Infrared and Raman spectroscopy of Li₂Ge₇O₁₅single crystals: spectra of the paraelectric and aristotype phases

Abstract

Polarized Raman and infrared specha of LiZGe70LS single crystals were measured in the frequency m g e 5-1000 cm-' at mom temperature. The spectra are analysed within the framework of the Landau thwry of Seucnual phase bnsitions from a (hypothetical) fully disordered deficient structure (aristotype). The mechanism of the phase transition is discussed in terms of ordering and shifts of ions.

Raman and dielectric spectra of the glass and single crystal of Li2Ge7O15 in the frequency range 3–1000 cm−1: I. Comparison of the structures of the crystal and initial glass

“…1-3. The data taken from [18,19] for the Li 2 Ge 7 O 15 crystal are also presented in Figs. 1 and 2.…”

“…Unfortunately, dielectric spectra of the Li 2 Ge 7 O 15 crystal at frequencies higher than 100 cm -1 are not available. The reflection spectra of the Li 2 Ge 7 O 15 single crystal for three crystallographic axes [18] and the glass of the same composition are shown in Fig. 3.…”

“…According to [18], the structure of the Li 2 Ge 7 O 15 single crystal under normal conditions is composed of strongly distorted layers that consist of GeO 4 tetrahedra and are linked together via GeO 6 octahedra into a threedimensional framework. This structure can be described by the crystal chemical formula Li 2 [Ge(Ge 2 O 5 ) 3 ].…”

“…The RAMAN AND DIELECTRIC SPECTRA 299 channels are occupied by Li + ions in such a way as to compensate for an excess negative charge produced by GeO 6 octahedra. A number of Li + ions coordinate four oxygen atoms belonging to two GeO 6 octahedra, and the other Li + ions coordinate two oxygen atoms of the same octahedron [18].…”

“…The glass and crystal of the Li 2 O · 7GeO 2 composition were chosen as objects of our investigation, because detailed information on the structure of the Li 2 Ge 7 O 15 crystal is available in the literature [18,19]. The Li 2 Ge 7 O 15 crystal is a ferroelectric and the study of its crystallization from the glass can be of considerable…”