Effect of the oxygen deficiency on the physical properties of Ca2MnO4−δ compounds

Dielectric spectroscopy of Ca2MnO4‐δ ceramics using equivalent circuit analysis

“…1. It can be seen that all samples present a single phase and it was verified that the sample with δ=0.0 crystalizes in the tetragonal structure becoming orthorhombic for δ>0.0 samples [6,7]. The morphological analysis, made by SEM microscopy, shows a decrease in the size of the grains with the increase of δ value.…”

“…3). For δ>0.20 a robust frustration magnetic phenomenon was observed [7], indicating that the sample δ=0.30 should present predominantly Mn 3+ ions. Therefore, the dielectric relaxation observed in this sample is due to the dipoles formed by these ions and the surrounding oxygen ions.…”

“…It was observed that the magnetic characteristics of these samples showed a divergence in the field-cooled and zero field-cooled curves [7] typical of a spin glass behavior, present in compounds with a strong exchange interactions and/or short-ranged ordering, which is in deep relation with the Mn 3+ /Mn 4+ ratio (Table 1). Electrically the increase of this ratio results in an increase of the conductivity at low frequencies, which is confirmed by the dc electrical measurements (Fig.…”

“…In fact, it was found that the electrical response of a ceramic material is not intrinsic, but dominated by many extrinsic factors such as grain boundary, electrodematerial interface, etc. [7,8]. With the recent progress of technological integrated circuits, high dielectric constant materials are increasingly required as they allow the fabrication of smaller size capacitive components.…”