Colossal permittivity and low dielectric loss in (Nb, Ga) co-doped SrTiO3 ceramics sintered in nitrogen atmosphere

Sr(Nb0.5Ga0.5)xTi(1-x)O(3) (x = 1 %, 2 %, 3 %, 5 %) (STNG) ceramics were synthesized in nitrogen atmosphere by a solid state method. All samples exhibited a cubic perovskite structure without secondary phase. With the increase of the co-doped concentration of Nb5+ and Ga3+, the grain sizes increased firstly and then decreased. The STNG ceramic with x = 3 % exhibited a colossal permittivity (CP) of 24502 and a low dielectric loss of 0.012 at 1 kHz and room temperature. Compared with those samples sintered in air, the samples sintered in nitrogen atmosphere have a higher dielectric constant with lower dielectric loss. The phase structure, surface morphology, element distribution, element valence states and dielectric properties of STNG ceramics were investigated. And the mechanism of colossal permittivity was also explored, which indicated that the CP could be attributed to the formation of [Ti4+center dot e- V-O(center dot center dot) - e center dot Ti4+] defect dipole.