Thermooptical properties of ferroelectric lead scandium tantalate PbSc_0.5Ta_0.5O₃ with a different degree of ordering

Abstract

Temperature variations of the refractive index have been studied in ferroelectric perovskites PbSc_0.5Ta_0.5O₃ (PST) with a different degree of ordering and in nonferroelectric crystal Pb₂ScTaO₆ (PST)' with pyrochlore-type structure. Measurements have been done at the wavelength 0.6328 μm in the temperature range from 120 to 1000 K. In ferroelectric perovskites a contribution of polarization to the index of refraction has been evaluated and it was found to exist ∼300 K above the ferroelectric transition temperatures. At low temperatures the polarization contribution to the index of refraction is as high as δn ^P ≃ 4 · 10⁻². It was found that the degree of ordering is clearly manifested in the position, shape and size of the δn(T)—anomaly near ferroelectric phase transition. Contrary to that the degree of ordering does not modify appreciably the general shape of δn(T)—curve at high temperatures.

Key Words:

• refractive index
• ferroelectric phase transitions