A small mass change of the BCZT powder mixture (-1.90 w%) occurred at 350 °C and is related to the combustion of residual absorbed solvents and organic impurities introduced during milling. The TG curve shows a distinct endothermic two-step carbonate decomposition process above 600 °C, which correlates with peaking CO2 releases in the mass-spectrometry curve at 717.5 °C and 932.7 °C, shown in Figure . The first reaction step accounts for a mass change of -3.55 w%, while the second corresponds to -13.04 w%, mirroring the ratio between CaCO3 and BaCO3 in the starting powder mixture. This observation confirms that the decomposition temperature of CaCO3 is lower than that of BaCO3 and is further supported by the TG curves recorded for the binary perovskites discussed below. The endothermic peak at 825 °C is related to the phase transition of BaCO3 from the orthorhombic 𝑃𝑚𝑐𝑛 (S.G. 62) to the trigonal 𝑅3 ̅ 𝑚 (S.G. 166) polymorph .