Interferometric determination of the temperature dependence of the refractive index of relaxor PLZT ceramics under DC bias

Changes in the refractive indices Δn1 and Δn3 of clamped transparent relaxor ferroelectric (9.5/65/35) and (9.0/65/35) PLZT ceramics were measured as a function of temperature ranging from −30 °C to 60 °C, and at various transversely applied DC electric fields E3DC. It was found that the refractive index of both PLZT compositions increased linearly with temperature under no DC bias, indicating a constant electronic polarizability of the samples in the tested temperature range. The rate of increase of Δn3 with temperature became higher for both compositions upon the application a DC bias field (E3DC=774kV/m) due to increased electronic polarizability of the samples, while the rate of increase of Δn1 with temperature remained unchanged and was independent of the DC field applied. The quadratic electro-optic coefficients of these two PLZT compositions were also obtained at 0, 20 and 40 °C, and a significant non-linearity was observed: an 85% decrease in the electro-optic coefficient of PLZT (9.5/65/35) was measured at 40 °C compared to 0 °C, while a similar 60% drop was measured for PLZT (9.0/65/35).