Dielectric composite materials including an electronically tunable dielectric phase and a calcium and oxygen-containing compound are disclosed. The tunable phase may comprise a material such as barium strontium titanate. The calcium/oxygen compound may comprise CaO or a transition metal-containing compound such as Ca₂Nb₂O₇ or CaTiO₃. The material may also include a rare earth oxide dopant such as CeO₂. The materials resist dielectric breakdown and possess improved combinations of electronic properties. The materials may be tailored for specific applications.