Barium-strontium titanate (BST) ceramics, co-doped with Sb and Mn oxides, were sintered on different powder beds: Sb-doped BST; Al2O3; or Sb,Mn-codoped BST powder. Phase formation, microstructure and the electrical properties of the samples were analysed. The PTCR behavior depended significantly on the type of powder bed used. The BST ceramic pellet sintered on the Sb-BST powder displayed the largest PTCR effect, with a rho(max)/rho(RT) ratio of similar to 10(6). This was an order of magnitude greater than for samples sintered on the other two powders. Complex impedance analysis confirmed that this was due to a large increase in grain boundary resistance at 250 degrees C.