Phase transitions in bismuth pyrostannate upon substitution of tin by iron ions

The Bi₂(Sn_1-хFe_х)₂O₇ (х = 0, 0.1, 0.2) compounds have been synthesized by the solid-state reaction technique. The structure of the synthesized compounds has been investigated in the temperature range of 80–500 K using the thermal expansion and ultrasound damping coefficients and IR spectroscopy. The shift -type structural transitions for the composition with х = 0.2 in the low-temperature region has been established. The effect of iron ions on the phase boundaries of the polymorphic transitions in the Bi₂Sn₂O₇ compound has been observed. Softening of the phonon modes near the phase transitions at different iron concentrations has been found.