Thermal Depolarization in the High‐Temperature Ternary Piezoelectric System <i>x</i> PbTiO ₃ – <i>y</i> BiScO ₃ – <i>z</i> Bi(Ni _1/2 Ti _1/2 )O ₃

Abstract

In the high‐temperature ternary perovskite piezoelectric system x PbTiO 3 – y BiScO 3 – z Bi ( Ni 1/2 , Ti 1/2 ) O 3 ( PT – BS – BNiT ), the addition of bismuth to the A site and nickel to the B site leads to compositions that exhibit diffuse relaxor‐like behavior. For these, depolarization temperature, not Curie point, is the critical value of temperature. Depolarization temperature ( T d ) is defined as the temperature at which the steepest loss in polarization occurs. This temperature is observed in poled materials through two different methods: loss tangent measurements and in situ d 33 . Across the ternary system, multiple dielectric anomalies occurred which was observed in dielectric tests where the dielectric peak broadens and becomes frequency dependent as BNiT content increased. For different compositions, the value of T d ranged between 275°C–375°C. Values for the piezoelectric coefficient increased with temperature up to d 33 = 1000 pC/N during in situ d 33 . High temperature (up to 190°C) and high field (up to 40 kV/cm) were also applied to test ferroelectric properties in these regimes.