ИСТИНА

The crystal phase Bi2GeO5 has ferroelectric properties with spontaneous polarization value comparable to BaTiO3 ceramic. This phase is metastable, so it can be hardly synthesized by standard crystal growth methods, but can be crystallized by heat treatment of bismuth-germanium oxide glasses. A variation of the initial oxides ratio and the heat treatment conditions may lead to crystallization of either a single phase or several phases? mixture. The secondary phases deteriorate the ferroelectric properties of ceramics so it?s necessary to control the phase purity. In the present research a single-phase Bi2GeO5 glass-ceramic has been successfully synthesized in the Bi2O3:GeO2 glasses with 40:60 and 45:55 molar ratio by several methods and under different crystallization conditions (temperature range 430-520ºC, duration 4-87 h). The structure and morphology of induced crystal phases as well as the influence of heat treatment conditions on crystallization result have been investigated by XRD, Raman spectroscopy and SEM. The 45Bi2O3:55GeO2 glass after crystallization at 460ºC during 87 h contains nano-sized Bi2GeO5 crystallites (15-30 nm). The optimal initial glass composition and crystallization conditions to produce a single Bi2GeO5 crystal phase has been found. This research was financially supported by the Ministry of Education and Science of the Russian Federation by SA 17.1.18.0026.01 (10.4702.2017/BC).