High temperature X-ray diffraction measurements in controlled partial pressures of oxygen are used to study the thermal expansion and point defect induced expansion, known as chemical expansion, of Zr0.2Ce0.8O2 - delta powder. The coefficient of thermal expansion agrees with previous values for undoped ceria. The coefficient of chemical expansion, on the other hand, is significantly less than in ceria, in agreement with a previous study by this group on Zr0.2Ce0.8O2 - delta. Contrary to previous studies of chemical expansion in ceria, with increasing 6, the chemical expansion coefficient increased, approaching the value for undoped ceria for large 6. This behavior is discussed in terms of availability of Zr for defect association. (C) 2014 Elsevier B.V. All rights reserved.