EFFECT OF Ca-SUBSTITUTION ON THE OPTICAL BAND GAP AND URBACH ENERGY OF BaTi2O5 BULK GLASS

Abstract

Optical transmittance of Ba 1-x Ca x Ti 2 O 5 (x=0, 0.01, 0.03) bulk glasses of ferroelectric BaTi 2 O 5 is measured at room temperature in the wavelength range 190–800 nm. The fundamental absorption edge located in the ultraviolet (UV) region tends to shift toward the longer wavelength region on increasing x. The optical band gap of 3.31 eV estimated for x=0 decreases on increasing x. The decrease in the optical band gap energy is related to the creation of non-bridging oxygen ions, which increase on Ca substitution. The observed increase in the Urbach energy with increasing x is associated with the possible increase of structural disorder in the ferroelectric BaTi 2 O 5-based bulk glass occurred by substituting Ca for Ba .