Correlation of the magnetic and transport properties with polymorphic transitions in bismuth pyrostannate Bi$_2$(Sn$_{1-x}$Cr$_x$)$_2$O$_7$

The correlation of the electrical, magnetic, and structural properties of Bi$_2$(Sn$_{1-x}$Cr$_x$)$_2$O$_7$ solid solutions has been investigated for two compositions with $x$ = 0.05 and 0.1. The temperatures of structural phase transitions and anomalies of the electrical resistance in the vicinity of these transitions at temperatures in the range 300 K $< T <$ 1000 K have been determined using differential scanning calorimetry. It has been found that the thermoelectric power changes sign upon the polymorphic transition. The paramagnetic Curie temperature and the chromium-ion spin have been found from the temperature dependence of the magnetic susceptibility in the range 4 K $< T <$ 1000 K and from the field dependence of the magnetic moment in magnetic fields of up to 6 T.