Fakhili Gulo

Octahedral niobium cluster-based solid state halides and oxyhalides: effects of the cluster condensation via an oxygen ligand on electronic and magnetic properties

The influences of an oxygen ligand on the structural, magnetic and electronic properties of octahedral niobium cluster-based oxides and oxychlorides are reported. The Nb6 metal cluster is edge-bridged by twelve inner ligands and additionally bonded to six apical ligands to form Nb6Li12La6 units (L = Cl, O) wherein oxygen and chlorine are perfectly ordered. Oxygen favours the interconnection of clusters via double Oi–a/Oa–i bridges in a similar way to the double Si–a/Sa–i bridges found in Chevrel phases based on face capped Mo6Li8La6 units. Periodic density functional theory (DFT) calculations confirm that increasing the number of inner oxygen ligands at the expense of chlorine atoms favours the 14 metal-electron (ME) count per octahedral cluster unit. It is also shown that weak interactions occur between neighbouring clusters. Indeed, magnetic measurements performed on AxNb6Cl12O2 (A = Rb, x = 0.816(8); A = Cs, x = 1) series containing 15-ME species evidence antiferromagnetic interactions at low temperatures. Broken-symmetry DFT calculations of exchange parameters within spin dimer analysis confirm the experimental results.

The oxychlorides in Nb6 cluster chemistry

Abstract The Nb 6 oxychlorides based on Nb 6 L 18 units that we have isolated, as well as another one recently reported in the literature, are reviewed. Each of them is structurally described through a relevant example: Cs 2 LuNb 6 Cl 17 O, Cs 2 UNb 6 Cl 15 O 3 , ScNb 6 Cl 13 O 3 , Ti 2 Nb 6 Cl 14 O 4 and KLu 3 Nb 6 Cl 15 O 6 , the structure of the latter has just been solved. They are discussed by comparison with the Nb 6 chlorides and Nb 6 oxides, considering the electronic and steric evolution of the Nb 6 L 18 unit upon increasing O/C1 ratio. The environments of the trivalent cations will be compared, specially those involving extra halogens in KLu 3 Nb 6 Cl 15 O 6 and Ti 2 Nb 6 Cl 14 O 4 .

Crystal structure of the inter­metallic compound SrCdPt

The title compound crystallizes in the TiNiSi structure type in the space group Pnma. St atoms are bonded to each other, forming six-membered rings with chair conformation whilst Pt atoms form zigzag chains of cadmium-centred tetrahedra, building up the three-dimensional network.

The octahedral cluster compounds of early transition metals: An original class of dielectric materials

Abstract Octahedral clusters of early transition elements appear either in the face-capped M6Li 8La 6 units for M = Mo, W, Re or in the edge-capped M6Li 2La 6 ones for M = Nb, Ta (L = oxygen, halogen, chalcogen). These units constitute the building blocks of a large variety of crystal structures. In most of them, owing to the steric hindrance of the ligands, the M6 clusters cannot interact and such materials are insulators. These units are usually centro-symmetric when all inner or apical positions are occupied by a same ligand. In contrast, in oxyhalides, chalcohalides and chlorofluorides, these positions are occupied by two different ligands either ordered or randomly distributed and thus, an acentric distribution of the anionic charges around the M6 cluster can appear. In this case the units act as permanent dipoles and dielectric relaxations can be observed. In this paper we recall the crystal structures of M6 cluster compounds built from acentric units and some relevant examples of unusual dielectric behaviour.

Effect of composition polymeric PVB binder on physical, magnetic properties and microstructure of bonded magnet NdFeB

The bonded magnet NdFeB has been made by using the hot press method and using Poly Vinyl Butiral (PVB) as a binder. The composition of polymeric binder was varied: 0, 2, 4, 6 and 7 % of weight. Both raw materials are weighed and mixed according to the composition of PVB, then formed by hot press with a pressure 30 MPa, a temperature of 160 ? C and holding time for 30 minutes. The bulk density was measured by using Archimedes method. SEM observation was done to determine the microstructure of bonded magnet NdFeB. The flux magnetic value was measured by using a Gauss meter and the measurement of hysteresis curves was done to know value of remanence Br, coercivity Hc and energy product BHmax by using VSM. According to the characterization results show that the best composition of PVB is 2 of weight. The properties of bonded magnet NdFeB of those compositions are the bulk density around 5.66 g/cm3. Flux Magnetic value: 1862 Gauss, Br value: 5000 kGauss, Hc value: 8.49 kOe and BHmax value : 5.10 MGOe. According of SEM observation results show that the polymer matrix of PVB appears to have covered on all surface grain and filled grain boundary.

Effect of Sintering Temperature to Physical, Magnetic Properties and Crystal Structure on Permanent Magnet BaFe12O19 Prepared From Mill Scale

Permanent magnet of Barium hexa Ferrite with formula BaFe12O19 has been made by metallurgy powder method from raw materials : Barium carbonate (BaCO3 E-merck) and Iron Oxide (Fe2O3 from mill scale). Both of raw materials have been mixed with stoichiometry composition by using a ball mill for 24 hours. The fine powder obtained from milling process was formed by using a hydraulic press at pressure 50 MPa and continued with sintering process. The sintering temperature was varied : 1150°C, 1200°C, 1250°C and 1300°C with holding time for 1 hour. The sintered samples were characterized such as : physical properties (bulk density, porosity and shrinkage), magnetic properties (flux density, remanence, coercivity and magnetic saturation) by using VSM and crystal structure by using XRD. According characterization results show that the crystal structure of BaFe12O19 does not change after sintering process, but the grain size tends to increase. The optimum condition is achieved at temperature 1250°C, and at this condition, the sample has characterization such as : bulk density = 4.35 g/cm3, porosity = 1.03% and firing shrinkage = 11.63%, flux density = 681.1 Gauss, remanence (σr) = 20.78 emu/g, coercivity (Hc) = 2058 Oe and magnetic saturation (σs) 45.16 emu/g.

Crystal structure and magnetic properties of Nd2Fe14B powder prepared by using high energy milling from elements metal Nd,Fe,B powders

The Nd2Fe14B powder has been made by using High Energy Milling (HEM) from mixed metal powders Iron (Fe), Neodymium (Nd) and Boron (B). The Nd, Fe and B powders were mixed according stoichiometric composition (atomic ratio Nd:Fe:B = 2: 14: 1) and milled and milling time was varied in 10, 20, and 40 hours by using HEM. Toluene liquid was used as milling media to protect of metal powders from oxygen. The measurement result of x- ray diffraction show that the optimum Nd2Fe14B phase already formed about 69,46% after milling 40 hours with crystallite size about 25.64 nm. The magnetic properties of milled powders were measured by using VSM at room temperature. The highest value of magnetic properties are obtained at powder milled in 40 hours, at this condition, it is obtained Ms = 122 emu/g, Mr = 81 emu/g, Hc = 5.54 kOe and BHmax = 11.01 MGOe.

Crystal structure of Sr2CdPt2 containing linear platinum chains

The title compound, Sr2CdPt2, adopts the Ca2GaCu2 structure type and exhibits linear platinum chains with two different Pt—Pt bonds of 2.7341 (13) and 3.2010 (14) Å.