I have carried out polarization measurement of PMN-PT ceramic sample with temperature through PE hysteresis loops and have found that polarization decreases upto 70 oC and then increases. In general, it is known that spontaneous polarization decreases with increasing temperature in ferroelectric systems and this is also seen in our case upto 70 oC. But I do not understand what makes the polarization increase again after 70 oC.
I have no idea about this polarization behavior. Kindly help me on this.