Infrared and Raman spectroscopy of Li2Ge7O15 single crystals: spectra of the paraelectric and aristotype phases

Polarized Raman and infrared spectra of Li2Ge7O15 single crystals were measured in the frequency range 5-1000 cm-1 at room temperature. The spectra are analysed within the framework of the Landau theory of structural phase transitions from a (hypothetical) fully disordered deficient structure (aristotype). The mechanism of the phase transition is discussed in terms of ordering and shifts of ions.