Abstract
Room temperature (R.T.) resistivity and the positive temperature coefficient of resistivity (PTCR) of Gd-Mn codoped BaTiO3 from powders obtained by hydrothermal synthesis were investigated. Mixtures of Gd(NO3)3, Mn(NO3)2, and BaTiO3 powders (average particle size ; 0.1 to 0.3μm) obtained by hydrothermal synthesis were dried and pressed into pellets with a diameter of 2 cm. Then, the pellets fired at the temperature range of 1230 to 1300°C for 2 h in air. By using BaTiO3 powders obtained by hydrothermal synthesis, relatively low R.T. resistivity and remarkable PTCR characteristics was observed for the samples fired at the temperatures lower than 1300°C. In particular, semiconductive sample was obtained and PTCR jump was more than 2 orders of magnitude for the sample fired at 1230°C by using BaTiO3 powders which have an average particle size of 0.2μm. Results of electron spin resonance indicated that changes of chemical states of Mn in the grain boundary significantly affected the PTCR properties.
