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

A series of binary rare-earth metal silicides RE5Si3 and ternary boron-interstitial phases RE5Si3Bx (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 P63/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 θp 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 RE5Si3Zx systems for different interstitial heteroatoms Z and different x contents from 0 to 1 give some support to this statement.