Y–Zn–Al system at 670 K

Abstract

Interaction of the components in the ternary Y–Zn–Al system at the temperature 670 K has been studied by means of the X-ray phase and structure analyses. Samples for investigation have been prepared by double sintering of previously pressed into pellets mixtures of powders of pure components. Pellets were sealed into evacuated quarts tubes and then heat-treated in the muffle furnace. Existence of the earlier known ternary aluminides, namely Y 3 Zn 3.25 Al 7.75 (space group Immm , La 3 Al 11 –type of structure), and YZnAl (space group P 6 3 / mmc , CaIn 2 –type of structure) has been confirmed and new ternary compound Y 4 Zn 22,34 Al 9,66 Zn 0,22 (Yb 8 Cu 16 Al 49 –type of structure, space group I 4/ mmm ) has been studied. Limit compositions of the solid solutions on the base of several Y–Al and Y–Zn binary compounds have been established: Y(Zn 0.90 Al 0.10 ) 12 (ThMn 12 –type of structure, space group I 4/ mmm , a = 0.88789(2), c = 0.52381(2) nm), Y 2 (Zn 0.95 Al 0.05 ) 17 (Th 2 Zn 17 –type of structure, space group R -3 m , a = 0.90006(4), c = 1.31388(6) nm), YZn 0.76 Al 0.24 (CsCl–type of structure, space group Pm -3 m , a = 0.35645(2) nm), Y(Al 0.93 Zn 0.07 ) 3 (BaPb 3 –type of structure, space group R -3 m , a = 0.61929(2), c = 2.1115(1) nm), and Y(Al 0.88 Zn 0.12 ) 2 (MgCu 2 –type of structure, space group Fd -3 m , a = 0.78486(2) nm). All solid solutions are formed due to the substitution of zinc and aluminum atoms in the crystallographic positions of the respective space groups. Other binary compounds don’t dissolve any significant amount of the third component. Ternary compounds with the structures of CaIn 2 and La 3 Al 11 –types have large homogeneity ranges, and their compositions can be described by formulas: YZn 0.90-1.05 Al 1.10-0.95 ( a = 0.4472(1)–0.4495(1), c = 0.7127(1)–0.7138(1) nm) and Y 3 Zn 3.15-4.10 Al 7.85-6.90 ( a = 0.4219(1)–0.4231(1), b = 1.2423(1)–1.2471(2), c = 0.9901(2)–0.9989(2) nm). However, the ternary compound Y 4 Zn 22 . 7 Al 9 . 5 Zn 0 . 2 , despite the statistical distribution of zinc and aluminum atoms in the structure, does not form noticeable homogeneity range. Crystal structure of the compounds YZn 1.02 Al 0.98 (CaIn 2 -type of structure, space group P 6 3 / mmc , Pearson’s symbol h P6, refined lattice parameters a = 0.44923(5), c = 0.7136(1) nm, R I = 0.072, R P = 0.126) and Y 4 Zn 22,34 Al 9,66 Zn 0,22 (Yb 8 Cu 16 Al 49 -type of structure, space group I 4/ mmm , Pearson’s symbol t I72,4, a = 0,86182(2), c = 1,65054(3) nm, R I = 0,078, R P = 0,127) has been studied from powder X-ray diffraction data. Isothermal section of the ternary Y–Zn–Al system has been constructed at 670 K and concentration range up to 70 at. % of yttrium. Keywords: intermetallic compound, crystal structure, phase equilibria.