Thermochromism and Electrical Conductivity in Doped SrTiO3

Large reversible thermochromic changes in pure and transition-metal-doped SrTi${\mathrm{O}}_3$ were observed which depend markedly on impurity concentration, anealing temperature, and especially on the rapidity of the quench. The material also changes its electrical properties from insulator to semimetallic, and for moderately and heavily doped samples, from semiconductor to metalliclike behavior. The optical and electrical properties are stable. Two intrinsic optical-absorption bands and two bands previously found in photochromic studies which depend on the transition-metal impurity are observed. A partial energy-level scheme for SrTi${\mathrm{O}}_3$ is proposed.