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

It is shown in this paper that the microscopic mechanism of the dielectric relaxation in Mn-doped strontium titanate (SrTiO3-ST) ceramics is associated with the off-center displacement of MnSr2+ 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 Sr1-xMnxTiO3 ceramic samples sintered in different atmospheres (air, oxygen and nitrogen) at 1500deg. C. First, it is shown that manganese is incorporated into the perovskite lattice of ST, preferably as Mn2+ at Sr sites. However, a small amount of Mn4+ at Ti sites is also observed when fired in air or oxygen flow. The concentration of MnTi4+ is the highest for sintering in oxygen, but firing in a reducing atmosphere (nitrogen) results solely in the incorporation of Mn2+ at Sr sites. Correspondingly, the dielectric relaxation observed in Sr1-xMnxTiO3 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 Mn2+ ions at the Sr sites of the highly polarizable ST lattice is the source of the observed relaxation behavior