BCMaterials Fortnightly Seminars #36

ANDRÉS MARTÍN

(BCMaterials)

INFLUENCE OF ND CONTENT AND OF NB AND CU ON GRAIN BOUNDARY INFILTRATION IN ND-LEAN ND-FE-B PERMANENT MAGNETS

The current high-energy permanent magnets commercially available use considerably large amounts of critical raw materials, such as Dy and Nd, to obtain high values of coercivity and increase their thermal stability. Considering the above we have focused on the development of high coercivity rare-earth-lean and Dy-free Nd-Fe-B permanent magnets by grain boundary engineering. We have studied the influence of Nd content and of Nb and Cu on both the crystallization and infiltration processes and on their microstructure and magnetic properties. The experiments were carried out on melt-spun amorphous ribbons of Nd₁₀Fe₈₄B₆, Nd₁₁Fe₈₃B₆, Nd₁₂Fe₈₁B₆Nb₁ and Nd₁₃Fe₈₁B₆ for the Nd content influence and of Nd₁₀Fe₈₄B₆, Nd₉Fe₈₄B₆Nb₁ and Nd₉Fe₈₄B₆Nb_0.5Cu_0.5 for the Nb and Cu influence. The techniques employed in this study include X-ray diffraction and electron microscopy for the microstructure and composition analysis and vibration sample magnetometer with fields up to 14 T for the magnetic properties analysis.

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JAGOBA MARTÍN

(BCMaterials)

SEQUENTIAL SINGLE–CRYSTAL–TO–SINGLE–CRYSTAL TRANSFORMATIONS IN A 3D POROUS HYBRID CONTAINING THE UNCOMMON PARATUNGSTATE A [W7O24]6– FRAGMENT AND CU(II)-TETRAAZACOMPLEXES

As one of the scarce examples of a coordination polymer based on a paratungstate A or heptatungstate fragment, the novel compound [{Cu(cyclam)}₆(W₇O₂₄)₂]·31 H₂O (1) (cyclam= 1,4,8,11–tetraazacyclotetradecane) has been synthetized and characterized. This porous structure changes its dimensionality from an initial 3D assembly to a layered arrangement [{Cu(cyclam)}₆(W₇O₂₄)₂]·24 H₂O (2) due to the rotation of alternate layers and consequent migration of a Cu atom to an adjacent WO₆ octahedra as a result of a thermally triggered single–crystal–to–single–crystal transformation upon partial dehydration. Total dehydration leads to the anhydrous [{Cu(cyclam)}₆(W₇O₂₄)₂] (3) which undergoes further structural changes associated to the simultaneous migration of Cu atoms and cluster rearrangement. While 1 and 2 show a single crystallographic type of channels, the rearrangement of copper atoms in 3 resulted in a crystal packing with two types of channels with slightly different sizes. All transformations are fully reversible at ambient conditions and occur in one day approximately. To our knowledge, 1 is the first {W₇}-based polyoxometalate that exhibits adsorption features as demonstrated by preliminar N₂ gas sorption experiments owing to its permanent porosity.