Oxygen vacancy revived phonon-glass electron-crystal in SrTiO3

Controlling oxygen vacancy in undoped SrTiO3 was used to realize the phonon-glass electron-crystal (PGEC) concept. The undoped SrTiO3 samples were synthesized through solid-state-reaction method in air and then reduced through annealing under low oxygen partial pressure conditions. We show that decreasing the oxygen partial pressure (Po-2) results in increase of the electrical conductivity, and the oxygen vacancies act as phonon scattering centers, which lead to decrease in the lattice thermal conductivity. Both the enhanced electrical conductivity (sigma) and reduced thermal conductivity (kappa) were achieved simultaneously through oxygen vacancy in undoped SrTiO3. This significantly increases the ratio of sigma/kappa that results in an enormously enhanced ZT value of about 13 times larger as compared with the samples reduced under relatively high Po-2. Density-functional theory calculations also reveal that oxygen vacancies in SrTiO3 reduce the band-gap, and consequently increase the electrical conductivity.