Heat capacity and electrophysical properties of $\mathrm{Gd}\mathrm{Ca}\mathrm{Cr}_2\mathrm{O}_{5.5}$ chromite

The solid-phase method is used to synthesize $\mathrm{Gd}\mathrm{Ca}\mathrm{Cr}_2\mathrm{O}_{5.5}$ chromite from chrome and gadolinium oxides and calcium carbonate. X-ray phase analysis is used to find that the compound is crystallized in tetragonal crystal system with the following lattice parameters: $a=10.77\mathring{A}$, $c=15.84\mathring{A}$, $V^\circ=183.3\mathring{A}{}^3$, $Z=16$, $V_{\text{unit cell}}=11.8\mathring{A}$; $\rho_{\text{X-ray}}=5.63$, and $\rho_{\text{pycn}}=5.55\pm0.05$ g/cm$^3$. An IT-S-400 calorimeter is used to measure the heat capacity of the compound in the temperature range from $298.15$ to $673$ K. Pronounced anomalous jumps are observed on the heat capacity curve at $448$ and $473$ K, which are apparently associated with second- order phase transitions. Equations describing the $C_p^\circ\sim f(T)$ dependence are derived, and the functions $C_p^\circ(T)$, $S^\circ(T)$, $H^\circ(T)$–$H^\circ(298.15)$, and $\Phi^{xx}(T)$ of chromite in the range from $298.15$ to $673$ K are calculated. The temperature dependences of dielectric permittivity and electric resistance of the compound are investigated in the range from $303$ to $383$ K to demonstrate that chromite under investigation exhibits semiconductor properties.