Thermophysical properties of Gd2Zr2O7 powders prepared by mechanical milling: Effect of homovalent Gd3+ substitution

Abstract

This contribution analyzes the thermophysical properties of Gd1.6Ln0.4Zr2O7 (Ln = La3+, Nd3+, Sm3+, Dy3+ and Er3+) ceramics synthesized at room temperature, by mechanically milling stoichiometric mixtures of high purity oxides. Regardless of chemical composition, powders milled for 27 h show XRD patterns similar to fluorite-type materials. Post-milling thermal treatments at 1500 °C, facilitates the evolution to the ordered pyrochlore derivative for Gd2Zr2O7, and the La3+-, Nd3+-, and Sm3+-containing materials. By contrast, samples containing the smaller lanthanides (Dy3+ or Er3+), maintain the fluorite structure. Thermal conductivity of the as-prepared samples was obtained as a function of temperature, from thermal diffusivity, heat capacity and density values, using sintered pellets. We found that doping has an important effect in lowering Gd2Zr2O7 thermal conductivity, with final values ranging from 1.22 to 1.94 W m−1 K−1; Nd3+- and Er3+-containing samples represent an optimum combination of defects and disordering of oxygen vacancies that generate the lowest conductivity values of all samples tested.