Piezoresistive Properties of Reduced Strontium Titanate

The piezoresistance effect has been investigated in reduced single-crystal strontium titanate in the temperature range from 4.2 to 296^∘{}K. At 296^∘{}K, the elastoresistance coefficients (m₁₁-m₁₂), m₄₄, and (m₁₁+2m₁₂) have been evaluated in samples having a wide range of electron concentrations. The piezoresistance results indicate that the conduction-band edge consists of two types of energy minima separated by several hundreths of an eV with the minimum at $k=0$ being the lowest in energy. Below approximately 110^∘{}K, the piezoresistance effect becomes very anisotropic and for certain crystallographic directions, a saturation of the piezoresistance is observed at stress values between 1×{}10⁸ and 2×{}10⁸ dyn/cm². The low-temperature piezoresistive properties appear to be a result of the cubic-to-tetragonal phase transition and it is postulated that these effects are due to a stress-induced alignment of the tetragonal domains.