Heat capacity and dielectric properties of multiferroics Bi$_{1-x}$Gd$_x$FeO$_3$ ($x$ = 0–0.20)

The heat capacity and the permittivity of multiferroics Bi$_{1-x}$Gd$_x$FeO$_3$ ($x$ = 0, 0.05, 0.10, 0.15, 0.20) have been studied in the temperature range 130–800 K. It has been found that insignificant substitution of gadolinium for bismuth markedly shifts the temperature of antiferromagnetic phase transition and increases the heat capacity over a wide temperature range. It has been shown that the temperature dependence of the excess heat capacity is due to the manifestation of three-level states. Additional anomalies characteristic of the phase transitions have been revealed in the temperature dependences of the heat capacity for the compositions with $x$ = 0.1 and 0.15 at $T\approx$ 680 K and $T\approx$ 430 K, respectively. The results of studies of the heat capacity have been discussed simultaneously with the data of structural studies.