Domain-Wall Motion under Mechanical Stresses and Giant Piezoresistivity in Thin Barium Titanate Ceramic Bars

Extremely large piezoresistance (stress-sensitive resistance), equivalent to a value of the gage factor (the magnitude of resistance change per strain) of > 10 ⁷ was observed in single grain boundaries formed in thin semiconducting barium titanate ceramic bars at room temperature. The samples were produced to have a grain structure consisting of single grains joined together in series and a diameter in the range 10-20,um. In this study, observation of ferroelectric domain structures and measurements of resistance were simultaneously carried out for some samples under cyclic mechanical stresses to closer look at the influence of the morphological change of ferroelectric domain structures on the grain boundary resistance in the materials. In a bar sample with a single grain boundary, a 90° domain wall was observed to appear and move from one end of the sample to the other during one cycle of the stress applied. It has been found that the observed large piezoresistance is closely connected with a drastic change of the domain structure in the vicinity of grain boundaries in the samples.