Transport Properties of KNb1-xMgxO3- Synthesized under High-Temperature and High-Pressure

Single phase KNb1-xMgxO3- (0.0～0.3) ion conductors were prepared using high temperature and high pressure method. The structural characteristics and ionic conductivities of KNb1-xMgxO3- solid solutions were investigated by XRD, TG-DTA and A-C impedance spectra measurements. The XRD results show that all the products crystallized in a single orthorhombic perovskite structure. High pressure promotes the process of solid state reactions and the temperature for forming KNb1-xMgxO3- solid solutions decreases under high pressure. With the increasing of doping amount, cell volume increases, which is related with substitution of Mg ion and existence of oxygen vacancies. Ionic conductivities measured by impedance spectroscopy showed that there is relatively high-resistance along grain bound-aries. The grain-boundary effect is very obvious. By imitating the impedance data, the conductivities of grain, grain boundary and bulk were obtained, the temperature dependence of the conductivities of all the solid solutions is linear. The bulk conductivities of KNb1-xMgxO3- solid solutions don't increase with the increasing of doping amount but achieve maximum at around x=0.1 (=1.210-3 Scm-1 at 700 ℃).