RELATIONSHIP BETWEEN LINEAR AND QUADRATIC ELECTRO‐OPTIC COEFFICIENTS IN LiNbO3, LiTaO3, AND OTHER OXYGEN‐OCTAHEDRA FERROELECTRICS BASED ON DIRECT MEASUREMENT OF SPONTANEOUS POLARIZATION

The spontaneous polarizations in LiNbO3, LiTaO3, and Ba2NaNb5O15 have been measured directly at room temperature by a field reversal method and found to be Ps (LiNbO3) = 0.71 C/m2, Ps (LiTaO3) = 0.50 C/m2, and Ps (Ba2NaNb5O15) = 0.40 C/m2. Using these values we show that the linear electro‐optic effect in these materials is related fundamentally to a biased quadratic effect associated with each BO6 octahedron. Based on this result, predictions are made of the spontaneous polarization in other oxygen‐octahedra ferroelectrics.

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