Crystal structure determination of new phase Ni₂SbTe₂ from Kunratice near Šluknov (Czech Republic)

F. Laufek^1,2, M. Drábek¹, R. Skála¹, I. Císařová²

¹Czech geological survey, Geologická 6, Praha 5, 152 00

²Charles University, Faculty of Science, Hlavova 8, Praha 2, 128 43

The new unnamed nickel antimonide telluride, Ni₂SbTe₂, was founded as 6 μm grain by Vavřín and Frýda (1998) at the Kunratice Cu-Ni deposit. This ternary phase is in close association with melonite; this assembly is included in pyrrhotine. The crystal structure was determined from synthetic analogue prepared using silica glass tube method. The stechiometric amounts of Ni, Sb and Te were loaded into silica tubes and sealed under vacuum. They were then heated in a programmable furnace at 400 °C, 800 °C for three weeks. The experiments were terminated either by quenching in a cold water bath or by slow cooling.

The crystal structure of Ni₂SbTe₂, prepared at 800 °C (terminated by quenching), determined from X-ray single diffraction data, is hexagonal, NiAs type with lattice parameters a=3.9108(2), c=5.2489(3), space group P6₃/mmc. The antimony and tellurium atoms occupy the crystallographic position 2c; the position 2a is occupied by nickel atoms.

The crystal structure of Ni₂SbTe₂, prepared at 400 ºC (terminated by slow cooling to 50 ºC within the intervals of 22 hours), originally described by Reynolds et. al. (2004), refined from X-ray single diffraction data, is hexagonal with lattice parameters a=3.9110(2), c=15.696(1), space group P6₃/mmc. The antimony and tellurium atoms occupy different crystallographic positions, antimony 2c and tellurium 4f.

The situation in the case of crystal structure of Ni₂SbTe₂, prepared at 400 ºC (terminated by quenching) is more complicated. The X-ray powder diffraction pattern corresponds to the disorder (high temperature) phase, nevertheless diffraction profiles of 201 and 110 lines are asymmetrical. This asymmetry disappears in powder pattern of Ni₂SbTe₂ prepared at 800 ºC (Figure 1,2). It was possible to observe weak reflections near 1/3 and 2/3 of the distance between the sharp diffractions on the photographs of reciprocal planes h0l obtained from electron diffraction (SAED). These weak diffractions systematically shifted from 1/3 to the left and from 2/3 to the right, i.e. closer to the sharp diffractions. The phase Ni₂SbTe₂ forms at 400 ºC a solid solution with end members having the composition of 42.1 % Ni, 13.0 % Sb, 44.9 % and 43.0 % Ni, 28.4 % Sb, 28.6 % Te (at. %).

Figure 1: Diffraction profil 110 line of Ni2SbTe2 prepared at 400 °C (above) and at 800 °C, Co rad.	Figure 2: Diffraction profil 210 line of Ni2SbTe2 prepared at 400 °C (above) and at 800 °C, Co rad.

Acknowledgements

This study was supported by a Grant Agency of Charles University (project number 43-203900). Financial support by a Grant Agency of Czech Republic (project number 205/02/1100) is also also gratefully acknowledged. We would like to express our thanks to Prof. Milan Rieder for his permanent interest in this work.

Reynolds T.K., Kelley R.F., DiSalvo F.J., J. Alloy Comp., 366 (2004) 136-144.

Vavřín I, Frýda J., Věštník ČGÚ 73 (1998) 177-180.