Variants of cation arrangement in the 36 net of tantalates and niobates with 1:1 stoichiometry

We have analyzed and tabulated the variants of mutual ordered arrangements of cations of two types with 1∶1 stoichiometry in cation matrices having planar trigon 3⁶ nets. A net with two nodes in its unit cell has a sole variant, which occurs in the wolframite type structure. With four nodes in the cell, there are two variants: the scheelite type and the variant found in α-and β-LaTaO₄. With 6 nodes, there are six, and with 8 nodes, more than 20 variants. In the ABO₄ (A=REE, B=Ta Nb) structural type (M'-fergusonite, fluorite, α-LaTaO₄, β-LaTaO₄, and fergusonite) having a more or less distorted face-centered cubic cation subcell in common, we have the wolframite type of arrangement for M'-fergusonite and fluorite, the scheelite type for fergusonite, and the partly scheelite type for α-and β-LaTaO₄. We offer a system for representing the atomic arrangement by recording the alternation of atoms in linear rows of three directions. Institute of Inorganic Chemistry, Siberian Branch Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 129–135, November–December, 1994 Translated by T. Yudanova