account of the degree of nonlinearity exhibited by these crystals under resonance condition. The purpose of this thesis is to investigate the piezoelectric and electromechanical properties of modified (1-x)Pb(Zn1/3Nb2/3)O3 - xPbTiO3 (PZNT) (x = 0.08, 0.09) and 0.68Pb(Mg1/3Nb 2/3)O3 - 0.32PbTiO3 (PMNT) single crystals under high power resonance conditions. Investigations were focused on the compositions close to the morphotropic phase boundary in the rhombohedral side.;Firstly, a resonance method for measuring the complex elastic and electromechanical properties of piezoelectric materials under high power operational conditions was developed. This method was applied to study the complex elastic and electromechanical properties of Pb(Zn1/3Nb2/3)O3 - PbTiO 3 (PZNT) and Pb(Mg1/3Nb2/3)O3 - PbTiO3 (PMNT) single crystals under high power operational conditions. Under resonant high-power drive, it was found that electromechanical nonlinearities are due to elastic ones, as the elastic and electromechanical properties were both found to scale with the square of the strain amplitude. The temperature (T) and ac electric field (Eac) dependence of the mechanical quality factor Qm was also determined. Iso-Qm curves were constructed that can be used to predict performance criteria for high power applications of piezoelectric materials.;Secondly, in order to improve the hard characteristics of PZN-based crystals, Mn, Fe and Co-doped Pb(Zn1/3Nb2/3)O3 (PZN) and PZNT single crystals were grown by modified flux technique.;Thirdly, in order to understand the behavior of the piezocrystals under high power drive, dielectric aging and loss mechanisms were studied.;Previously, dielectric losses in piezoelectric has been attributed to the domain wall contributions. However, it was found that in piezocrystals, structural irregularities and polarocaloric effect make significant contribution. (Abstract shortened by UMI.)...