Mixed Tellurides Ni3-xGaTe2 (0 ≤ x ≤ 0.65): Crystal and Electronic Structures, Properties, and Nickel Deficiency Effects on Vacancy Ordering

• Published in: European Journal of Inorganic Chemistry Vol. 2010; no. 9; pp. 1395 - 1404
• Main Authors: Isaeva, Anna A., Makarevich, Olga N., Kuznetsov, Alexey N., Doert, Thomas, Abakumov, Artem M., Van Tendeloo, Gustaaf
• Format: Book Review
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-03-2010; WILEY‐VCH Verlag
• Subjects: Electron microscopy; Layered compounds; NiAs derivatives; Nickel chalcogenides; Subvalent compounds
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200901027

The Ni3–xGaTe2 series of compounds (0 ≤ x ≤ 0.65) was synthesized by a high‐temperature ceramic technique at 750 °C. Crystal structures of three compounds in the series were determined by X‐ray powder diffraction: Ni2.98(1)GaTe2 (RI = 0.042, Rp = 0.023, Rwp = 0.035), Ni2.79(1)GaTe2 (RI = 0.053, Rp = 0.028, Rwp = 0.039), Ni2.58(1)GaTe2 (RI = 0.081, Rp = 0.037, Rwp = 0.056); the structures were verified by electron diffraction and, for the former compound, high‐resolution electron microscopy. The compounds crystallize in a hexagonal lattice with P63/mmc, and the structures can be regarded as a hexagonal close‐packed array with a –Ga–Te–Te– stacking sequence. The octahedral and trigonal bipyramidal voids in the hcp structure are selectively filled with Ni atoms to form one entirely occupied and two partially occupied sites, thus allowing variations in the nickel content in the series of compounds Ni3–xGaTe2 (0 ≤ x ≤ 0.65). A superstructure with asup = 2asub (P63/mmc) has been identified for Ni3–xGaTe2 (0.5 ≤ x ≤ 0.65) by electron diffraction. Real‐space, high‐resolution images confirm an ordering of Ni atoms and vacancies inthe ab plane. Quantum‐chemical calculations performed forNi3–xGaTe2 (x = 0, 0.25, 0.75, 1) suggest anisotropic metallic conductivity and Pauli paramagnetic behavior that are experimentally confirmed for Ni3GaTe2.
The NiAs‐derivative crystal structure of mixed tellurides Ni3–xGaTe2 (0 ≤ x ≤ 0.65) hosts a variable content of Ni atoms in 2D heterometallic Ni/Ga slabs and Te‐confined van der Waals gaps. At low values of Ni content, x < 0.5, the extra Ni atoms arrange in a superstructural ordered fashion aimed to relax the structural strain between the occupied and vacant sites in the ab plane.