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Abstract
In this work, ellipsometric investigation of high temperature phase transitions in PbZr0.235 Ti0.765O3 (PZT) and (Zn0.7Li0.3)O thin films are presented. Ellipsometric measurements were performed by means of a J. A. Woollam spectral ellipsometer operating in rotating analyzer mode. The main ellipsometric angles Ψ and Δ were measured in the spectral range from 200 to 1200 nm. High temperature measurements were carried out with a specially designed heating system. The samples were heated up to 550°C. The temperature dependences of the refractive index and absorption coefficient at fixed wavelengths and the optical gap Eg were calculated from ellipsometric data. High sensitivity of ellipsometry allowed us to observe the well-known ferroelectric → paraelectric phase transition and to find a new phase transition in PZT films. High temperature measurements performed for (Zn0.7Li0.3)O films didn't confirm the ferroelectric phase transition at ∼70°C described in [1]. However, strong changes of ellipsometric parameters at 470°C and change of band gap temperature behavior at 300°C were found. The determination of the absorption gap temperature dependence near this temperature confirmed strong structural changes.