Pressure and electric field effects on piezoelectric responses of KNbO ₃

The dielectric and piezoelectric properties of a KNbO ₃ single crystal under applied hydrostatic pressure and positive bias electric field are investigated using phenomenological Landau-Ginzburg-Devonshire thermodynamic theory. It is shown that the hydrostatic pressure effect on the dielectric and piezoelectric properties is similar to temperature, suggesting a common underlying mechanism for the piezoelectric anisotropy and its enhancement. The stable phase diagram of KNbO ₃ as a function of temperature and positive bias electric field is constructed. The maximum piezoelectric coefficient d 33 o varying with temperature and electric field is calculated.