Dielectric and calorimetric studies of ferroelectric phase transitions in Li_(2–x)Na_xGe₄O₉ crystals

Abstract

Ge 4 O 9 crystals were studied. Experiments were carried out by means of classical dielectric measurements and using an AC calorimetric specific-heat measuring system. Critical behaviour is explained within Landau theory. The expansion coefficients of the state equation are determined.

Soft-phonon mode observation in Li2Ge4O9 phase above room temperature

“…Particularly, glassy/crystallized ferroelectric phases consisting of network-intermediate oxides with highly polarizable d 0 -transition metal ion have been extensively investigated so far. [1][2][3][4] On the other hand, some compounds consisting of a typical glass-former, GeO 2 , possess intriguing dielectric properties, e.g., LaBGeO 5 and Na 2 CaGe 6 O 14 ; 5,6 Lithium tetragermanate, Li 2 Ge 4 O 9 , is reported to be a ferroelectric phase with T c $ À93 C. 7,8 Although Li 2 Ge 4 O 9 phase is not described in the phase diagram of Li 2 O-GeO 2 system, 9 the phase crystallizes through the melt/glass-ceramics route. 10 In addition, an isostructural ferroelectric LiNaGe 4 O 9 (T c $ À160 C), in which Li þ is substituted by Na þ , is also present.…”