The Heat Capacity and Thermodynamic Functions of Ternary Manganites $\text{DyM}^{\text{I}}\text{MgMn}_2\text{O}_6$ $(\text{M}^{\text{I}}$ - $\text{Na}$, $\text{K}$, $\text{Cs})$ in the Temperature Range from $223$ to $673$ K

The solid-phase method is used to synthesize ternary manganites of composition $\text{DyM}^{\text{I}}\text{MgMn}_2\text{O}_6$ $(\text{M}^{\text{I}}$ - $\text{Na}$, $\text{K}$, $\text{Cs})$; their X-ray investigation is performed to demonstrate that they all crystallize in orthorhombic system. Their heat capacity is determined experimentally in the range from $223$ to $673$ K, equations are derived which describe the dependences $C^{\circ}_p \sim f(T)$, and the thermodynamic functions $C^{\circ}_p(T)$, $H^{\circ}(T) - H^{\circ}(298.15)$, $S^{\circ}(T)$, and $\Phi^{**}(T)$ are calculated. Second-order phase transitions are observed in the process of investigation of heat capacity.