The properties of $x$BiFeO$_{3}$–$(1-x)$SrTiO$_{3}$ ($x$ = 0.2 $\div$ 1.0; $\Delta x$ = 0.1) solid solutions: Mössbauer studies

The magnetic structure and phase transition in $x$BiFeO$_{3}$–$(1-x)$SrTiO$_{3}$ solid solutions, where $x$ is from 0.2 to 1.0 with a step of 0.1, are studied systematically with Mössbauer spectroscopy. The multiferroic BiFeO$_3$ was modified via incorporation of a perovskite SrTiO$_{3}$, and $x$BiFeO$_{3}$–$(1-x)$SrTiO$_{3}$ solid solutions that possess both ferrimagnetic and ferroelectric properties at room temperature were prepared. X-ray diffraction data indicate that there are no any additional phases in the $x$BiFeO$_{3}$–$(1-x)$SrTiO$_{3}$ systems, whereas Mössbauer data show that there is a mullinite (Bi$_2$Fe$_4$O$_9$), when amount $x$ of SrTiO$_3$ in the solid solution is from 1.0 to 0.8. The Mössbauer spectra of the $x$BiFeO$_{3}$–$(1-x)$SrTiO$_{3}$ system at room temperature show that when amount of BiFeO$_3$ in the solid solution decreases, the magnetic hyperfine field values decrease as well and the widths of absorption line increase due to the weakening of the magnetic exchange interaction. The Mössbauer spectra of the systems with $x<$ 0.5 indicate that the solid solution is paramagnetic. A relationship between the intensity of Zeeman lines and an amount of BiFeO$_3$ in BiFeO$_3$–$(1-x)$SrTiO$_3$ solid solution showed that the transition of this system to the paramagnetic state proceeded at room temperature, when $x$ value was 0.4 (between $x$ = 0.3 and 0.5).