Ukrainian Journal of Physical Optics 

Institute of Physical Optics, Laboratory of gradient optics, polarimetry and phase transitions, 23 Dragomanov Str., 79005, L’viv, Ukraine

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In this paper combined piezo-electrooptical effect in Pb₅Ge₃O₁₁ crystals was studied. The temperature dependencies of birefringence change d(Dn)₁₃ for the lead germanate crystals at proper ferroelectrical phase transition were investigated under the influence of mechanical strain s₃₃. It was shown that the application of compressive strain s₃₃ leads to the increasing of phase transition temperature and dT_c/s₃₃=0.47*10^-6 Km²/N. The temperature change of birefringence can be described by a quadratic electrooptical effect induced by spontaneous polarization. The calculated value of the Kerr effect coefficient for the paraelectrical phase is n₃³ R₃₃₃₃-n₁³ R₁₁₃₃ =0.9 m⁴/C².The temperature dependence of piezooptical constants for the lead germanate crystals n₃³p₃₃₃₃ -n₁³p₁₁₃₃ was experimentally studied. It was shown that these dependences are described by a combined piezo-electrooptical effect induced by spontaneous polarization and external mechanical strain. The temperature change of n₃³p₃₃₃₃ -n₁³p₁₁₃₃ is proportional to the square of P_s. The calculated value of the coefficients of combined piezo-electrooptical effect  is n₃³N₃₃₃₃ -n₁³N₁₁₃₃==0.73x10^-8 m²/NC².

Keywords: combined effects, piezo-electrooptical effect, ferroelectrical phase transition, lead germanate crystals

doi 10.3116/16091833/2/4/187/2001