Heterovalent and A-atom effects in A(B'B'')O3 perovskite alloys

TL;DR

This study uses first-principles calculations to explore how heterovalent and A-atom effects influence the energetic, structural, and dielectric properties of specific A(B'B'')O3 perovskite alloys, revealing key electrostatic and relaxation mechanisms.

Contribution

It provides new insights into the roles of electrostatic interactions and atomic relaxations in stabilizing structures and affecting dielectric properties in heterovalent versus homovalent perovskite alloys.

Findings

Electrostatic interactions stabilize compositional order in BZN.

Cell relaxations destabilize ordered structures in PZN.

Zr in PZT shows anomalous effective charge, Zn's charge is near ionic value.

Abstract

Using first-principles supercell calculations, we have investigated energetic, structural and dielectric properties of three different A(B'B'')O_3 perovskite alloys: Ba(Zn_{1/3}Nb_{2/3})O_3 (BZN), Pb(Zn_{1/3}Nb_{2/3})O_3 (PZN), and Pb(Zr_{1/3}Ti_{2/3})O_3 (PZT). In the homovalent alloy PZT, the energetics are found to be mainly driven by atomic relaxations. In the heterovalent alloys BZN and PZN, however, electrostatic interactions among B' and B'' atoms are found to be very important. These electrostatic interactions are responsible for the stabilization of the observed compositional long-range order in BZN. On the other hand, cell relaxations and the formation of short Pb--O bonds could lead to a destabilization of the same ordered structure in PZN. Finally, comparing the dielectric properties of homovalent and heterovalent alloys, the most dramatic difference arises in connection with the effective charges of the B' atom. We find that the effective charge of Zr in PZT is anomalous, while in BZN and PZN the effective charge of Zn is close to its nominal ionic value.