Piezoresistive Properties of Reduced Strontium Titanate

Abstract

The piezoresistance effect has been investigated in reduced single-crystal strontium titanate in the temperature range from 4.2 to 296\ifmmode^\circ\else\textdegree\fi{}K. At 296\ifmmode^\circ\else\textdegree\fi{}K, the elastoresistance coefficients (${m}_{11}\ensuremath{-}{m}_{12}$), ${m}_{44}$, and (${m}_{11}+2{m}_{12}$) 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\ifmmode^\circ\else\textdegree\fi{}K, the piezoresistance effect becomes very anisotropic and for certain crystallographic directions, a saturation of the piezoresistance is observed at stress values between 1\ifmmode\times\else\texttimes\fi{}${10}^{8}$ and 2\ifmmode\times\else\texttimes\fi{}${10}^{8}$ dyn/${\mathrm{cm}}^{2}$. 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.