Electron-microscope study of the crystal structures of mixed oxides in the systems Rb₂O-Ta₂O₅, Rb₂0-Nb₂O₅ and K₂O-Ta₂O₅ with composition ratios near 1:3. II. Various intergrowth phases and two-dimensional ordering of pentavalent ions

In part I, the preceding paper, structural models were proposed on the basis of high-resolution electron microscopy for phases previously designated as 11L, 9L and 16L, which were found to exist in the title systems. Two types of blocks were found, which are composed of five and six layers of octahedra. In the present paper, various intergrowth phases which are composed of the two types of blocks are described. A new notation is proposed to denote these intergrowth phases as well as the 11L, 9L and 16L structures. Two-dimensional ordering of pentavalent ions in the six-layer block is found, giving rise to diffuse scattering in electron diffraction patterns. Two-dimensional images, calculated on the basis of the proposed model, are found to reproduce the observed images.