Mn5Si3-type host-interstitial boron rare-earth metal silicide compounds RE5Si3: Crystal structures, physical properties and theoretical considerations

摘要

A series of binary rare-earth metal silicides RE5Si3 and ternary boron-interstitial phases RE5Si3B, (RE = Gd, Dy, Ho, Lu, and Y) adopting the Mn5Si3-type structure, have been prepared from the elemental components by arc melting. Boron "stuffed" phases were subsequently heated at 1750 K within a high-frequency furnace. Crystal structures were determined for both binary and ternary series of compounds from single-crystal X-ray data: hexagonal symmetry, space group P6(3)/MCM, Z = 2. Boron insertion in the host binary silicides results in a very small decrease of the unit cell parameters with respect to those of the binaries. According to X-ray data, partial or nearly full boron occupancy of the interstitial octahedral sites in the range 0.6-1 is found. The magnetic properties of these compounds were characterized by the onset of magnetic ordering below 100 K. Boron insertion induces a modification of the transition temperature and theta p values in most of the antiferromagnetic binary silicides, with the exception of the ternary phase Er5Si3Bx which was found to undergo a ferromagnetic transition at 14 K. The electrical resistivities for all binary silicides and ternary boron-interstitial phases resemble the temperature dependence of metals, with characteristic changes of slope in the resistivity curves due to the reduced electron scattering in the magnetically ordered states. Zintl-Klemm concept would predict a limiting composition RE5Si3B0.6 for a valence compound and should then preclude the stoichiometric formula RE5Si3B. Density functional theory calculations carried out on some RE(5)Si(3)Z(x) systems for different interstitial heteroatoms Z and different x contents from 0 to 1 give some support to this statement. (c) 2006 Elsevier Inc. All rights reserved.