THE DISTRIBUTION OF DOPING ATOMS IN Ta₂NiSe₇ STUDIED BY X-RAY DIFFRACTION

J. Luedecke, M. Dierl and S. van Smaalen

Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany

Keywords: impurities, phase transitions, modulated structures

The effect of doping of Ta₂NiSe₇ with transition metal atoms on its physical properties and structure has been investigated. Ta₂NiSe₇ exhibits a phase transition at 52.5 K towards a modulated phase [1]. The incommensurate distortion present in the low temperature phase was attributed to the formation of a charge density wave (CDW). Both the room temperature structure and the low temperature modulated structure have been determined by x-ray diffraction [2-3].

Ta_(2-x)Me_xNiSe₇ with x as transition metal atoms was synthesized using the gas transport technique. X varied between 0.01 and 0.6. The samples have been investigated by x-ray diffraction collecting reflections up to q = 47^o. Careful analysis of the observed data including absorption correction with crystal shape refinement revealed the distribution of the dopand atom over both Ta sites and the Ni site. Furthermore the influence of the doping on the physical and structural properties like phase transition temperature, conductivity and modulation amplitudes will be discussed.

1. R.M. Fleming, S.A. Sunshine, C.H. Chen, L.F. Schneemeyer, J.V. Waszczak, Phys. Rev. B, 42, 4954 (1990)
2. S.A. Sunshine, J.A. Ibers, Inorg. Chem., 25, 4355 (1986)
3. A. Spijkerman, A. Meetsma, J.L. de Boer, Y. Gao, S. van Smaalen, Phys. Rev. B, 52, 3892 (1995)