## 2 Experimental Part
The data from differential thermal analysis (DTA) show that in the temperature range of 276-368 \({}^{\circ}\)C, a broad endothermic peak with a heat absorption of 110.98 J/g is observed, likely associated with the removal of adsorbed moisture. In the range of 420-510 \({}^{\circ}\)C (heat absorption: 34.46 J/g), the removal of residual moisture likely occurs. An endothermic peak in the range of 830-866 \({}^{\circ}\)C corresponds to the final stage of the formation of the target phase  
Figure 3: The TGA/DTA curve for the formation of NdNa\({}_{2}\)NiMnO\({}_{5}\) from the starting materials. NdNa\({}_{2}\)NiMnO\({}_{5}\), with heat absorption of 15.06 J/g. At this stage, the structure undergoes final ordering, resulting in the formation of the target phase. Subsequent peaks become less intense as the reaction completes its stages. These peaks align well with the mass losses observed in the TGA curve, particularly in the ranges of 220-400 \({}^{\circ}\)C and 760-900 \({}^{\circ}\)C.  
For NdK\({}_{2}\)NiMnO\({}_{5}\), the thermogravimetric analysis of the reaction demonstrates that the primary mass loss occurs in several stages (Figure 4). At 30-216 \({}^{\circ}\)C, a 4% total mass loss is observed, attributed to the removal of adsorbed moisture from the sample's surface, which is typical in the initial heating stages. Up to 375 \({}^{\circ}\)C, decomposition of potassium carbonate (K\({}_{2}\)CO\({}_{3}\)) occurs with the release of CO\({}_{2}\), resulting in a 4.2% mass loss. At 374-500 \({}^{\circ}\)C (1.73%) and 500-560 \({}^{\circ}\)C (0.86%), the removal of crystallization moisture is completed. Up to 732 \({}^{\circ}\)C, active interaction of oxides (Nd\({}_{2}\)O\({}_{3}\), NiO, Mn\({}_{2}\)O\({}_{3}\)) potentially leads to the formation of intermediate compounds and the initiation of the target phase, NdK\({}_{2}\)NiMnO\({}_{5}\). A residual CO\({}_{2}\) release is possible, with a mass loss of approximately 2.78%. At 730-805 \({}^{\circ}\)C (1.67% mass loss), this likely marks the formation of NdK\({}_{2}\)NiMnO\({}_{5}\). At 960 \({}^{\circ}\)C, the main stage of completing the solid-state reaction and final formation of the target phase occurs. This step may involve structural rearrangement and the removal of the last traces of CO\({}_{2}\). The DTA curve shows three endothermic peaks associated with the main reaction processes: at 72-174 \({}^{\circ}\)C, a peak with an enthalpy of 111.87 J/g, corresponding to the removal of physically adsorbed and chemically bound water from the sample; at 260-362 \({}^{\circ}\)C, a peak with an enthalpy of 102.37 J/g, also associated with the removal of bound water; and at 401-498 \({}^{\circ}\)C, a peak with an enthalpy of 21.83 J/g, indicating the conclusion and initial stages of oxide interactions, resulting in the formation of intermediate phases. These endothermic processes align well with the mass losses observed in the TGA analysis. The graph in Figure 5 presents the range between 100 and 98.6%, indicating that the weight loss compared to the total sample weight is very small, amounting to 1.4%. As shown in Figure 5, for NdNa\({}_{2}\)NiMnO\({}_{5}\), an endothermic peak is observed at 30-260 \({}^{\circ}\)C, associated with the removal of adsorbed water. At 620-756 \({}^{\circ}\)C, an exothermic effect is observed, likely corresponding to a first-order phase transition related to structural rearrangements. The compound does not decompose up to 1000 \({}^{\circ}\)C. A slight deviation of  
Figure 4: The TGA/DTA curve for the formation of NdK\({}_{2}\)NiMnO\({}_{5}\) from the starting materials. the TGA curve at high temperatures, around 1000 \({}^{\circ}\)C, is probably related to slow congruent or incongruent evaporation of the compound. The graph in Figure 6 presents the range between 100 and 98.6%, indicating that the weight loss compared to the total sample weight is very small, amounting to 1.4%.