Optical properties of highly reduced SrTiO{sub 3{minus}x}

The reflectance of highly reduced SrTiO{sub 3{minus}x} has been studied in samples where the carrier concentration{emdash}or oxygen-vacancy density {emdash} varies from about 10{sup 18} to 10{sup 21} cm{sup {minus}3}. Several phonon modes are strongly influenced by oxygen-vacancy density. Oxygen reduction induces a mid-infrared band whose oscillator strength scales with carrier density. In highly reduced samples, a weakly localized plasmon mode develops. {copyright} {ital 1999} {ital The American Physical Society}