Heat Capacity and Electrophysical Properties of GdCaCr₂O_5.5 Chromite

Abstract

The solid-phase method is used to synthesize GdCaCr₂O_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 Å, c = 15.84 Å, V = 183.3 ų, Z = 16, V _{unit cell} = 11.8 Å, ρ_X-ray = 5.63, and ρ_pycn = 5.55+0.05 g/cm³. 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 ≈ f(T) dependence are derived, and the functions C _p (T), S(T), H(T) - H(298.15), and Φ^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.