Studies on dielectric behaviour of an oxygen ion conducting ceramic -: CaMnO3-δ

An oxygen deficient ceramic oxide having perovskite structure has been prepared by the conventional solid state reaction method. X-ray diffraction studies have confirmed the sample formation in single phase polycrystalline form. The scanning electron micrographs have confirmed polycrystalline texture of the material alongwith indications of porous microstructure. The temperature dependence of the dielectric properties (permittivity/loss tangent) in the sub-ambient and ambient temperature region suggests the possibility of a strong dipolar ordering. The appearance of maxima in both the permittivity and loss factor pattern at a very close temperature range (epsilon(max)similar to 1879 at 29 degrees C, tan delta(max)similar to 9.7 at 35 degrees C at a common frequency of 10 kHz) supports the presence of dipolar interaction in CaMnO3-delta. It has been attributed to a strong interaction of the oxide ion-oxygen vacancy pair in the crystal lattice of an oxygen deficient perovskite (CaMnO3-delta) that in turn reduces the net mobility of oxygen ion at lower temperatures and imparts it a higher dielectric permittivity as well as high loss factor close to room temperature. A decrease in the permittivity and monotonous increase in loss factor with rise in temperature above the ambient value Suggest a thermally activated weakening of the dipolar ordering in the system. In view of a very high value of loss factor at and above room temperature, it would be premature to conclude the existence of ferroelectric ordering in the material system just by the presence of a peak in both the permittivity and loss factor pattern.