Coupled In/Te and Ni/vacancy ordering and the modulated crystal structure of a B8 type, Ni3±xIn1−yTe2+y solid solution phase

The commensurate superstructures of a NiAs/Ni2In type parent structure, Ni3.32InTe2 and Ni3.12In0.86Te2.14 (q=γ[0 0 1]*, γ=2/3) as well as one dimensionally incommensurate structure of Ni3InTe2 (γ=0.71) were refined from neutron powder diffraction data (Rwp=4.77%, 4.53% and 4.91% for the three structures, respectively, at 298 K). The commensurate structures were refined in the P63/mmc space group (c=3cNiAs). The stacking sequence at the hcp array is -In/Te/Te/- and the trigonal bipyramidal site within the In layer, Ni(2), is partially occupied while it is empty in the Te layers. The octahedral position in between the In and Te layers, Ni(1a), is fully occupied while the octahedral position in between two adjacent Te layers, Ni(1b), is partially occupied. With decreasing In and Ni content, the modulation wave vector, γ, was found to increase continuously until γ=1. From this, crenel functions to describe the whole homogeneity range of the solid solution were constructed with the length of the atomic domains ΔTe=γ (and hence ΔIn=ΔNi=1−γ) and ΔNi(1b)=γ/2 (and hence ΔNi(1a)=1−γ/2) which were then used for the refinement of the incommensurate structure of Ni3InTe2. The corresponding effect in real space is that the single In layers separating double layers of Te occur less frequent when γ in increasing until at γ=1 the CdI2 type structure of Ni1+xTe2 is reached.