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Propagation of heat pulses in NaF has been studied to higher temperatures in a purer crystal than studied by McNelly et al. At the highest temperautres the second-sound velocity fails to level off at the theoretically predicted limiting value.

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The temperature dependence of the second-order Raman spectrum of SrTiO3 and KTaO3 has been observed over the temperature range 4°—473°K using the mercury 4358-Å exciting line. From group-theoretical arguments for cubic perovskite lattices the spectra have been interpreted in terms of phonon pairs at critical points in the Brillouin zone using the experimental and theoretical dispersion curves determined by Cowley for SrTiO3. Limited neutron data are available for KTaO3, but the spectrum has been interpreted by analogy with the results for SrTiO3. The energies of the phonon branches at the critical X point in the Brillouin zone have been deduced from the observed Raman spectra.