A Quantum Chemical Study on Hexanuclear Cluster Halides of Rare Earth Elements and Their Interstitial Compounds

The electronic structures of rare earth cluster halides R(R_6X_(12)) and their interstitial compounds R_7X_(12)Z were studied by the DV-X_(?) method (R=Sc,Y,Pr,Gd or Er;X=Cl,Br or I;Z=B,C,N,Fe,Co or Ru).The results show that because f electrons in empty rare earth cluster are screened,their orbitals are more difficult to overlap each other,a deficiency of skeleton orbitals in cluster causing the system to be unstable.They are easily condensed into chain compound R_2X_3 or R_5X_8.If a light atom of main group is embedded into octahedral cluster,bonding orbitals formed from interstitial atom and rare earth cluster strengthen cluster skeleton bond in the system to reach structural stability.If embedded atom belongs to transition metal,bonding orbitals composed of that of interstitial atom and rare earth cluster take the place of original cluster skeleton orbitals to form heteronuclear metal cluster (or double-coordination compound).

Magnetocaloric effects in Fe_4MnSi_3B_x interstitial compounds

The magnetic properties and magnetocaloric effect in Fe4MnSi3B~ compounds with x=0, 0.05, 0.10, 0.15, 0.20, 0.25 have been investigated. X-ray diffraction study shows that all these compounds investigated crystallize in the MnsSi3-type structure with space group P63/mcm. Boron insertion in the host ternary silicide Fe4MnSi3 does not change the crystal symmetry, only leads to an increase of the lattice parameters, indicating the B atoms entered the interstitial sites. With increasing B content, the Curie temperature shifts to higher temperatures. The maximal magnetic-entropy changes of the Fe4MnSi3Bx compounds with x=0, 0.10 and 0.20 are about 1.8 J/（kg.K）, 1.8 J/（kg-K） and 1.6 J/（kg.K）, respectively, for a field change from 0 to 1.5 T.

Nitridation process effect on crystal structure and magnetic properties of TbCuT-type SmFe9 alloys

The effect of nitridation process, i.e. temperature and time, on crystal structure and magnetic properties of SmFe9Nx inter- stitial compounds was systematically investigated. After nitridation treatment, nitrogen atoms were incorporated into SmFe9 alloys to form SnaFe9Nx interstitial compounds, which increased the distance of Fe-Fe and enhanced Fe-Fe interaction. As a result, SmFe9Nx interstitial compounds had a higher Curie temperature and more excellent magnetic properties than SmFe9 alloys. The relationships between nitridation temperature, nitridation time, nitriding efficiency, magnetic properties and phase transition were researched. It could be concluded that nitriding efficiency was strongly associated with magnetic properties and phase transition at different tem- peratures. The nitriding efficiency also had a connection with magnetic properties under different time, while no obvious phase transi- tion was found during that process. By studying nitridation process under a series of temperatures and time in this experiment, a suit- able nitridation temperature （713 K） and an ideal length of nitridation time （8 h） was decided, which would produce the optimal mag- netic behavior of SmFegNx interstitial compounds.