Synthesis and characterization of Sn2+ oxides with the pyrochlore structure

During synthesis of S n 2 2 + M 2 X 6+ x compounds with the pyrochlore structure, some disproportionation of the Sn2+ always occurred. This in turn led to some incorporation of Sn4+ into the octahedral (M) sites of the pyrochlore structure. The actual amount of Sn4+ incorporation was determined by 119Sn Mِssbauer spectroscopy for two compounds. Mِssbauer spectroscopy also indicated that Sn2+ was strongly displaced from its ideal site in the pyrochlore structure. The compounds Sn2TiNbO6F, Sn2Ti0.9Ta1.1(O,F)7, S n 2 2 + ( S n 0.25 4 + W 1 .22 S c 0 .53 ) O 6 .96 , and S n 1.4 2 + ( S n 0.19 4 + T i 1 .06 W 0 .75 ) O 6 .15 with the pyrochlore structure are yellow to red with band gaps determined from diffuse reflectance ranging from 1.9 to 2.3 eV. The dielectric constant of Sn2+ pyrochlores examined ranged from 31 to 149.