## 2 Experimental Part
Systematic errors and data reproducibility are critical aspects of scientific research. Systematic errors (e.g., weighing errors of \(\pm\)0.5 \(\times\) 10\({}^{-4}\) g, with an average relative error of approximately 1.36% in repeated calibrations with a copper sample, including instrument verification using a standard, etc.) in our case were negligible compared to the random component. According to error theory, when the random error is significantly greater than the sum of the systematic error and the instrument scale error, the accuracy of the instrument measurements will be determined by the random error [24; 25]. Repeated calibration, error evaluation, comparison with existing results, and monitoring the stability of sample properties--all these measures not only minimize systematic errors but also ensure high data reproducibility in our studies. Additionally, the device was tested for determining the heat capacity of \(\alpha\)-Al\({}_{2}\)O\({}_{3}\) (\"p.a.\", TU 6.09-426-75, LenReaktiv, St. Petersburg, Russia) over a wide temperature range. The verification was carried out by conducting repeated parallel measurements in the temperature range of 173-673 K, with increments of 25 K. At each temperature point, five parallel measurements were performed. The results were then averaged and processed using statistical methods to improve accuracy. Liquid nitrogen was used as a coolant to achieve the required low temperatures and ensure stable experimental conditions. Table 3 presents the results of calorimetric studies, showing the experimental values of the heat capacity of \(\alpha\)-Al\({}_{2}\)O\({}_{3}\) obtained during the measurements. These data provide a clear representation of the temperature dependence of heat capacity within the studied range and enable comparison with literature data [26], confirming the accuracy and reliability of the conducted experiments. The results of heat capacity measurements for \(\alpha\)-Al\({}_{2}\)O\({}_{3}\) in the temperature range of 173-673 K showed good agreement with the literature data [26], taking into account the accuracy of the IT-C-400 calorimeter. To facilitate the comparison of experimental data with those in [26], interpolation of measurements was performed. The original data from our work were presented in 25 K increments, while in [26], the values of C\({}^{0}_{\text{p}}\) (heat capacity at constant pressure) are provided in increments of 10 and 50 K. Consequently, the experimental results were expressed with these intervals using the derived equation for the dependence of C\({}^{0}_{\text{p}}\) on temperature (C\({}^{0}_{\text{p}}\)-f(T)). It was also demonstrated that the actual measurement errors are significantly lower than the maximum allowable accuracy of the device, not exceeding 10%. This highlights the high reliability of the obtained data. To study phase transitions on the C\({}^{\circ}\)p-f(T) curve in neodymium manganites, the temperature dependence of the heat capacity of the standard substance barium titanate (BaTiO\({}_{3}\)) was investigated using the same IT-C-400 calorimeter. BaTiO\({}_{3}\) was used in the \"p.a.\" qualification (TU 6-09-3963-84, LLC VitaReaktiv, Dzerzhinsk, Russia). To confirm compliance with standards, BaTiO\({}_{3}\) underwent X-ray phase analysis using the DRON-2.0 setup. The diffraction maxima of BaTiO\({}_{3}\) obtained during the experiment (4.04; 2.87; 2.35; 2.05; 1.83; 1.66; 1.44 A) completely matched the reference values from the ASTM database [27], indicating a high degree of purity and phase identity of the sample.