Controlled crystallization and ionic conductivity of a nanostructured LiAlGePO4 glass–ceramic

Abstract

a b s t r a c tA Li 1.5 [Al 0.5 Ge 1.5 (PO 4 ) 3 ] glass composition was subjected to several crystallization treatments to obtain glass-ceramics with controlled microstructures. The glass transition (T g ), crystallization onset (T x ) and melting (T m ) temperatures of the parent glass were characterized by differential scanning calorimetry (DSC). The glass has a reduced glass transition temperature T gr = T g /T m = 0.57 indicating the possibility of internal nucleation. This assumption was corroborated by the similar DSC crystallization peaks from monolithic and powder samples. The temperature of the maximum nucleation rate was estimated by DSC. Different microstructures were produced by double heat treatments, in which crystal nucleation was processed at the estimated temperature of maximum nucleation rate for different lengths of time. Crystals were subsequently grown at an intermediate temperature between T g and T x . Single phase glass-ceramics with Nasicon structures and grain sizes ranging from 220 nm to 8 lmwerethensynthesizedand the influence of the microstructure on the electrical conductivity was analysed. The results showed that the larger the average grain size, the higher the electrical conductivity. Controlled glass crystallization allowed for the synthesis of glass-ceramics with fine microstructures and higher electrical conductivity than those of ceramics with the same composition obtained by the classical sintering route and reported in literature.

Determination of crystallization kinetics parameters of a Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glass by differential scanning calorimetry

“…In this way, taking the result of the Avrami coefficient, n = 3 combined with the micrographs presented in Figure 2 which show the cross-sectional area of spherical crystals, it is possible to conclude that the Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 glass crystallizes mainly in the volume. These results, combined with some other characteristics, such as the reduced glass transition temperature T gr = 0.57 [8] points towards homogeneous nucleation. Furthermore, an Avrami coefficient of 3.0 is in accordance with that determined by Kun et al 6 for a similar glass composition.…”

“…This assumption is corroborated by the fact that the maximum crystal growth rates usually occurs at temperatures close to the melting temperature, as was demonstrated by Fokin et al 18 for several silicate glasses. In the case of LAGP, the melting point of the crystals is 1130 °C 8 . Figure 2 show cross-sectional area of spherical crystals and confirm that the crystallization of the LiGe 2 (PO 4 ) 3 phase occurs mainly in the volume, as already predicted by Cruz et al 8 .…”

“…In the case of LAGP, the melting point of the crystals is 1130 °C 8 . Figure 2 show cross-sectional area of spherical crystals and confirm that the crystallization of the LiGe 2 (PO 4 ) 3 phase occurs mainly in the volume, as already predicted by Cruz et al 8 . Figure 3a shows the thermograms obtained by subjecting 50 mg samples to different heating rates (3, 5, 8 and 10 °C/min).…”

“…In fact, Cruz et al 8 provided strong evidence that Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 glass presents volume, supposedly homogeneous, crystallization.…”

PREPARATION OF Li_1.5Al_0.5Ge_1.5(PO₄)₃ SOLID ELECTROLYTE BY SOL-GEL METHOD

“…The LAGP has an advantage for electrochemical window because Ge 4+ is insensitive to reduction 12 in contrast with Ti 4+ . The LAGP preparation has been performed by melt-quenching [13][14][15] or solid-solution method 16 . These methods need high temperature (> 1000 o C).…”