Electrical transport properties of R1.9Cu9.2Sn2.8 compounds

Abstract

Electrical transport properties of the R 1.9 Cu 9.2 Sn 2.8 (R = Y, Ce, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) compounds with the Dy 1.9 Cu 9.2 Sn 2.8 structure type (space group P 6 3 / mmc ) were studied. Polycrystalline samples were prepared by arc melting of the stoichiometric amounts of the constituent elements (nominal purities: rare earth metals − 99.9 wt. %, Cu − 99.99 wt. %, Sn − 99.999 wt. %) on a water-cooled copper hearth under a protective Ti-gettered argon atmosphere. Subsequently the buttons were annealed at 1 070 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-2.0M, Fe K α radiation) and Scanning Electron Microscopy (REMMA 102-02 electron microscope equipped with an energy-dispersive spectroscopy X-ray analyser). XRPD data were collected in the transmission mode on a STOE STADI P diffractometer (Cu K α 1 radiation). The temperature dependencies of electrical resistivity ( r ( T )) of R 1.9 Cu 9.2 Sn 2.8 stannides were measured employing two-probe method on millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples in the temperature range 4.2-300 K (R = Ce, Gd, Tb, Dy, Ho, Er, Tm, Yb) and 11-300 K (R = Y, Sm, Lu). Electrical resistivity measurements showed that the resistivity values of the all studied compounds increase with temperature indicating metallic type of conductivity. For Y 1.9 Cu 9.2 Sn 2.8 and Lu 1.9 Cu 9.2 Sn 2.8 stannides, which contain nonmagnetic elements Y and Lu, the absence of transition on the r ( T ) dependences at low temperatures is consistent with the Pauli paramagnetism of compounds. The temperature dependence of the resistivity of Yb 1.9 Cu 9.2 Sn 2.8 compound is almost linear at high temperatures, at low temperature part there is a slight increase in resistivity, which is characteristic of Kondo systems. Change of the resistivity caused by magnetic ordering was not observed in the studied temperature interval for the R 1.9 Cu 9.2 Sn 2.8 compounds where R are Gd, Tb, Ho, Er. The slope change of the resistivity at low temperature part of r ( T ) dependencies for the R 1.9 Cu 9.2 Sn 2.8 compounds with R=Ce, Dy, Tm is associated with their magnetic ordering. Keywords : intermetallics, electrical resistivity, X-ray analysis, crystal structure.