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Stability and crystal chemistry of the ternary borides M2(Ni21−xMx)B6 (M Ti, Zr, Hf)
No full textA crystallochemical study was undertaken to investigate the structural stability and the compositional
extent of the ternary borides M2(Ni21-xMx)B6 (M = Ti, Zr, Hf). This phase often occurs during the production
of MB2 joints by means of NieB brazing alloys. Samples with the nominal compositions M2Ni21B6
and M3Ni20B6 were synthesized by arc melting and characterized by optical and electron microscopy, and
X-ray diffraction. Crystal structure refinements were performed by the Rietveld method. The compositional
boundaries of the ternary phases were experimentally determined and found strictly related to the
M/Ni size ratio. The stability of this structure is mainly determined by the capability of the structure to
expand under the effect of the Ni substitution by the M atom. The CALPHAD modeling of the three MeNi
eB ternary systems in the Ni-rich corner of the phase diagram, performed on the basis of the obtained
structural data, shows a good agreement with experimental results
Tetragonal to triclinic structural transition in the prototypical CeScSi induced by a two-step magnetic ordering: a temperature-dependent neutron diffraction study of CeScSi, CeScGe and LaScSi
No full textAn investigation on the ground state magnetism of CeScSi, CeScGe (tetragonal CeScSi-type, tI12, space group I4/mmm) by temperature-dependent powder neutron diffraction has been carried out, as debated and controversial data regarding the low temperature magnetic behaviours of these two compounds were reported. Our studies reveal that, while cooling, long-range magnetic ordering in CeScSi and CeScGe takes place by a two-step process. A first transition leads to a magnetic structure with the Ce moments aligned ferromagnetically onto two neighbouring tetragonal basal a-b planes of the CeScSi-type structure; the double layers are then antiferromagnetically coupled to each other along the c-axis. The transition temperature associated with the first ordering is T N ~ 26 K and T N ~ 48 K for the silicide and the germanide, respectively. Here the spin directions are rigorously confined to the basal plane, with values of the Ce magnetic moments of μ Ce = 0.8-1.0 μ B. A second magnetic transition, which takes place at slightly lower temperatures, results in a canting of the ordered magnetic moments out of the basal plane which is accompanied by an increase of the magnetic moment value of Ce to μ Ce = 1.4-1.5 μ B. Interestingly, the second magnetic transition leads to a structural distortion in both compounds from the higher-symmetry tetragonal space group I4/mmm to the lower-symmetry and triclinic I-1 (non-standard triclinic). Magnetic symmetry analysis shows that the canted structure would not be allowed in the I4/mmm space group; this result further confirms the structural transition. The transition temperatures T S from I4/mmm to I-1 are about 22 K in CeScSi and 36 K in CeScGe, i.e. well below the temperature of the first onset of antiferromagnetic order observed in this work (or below the ordering temperature, previously reported as either T C or T N). This result, along with the synchronism of the magnetic and structural transitions, suggests a magnetostructural origin of this structural distortion. We have also carried out powder neutron diffraction for LaScSi as a non-magnetically-ordering reference compound and compared the results with those of CeScSi and CeScGe compounds
The R<sub>10</sub>Pd<sub>21</sub> compounds (R = Y, Pr, Nd, Sm, Gd–Lu). Crystal structure and magnetism of the ‘RPd<sub>2</sub>’ phases
No full textThe unknown RPd2, for many years expected to be a simple Laves phase, is actually a much more complex compound with stoichiometry R10Pd21.</p
Self-magnetic compensation and shifted hysteresis loops in ferromagnetic samarium systems
No full textTWO EXOTIC AND UNIQUE FAMILIES OF RARE EARTH INTERMETALLIC COMPOUNDS
No full textThe rare earth metals form two unique, one of a kind, families of intermetallic compounds. One family crystallizes in the simple cubic CsCl, B2-type structure with 2 atoms in the unit cell; while the second family has the complex orthorhombic Nd11Pd4In9-type structure with 48 atoms in the unit cell. The first family, the RM compounds with the B2-type structure,
where R is a rare earth metal and M = Cu, Ag, and Au, are ductile phases. Some non-rare earths containing B2 phases have also been studied and most were found to follow the criteria for ductility/brittleness established by the RM phases. The second family, the R11M4In9 phases where M = Ni, Pd and Pt, form a fibrous microstructure.
The microstructure is self-assembled
directly from the melt (whether rapidly or slow cooled) and is probably due to the large aspect
ratio of 6.0 for the b/c lattice parameter ratio and the very short In-In bonds in the a-b plane
which give rise to kinetic hindrance during solidifying and prevent the crystal from growing in
the a and b directions
Systematics and anomalies in formation and crystal structures of RScSb and R3Sc2Sb3 rare earth compounds
No full textElectronically- and crystal-structure-driven magnetic structures and physical properties of RScSb (R = rare earth) compounds: a neutron diffraction, magnetization and heat capacity study
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