Dielectric properties of pure and Mn-doped CaCu3Ti4O12 ceramics over a wide temperature range

The effect of manganese doping on the dielectric properties of CaCu3Ti4-xMnxO12 (x = 0, 0.02, 0.04) were investigated over a broad temperature range (93-723 K) in the frequency range from 100 Hz to 10 MHz. Two dielectric relaxations and two dielectric anomalies were observed. The low-temperature relaxation appearing in the temperature range below 200 K is the characteristic relaxation for CaCu3Ti4O12. This relaxation was attributed to the polaron relaxation due to electron hopping between Ti3+ and Ti4+ states. Due to the negative factors of notable decreases in the Ti3+/Ti4+ and Cu3+/Cu2+ ratios and the concentration of oxygen vacancies as revealed by X-ray photoemission spectroscopy, Mn-doping was found to gradually destroy rather than move this relaxation to a higher temperature. The high-temperature relaxation occurring around room temperature was found to be a Maxwell-Wagner relaxation caused by grain boundaries. Our results confirm that the colossal dielectric behavior in the tested samples results from both polaron and Maxwell-Wagner relaxations, but is predominated by the latter relaxation. The low-temperature anomaly behaves as a phase-transition-like behavior. It was argued to be created by oxygen vacancies transition from static disorder to dynamic disorder. The high-temperature anomaly is an artificial effect caused by negative capacitance.