LAUSR

Abstract To explain the ability of lanthanum zirconate (La 2 Zr 2 O 7 , LZ) and various doped forms of LZ to function as catalysts, an understanding of LZ surface structures is needed. Accordingly, certain LZ surfaces that are expected to be prevalent in prepared samples of LZ, namely, the low-index (001), (011), and (111) surfaces, are examined at the level of density-functional theory. All possible surface terminations of these surfaces formed by cleaving a perfect LZ crystal, termed ideal surface terminations, are considered, as well as several defective surface terminations of a given surface. Surface energies and surface free energies are computed, and surface phase diagrams (SPDs) of the (001), (011), and (111) surfaces are obtained. From these SPDs, the thermodynamically preferred surface termination of the (001), (011), or (111) surface is concluded to be nonideal over a large range of temperature and oxygen gas partial pressure conditions. This finding is unchanged if the SPDs are determined more accurately by taking into account certain vibrational contributions obtained from computed phonon dispersions. In addition to this finding, a way to use results to characterize the surfaces of synthesized LZ crystallites is discussed, but the shapes or dimensions of the crystallites first need to be obtained.