Structure and Electronic Effects from Mn and Nb Co-doping for Low Band Gap BaTiO₃ Ferroelectrics

Abstract

We have investigated the doping-induced local structural and electronic effects in the recently developed low band gap room temperature ferroelectric Mn-Nb co-doped BaTiO3. Experimental and theoretical Raman spectroscopies are utilized to quantify the Ti off-centering, identified to be the intrinsic origin of ferroelectricity in these systems. Mn and Nb exhibit contrasting doping behaviors that have remarkable effects on BaTiO3 functionality. Jahn-Teller distorted Mn3+ is primarily associated with lowering of the bulk band gap, while charge-compensating Nb5+ off-centers within the O-6 octahedra, creating a polar mode that stabilizes the ferroelectric ground state. The charge neutral aliovalent Mn3+-Nb5+ pair effectively couples to the inherent ferroelectric instability of the BaTiO3 lattice, restoring some spontaneous polarization lost by doping Mn3+ (d(4)) ions at Ti4+ (d(0)) sites.