THE INCOMMENSURATE STRUCTURE OF 1T-TaS₂. A. Spijkerman, A. Meetsma, G.A. Wiegers, S. van Smaalen^*) and J.L. de Boer. Dept.of Chemical Physics, Nijenborgh 4, 9747 AG Groningen, The Netherlands. ^*) Lehrstuhl f. Kristallograpie, D-95440, Bayreuth, Germany

The structure of 1T-TaS₂ was studied earlier by several authors and attracted attention for its star of David like clustering of the Ta-atoms (13 in a cluster) in the incommensurate roomtemperature phase. The structure was studied in detail by Brouwer (1978, Thesis) and by Yamamoto (1983, Phys. Rev. B. 27, 7823-7826). The first author used a x x 3c supercell (equivalent to the commensurate approximation 3/13, 1/13, 1/3 of the q-vector which in reality is 0.245, 0.068, 1/3), both for the intensity measurements as well as for the structure refinement, whereas the second author used Brouwers intensity data in an incommensurate superspace description. Both authors adopted spacegroup in the refinements.

There are several unsatisfactory aspects in the just mentioned state. First the intensities of the by the supercell approximated satellite positions were of course not collected at their true positions. Secondly both Brouwer and Yamamoto were aware of the existence of other classes of satellites but these were just not measured; moreover Yamamotos description of these higher order satellites (6 around each of the 12 fundamental satellites) was misplacing 2 of these 6.

We remeasured the structure factors, now associating 84 satellites to each main reflection and refined the data using the program Jana94 (Petricek). Complete results including the choice of spacegroup, together with a comparison with previous structure models, will be presented.