Electrical properties of the positive temperature coefficient of resistivity materials with 490 °C critical temperature

This work successfully obtains a positive temperature coefficient of resistivity characteristics with critical temperature (T-c) at around 490 and 420 degrees C for PbTiO3 (PT), and (Pb0.9Sr0.1)TiO3 (PST) materials, respectively. The tetragonality of these materials are (c/a)(PT)=1.065 and (c/a)(PST)=1.046. In addition, the donor level of Y3+ ions in PT materials [(E-d)(PT)=0.09-0.11 eV] is smaller than that in PST materials [i.e., (E-d)(PST)=0.29-0.40 eV]. The resistivity jumping ratios of the two materials are similar, that is, (rho(max)/rho(min))(PT)congruent to 10(2.2) and (rho(max)/rho(min))(PST)congruent to 10(1.6). Multiple-T-c resistivity-temperature (rho-T) characteristics are observed, that is ascribed to the formation of an incomplete core-shell microstructure with the Pb-deficient shell not entirely surrounding the stoichiometric core. (C) 1998 American Institute of Physics. [S0021-8979(98)03903-6].