Raman and Dielectric Spectra of the Glass and Single Crystal of the Composition Li_2Ge_7O_(15) in the Frequency Range 3-1000 cm~(-1):II.The Influence of Phase Separation

摘要

The Raman spectra of Lk_2O centre dot 7GeO_2 glasses,which are heat treated under different conditions at temperatures near the temperature corresponding to the first exothermal peak in the DTA curve,are measured in the frequency range 20-1100 cm~(-1).A comparative analysis of the measured spectra with the use of the data available in the literature and the X-ray diffraction results demonstrates that the glass undergoes phase separation and that phases of compositions close to GeO_2 and Lk_2O centre dot 4GeO_2 precipitate at the initial stage.The ordering of both phases varies significantly within the sample and,on the average,is substantially higher than that in the initial glass.This confirms the known assumptions made by researchers that crystal nuclei with a Lk_2O centre dot 4GeO_2 structure arise during heat treatment of lithium germanate glasses.At the phase separation stage under investigation,the phases are formed as nanoinhomogeneities that only slightly affect the transparency and,in the course of heat treatment,increase in size with a further ordering of the structure.