Construction of Crystal Structures of Metal Oxide Phosphates Containing Dynamic Distortions

点击翻译按钮获取中文摘要

This research was aimed to develop new materials by combining MO_6 octahedral units and XO_4 tetrahedral units. At the first stage of the research, compounds with the tetrahedra : octahedra ratio of 1:1 were systematically searched and the existence of a series of isostructural compounds were revealed. These compounds contained Ti, Zr, Ru, Mn, or Nb as M^<IV>, Nb or Ta as M^V, and K, Rb, or Cs as A. The relation of dielectric properties of these compounds with the elements composing the compounds was clarified. At the later stages of the research, the research was extended to the compounds with the tetrahedra : octahedra ratio smaller than 1:1, and especially the compounds with the ratio 1:3 were studied. In this study, new compounds including K_<2+x>Ti_xNb_<3-x>O(PO_4)(0.5 <x <0.6) were synthesized. In the niobium-phosphate system, where we focused our efforts, unexpected compounds were discovered in the last year of the research period. The compounds showing the X-ray diffraction pattern which showed isostructural relationship with pyrochlore structure. The pyrochlore structure has the network consisting only of MO6 octahedra while the compounds prepared contained the tetrahedral element (P). The only compound which has similar structural feature is CsAsTiO_5 and the compounds prepared in this research showed the possibility of many compounds in which MO_6 octahedra were replaced by XO_4 tetrahedra. We attempted also the preparations with XO4 units other than phosphates. We prepared a new germanium compound Cs_8Nb_<10>Ge_6O_<41> ain germanate system, and obtained a new arsinate RbZrO(AsO_4) which seems to have a new structure.