Ionic Conductivity in Multiphase Li₂O-7GeO₂Compounds

Abstract

Crystallization of Li2O-7GeO2 glass was carried out on heating, simultaneously differential scanning calorimetry and electric properties were studied. Morphology of the phase states obtained at glass devitrification was examined by atomic force microscopy. It was shown that amorphous phase of Li2O-7GeO2 was crystallized in stages through the intermediate state with increased conductivity σ. In the intermediate state the sample volume was occupied by nanometer-sized nuclei with ordered structure surrounded by internuclear amorphous medium. Complete glass crystallization occurred through transformation of nanometer-sized nuclei into micrometer-sized crystallites and was accompanied by a sharp and irreversible decrease of conductivity. Atomic force microscopy of the samples heat-treated in different ways showed that Li2O-7GeO2 glass crystallization was suppressed near the surface and mainly proceeded within the sample bulk. Charge transfer in amorphous, nanocrystalline intermediate and polycrystalline phases of Li2O-7GeO2 was associated with motion of the weakly bound Li ions.

Thermal analysis of Li2-хNaxGe4O9 glasses crystallization

“…It is important that the glasses of LNG and Li1.8N0.2G are crystallized through a single stage. Such case is quite different from the situation observed for Li2O-xGeO2 compounds with x=7, 11.5, 18 [5][6][7][8][9] where amorphous state is ordered through the intermediate metastable phase. The intermediate phase is characterized by the appearance of the metastable lithium tetragermanate nuclei and thermodynamically stable lithium heptagermanate crystallites.…”

“…The intermediate phase is characterized by the appearance of the metastable lithium tetragermanate nuclei and thermodynamically stable lithium heptagermanate crystallites. Accordingly, the intermediate phase in Li2O-xGeO2 glassceramics [5][6][7][8][9] combines structural and chemical segregation.…”

“…It was repeatedly shown that nanometer sized structuring was an effective approach to enhance ionic conduction [4]. Thus, the authors of [5][6][7][8][9] by using the technology of controlled glass crystallization prepared the nanometer structured Li2O-xGeO2 glass-ceramics with significantly increased ionic conduction as compared with crystalline as well as amorphous compounds. The effect was attributed to an increase of a number of weakly bound lithium ions as well as unoccupied positions accessible for light ions.…”

“…It is of interest to apply the technology of structuring on nanometer level developed in [5][6][7][8][9] to LNG and L2-хNхG solid solutions. One may expect that the size of nanometer crystal nuclei should strongly influence ionic conduction in composite glass-ceramic compounds.…”

Conductivity of lithium heptagermanate glasses and single crystals doped with 3d- ions

“…Pure and doped with Cr (0.06 wt%) and Mn (0.06 wt%) lithium heptagermanate glasses were obtained by quenching the melts as described in [2][3][4]. The estimated quenching rate was about ~10 3 K/s.…”