Construction of Crystal Structures of Metal Oxide Phosphates Containing Dynamic Distortions

本研究旨在将MO_6八面体单元与XO_4四面体单元相结合，开发新型材料。在研究的第一阶段，系统地搜索了四面体：八面体比例为1:1的化合物，发现了一系列同构化合物的存在。这些化合物含有Ti、Zr、Ru、Mn、Nb为M^<IV>， Nb或Ta为M^V， K、Rb或Cs为a。这些化合物的介电性能与组成化合物的元素之间的关系得到澄清。在研究的后期，将研究范围扩大到四面体：八面体比例小于1:1的化合物，特别是对比例为1:3的化合物进行了研究。本研究合成了K_<2+x>Ti_xNb_<3-x>O(PO_4)（0.5 <x <0.6）等化合物。在我们集中精力的铌-磷酸盐体系中，在研究期的最后一年发现了意想不到的化合物。x射线衍射图显示化合物与焦绿石结构呈等构关系。焦绿盐结构具有仅由MO6八面体组成的网络，而所制备的化合物含有四面体元素(P)。唯一具有类似结构特征的化合物是CsAsTiO_5，本研究制备的化合物显示了许多化合物中MO_6八面体被XO_4四面体取代的可能性。我们也尝试用磷酸盐以外的XO4单元来制备。我们在锗酸盐体系中制备了一种新的锗化合物Cs_8Nb_<10>Ge_6O_<41>，得到了一种新的砷酸盐RbZrO(AsO_4)，它似乎具有新的结构。

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.