Raman spectra of the second order in crystals Part III. Quartz

Abstract

A detailed study has been made of the Raman effect in quartz using the λ2536.5 mercury radiation as exciter. The spectrum consists of 43 Raman lines, nearly half of them have been recorded for the first time. Of these, fourteen Raman lines including two doublets constitute the internal oscillation spectrum of the unit cell of the quartz lattice. The frequency shifts of these have been very accurately determined. Of the remaining 29 lines which constitute the second order spectrum of quartz, 17 have been satisfactorily explained as octaves and combinations of some of the principal frequencies. The 12 Raman lines which are not explicable as combinations and overtones of the principal frequencies, constitute in part the superlattice spectrum of quartz to be expected on the basis of the Raman theory of crystal dynamics. The specific heat of quartz has been evaluated on the assumption that the vibration spectrum consists of only 16 principal frequencies, 12 appearing in the Raman effect and 4 in the infra-red absorption. The calculated values of the specific heat were lower than the observed values over the range of temperature from 25.8°T to 803 .6°T. It is pointed out that the neglect of the super-lattice frequencies is responsible for the above discrepancy. The Brillouin components due to longitudinal sound waves in quartz have been successfully photographed using an aluminised Fabry-Perot etalon. The dependence of the form of the interference pattern on crystal orientation has been quantitatively accounted for on the basis of the variation of acoustic velocity with direction inside the crystal. A complete bibliography on the Raman effect and infra-red studies in quartz is also appended.