Wide band gap tunability in complex transition metal oxides by   site-specific substitution
  Fabricating complex transition metal oxides with a tuneable band gap without compromising their intriguing physical properties is a longstanding challenge. Here we examine the layered ferroelectric bismuth titanate and demonstrate that, by site-specific substitution with the Mott insulator lanthanum cobaltite, its band gap can be narrowed as much as one electron volt, while remaining strongly ferroelectric. We find that when a specific site in the host material is preferentially substituted, a split-off state responsible for the band gap reduction is created just below the conduction band of bismuth titanate. This provides a route for controlling the band gap in complex oxides for use in emerging oxide opto-electronic and energy applications. 
Woo Seok Choi, Matthew F. Chisholm, David J. Singh, Taekjib Choi,   Gerald E. Jellison Jr and Ho Nyung Lee
cond-mat.mtrl-sci cond-mat.mes-hall cond-mat.str-el