Study on electrical and structural properties in SiO2 substituted Li2O-Al2O3-GeO2-P2O5 glass-ceramic systems

Abstract

Two different LAGP glasses with nominal compositions a) Li1.5Al0.5Ge1.5P2.9Si0.1O12 (LAGP1) b) Li1.5Al0.5Ge1.5P2.5Si0.5O12 (LAGP2) were prepared to see the effect of SiO2 substitution in place of P2O5 on their phase formation and electrical properties. Different heat schedules were applied to see the phase evolution in these glass-ceramics (GC). The electrical conductivity of the glass-ceramics samples was measured using impedance analyzer in the frequency range of 0.1–106 Hz and temperature range of 300–373 K. XRD confirm presence of pure LiGe2(PO4)3 in LAGP1 GC sample whereas LAGP2 shows additional minor phases along with LiGe2(PO4)3. In LAGP2 GC XRD patterns showed a little shift in peak position as compared to LAGP1 GC because of SiO2 substitution. LAGP1 shows ionic conductivity value of around 2.45 ×10−4 S/cm at room temperature (RT) for the sample heat treated at 750 oC whereas the LAGP2 GC sample shows maximum conductivity of 8.95 ×10−6 S/cm for the sample heat treated at 700 °C. The conductivity value increased to nearly one order higher with increase in temperature upto 333 K. The lower conductivity value of LAGP2 sample is due to presence of additional minor insulating phases in the sample. The activation energies for dc conductivity was calculated as 0.43 eV and 0.48 eV for LAGP1 and LAGP2, respectively. Ionic mobility of these samples were determined using the permittivity and loss factor and the mobility value is higher for LAGP1 GC (1.34 ×10−3 cm2/V-s) as compared to LAGP2 GC sample (3.56 ×10−6 cm2/V-s). Microstructure of glass- ceramics samples shows growth of very fine structure of around 100 nm size in LAGP1 GC where as in LAGP2 GC microstructures are looking like small globules of less than 100 nm sizes and are interconnected to form a chain like structure. LAGP1 GC with high ionic conductivity is found to have more potential advantages over LAGP2 GC for use in Li-ion battery.