Ab initio study of dipolar defects and 180 degrees domain walls in PbTiO3

We have calculated the electronic and ionic structures for oxygen-vacancy-i mpurity-metal complexes and 180 degrees domain walls in PbTiO3 using a firs t-principles total energy method. The binding energy of an oxygen vacancy t o a Pt impurity in PbTiO3 is calculated to be similar to 3.0 eV. The comple x is strongly polar, stabilized by electron capture, and pins the polarizat ion of the surrounding lattice. Domain walls are found to be Pb-centered an d extremely narrow with a width of only about two lattice constants. The en ergy density of a domain wall is calculated to be similar to 150 erg/cm(2.) (C) 1999 Elsevier Science Ltd. All rights reserved.