Synthesis and characterization of Sn2+ oxides with the pyrochlore structure

During synthesis of Sn22+M2X6+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 Mössbauer spectroscopy for two compounds. Mössbauer 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, Sn22+(Sn0.254+W1.22Sc0.53)O6.96, and Sn1.42+(Sn0.194+Ti1.06W0.75)O6.15 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.