A ceramic composition of matter includes a solvent material and a solute material. The solvent material comprises zirconia or hafnia, or a mixture thereof, which is stabilized with a stabilizing oxide. The solute material comprises a metal oxide of the formula, XaOb, where X is a metallic element, O is oxygen, and “a” and “b” are stoichiometric coefficients. The difference in density between the solvent material and the solute material is less than about 30%.