Stöger Berthold, Weil Matthias, Zobetz Erich, Giester Gerald
Institute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria.
Acta Crystallogr B. 2009 Apr;65(Pt 2):167-81. doi: 10.1107/S0108768109002997. Epub 2009 Mar 16.
Single crystals and microcrystalline samples of the calcium tellurate(IV) phases alpha-, beta-, beta'- and gamma-CaTeO3 as well as of two solid solutions Ca(x)Sr(1-x)TeO3 (x = 0.55 and 0.77) have been synthesized and characterized by X-ray diffraction and thermal analysis. A comparative description of the structures and the relations between the polymorphs is given. The main building units of the hitherto unknown structures are isolated [Te(IV)O3]2- units and [(Ca,Sr)O(x)] (x = 6-8) polyhedra. All structures exhibit channels in which the Te(IV) electron lone pairs protrude. The low-temperature phase alpha-CaTeO3 is stable up to 1168 K. It exhibits nearly cylindrical channels (diameter approximately 4 A) and differs structurally from the other phases, whereas the metastable high-temperature phases are closely related to each other. They feature oval channels (shortest and longest diameter approximately 2 and 8 A). Gamma-CaTeO3 can be described as an order-disorder (OD) structure of two non-polar layers with layer groups p12(1)/m1 and p12(1)1. The gamma-CaTeO3 crystal under investigation consists of two polytypes with a maximum degree of order. The two phases Ca(x)Sr(1-x)TeO3 (x = 0.55 and 0.77) are isostructural to the MDO1 polytype of gamma-CaTeO3. Beta-CaTeO3 shows a distinct reversible phase transition at approximately 293 K. The low-temperature modification beta'-CaTeO3 as well as its high-temperature modification beta-CaTeO3 can be considered as threefold superstructures along [100] based on the MDO1 polytype of gamma-CaTeO3.
已经合成了碲酸钙（IV）相α-、β-、β'-和γ-CaTeO₃的单晶和微晶样品，以及两种固溶体Ca(x)Sr(1 - x)TeO₃（x = 0.55和0.77），并通过X射线衍射和热分析对其进行了表征。给出了多晶型物的结构及其之间关系的比较描述。迄今未知结构的主要构建单元是孤立的[Te(IV)O₃]²⁻单元和[(Ca,Sr)O(x)]（x = 6 - 8）多面体。所有结构都呈现出通道，其中Te(IV)电子孤对突出。低温相α-CaTeO₃在高达1168 K时稳定。它具有近乎圆柱形的通道（直径约4 Å），并且在结构上与其他相不同，而亚稳高温相彼此密切相关。它们具有椭圆形通道（最短和最长直径约2 Å和8 Å）。γ-CaTeO₃可以描述为具有层群p12(1)/m1和p12(1)1的两个非极性层的有序-无序（OD）结构。所研究的γ-CaTeO₃晶体由具有最大有序度的两种多型组成。两种相Ca(x)Sr(1 - x)TeO₃（x = 0.55和0.77）与γ-CaTeO₃的MDO1多型同构。β-CaTeO₃在约293 K处显示出明显的可逆相变。低温变体β'-CaTeO₃及其高温变体β-CaTeO₃可以被认为是基于γ-CaTeO₃的MDO1多型沿[100]方向的三重超结构。
