Acta Crystallographica Section B

Volume 65, Part 2 (April 2009)

research papers

 

Polymorphism of CaTeO₃ and solid solutions Ca_xSr_1 - xTeO₃

B. Stöger, M. Weil, E. Zobetz and G. Giester

Abstract: Single crystals and microcrystalline samples of the calcium tellurate(IV) phases -, -, '- and -CaTeO₃ as well as of two solid solutions Ca_xSr_1 - xTeO₃ (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^IVO₃]^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 -CaTeO₃ is stable up to 1168 K. It exhibits nearly cylindrical channels (diameter  4 Å) 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  2 and 8 Å). -CaTeO₃ can be described as an order-disorder (OD) structure of two non-polar layers with layer groups p12₁/m1 and p12₁1. The -CaTeO₃ crystal under investigation consists of two polytypes with a maximum degree of order. The two phases Ca_xSr_1 - xTeO₃ (x = 0.55 and 0.77) are isostructural to the MDO₁ polytype of -CaTeO₃. -CaTeO₃ shows a distinct reversible phase transition at  293 K. The low-temperature modification '-CaTeO₃ as well as its high-temperature modification -CaTeO₃ can be considered as threefold superstructures along [100] based on the MDO₁ polytype of -CaTeO₃.

Keywords: order-disorder theory; polymorphism; superstructure.

	Structure factor file (CIF format) (241.6 kbytes) [ doi:10.1107/S0108768109002997/sn5078alphasup2.hkl ] Contains datablock alpha
	Structure factor file (CIF format) (1261.1 kbytes) [ doi:10.1107/S0108768109002997/sn5078b-CaTeO3-275sup3.hkl ] Contains datablock b-CaTeO3-275
	Structure factor file (CIF format) (1266.8 kbytes) [ doi:10.1107/S0108768109002997/sn5078b-CaTeO3-295sup4.hkl ] Contains datablock b-CaTeO3-295
	Structure factor file (CIF format) (677.3 kbytes) [ doi:10.1107/S0108768109002997/sn5078b-CaTeO3-325sup5.hkl ] Contains datablock b-CaTeO3-325
	Structure factor file (CIF format) (677.3 kbytes) [ doi:10.1107/S0108768109002997/sn5078b-CaTeO3-350sup6.hkl ] Contains datablock b-CaTeO3-350
	Structure factor file (CIF format) (611.0 kbytes) [ doi:10.1107/S0108768109002997/sn5078bprime-CaTeO3-200sup7.hkl ] Contains datablock bprime-CaTeO3-200
	Structure factor file (CIF format) (656.1 kbytes) [ doi:10.1107/S0108768109002997/sn5078bprime-CaTeO3-250sup8.hkl ] Contains datablock bprime-CaTeO3-250
	Structure factor file (CIF format) (659.2 kbytes) [ doi:10.1107/S0108768109002997/sn5078bprime-CaTeO3-275sup9.hkl ] Contains datablock bprime-CaTeO3-275
	Structure factor file (CIF format) (293.1 kbytes) [ doi:10.1107/S0108768109002997/sn5078g-CaTeO3sup10.hkl ] Contains datablock g-CaTeO3
	Structure factor file (CIF format) (160.2 kbytes) [ doi:10.1107/S0108768109002997/sn5078Ca0.55Sr0.45TeO3sup11.hkl ] Contains datablock Ca0.55Sr0.45TeO3
	Structure factor file (CIF format) (147.0 kbytes) [ doi:10.1107/S0108768109002997/sn5078Ca0.77Sr0.23TeO3sup12.hkl ] Contains datablock Ca0.77Sr0.23TeO3

To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.

The download button will force most browsers to prompt for a file name to store the data on your hard disk.

Where possible, images are represented by thumbnails.

Copyright © International Union of Crystallography
IUCr Webmaster