We investigated the Raman spectra of thermally reduced and untreated Y- and Ca-stabilized cubic zirconia. A substantial decrease in Raman activity was observed in the acoustic mode region upon reduction. Analyses of these spectra as a phonon density of states and of the observed spectral changes indicate that the reduced states are more ordered than the untreated one. This is consistent with a nonrandom arrangement of vacancies, which produces the superposition of periodic sequences of vacancies within domains. This, in turn, causes the increment in coherence length of phonons that is manifested as a decrease in acoustic mode activity.

The theory of lattice dynamics in the harmonic approximation using a rigid-ion model due to Born and Huang ͓Dynamical Theory of Crystal Lattices ͑Oxford University Press, New York, 1954͔͒, is applied to ionic crystals of the R 2 M X 6 type with antifluorite structure namely, K 2 SnCl 6 , K 2 PtBr 6 , Cs 2 SnBr 6 , and Rb 2 SnBr 6 in the cubic phase. The model expresses the potential energy as the sum of long-range Coulomb interactions and repulsive short-range interactions between ions in the primitive cell. A function of axially symmetric type is used to approximate the short-range part, and the number of force constant parameters were reduced utilizing stability conditions in the manner described by Katiyar ͓J. Phys. C 3, 1087 ͑1970͔͒. The remaining constants were determined by a nonlinear least-squares analysis of some experimental frequencies at the critical point ⌫. The long-range contributions were calculated using the Ewald transformation as described by Cowley ͓Acta Crystallogr. 15, 687 ͑1962͔͒. Phonon frequencies and the normal modes of vibrations at the zone center were obtained; of particular interest is the resulting lowest librational frequency for each crystal. We obtained excellent agreement between the calculated and the observed frequencies. The resulting effective charge parameters indicated that these crystals are partially ionic. In general, the results offered a better vision of the structural phase transition mechanism involving the rotational mode T 1g .

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Tin oxide low dimensional structures increasingly attract attention due to their wide application area. Indeed, by attaining new morphologies and properties the potential applications might increase the device portfolio. Furthermore, an adequate combination of doped SnO2 nano‐ and micro‐structures could enable multi‐functionality and totally new applications. The latter might be the case of low dimensional tin oxide structures emitting in the near infrared range, which is below the energy of the common visible luminescence of tin oxide. The ability to obtain near infrared luminescence from tin oxide is tested by doping in‐situ during a vapor–solid growth using Li, Cu, and Cr containing precursors in the initial mixture with tin oxide or metallic tin powders. Luminescence around 1.5 eV is obtained for all the samples with morphologies varying from microtubes to rods and belts depending on the specific dopant and the Sn‐based precursor.