Characterization of nonstoichiometry CaCu3Ti4O12 precursors with different calcium and copper Molar Ratio via Modulated Thermogravimetry and Differential Scanning Calorimetry at 30-1000 °C

Calcium copper titanate (CCTO) has received tremendous attention in recent years due to its giant dielectric constant. The relationship between thermal properties and structural properties in materials gives a significant improvement of their properties. Yet the research on thermal properties of CCTO compounds is not enough. The chemical and thermal properties that influence the mass changes, enthalpy, heat capacity, and CCTO structure at oxidation can be observed by simultaneous Thermogravimetry & Differential Scanning Calorimetry measurement (TGA/DSC). In this study, the chemical formula consists of excess and deficiency of the Ca and Cu cation. The prepared CCTO chemical formulation is CaCu3Ti4O12 (controlled), Ca1+xCu3Ti4O12+x, Ca1–xCu3Ti4O12–x, CaCu3+xTi4O12+x, and CaCu3–xTi4O12–x. The weighed samples powders then undergo the heating routes of TGA/DSC using isothermal induction of time and temperature at 1000 °C with oxygen gas. Then the final product was characterized by using X-ray diffraction. The oxygen absorption trend is decreased when the x value is increased in the CaCu3+xTi4O12+x system. The ΔHcry is decreasing as the Cu element is excessive in the CaCu3+xTi4O12+x system. The Cp evaluations are significantly increased with a higher Cu component in the CaCu3+xTi4O12+x system. The CaCu3–xTi4O12–x system for x = 0.10 causes more secondary phases and trigger more oxidation gain compare with other reduced Cu. The decrease in heat capacity from x = 0.02 to 0.08 in the CaCu3–xTi4O12–x system was due to less energy needed to generate CCTO crystallization compared with x = 0.0 with more crystallization phase structure. The difference in lattice planes of CaCu3–xTi4O12–x system at higher substitution x = 0.10 where the secondary phase is considerably more when excessive Cu element. The trends of the mass gain show decreasing in mass gain as Ca content is increased in the Ca1+xCu3Ti4O12+x system. The difference in heat capacity is related to the XRD lattice parameters in the Ca1+xCu3Ti4O12+x system. The (220) lattice peaks intensity are decreased from x = 0.0 to 0.5 but then slightly increased for sample x = 0.10 in Ca1+xCu3Ti4O12+x system. The result reveals the thermal properties and microstructural properties are strongly related to reducing of Ca cation in the Ca1–xCu3Ti4O12–x chemical formula on their isothermal oxidation at 1000 °C. The oxidation mass changes, enthalpy, heat capacity, and structural formation are significantly affected by the excess and deficiency of Ca and Cu cation composition in the prepared CCTO system.