Electronic properties of A-site substituted lead zirconate titanate:: Density functional calculations

First-principles density functional theory calculations have been applied to study the electronic and optical properties of A-site substituted lead zirconate titanate (PZT), where group IIIA and group VB elements partially substitute Pb sites. The conduction band minima in the group IIIA element substituted PZT systems are found to be shared by Ti 3d and dopant states, which reduce the occupation on Ti 3d states by the electrons. Moreover, correlations between dopant electrons introduce the Mott-Hubbard band gap into PZT, which is intrinsically a charge-transfer insulator. This leads to a systematic reduction of energy and optical band gaps with increased atomic number of group IIIA substitutes. Similar chemical trend was found for group VB substitutes, which is, however, closely related to the electron bandwidth of Ti 3d states in the charge-transfer band gaps. All the trivalent substitutes are confirmed to effectively dilute the concentration of the oxygen vacancies under Pb-deficient conditions by our theoretical calculations.