The Electromechanical Behavior of BaTiO3Single-Domain Crystals

The electromechanical response of BaTi${\mathrm{O}}_3$ single-domain crystals was investigated as a function of temperature from room temperature to above the Curie point. It was found that when we eliminate domain effects, either by using a perfect single-domain crystal or by aligning the domains by an external electric field, we are dealing with a true linear piezoeffect. The linear piezoeffect was measured by both a static and a dynamic method. The values of the $d_{31}$ piezoelectric coefficient were compared with those calculated from the dielectric constant and the spontaneous polarization. The behavior of the piezoelectric resonance frequency was observed also through the same temperature range. Although the crystal is cubic above the Curie point and has a center of symmetry, the piezoelectric response persisted under the application of an external d.c. field because the external field will induce a tetragonal crystal structure through the electrostrictive effect, so that the crystal becomes piezoelectric again above the Curie point. Optical and dielectric measurements were found to verify these results.