Hysteresis loop of the ceramic is measured by Sawyer-Tower circuit shown in
Fig.1 . A sinusoidal field of Vrms and 50 Hz is applied to the sample with fixed C0.
The voltage across the ceramic (Cs) is recorded on the horizontal axis (X-axis) of the
oscilloscope, while the voltage across the capacitor (C0), which is proportional to the
polarization on the sample Cs, is recorded on the vertical axis (Y-axis) of the
oscilloscope. The measurement is carried out at room temperature.
To produce the uniaxial compressive pre-stress, a specially designed press,
shown in Fig.2, is used. In this device, force generated by a hydraulic press is
transmitted to the sample through a carefully aligned cylinder steel. The stress is
applied until the maximum value which the sample can endure and then is reduced to
zero.