Formation, microstructure, and electrophysical properties of positive temperature coefficient of. resistance ceramics of the systems (Ba0.996Y0.004)TiO3 and (Ba0.746Ca0.1Sr0.15Y0.004)TiO3 with manganese as acceptor dopant have been investigated. Is has been shown that manganese ions increase the potential barrier at grain boundaries and form a high-resistance outer layer in PTCR ceramics. The resistance of grains, outer layers and grain boundaries, and the value of the temperature coefficient of resistance as a function of the manganese content of positive temperature coefficient of resistance materials have been investigated. (C) 2003 Elsevier Ltd. All rights reserved.