Large variation is found in the reported values of the principal indices of BaTiO<sub>3</sub>. According to Wemple <i>et al.</i> and Johnston, <i>n</i><sub>0</sub> should be greater than 2.425 (λ<sub>Na</sub>), whereas according to Lawless and DeVries and other workers it is of the order of 2.370. The methods employed by these workers involve the passage of light through the body of the crystal. We have used the phenomenon of polarization by reflection to determine these indices and have found <i>n</i><sub>0</sub> = 2.428 ± 0.002 and <i>n</i><sub><i>e</i></sub> = 2.371 ± 0.0045, closely agreeing with the earlier workers. The method is described at length because it is not common. ts accuracy has been demonstrated by redetermining the principal indices of calcite.
© 1980 Optical Society of AmericaPDF Article