Heat capacity and electrophysical properties of GdMeFe2O5(Me — Li, Na, K, Cs)-type ferrites

The heat capacity of GdMeFe2O5(Me — Li, Na, K, Cs) is investigated within the temperature range of 298.15–673 K by a calorimetric method. λ-points are revealed in the Cp○(T) curves at 448 K and 598 K in GdLiFe2O5, at 473 K and 573 K in GdNaFe2O5, at 448 K and 598 K in GdKFe2O5, and at 448 in GdCsFe2O5 related to a phase transition of the second kind. The temperature dependencies are calculated for the thermodynamic functions Cp○(T), H○(T)-H○(298.15), S○(T), and Φ**(T). The electrophysical characteristics of the synthesized ferrites are studied within the temperature range of 303–493 K: Effects similar to those found in the Cp○(T) curves are also revealed in the logɛ(T) and logR (T) curves. The compositions are shown to exhibit a semiconductor-type electrical conductivity. At the Tcond points of the ferrites, the semiconductor-type conductivity changes the metal type one and both the capacities and permittivities vary sharply, and that may be related to a ferroelectric phase transition (the Curie and the Neel points). These effects provide a certain possibility to clarify the nature of the λ-points in the Cp○(T) curves.