Structure cristalline des composés intermétalliques T ₄Co₃ (T = Y, Gd, Tb, Dy, Ho, Er et Tm)

Abstract

The crystal structure of intermetallic compounds T4Co3, where T is yttrium or a rare earth metal of the second series, has been determined on a single crystal with composition Ho4Co3,07. The crystallographic trait cell is hexagonal; its parameters are a= 11,4, c=3,99 /~. The space group is P63/m. One of the three Co sites is only partially filled at random.

On the structural and magnetic properties of the ternary silicides Ce6M1.67Si3 (M=Co, Ni) and Ce5Ni1.85Si3

“…This position is strongly delocalised along the z-axis to manage realistic Ni-Ni distances. One can observe that our chemical composition deduced from microprobe analysis and structural refinement and the compositions reported from structural refinements by Prots and Jeitschko [2,3] are in good agreement with the limit composition proposed by Lemaire et al [10]. Prots and Jeitschko have proposed a relationship between the occupancy ratio of Ni1 and Ni3 and the overall composition.…”

“…This latter composition is not compatible with the steric strains in this structural type. Indeed, as firstly proposed by Lemaire et al [10] for RE 4 Co 3.07 (or RE 6 Co 4.61 ) series (RE ¼ rare earth), the steric strains between positions of Co in the chain (00z) imply a non-stoichiometry of these phases, empty space are needed to manage realistic Co-Co distances. The overall formula of the series RE 6 Co 4.61 can be expressed as RE 6 Co 1.61 Co 3 , to emphasise the structural similarity with Ce 6 Ni 1.67 Si 3 .…”

“…10(b)) confirming the occurrence of magnetic ordering below T t . Valuable information can be obtained from the entropy associated with the magnetic ordering of Ce 6 Ni 1.67 Si 3 , which is estimated from the magnetic contribution to the specific heat in the low-temperature range as C pmag ¼ C p -(gT+bT 3 ) (between 10 C p /T ¼ g+bT 2 yields an electronic coefficient g ¼ 144 mJ/ Ce-mol K 2 smaller than that determined for Ce 6 Co 1.67 Si 3 and phonon constant b ¼ 2.29 10 À4 J/Ce-mol K 4 ). At T t , the magnetic entropy reaches 3.75 J/Ce-mol K ¼ 0.65 RLn2 which is smaller than RLn2 ¼ 5.76 J/Ce-mol K, the value of magnetic entropy expected for a doublet ground state of Ce 3+ .…”

The new ternary silicides RE6Co1.67Si3 (RE=Ce, Nd, Gd, Tb, Dy) investigated by X-ray diffraction and magnetization measurements

“…Gd 6 Co 1.67 Si 3 crystallizes with the hexagonal "Ce 6 Ni 2 Si 3 " structure type (space group P6 3 /m). As previously evidenced by Lemaire et al [2] and Prots' and Jeitschko [3,4] for homologous compounds Gd 6 Co 4.61 , La 6 Ni 1.54 Si 3 and Nd 6 Ni 1.66 Si 3 , these phases are non-stoichiometric and the overall formula should be written as Ce 6 Ni 2−δ Si 3 . Using X-ray powder or single crystal diffraction, an ordered distribution between Co and Si was found in Gd 6 Co 1.67 Si 3 and Ce 6 Co 1.67 Si 3 [1,5], one site being not fully occupied by Co for steric reasons.…”

Thermodynamic assessments of the Co–Er and V–Er systems

“…The phase equilibria and the intermetallic compounds in the Co-Er system have been studied by a number of investigators [13][14][15][16][17][18][19]. However, the reports on the existence of some compounds and relevant phase relationship by different investigators are inconsistent.…”