Study on the main factors affecting the breakdown voltage of (Bi0.5Na0.5) TiO3-added (Ba0.659Pb0.341)TiO3 PTCR ceramic materials

The breakdown voltage (V-b) was studied for (Bi0.5Na0.5)TiO3 (BNT)-added positive temperature coefficient of resistance (PTCR) ceramic samples based on (Ba0.659Pb0.341)TiO3, which were prepared by a traditional solid-reaction method and sintered in an air atmosphere. By measuring the electrical properties and microstructures of the materials, the breakdown voltage was found to depend on neither the room-temperature resistivity nor the maximum resistivity, but on the grain size (D) of the samples to some extent. With a decrease in the grain size, the V-b value increases rapidly, especially for samples with fine grains. With the help of Heywang-Jonker theory, the depletion width (L-D) was calculated to determine the dominant factor affecting the V-b value using the approximate equation V-b= 600 x L-D/D + 100; i.e., the breakdown voltage is approximate directly proportional to the ratio of L-D/D. However, the room-temperature resistivity increased slightly with L-D/D, and the PTC performance remained at a high level (alpha > 34%, R-max/R-min > 1 x 10(3)). It is more advantageous to increase the breakdown voltage by adjusting L-D/D than by reducing grain size alone. The variations in the grain size and the depletion layer width of different samples are mainly due to the generation of V-Na ' and V-Bi' inside of the lattice. The ratio of L-D/D can also be used to explain the variation in room-temperature resistivity.