NEW VARIANT OF THE STRUCTURE OF THE Li_1+xZn_0.5-1.5Al_1.5-0.5 INTERMETALLIC COMPOUND

Volodymyr Pavlyuk¹, Grygoriy Dmytriv¹, Oksana Bodak¹, Julia Stepien-Damm**

¹Inorganic Chemistry Department, Ivan Franko Lviv State University, Kyryla I Mefodia str. 6, 290005 Lviv, Ukraine
²W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Oklna str. 2, 50950 Wroclaw, Poland

pavl@chem.franko.lviv.ua

Keywords: intermetallic compound, crystal structure, structure type, lithium, zinc, aluminium.

d-compound found in the Li-Zn-Al system [1] and [2] proposed for it structure type Mg₃₂(Zn,Al)₄₉. But this suggestion based only on the comparison of Debye-Sherer photographs of compounds with composition from concentrating interval LiZn_0.5-1.3Al_1.5-0.7 with early investigated compound Li₃CuAl₅, in other words, refinement of crystal structure don't carried out.

During investigation of the Li-Zn-Al system at 470 K we confirm existence of compound with wide homogeneity range along isoconcentrate of 0.33 atomic part of Li Li_1+xZn_0.5-1.5Al_1.5-0.5 and accurate composition and lattice periods by powder diffractograms (powder diffractometr DRON-2.0, FeK-radiation) for this compound: a=1.4017(3)1.3904(3) nm; increasing of lattice period with changing x from 0 to 0.06 part of Li is 0.0023 nm.

Also we obtained single crystal from alloy with composition LiZnAl for structural investigation (single crystal diffractometr KM-4, MoK-radiation with graphite monochromator, / scan mode, 4270, number of unique (hkl) - 434). Finally, structure refined in space group, LiCuSi structure type (R=0.044), atomic parameters presented in the table.

Our model of structure of the Li_1+xZn_0.5-1.5Al_1.5-0.5 compound differ from model [2] in two moments: the first, site 2(a) is vacant (in model [2] this site occupy by Al atoms); the second, one from sites 12(e) occupy by Li atoms (in model [2] both sites 12(e) occupy statistical mixtures of Zn and Al atoms).

For statistical mixture of Zn and Al in general characteristic icosahedral coordination of polyhedrons (coordinating numbers 11 for M3, 12 for M2 and M4 and 14 for M1). For Li atoms characteristic more complicated polyhedrons with coordinating numbers 15 for Li1 and 16 for Li2 and Li3.

Table

Atomic parameters of the LiZnAl compound

1. T.A.Badajeva, P.Ya.Saldau, J. General Chem. 13 (1943) 643-660.
2. E.E.Cherkashyn, P.I.Krypiakevich, G.I.Oleksiv, Crystallography 8 (1963) 846-851.