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Polarized IR and Raman spectra, temperature dependence of phonons and lattice dynamic calculations for M′2M″Ge2O7 pyrogermanates (M′ = Sr, Ba; M″ = Mg, Zn)



Infrared and Raman spectra of the polycrystalline samples and single crystals of Sr2ZnGe2O7, Ba2ZnGe2O7, Ba2MgGe2O7 and Sr2MgGe2O7 were measured. The temperature dependence of phonons was studied in the range 4–295 K. The discussion of the results is based on the factor group approach for the tetragonal equation image space group with Z = 2. The discussion of the internal vibrations of the Ge2O7 unit and external modes is made on the basis of the literature data and phonon calculations. The results obtained for the spontaneous Raman scattering were used in the discussion of the stimulated Raman spectra of the studied materials. Copyright © 2010 John Wiley & Sons, Ltd.