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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.

The room-temperature spontaneous polarizations in LiNbO3, LiTaO3, Ba2NaNb5O15, Sr0.5Ba0.5Nb2O6, Ba1.1Sr0.9NaNb5O15, and Sr2KNb5O15 have been measured directly by a pulsed field method using an aqueous solution of LiCl as the electrode material. The experimental results are: P8 (LiNbO3) = 0.71±0.02 C/m2, P8 (LiTaO3) = 0.50±0.01 C/m2, P8 (Ba2NaNb5O15) = 0.40±0.01 C/m2, P8 (Ba1.1Sr0.9NaNb5O15) = 0.36±0.01 C/m2, P8 (Sr2KNb5O15) = 0.25±0.01 C/m2, and P8 (Sr0.5Ba0.5Nb2O6) = 0.25±0.01 C/m2. Experimental techniques are presented, and the advantages of the pulsed-field method over hysteresis-loop methods are discussed.

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