Correlations of Crystal and Electronic Structure via NMR and X-ray Photoelectron Spectroscopies in the RETMAl₂(RE = Sc, Y, La–Nd, Sm, Gd–Tm, Lu; TM = Ni, Pd, Pt) Series

Abstract

A total of 35 intermetallic aluminum compounds have been synthesized from the elements via arc melting and characterized by powder X-ray diffraction. A total of 15 of them have been previously reported; however, detailed property investigations were missing. Compounds of the RETMAl2 (rare earth metal RE = Sc, Y, La–Nd, Sm, Gd–Tm, Lu) series with transition metal TM = Ni, Pd, and Pt crystallize isostructurally in the orthorhombic MgCuAl2 type structure (Cmcm, oC16, fc 2). Single-crystal X-ray diffraction investigations were conducted on YNiAl2, LaNiAl2, YPdAl2, ScPtAl2, and YPtAl2. The TM and Al atoms form a [TMAl2]δ− polyanion, the RE atoms reside in cavities within the framework. While the Sc, Y, La, and Lu compounds exhibit Pauli-paramagnetic behavior, consistent with all atoms being closed shell, the other RETMAl2 compounds show paramagnetism along with magnetic ordering at low temperatures, in line with an open-shell trivalent oxidation state for the RE atoms. Solid-state 27Al NMR investigations were carried out on the Pauli-paramagnetic samples, all showing only a single central transition, in line with one crystallographic site for the respective atoms. The observed quadrupolar coupling constants and electric-field-gradient asymmetry parameters were found to be in good agreement with the density-functional-theory-calculated values. Isotropic resonance shifts are dominated by the Fermi-contact interactions with s-conduction electron densities at the Fermi edge (Knight shifts). The bonding characteristics mirror the electronic density of states and crystal chemistry of the family of intermetallic compounds under consideration. Both the Knight shifts and quadrupolar coupling constants can be predicted based on element-specific increments.

Extending the knowledge on the quaternary rare earth nickel aluminum germanides of the RENiAl4Ge2 series (RE=Y, Sm, Gd–Tm, Lu) – structural, magnetic and NMR-spectroscopic investigations

“…Furthermore, the significant difference in the isotropic magnetic (de-)shielding contributions, δ iso ms , between Al1 and Al2 signifies a large difference between the s-density of states (s-DOS) at the Fermi level for these two aluminum species. While the values measured for Al1 are comparable to those obtained in numerous other intermetallic compounds [18,20,22,75], resulting in a substantial Knight shift contribution, Simulation of the spectra of Figure 9 right (method 1). b F1/F2 Center of gravity analysis of the TQ spectra (method 2).…”

From 3D to 2D: Structural, Spectroscopic and Theoretical Investigations of the Dimensionality Reduction in the [PtAl2]δ− Polyanions of the Isotypic MPtAl2 Series (M=Ca–Ba, Eu)

“…[97] For ScPtAl (TiNiSi-type) d iso ms = 403 ppm (7.05 T) was observed, [98] whereas for the isostructural MgCuAl 2 -type representatives REPtAl 2 ,i sotropic values of d iso ms = 419 (ScPtAl 2 ), 422 (YPtAl 2 )a nd 467 ppm (LuPtAl 2 )w ere reported. [58] The larger Knight shifts in the presentc ompounds indicatet hat in these compounds the Fermi edge s-electron density of states at the 27 Al nuclei is higher than in the rare earth compounds. This interpretation may be rationalized on the basis of the lower electronegativity of the alkaline-earth elements compared to the rare earth elements.…”

“…The isotropic Knight shifts of δ iso ms =711 (CaPtAl 2 ), 750 (SrPtAl 2 ) and 767 ppm (BaPtAl 2 ) are in the range of other alkaline earth intermetallics, for example, Ba 3 Pt 4 Al 4 (own type) which exhibits two distinct crystallographic sites ( δ iso ms =762 and 1031 ppm at 9.4 T) . For ScPtAl (TiNiSi‐type) δ iso ms =403 ppm (7.05 T) was observed, whereas for the isostructural MgCuAl 2 ‐type representatives RE PtAl 2 , isotropic values of δ iso ms =419 (ScPtAl 2 ), 422 (YPtAl 2 ) and 467 ppm (LuPtAl 2 ) were reported . The larger Knight shifts in the present compounds indicate that in these compounds the Fermi edge s‐electron density of states at the 27 Al nuclei is higher than in the rare earth compounds.…”

“…For these 1‐1‐2 representatives the gallides ( MT Ga 2 ; M =Ca, Sc, Y, Gd–Lu; T =Ni, Pd, Pt, Au), the indides ( MT In 2 ; M =Na, Ca–Ba, Y, La–Nd, Eu–Dy, Yb; T =Ru, Rh, Ir, Ni, Pd, Pt, Cu, Au and Eu 1− x Sr x PtIn 2 ), the thallides ( MT Tl 2 ; M =Sr, Eu; T =Pd, Pt), the silicide ScPt 2 Si, the stannides MT Sn 2 ( M =Ca, Eu, Yb; T =Rh, Ir, Pd) and the phosphide PdNi 2 P have been reported. For aluminum finally, the representatives MT Al 2 ( M =Sc, Y, La–Nd, Sm, Gd–Lu; T =Co, Ni, Cu, Pd, Pt) have been prepared. Here, we report on the synthesis, crystal and electronic structures, magnetism, 27 Al and 195 Pt MAS‐NMR, XPS and 151 Eu Mössbauer spectroscopic properties of the platinide series M PtAl 2 , with M being an alkaline earth metal or europium ( M =Ca, Sr, Ba, Eu).…”

Magnetic and transport properties of a new ferromagnetic orthorhombic compound CePtAl2

“…Ce-based compounds are the promising candidate showing coexistence since they have the same strong correlation between f-electrons and conduction electrons as U-based compounds. We have focused on new compounds RPtAl2 (R = Sc, Y, La-Nd, Sm, Gd-Tm, Lu) [2]. As shown in the figure 1, RPtAl2 crystallizes in the orthorhombic MgCuAl2-type structure (space group Cmcm, D2h 17 , No.…”