THE EFFECTS OF CATION SUBSTITUTION ON THE HOLLANDITE-TYPE STRUCTURE

Hollandite-type tunnel structures of K//1//. //5//0Al//1//. //5//0Ti//6//. //5//0O//1//6 and Rb//1//. //4//7Al//1//. //4//7Ti//6//. //5//53O//1//6 were refined; final R-and wR-factors were 2. 24/3. 30 and 2. 98/3. 32%, respectively. The structures were compared with those of K//1//. //5//4Mg//0//. 7//7Ti//7//. //2//3O//1//6 and BaAl//2Ti//6O//1//6 from the viewpoint of crystal chemistry. The substitutions of K by Rb and Ba make an anisotropic deformation on the frameworks relative to that of K//1//. //5//0Al//1//. //5//0Ti//6//. //5//0O//1//6, whereas the replacement of Al by Mg changes more uniformly the network by enlarging octahedra themselves. The octahedron in the three priderites, (Rb, K, or Ba)//xAl//yTi//8// minus //yO//1//6, becomes larger and gets more regular in that order, but the off-center displacement of the octahedral cation also becomes larger.