The aim of this paper was to investigate the structure and thermal properties of zirconia ceramics co-doped with rare earth (RE) elements in equimolar concentrations. We prepared (1 − x)ZrO2 − x(yLa2O3 + yNd2O3 + ySm2O3 + yGd2O3 + yYb2O3) (x = 0.2; y = 0.2) powders by a hydrothermal method in mild conditions (200 °C, 2 h, 60–100 atm.) The powder was analyzed by XRD, SEM-EDAX, BET, and FT-IR after synthesis and heat treatments at 1200 °C and 1500 °C. The samples exhibit good thermal stability, with a single cubic phase presented after heat treatment at 1500 °C. The compound exhibits a low thermal conductivity (0.61 W·m−1·K−1), a low heat capacity (0.42 J·g−1K−1), and a low thermal diffusivity (0.34 mm2·s−1). The values are lower than reported for conventional RE-doped zirconia.
