Critical phenomena and phase transition in SOL-GEL derived ferroelectric PLZT thin films

Abstract

Lanthanum doped Pb(Zr, Ti)O₃ thin films have been fabricated by the solgel deposition technique. The small-signal dielectric constant ϵ has been investigated in the temperature range of 25°C to 550°C. The maximum value in the dielectric constant occurs at certain temperature for each particular composition. The apparent critical temperature is close to the Curie temperature reported in literature for the bulk material with similar composition. Lanthanum modified PbTiO₃ and PbZrTiO₃ have shown lower and broaden peaks. Ferroelectric hysteresis loops have been observed. The shape of the loop, the amplitude of the remnant polarization, and the coercive field significantly changed when the films were heated across the critical temperature that appeared in the dielectric constant curve. The critical temperature is assumed to be associated to the phase boundaries between the paraelectric-cubic and the ferroelectric tetragonal phases. A diffuse phase transition region were observed in lanthanum doped films.