Raman and Dielectric Spectra of the Glass
and Single Crystal of the Composition Li₂Ge₇O₁₅
in the Frequency Range 31000 cm¹:
II. The Influence of Phase Separation

V. N. Sigaev^a, S. V. Lotarev^a, E. N. Smelyanskaya^a, P. D. Sarkisov^a, A. A. Volkov^b,
G. A. Komandin^b, V. V. Koltashev^c, and V. G. Plotnichenko^c

^a Mendeleev University of Chemical Technology, Miusskaya pl. 9, Moscow, 125130 Russia

e-mail: sigaev@aha.ru

^b Institute of General Physics, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 117924 Russia

^c Research Center of Fiber Optics, Institute of General Physics, Russian Academy of Sciences,
ul. Vavilova 38, Moscow, 119991 Russia

Received January 26, 2005

Abstract—The Raman spectra of Li₂O · 7GeO₂ 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 separa-
tion and that phases of compositions close to GeO₂ and Li₂O · 4GeO₂ precipitate at the initial stage. The order-
ing 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 Li₂O ·
4GeO₂ 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.

DOI: 10.1134/S1087659606050014

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