Investigation of RNiIn2-xGax (R = Y, Gd) systems

Abstract

The interaction of the components in R NiIn 2- x Ga x ( R = Y, Gd) systems at 873 K by means of X-ray phase and partially local X-ray analysis was investigated in full concentration range. The samples for the investigation were synthesized by arc-melting technique with subsequent annealing at 873 K for a month. Phase analysis was carried out by X-ray powder diffraction (DRON-2.0M, Fe K α-radiation, PANalytical X’Pert Pro, Cu K α-radiation and Stoe Stadi P, Cu K α 1 -radiation) and, partially, EDX analysis (REMMA-102-02). The limit of solubility of respective p -elements in R Ni X 2 ( R = Y, Gd; X = In, Ga) compounds were determined and parameters of unit cell were refined: YNiIn 2.00-1.50 Ga 0-0.50 (MgCuAl 2 -type structure): a = 0.4314–0.4284(1), b = 1.0406–1.0351(2), c = 0.7276–0.7136(2) nm; V = 0.3266–0.3164(1) nm 3 ; YNiIn 1.25-0.75 Ga 0.75-1.25 (PrNiIn 2 -type structure): a = 0.4223(2)–0.4187(2), b = 1.7278(1)–1.7078(8), c = 2.0910(1)–2.0773(9) nm; V = 1.5256(2)–1.4855(1) nm 3 ; YNiGa 2.00-1.50 In 0-0.50 (MgCuAl 2 -type structure): a = 0.4130–0.4179(1), b = 1.0050–1.0166(1), c = 0.6620 – 0.6787(1) nm; V = 0.2748–0.2884(1) nm 3 ; GdNiIn 2.00-1.50 Ga 0-0.50 (MgCuAl 2 -type structure): a = 0.4335–0.4273(3), b = 1.0452–1.0351(6), c = 0.7327–0.7288(5) nm; V = 0.3320–0.3223(3) nm 3 ; GdNiIn 1.25-0.70 Ga 0.75-1.30 (PrNiIn 2 -type structure): a = 0.4258(1)–0.4238(1), b = 1.7038(23)–1.7239(4), c = 2.0454(6) – 2.1019(5) nm; V = 1.4837(8)–1.5358(6) nm 3 ); GdNiGa 2.00-1.50 In 0-0.50 (NdNiGa 2 -type structure): а = 0.4120–0.4152(1), b = 1.7540–1.7546(6), с = 0.4082–0.4074(1) nm; V = 0.2950–0.2967(2) nm 3 . The substitution of indium atoms by gallium atoms leads to structure transformation: from phases with MgCuAl 2 -type structure to phases with PrNiIn 2 -type structure. These phases have a different metric but similar structure. The phases with MgCuAl 2 -type structure can be presented as penta-, tetra- and trigonal prisms stacking. Pentagonal prisms are centred by Gd atoms and form infinity chains along z axis when tetragonal and trigonal prisms form a mosaic stacking. A similar stacking of these types of prisms is also characteristic for the GdNiIn 1.0 6 Ga 0.9 4 compound with PrNiIn 2 -type structure. The increasing of gallium concentration leads to second structure transformation: phases with PrNiIn 2 -type structure transform to phase with MgCuAl 2 and NdNiGa 2 -type structure in YNiIn 2- x Ga x and GdNiIn 2- x Ga x systems respectively. The crystal structure of GdNiIn 1.0 6 Ga 0.9 4 compound was refined from powder X-ray diffraction data (PrNiIn 2 -type structure, space group Cmcm , a = 0.4220(2), b = 1.7168(6), c = 2.0896(8) nm; R Bragg = 0.099; R f = 0.090). The formation of solid solutions, new quaternary phases and character of the unit cell parameters variation in the studied systems were briefly discussed. Keywords : indium, solid solution, powder method, crystal structure.