A stress-sensing ceramic device based on PTCR barium titanate

Positive temperature coefficient of resistance (PTCR) barium titanate is used as the base material for a ceramic sensor which employs piezoresistivity to detect changes in applied stress. Tape-cast sheets of undoped (insulating) and PTCR (semiconducting) BaTiO₃ are laminated to produce a three-layer “trilaminate”-a sintered structure which has two PTCR layers separated by an insulating layer. The trilaminate is exposed to mechanical stress in a four-point bend configuration (placing one semiconducting layer completely in tension, the other in compression), and the resistivities for both stress states are measured concurrently as functions of the applied stress magnitude. The piezoresistivity coefficient (π) is calculated from the slope of the linear resistivity-stress response. Piezoresistivity results are presented versus PTCR layer composition (counterdopant species) and furnace cooling conditions (grain boundary oxidation level). These results are interpreted with respect to Heywang´s model of the gain boundary potential barrier