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

The Bi2(Sn1-хFeх)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.