Behavior of the ferroelectric polarization as a function of temperature in sol-gel derived strontium bismuth tantalate thin films

Strontium bismuth tantalate (SBT) thin films of nominal composition Sr0.8Bi2.2Ta2O9 have been prepared on (111)Pt/TiO2/SiO2/(100)Si substrates by Chemical Solution Deposition (CSD) methods, using two different thermal treatments of crystallization. The evolution of the ferroelectric polarization as a function of temperature has been studied using hysteresis loops, thermo stimulated current (TSC) measurements and the evolution of the pyroelectric coefficient (γM) with temperature. The results of remnant polarization (Pr) obtained from hysteresis loops and γM as a function of temperature showed different trends, indicating the presence of polarizing bias field in the prepared thin films due to induced asymmetry of the electrical and mechanical conditions produced at the top and bottom film electrode interfaces. The competition between internal bias fields due to differences in contact potentials of bottom and top electrodes and flexoelectric bias fields induced by stress gradient, can be in the origin of the γM fluctuation with temperature. A critical temperature (T*) is found that can be explained as the crossover between the dominant effects. It can be related to a possible ferroelectric-ferroelectric phase transition previously reported. The results also indicate that the Pr is not stable for temperatures over ≈425 K.