Optical absorption edge of SrTiO3 around the 105-K phase transition

The wavelength-modulated absorption and reflection spectra of SrTiO3 have been measured as functions of temperature. Over a 60-K temperature range around the structural phase transition the band gaps of both high- and low-temperature phases are observed simultaneously. This effect and an associated band-gap shift are attributed to the fluctuations at the second-order phase transition. © 1971 The American Physical Society.