Extremely Large Dielectric Permittivity And Humidity Sensing Properties In Ce And Y Doped BaZrO₃ Ceramics

Ce/Y-doped BaZrO3 ceramics are important electrolyte materials for solid oxide fuel cells.Their dielectric properties and their sensitivity to environmental humidity directly affect the performance of the battery.To this end,this thesis focuses on the dielectric and humidity sensing properties of Ce and Y doped BaZrO3 ceramics,selecting dense BaZr0.1Ce0.7Y0.2O3-δ and BaZr0.4Ce0.4Y0.2O3-δ ceramics as the study objects,the samples were prepared by glycine nitrate combustion method,their dielectric and humidity sensing properties were systematically studied.The results obtained are as follows:(1)BaZr0.1Ce0.7Y0.2O3-δ and BaZr0.4Ce0.4Y0.2O3-8 ceramics exhibit colossal dielectric behavior at temperatures below about 600 K,and colossal dielectric behavior consists of two relaxations with the low-temperature and high-temperature relaxations being caused by a pair of dipoles formed by oxygen vacancies(Vo..)and hydroxyl ions(OHo.)with Y3+ ions,respectively.In the temperature higher than-600 K,the samples show two dielectric anomalies with extremely large dielectric permittivity over 106.It is argued that the low-temperature dielectric anomaly is the typical pseudo-relaxor behavior caused by ion-hopping-motion.While the high-temperature dielectric anomaly results from the negative capacitance effect.(2)The capacitance response of BaZr0.4Ce0.4Y0.2O3-δ(BZCY)was studied by changing the water vapor content.The impedance spectra and DC bias measurements were performed on the samples under different relative humidity(RH),and the humidity sensitivity of BZCY was explored.The results show that the adsorption of water molecules affects the BZCY/electrode interface and the barrier capacitance at the grain boundary,further changing the total capacitance of BZCY.In addition,new low frequency polarization relaxations were observed at high RH.The new polarization relaxation may be related to polarization phenomena and space charge polarization caused by physically adsorbed water molecules.