Dependence of dielectric properties of manganese-doped strontium titanate ceramics on sintering atmosphere

Abstract

It is shown in this paper that the microscopic mechanism of the dielectric relaxation in Mn-doped strontium titanate (SrTiO 3–ST) ceramics is associated with the off-center displacement of Mn Sr 2 + ions. This was accomplished by studying the dielectric properties and electron spin resonance spectroscopy in combination with X-ray powder diffractometry and scanning electron microscopy techniques in Sr 1− x Mn x TiO 3 ceramic samples sintered in different atmospheres (air, oxygen and nitrogen) at 1500 °C. First, it is shown that manganese is incorporated into the perovskite lattice of ST, preferably as Mn 2+ at Sr sites. However, a small amount of Mn 4+ at Ti sites is also observed when fired in air or oxygen flow. The concentration of Mn Ti 4 + is the highest for sintering in oxygen, but firing in a reducing atmosphere (nitrogen) results solely in the incorporation of Mn 2+ at Sr sites. Correspondingly, the dielectric relaxation observed in Sr 1− x Mn x TiO 3 markedly increases in intensity and slightly shifts towards a higher temperature for ceramics sintered in nitrogen compared with those fired in air or oxygen. All these facts are consistent with a suggestion that the off-center displacement of Mn 2+ ions at the Sr sites of the highly polarizable ST lattice is the source of the observed relaxation behavior.