The effect of cation substitution on polymorphic transitions in bismuth pyrostannate Bi 2Sn 2O 7

The goal of this work is to develop a new technology of sensor materials required for gas sensing devices used in missile. The aim of this work is to study the effect of doping cations with different valency on the crystallographic structure, dielectric and electrical properties of pyrochlore compound Bi 2Sn 2O 7 with selectivity to gases. Polycrystalline compounds Bi 2(Sn 1-xMe x) 2O 7, where Me = Mn, Cr, x = 0, 0.05 have been synthesized by conventional solid-state reaction. According to the X-ray powder diffraction research, our sample consists of two polymorphs phases: cubic and rhombic. Two new structural transition are found in Bi2 (Sn 0.95Cr 0.05) 2O 7 solid solutions by scanning calorimetry, as compared to bismuth pyrostannate Bi 2Sn 2O 7. Ions Mn 4+ leads to shift of phase boundary of polymorphic transitions towards lower temperatures, and the phase α→β-transition at about 370 K, which is characteristic for Bi2(Sn1-xCrx)2O7, where x = 0, 0.05 is suppressed. The polymorphic transition at T = 543 K for Bi 2(Sn 0.95Mn 0.05) 2O 7 occurs with calorification, in contrast to Bi 2(Sn 1-xCr x) 2O 7, where x = 0, 0.05. The relationship between structural, electrical and dielectric properties is investigated. Anomalies in the temperature dependence of electrical resistivity and dielectric permeability (real and imaginary part) as in the low region temperatures as in the high region temperature are found. These features are explained within a model of martensitic phase transitions. The temperature of the structural phase transitions correlates with temperature of maximum of the electrical resistivity in the temperature range 300 2(Sn 1-xCr x) 2O 7, x = 0, 0.05 was found by scanning calorimetry method.