PIEZORESISTIVITY IN PTCR BARIUM-TITANATE CERAMICS - I, EXPERIMENTAL FINDINGS

Positive temperature coefficient of resistance (PTCR) barium titanate is the active material in a ceramic sensor which employs piezoresistiv ity to detect changes in applied stress. High-purity, chemically prepa red barium titanate is donor-doped with 0.30 at.% lanthanum, and <0.10 at.% of a transition-metal counterdopant may be added to enhance the PTCR effect. Tape-cast sheets of undoped and PTCR BaTiO3 are laminated to produce a three-layer ''trilaminate''-a sintered structure which h as two semiconducting PTCR layers separated by an insulating layer. Th e trilaminate is stressed in a four-point bend configuration (placing one semiconducting layer completely in tension, the other in compressi on), and the resistivities for both stress states are measured concurr ently as functions of applied stress and temperature. Results are pres ented for various semiconducting layer compositions and sintering cond itions.