Determination of the Low-Frequency Linear Electro-Optic Effect in Tetragonal BaTiO_3†

The magnitude of the linear electro-optic effect at 5461 Å in single-crystal barium titanate has been determined in the temperature range from 5° to 120°C. The low-frequency or stress-free values were obtained for r42 and rc = r33 − (na/nc)3r13. The polarimetric measurement did not separate r33 from r13. The quantity r42 was found to vary as Ka, the dielectric constant effective for the a-directed electric field. Similarly, rc was approximately proportional to KcPs, the product of the "c" dielectric constant and spontaneous polarization, but did not rise quite as fast as KcPs with increasing temperature. The difference was outside experimental uncertainty. The values found at 25°C were rc = 1.08×10−8 cm/V; r42=16.4×10−8 cm/V.