Using first-principles calculations, we have carried out a systematic comparative study of the microscopic atomic defect configurations in cubic and tetragonal yttria-stabilized zirconia (YSZ) and their correlation with the macroscopic lattice parameters and relative phase stability, as a function of Y concentration. We found that Y atoms sit at the second-nearest-neighbor cation sites to oxygen vacancies and repel each other; oxygen vacancies form pairs and these pairs repel each other. Using the optimized defect configurations as inputs, we correctly identify the experimentally observed tetragonal to cubic transition point and predict the changes of lattice parameters with the increasing Y concentration, in excellent agreement with experiment. Our studies reveal an interesting correlation between the microscopic atomic defect configuration and macroscopic lattice properties. (C) 2012 Elsevier B.V. All rights reserved.