Home – Home – Jornals – Chemistry for Sustainable Development 2016 number 5

New solid solutions of bismuth titanates with the pyrochlore-type structure Bi_{2 - y} In _x Ti₂O_{7 - δ} ( y = 0.4 at x = 0.2-0.6; y = 0.6 at x = 0.4-0.6) and Bi_{2 - y} Mg _x Ti₂O_{7 - δ} ( y = 0.4 at x = 0.05-0.3; y = 0.6 at x = 0.1-0.6) were obtained using solid-phase synthesis and the method of burning nitrate-organic precursors. The formation of single-phase compounds with the pyrochlore-type structure was confirmed by XPA method. According to results of qualitative elemental analysis and local microanalysis, the chemical composition of the samples remains unchanged after high temperature annealing. Based on comparison of the pycnometric and X-ray densities of compounds, the distribution variant of dopant atoms (In, Mg) according to X-ray positions of the pyrochlore structure was proposed. It was shown that indium and magnesium atoms populated initially vacant A (Bi)-positions of the pyrochlore structure. With increasing the dopant content a part of In and Mg atoms occupy Vi (Ti)-position. The results of the full-profile treatment of diffractogram of the compound Bi_1.6In_0.4Ti₂O₇ performed with various options of the dopant (In) distribution, coincide with the results of the comparison micrometrical density and the densities calculated for a certain cation distribution - hitting all of the indium atoms in vacant A (Bi) positions. It was determined that the presence of bismuth and vacancies in the oxygen sub-lattice O^¢ of the pyrochlore structure led to the appearance of the proton conductivity in a wet atmosphere in a temperature range of 240-640 °C. Compounds Bi_1.6In_0.2Ti₂O_6.7 and Bi_1.4Mg_0.1Ti₂O_6.2 are characterized by the value of proton conductivity equal to 2.2 10^-6 S/cm at a temperature of 400 °C and frequency of the supplied field of 1 kHz, which is by 1.5-2 orders of magnitude higher when measuring this parameter under the conditions of the dry air atmosphere.