We have been trying to find new oxide compounds with large thermal expansion coefficients and low thermal conductivities by means of a material calculation technique. Among thousands of compounds in the databases, we found that there were some materials with low thermal conductivities and large thermal expansion coefficients in the group of strontium-niobium oxides. For example, Sr4Nb2O9 has a thermal expansion coefficient of 14.510-6 / and thermal conductivity of 1.0 W/mK, although a slight amount of other phases appear during long-term annealing. These thermal properties are better than those of yttria-stabilized zirconia, which is the standard material for thermal barrier coatings. To prevent the precipitation of other phases, we prepared the solid solutions, Sr4Nb2-xMxO9. In this study, the thermal conductivities and thermal expansion coefficients of these solid solutions were measured, and their thermal stabilities were evaluated by long-term annealing.