Thermal behavior of Ni-doped CaCu3Ti4O12 ceramics
The calcium-copper titanate has attracted the attention of scientists in connection with the manifestation of gigantic values of permittivity in a wide frequency (102 -106 Hz) and temperature ranges (100 - 600 K), while not being a ferroelectric. In this article, we report on the results of studies of the thermal behavior of Ni-doped CCTO by thermal analysis methods. The interest in this work is due, first of all, to the fact that earlier, for iron-containing compounds, we found a reproducible low-temperature exothermic effect in the temperature range of 506 - 573 K, the nature of which has not been fully elucidated. It is only known that such a behavior of ceramics is recorded by the impedance spectroscopy data, it is not associated with the phase transition and is weaker for an undoped CCTO. Samples of Ni-doped CaCu3Ti4O12 ceramics of the composition CaCu3Ti4-4xNi4xO12-δ and CaCu3-3xNi3xTi4O12 (x = 0.005, 0.01, 0.02, 0.03, 0.04, 0.06) were obtained by the solid-phase synthesis method. According to the XRD results, copper (II) oxide may be present in trace amounts in all samples. The X-ray picture of CaCu3Ti4-4xNi4xO12-δ samples (x ≥ 0.04) revealed calcium titanate reflexes. The thermal behavior of the samples was studied by DSC and thermogravimetry methods up to 1323 K. The reproduced exothermic effect in the temperature range 487 - 653 K and endothermic at 1269 K (1285 K) for CaCu3-3xNi3xTi4O12 (CaCu3Ti4-4xNi4xO12-δ) are observed on the DSC curves of the synthesized samples of both series, associated with thermal dissociation of CuO impurities. Thermogravimetric curves in both cases show a mass loss of samples of no more than 0.35 mass.%. Samples analyzed by FTIR and mass spectrometry.