Y–Cr–Ge ternary system at 1 070 K

Abstract

This paper is part of a systematic study of the interaction of rare earth metals with transition metals and germanium. Polycrystalline samples were prepared by arc melting of the stoichiometric amounts of the constituent elements (nominal purities: Y − 99.9 wt. %, Cr − 99.99 wt. %, Ge − 99.999 wt. %) on a water-cooled copper hearth under a protective Ti-gettered argon atmosphere. Subsequently the buttons were annealed at 1070 K for 720 h in evacuated silica tubes, followed by quenching in cold water. Quality of the prepared samples was tested by X-ray powder diffraction (diffractometer DRON-2.0, Fe K α radiation) and Scanning Electron Microscopy (JEOL JSM-7600F electron microscope equipped with an energy-dispersive spectroscopy (EDS) X-ray analyser). XRPD data were collected in the transmission mode on a STOE STADI P diffractometer. Calculations of the crystallographic parameters were performed using the Full Prof Suite program packages. The microhardness was measured using a Microhardness Tester FM-100. The square-based pyramidal diamond was pressed using a force of10 pound for a loading time of 10 s; at least eight areas across each joint were tested in our measurements to obtain an average value. In the Y–Cr–Ge system at 1070 K two ternary compounds were found. The existence of YCr 6 Ge 6 (structure type MgFe 6 Ge 6; space group P 6/ mmm ; Pearson symbol hP 13; a = 5.1692(2), c = 8.2649(9) Å) was confirmed. The crystal structure refinements of YCr 0 .23 Ge 2 was performed using X-ray powder diffraction method (CeNiSi 2 structure type; space group Cmcm ; Pearson symbol oS 16; a = 4.12792(6), b = 15.8899(2), c = 4.00530(5) Å). The atomic parameters are: Y in (4c): 0 y ¼, y = 0.1048(1), B iso = 0.50(4) (hereafter Å 2 ); Cr in (4c) y = 0.2975(7); site occupations G = 0.23(0), B iso = 0.66(1); Ge1 in (4c), y = 0.4492(1), B iso = 0.50(4); Ge2 in (4c), y = 0.7477(1); B iso = 0.89(1); R Bragg = 0.0770, R F = 0.0671). Binary germanide Cr 3 Ge (structure type Сr 3 Si) dissolves up to 3 at. % Y, as evidenced by changes in the lattice parameter а = 4.6303(1) for Cr 3 Ge, а = 4.6313(2) Å for Y 3 Cr 7 5 Ge 2 2 sample. The results of the measurement of microhardness of Y 3 Ge 4 , Cr 3 Ge, YCr 6 Ge 6 compounds indicated its dependence on the composition and crystalline structure of the compound. Keywords: X-ray diffraction, EDX, phase equilibria, crystal structure, microhardness.