On the Structure of Tapiolite Formed by Solid State Reactions

Abstract

The structure of tapiolite formed by the solid state reactions of tantalum pentoxide with iron oxides is discussed. Reactions were carried out in the following systems. (1) In the FeO–Ta₂O₅ system, ordered tapiolite was formed on heating in vacuum at 1050°C for 10 hr. It has a trirutile structure and is isomorphous with ZnSb₂O₆. (2) In the Fe₃O₄–Ta₂O₅ system, a disordered tapiolite produced under the same condition as mentioned above is isomorphous with SnO₂. (3) In the Fe₂O₃–Ta₂O₅ system, a disordered tapiolite was also formed on heating in air at 1200°C for 24 hr.
The lattice constants of the three synthetic tapiolites are as follows : (1) a₀=4.750 (Å), c₀=9.205 (Å); (2) a₀=4.708 (Å), c₀=3.075 (Å); (3) a₀=4.681 (Å), c₀=3.051 (Å).
The above facts suggest that the interplanar spacings of the three synthetic tapiolites decreased in proportion as the iron valency increased, and that the composition and structure of tapiolite depend closely on the size of the iron ion.