Knowledge Bank

The Raman spectrum of $KTaO3$ has been measured as a function of temperature from $300\circ K$ to $8\circ K$. An argon-ion laser was used as the illuminating source and the scattered light was analyzed with an in-tandem grating spectrometer. The spectrum consisted entirely of second order Raman processes originating for the most part from the Brillouin zone boundary where the combined density of states tends to be very large. No first order Raman spectra were observed, in agreement with the known selection rules for the cubic perovskite structure. The scattering tensor deduced from the observed spectra appeared to be largely if not entirely diagonal, but the magnitude and sign of the individual diagonal elements were not investigated. Further, the predominant structural features of the spectrum are due to combinations and overtones between transverse modes. Two rather weak longitudinal overtones were found and other similar two-phonon spectra might be hidden under other more intense spectra. The assignment of the second order Raman peaks are discussed and the derived single phonon energies are compared with the limited amount of neutron diffraction data available.