First-principles calculations of the atomic and electronic structure ofSrZrO3 andPbZrO3 (001) and (011) surfaces

Abstract

We present the results of calculations of surface relaxations, rumplings,energetics, optical band gaps, and charge distribution for theSrZrO3 andPbZrO3 (001) and (011) surfaces using the ab initio code CRYSTAL and a hybriddescription of exchange and correlation. We consider both SrO(PbO) andZrO2 terminations of the (001) surface and Sr(Pb), ZrO, and O terminations of the polarSrZrO3 andPbZrO3 (011) surfaces. On the (001) surfaces, we find that all upper and thirdlayer atoms relax inward, while outward relaxations of all atoms in thesecond layer are found with the sole exception of the SrO-terminatedSrZrO3 (001) surface second layer O atom. Between all (001) and (011) surfaces the largestrelaxations, more than 15% of the bulk lattice constant, are for the Sr- and Pb-terminatedSrZrO3 andPbZrO3 (011)surface upper layer Sr and Pb atoms. Our calculated surface rumpling for the SrO- and PbO-terminatedSrZrO3 andPbZrO3 (001) surfaces (6.77and 3.32% of a0) are by a factor of ten larger than the surface rumpling for theZrO2-terminated(001) surfaces (−0.72 and 0.38% of a0, respectively). In contrast to the surface rumpling, the (001)surface energies are comparable and in the energy range from 0.93 eV/cell for theZrO2-terminatedPbZrO3 surfaceto 1.24 eV/cell for the ZrO2-terminated SrZrO3 surface. In contrast to the (001) surface, different terminations of theSrZrO3 andPbZrO3 (011) surfaces lead to very different surface energies ranging from 1.74 eV/cell for the Pb-terminatedPbZrO3 (011) surfaceto 3.61 eV/cell for theZrO-terminated SrZrO3 (011) surface. All our calculated (011) surface energies are considerably largerthan the (001) surface energies. Our calculated optical band gap for theSrZrO3 bulk,5.31 eV, is in fair agreement with the experimental value of 5.6 eV. All our calculated optical band gaps forthe SrZrO3 and PbZrO3 (001) and (011) surfaces are reduced with respect to the bulk. We predicta considerable increase in the Zr–O chemical bond covalency near theSrZrO3 andPbZrO3 (011) surfaces as compared both to the bulk and to the (001) surface.