ИСТИНА

We have investigated a family of mixed nickel-group 13-15 metal tellurides with the general formula Ni3-xMTe2 (m=Ga, In, Ge, Sn, Sb) with x varying from 0 to 1. The compounds were characterized using XRD, EDX, ED, HRTEM. Their average structures are based on the NiAs-type subcell with a~4Å and c~5Å, with c parameter being tripled. This superstructure is generated by both main group elements to form an hcp array with an ordered –M–Te–Te– stacking sequence along the c axis, with Ni vacancies present both in the heterometallic fragments and between the Te atoms, the latter thus forming van der Waals gap. Depending on the main group metal, these compounds show different behavior with respect to the variations of Ni content. At x=0 the only difference in the structures for different M is in the distribution of Ni between the positions in the heterometallic fragments and van der Waals gap: for M=Ga, Ge this ratio is ca. 70/30, while for In, Sn it is ca. 30/70, for M=Sb it is 50/50. As x increases, the loss of Ni results in the dramatic structural differences. The compounds with M=Ga, Ge lose Ni from the heterometallic layer and the ordering of the vacancies leads to the new unit cell with a=b=2xasub, while the ones with M=Sn, In, show the ordering of the van der Waals Ni positions resulting in the modulations along the c axis.