Influence of the partial substitution of Y2O3 with Ln2O3 (Ln = Nd, Sm, Gd) on the phase structure and thermophysical properties of ZrO2–Nb2O5–Y2O3 ceramics Original Research Article

The low thermal conductivity, elevated phase-transformation temperature and improved mechanical properties make the ZrO2–Nb2O5–Y2O3 system a promising candidate for thermal barrier coatings. In this study, the influences of the partial substitution of Y2O3 with equimolar Ln2O3 (Ln = Nd, Sm, Gd) on the phase structure and thermal properties of ZrO2–Nb2O5–Y2O3 ceramics have been investigated. X-ray diffraction analysis indicates that these compositions consist of the pure non-transformable tetragonal phase and have an obviously higher tetragonality c/a than the binary ZrO2 systems. Nevertheless, the partial substitution leads to a decrease in the tetragonality. The thermal conductivity measurement shows that these compositions have low and temperature-independent thermal conductivities, as well as more than 10% reduction in the thermal conductivity due to the partial substitution. Among these rare-earth oxides, Nd2O3 is the most effective oxide for lowering the thermal conductivity. Their thermal conductivities well agree with a point-defect scattering model. The model predicts that the phonon scattering associated with the elastic field around a point defect makes the principal contribution to the reduction of the thermal conductivity for these compositions. This research indicates potential applications of ZrO2–Nb2O5–Y2O3 ceramics for thermal barrier coatings as well as the need for further studies.