Phase Formation and Crystal Structures of Lacu13–XSix Compounds at 870°K.

We study phase equilibria in a section of 7.14 at.% La in the La–Cu–Si ternary system at 870°K by the methods of X-ray phase diffraction and structural analysis. The existence of two new LaCu9.61Si3.39 and LaCu8.37Si4.63 ternary compounds is established and their crystal structures are studied by the X-ray powder diffraction method. Both compounds are the first representatives of the NaZn13 structural type and its CeNi8.5Si4.5 tetragonally deformed superstructure in the R–Cu–Si systems. We also analyze structural transformations based on the NaZn13 structural type, as well as the affinity of the investigated compounds with the structures of binary and ternary lanthanum and copper silicides with respect to the closest coordination surrounding of the least electronegative atoms. Finally, we illustrate structural relationships between the investigated compounds and simple crystal structures (of copper and silicon) with which they are in phase equilibria in the La–Cu–Si system. [ABSTRACT FROM AUTHOR]