CRYSTAL STRUCTURE OF Li2CuGa AND LiCu2Ga COMPOUNDS

K. Zaitseva, G. Dmytriv


DOI: http://dx.doi.org/10.30970/vch.6301.082

Abstract


Lithium alloys continue to be promising materials for anodes of chemical current sources, so the search for new lithium-containing intermetallic phases and the study of their crystal structure were the task of our study.

In continuation of the study of the Li–Cu–Ga system, two alloys of Li2CuGa and LiCu2Ga were synthesized. The alloys were synthesized in an electric arc furnace in an atmosphere of purified argon from portions of pure components (content of the main component: Lithium ≥ 99.8 wt. %, copper and gallium ≥ 99.99 wt. %). The alloys were homogenized at 200 °C for two months in tantalum containers sealed in evacuated quartz ampoules. After annealing, the alloys were stored under a layer of purified and dehydrated paraffin oil. X-ray powder diffraction patterns from the synthesized alloys were obtained on a powder diffractometer DRON-2.0 M (FeKα-radiation).

By comparing the obtained diffractograms with previously studied alloys, it was assumed that the compounds Li2CuGa and LiCu2Ga will be isostructural with the phases Li2AgIn and LiAg2In. Based on these models, the crystal structure was refined by the Rietveld method: Li2CuGa, (Li2AgSb, F–43m, a = 6.0942 (7) Å; RBr = 0.0789, RF = 0.0482); LiСu2Ga (Cu2MnAl, Fm–3m, a = 5.8964 (8) Å; RBr= 0.0711, RF = 0.0311).

In the Li–Cu–Ga system, two ternary compounds are formed with the ratio of components 2:1:1 and 1:2:1, which is quite interesting because Li, Cu and Ga atoms differ greatly by nature (s-metal, d-metal and p-metal) and size (metal radii: Li – 1.52 Å; Cu – 1.28 Å; Ga – 1.35 Å). Nevertheless, in the structures of both compounds all atoms have a similar coordination of atoms - rhombododecahedron and identical values of interatomic distances: in the structure of the compound Li2CuGa eight distances with a length 2.6389 Å and six distances – 3.0471 Å; in the structure of the LiCu2Ga compound there are eight distances with a length of 2.5532 Å and six distances with a length of 2.9482 Å.

 Keywords: lithium, copper, gallium, X-ray powder diffraction method, crystal structure.


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