THE EFFECT OF PROCESSING VARIABLES ON THE MECHANICAL AND ELECTRICAL-PROPERTIES OF BARIUM-TITANATE POSITIVE-TEMPERATURE-COEFFICIENT-OF-RESISTANCE CERAMICS .2. SINTERING ATMOSPHERES

The effect of sintering atmospheres on the mechanical and electrical properties of four formulations of n-doped barium titanate PTCR ceramics has been investigated. Under sintering atmospheres with an oxygen partial pressure greater than 0.2 bar, it was found that the PTCR effect was unchanged up to a 100% oxygen atmosphere. Similarly mechanical strength, (measured by diametral compression and four-point bending of beams) and fracture toughness were little changed. However, at lower oxygen partial pressures, PTCR effects were reduced. The change in resistance was reduced from three orders of magnitude to one order of magnitude for one formulation. The corresponding strength and fracture toughness (measured by pure bending of small beams) were also significantly reduced from 83 MPa to 48 MPa and 1.0 MPa M1/2 to 0.35 MPa M1/2, respectively.