Specific features of local structural, valence, and magnetic states of iron ions in the perovskite Bi$_{0.5}$Ca$_{0.5}$FeO$_3$

The perovskite Bi$_{0.5}$Ca$_{0.5}$FeO$_3$ has been investigated using the Mössbauer effect at temperatures of 295 and 675 K. The measured temperature of the magnetic phase transition (Néel temperature) is $T_N$ = 640 $\pm$ 10 K. Above the Néel temperature, there are two nonequivalent structural states of iron ions. In the perovskite Bi$_{0.5}$Ca$_{0.5}$FeO$_3$ at room temperature, there are seven most probable nonequivalent magnetic states of iron ions with significantly different values of the hyperfine interaction parameters. Four iron states correspond to Fe$^{3+}$ ions in the octahedral oxygen environment, and three iron states correspond to Fe$^{3+}$ ions in the tetrahedral oxygen environment.