Raman spectrum of strontium titanate

Abstract

The Raman spectrum of strontium titanate has been recorded using λ 4358 of mercury as exciter. The observed spectrum consists of 7 Raman lines, one of which is of low frequency, as expected from the recent theory of Cochran. 6 of these Raman lines have been interpreted as the first order spectrum arising from a small deviation of the cubic strontium titanate from its idealized symmetry. It has been shown that one normal mode of SrTiO₃ neglected by J. T. Last, will be really active in infrared absorption in the region of 440 cm^–1 and that it has to be taken into account in the interpretation of the infrared spectra of titanates. The four vibrational modes of the unit cell of SrTiO₃ correspond to frequencies of 90, 335, 441 and 620 cm^–1 observed in Raman effect. The large width of the Raman lines and the additional lines at 256 cm^–1 and 726 cm^–1 have been attributed to a splitting of the longitudinal and transverse optical modes. With the observed frequencies it has been found possible to account for in a satisfactory manner the specific heat of SrTiO₃ in the range 54·84°K to 1800°K.