Study On Charge-Discharge Properties Of High Energy Density Glass-Ceramic Composites

PbO-SrO-Na2O-Nb2O5-SiO2 (PSNNS), PbO-BaO-Na2O-Nb2O5-SiO2 (PBNNS) and BaO-SrO-Na2O-Nb2O5-SiO2 (BSNNS) glass-ceramic nanocomposites had been prepared with controlled crystallization method. Crystallization behaviors of glass-ceramics had been characterized and the dielectric and charge-discharge properties had been investigated by microscopic analysis and impedance spectroscopy. The main contents of the research are as follows:Series of glass-ceramic samples had crystallized at 750℃ and 900℃ from 1 to 1000 min, respectively. X-ray diffraction results showed that the precipitated phases are indexed as pervoskite phase of NaNbO3 and corresponding tungsten-bronze phase. Crystallization had finished in a very short time. With increased crystallization time, the precipitated phases were unchanged and the intensity of diffraction peaks was not enhanced. Transmission electron microscopy results characterized that the ceramic phases distributed in residual glass matrix homogeneously. The grain size increased from dozens of nanometers to hundreds of nanometers with increasing crystallization time.Dielectric properties had been studied by LCR meter and ferroelectric tester. The 900℃ samples had higher dielectric constant and stronger polarization behaviors than 750℃ samples. And the dielectric constant and dielectric loss increased with increased crystallization time. Generally speaking, the polarization curves are very thin and the polarization has linear relationship with electric field. With increased crystallization time, the remanet polarization increased and the glass-ceramic samples had stronger ferroelectric property.Charge-discharge properties had been investigated with polarization curves and pulse discharge circuit which corresponding quasi-static discharge and pulse discharge conditions. In quasi-static condition, PSNNS and PBNNS had high energy density, and the maximum values achieved 0.172 J/cm3 and 0.197 J/cm3 at 10 kV/mm; PSNNS and BSNNS had excellent energy efficiencies which higher than 85.0% and 83.5%, respectively. With increased crystallization time, the energy density increased and the efficiency reduced gradually. In pulse discharge condition, for PSNNS glass-ceramics, pulse discharged energy density increased gradually and the corresponding energy efficiency significantly reduced from 65.1%to 82.4% with increased crystallization time. Obviously, the pulse discharged energy efficiency was much lower than quasi-static efficiency.Electrochemical impedance spectroscopy results showed that the polarization relaxation time prolonged with increased crystallization time which may cause to variation of charge-discharge properties. For the same sample, grain relaxation times were much different with grain boundary relaxation times. It could explain that pulse discharge energy efficiencies were much lower than quasi-static efficiencies for the same samples.