Characterization of novel cation-ordered compounds with fluorite and α-PbO2 related structures prepared by oxidation of Sn–Nb–O pyrochlore

Sol–Gel Synthesis of Tunable Cerium Titanate Materials

“…Several characterization techniques have been used in order to elucidate the pyrocholore to fluorite phase transition after oxidation of a pyrochlore structure. [11,12] According to literature, [13] the oxidation of a Ce 3+ pyrochlorerelated structure may proceed smoothly at a low temperature, maintaining the ordered arrangement of the constituent cations, but with Ce 3+ and Ce 4+ ions. The cerium oxidation process has an important influence in the final properties due to the creation of crystalline defects in the structure.…”

α-PbO₂-related phase appearing in the Sn^IV–Ta–O system transformed from cation-ordered fluorite-related phase

“…5) We previously reported the oxygen-intercalation into the Sn NbO pyrochlore phase containing Sn II ions. 8), 9) In that case, we observed surprise transformation from pyrochlore phase to cationordered ¡-PbO 2 and rutile related phases in addition to the transformation from pyrochlore phase to cation-ordered fluorite phase. Specifically, when the pyrochlore-type Sn IV and Nb V are very small for the fluorite-related structure, the transiently formed fluorite-related phase immediately transformed into ¡-PbO 2 and rutile-related phases.…”

“…According to a previous study, Ce III 9 which has two tetrahedral sites and one octahedral site, the occupancy of Ta ion in the octahedral site tends to be higher than that of Nb ion. 31) These showed that the high coordination number was more stable for Ta ion than Nb ion.…”

Epitaxial growth of tin(II) niobate with a pyrochlore structure

“…Sn-Nb-O pyrochlore crystals are fabricated, for example, by calcining SnO together with Nb 2 O 5 at 1173 K in a vacuumed ampule [4]. Although the valence state of tin is mainly 2 þ in such a sample, it is reported that approximately 10-20% of tin ions exhibit the 4 þ state and occupy the niobium sites, which leads to non-stoichiometric compositions such as Sn 2 þ 1.62 (Nb 1.86 Sn 4 þ 0.14 )O 6.55 and Sn 2 þ 1.52 (Nb 1.59 Sn 4 þ 0.41 )O 6.32 [5,6]. The Sn-Nb-O pyrochlore has an optical absorption threshold in the visible region, e.g., 2.38 eV for Sn 2 þ 1.62 (Nb 1.86 Sn 4 þ 0.14 )O 6.55 [5].…”

“…Although the valence state of tin is mainly 2 þ in such a sample, it is reported that approximately 10-20% of tin ions exhibit the 4 þ state and occupy the niobium sites, which leads to non-stoichiometric compositions such as Sn 2 þ 1.62 (Nb 1.86 Sn 4 þ 0.14 )O 6.55 and Sn 2 þ 1.52 (Nb 1.59 Sn 4 þ 0.41 )O 6.32 [5,6]. The Sn-Nb-O pyrochlore has an optical absorption threshold in the visible region, e.g., 2.38 eV for Sn 2 þ 1.62 (Nb 1.86 Sn 4 þ 0.14 )O 6.55 [5]. While little is known about its electrical transport property, a recent first-principles calculation has shown that this compound had a unique electronic structure around its valence band maximum (VBM) due to the presence of tin(II) [3].…”