First principle studies of electronic and magnetic properties of Lanthanide-Gold (RAu) binary intermetallics
Introduction
Noble metals (Cu, Ag, Au) based compounds are attractive for material scientists for their high oxidation and corrosion resistance, high stability, good strength, ductile and magnetic nature, very high melting points, good conductance and wide-range applications in high-temperature structural materials [1]. Generally the intermetallics with B2 or CsCI structure that contains one transition and a simple metal atom exhibit diverse physical phenomena. They are best for the systematic study of magnetic properties, electronic structure, cohesive properties, charge transfer and chemical bonding [2]. This class of compounds is antiferromagnetic [3] and metallic in nature with no band gap. The binary alloys of gold with the rare-earth elements are characterized by the cubic CsCl-type crystal structure B2 with space group Pm3m (No. 221), having the Wyckoff positions: R atom at (0,0,0) and Au atom at (0.5,0.5,0.5) [4], [5], [6] except CeAu [5] which has CrB type crystal structure [7], [8]. However experiments also show the cubic CsCl-type structure for CeAu compound [9]. Lanthanides in these compounds are trivalent [7], [10], [11] except Yb which is divalent [12]. Therefore, some of the physical properties of Yb such as the metallic radius, electronegativity etc are quite different than those of the normal trivalent rare-earth metals.
The compounds of lanthanides is the first group of atoms containing f-orbital [13]. One of the interesting subgroups of lanthanide compounds is the noble metals (Cu, Ag and Au) based stable lanthanides. Among this group the most stable compounds are those of Au with the rare-earth elements [14]. The bond stabilities are in the order of Rau≫RCu>RAg (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) [15].
Ionic as well as metallic bonds are present between gold and lanthanide atoms [7], [16], [17]. Electron transfer from the rare-earth metal to gold occurs as the electronegativity difference of these atoms are favorable for ionic bond formation [18]. The ionic and metallic bonding in these intermetallics can be confirmed from the fact that these compounds have high melting points [16], [19], [20], [21] high dissociation energies [7], [16], [22] and high bond energies [23]. The stable nature of these compounds is due to the large electronegativity difference (>1.13) and equiatomic stoichiometry of gold and lanthanides [10], [15], [19]. There exists a correlation between the stability trend and the relative melting behavior of these compounds [17]. Their melting points increase steadily as a function of atomic number from 1372 °C for CeAu to 1780 °C for LuAu respectively, with the exception of YbAu whose melting point is 1292 °C [6]. The low melting point of YbAu is attributed to the divalency of Yb in YbAu [24].
The RAu compounds were synthesized by reacting the reactants in a sealed boron nitride container at 1372K temperature [25]. The reactions were highly exothermic and the heat evolved was used to sustain the reaction [17], [23] and stable compounds were formed [26]. The CsCl structure for these compounds was confirmed by X-ray diffraction [26], [27].
Although these compounds are very important due to their interesting physical properties, but even then limited experimental as well as theoretical studies are reported on them, that make their applications limited. To the best of our knowledge no experimental or theoretical work has been reported on the electronic structure of these compounds, and similarly almost no theoretical work is available on the magnetic properties of these compounds. In this paper we explore the electronic structure and magnetic properties of these compounds, using the full potential linearized augmented plane waves (FP-LAPW) method within the framework of density functional theory.
Section snippets
Computational details
Electronic and magnetic properties of RAu(R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), compounds are explored with the full potential linearized augmented plane waves (FP-LAPW) method with the GGA, [28], [29] GGA+U [30], [31], [32] and HF exchange correlation functional [33] to solve the Kohn–Sham equations [34]. Details of the FP-LAPW method and WIEN2k package used in the present calculations were discussed previously [35]. For accurate and converged results by GGA+U an approximated
Chemical bonding
Charge distribution around the atom determines the nature of chemical bonding and we calculated the electronic charge density for RAu (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds. The Contour-plots of charge density for RAu compounds are shown in Fig. 1. It is obvious from the plots that there is not much bonding charge that may link the R and Au atoms covalently. The charge density distribution is spherically symmetric about each atom that shows that these compounds have
Conclusion
In summary this work reports the investigation of electronic and magnetic properties of RAu intermetallics (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) which are studied for the first time using GGA, GGA+U and HF based on DFT. Our results of magnetic properties show that the results of HF are much consistent with the available experimental data as compared to GGA and GGA+U. The chemical bonding are explained on the basis of electronic charge densities. The bond between R and Au are
References (48)
- et al.
Magnetic characteristics of some 1: 1 compounds of the lanthanides with gold and aluminum
J. Less Common Met.
(1966) Stoichiometry, crystal structures and some melting points of the lanthanide-gold alloys
J. Less Common Met.
(1971)- et al.
Theoretical calculation of thermodynamic data for gold-rare earth alloys with the embedded-atom method
J. Alloy. Compd.
(2006) Alloying behavior of the rare earth metals with gold: the Ho–Au, Er–Au and Tm–Au systems
Intermetallics
(2002)- et al.
The ytterbium-gold system
J. Less Common Met.
(1969) Electronic structure and magnetic properties of lanthanide 3+ cations
Chem. Phys. Lett.
(2013)Stability of rare-earth-containing high-temperature molecules
J. Less Common Met.
(1985)- et al.
Comments on the formation thermodynamics of selected groups of rare earth compounds
J. Alloy. Compd.
(2001) - et al.
Thermochemistry of some binary alloys of gold with the lanthanide metals by high temperature direct synthesis calorimetry
J. Alloy. Compd.
(2004) - et al.
Thermochemistry of some binary alloys of gold with the lanthanide metals by high temperature direct synthesis calorimetry
J. Alloy. Compd.
(2004)
Materials informatics for the design of novel coatings
Surf. Coat. Technol.
DFT calculations of solids with LAPW and WIEN2k
J. Solid State Chem.
Electronic structure of cubic perovskite SnTaO 3
Intermetallics
Electronic structure and stability of Mg–Ce intermetallic compounds from first-principles calculations
J. Alloy. Compd.
Empirical correlation between melting temperature and cohesive energy of binary Laves phases
J. Phys. Chem. Solids
Magneto-electronic studies of anti-perovskites NiNMn3 and ZnNMn3
Comput. Mater. Sci.
Magneto-electronic studies of the inverse-perovskite (Eu3O)
J. Magn. Magn. Mater.
Ductility in intermetallic compounds
Adv. Eng. Mater.
Cohesive, electronic and magnetic properties of the transition metal aluminides FeAl CoAl and NiAl
J. Phys.: Condens. Matter
The neodymium-gold phase diagram
Metall. Mater. Trans. A
A Study of CsCl Type Intermediate Phases Involving Rare Earth Elements (Dissertation thesis)
Alloying and strengthening of gold via rare earth metal addition
Gold. Bull.
A survey of gold intermetallic chemistry
Gold Bull.
Solid solubility metastable extension of rare earth metals in gold
Gold Bull.
Cited by (11)
Theoretical approach for calculation of dielectric functions of plasmonic nanoparticles of noble metals, magnesium and their alloys
2020, Optical MaterialsCitation Excerpt :Though the mixing of model and density functional Hamiltonians is not well justified, such approach, due to the high computational efficiency, is widely applied for semiconductors and insulators [28,29]. The applications to metals, half-metals [30,31] and conducting intermetallides [32] are rare due to the possible errors in ground state properties induced by the internal details of DFT+U implementation (i. e. double-counting compensation scheme [28]). In the present study, we employed DFT+U approach to reproduce the dielectric functions of gold and silver metals and showed that the selected Hubbard parameters allow to improve the estimation of ground state properties compared to those achieved with LDA-DFT.
Effects of A-Site cation on the Physical Properties of Quaternary Perovskites AMn<inf>3</inf>V<inf>4</inf>O<inf>12</inf> (A= Ca, Ce and Sm)
2020, Materials Chemistry and PhysicsCitation Excerpt :It is obvious from Table 4 that melting points are 2812.45, 2832.96 and 3014.63 ± 300 K respectively for CaMn3V4O12, CeMn3V4O12 and SmMn3V4O12. The melting temperature of SmMn3V4O12 is higher than the rest due to its high cohesive energy, because of direct relation between cohesive energy and melting point [54]. From the melting and Debye temperature it is concluded that for the understudy compounds the operateable temperature ranges are 62.24–2812.45, 61.88–2832.96 and 63.71–3014.63 K for CaMn3V4O12, CeMn3V4O12 and SmMn3V4O12 respectively.
Physical properties and possible applications of gold-based rare earth intermetallics (R-Au): A review
2019, Journal of Magnetism and Magnetic MaterialsCitation Excerpt :No experimental studies have not yet reported on the magnetic moments of PrAu, NdAu and LuAu intermetallics. Ahmad et al. recently [165] computed magnetic characteristics of R-Au alloys using Perdew-Burke-Ernzerhof (PBEsol) [166], GGA+U [167], B3LYP and B3PW91 [168] potentials in DFT frame work. The computed magnetic behavior and effective magnetic moments of all 1:1 RAu intermetallics are listed in Table 9.
Strongly correlated intermetallic rare-earth monoaurides (Ln-Au): Ab-initio study
2018, Journal of Rare EarthsCitation Excerpt :Due to this fact we used DFT instead of other sophisticated method in the present work for our calculations. In this work, we performed spin polarized calculations using the full-potential linearized augmented plane waves (FP-LAPW) method based on the density functional theory (DFT) employing the exchange-correlation potentials of the generalized gradient approximation (GGA) with two different parameterizations i.e. PBE and PBEsol33–36 as well as GGA with Hubbard U potential (GGA + U) as implemented in the wien2k code.37–39 The number of k-points was optimized and all the calculations are performed at 1000 k-points.
First principle studies of structural, magnetic and elastic properties of orthorhombic rare-earth diaurides intermetallics RAu<inf>2</inf> (R=La, Ce, Pr and Eu)
2018, Materials Chemistry and PhysicsCitation Excerpt :Au atom and the interstitial regions have negligible magnetic moments. In conclusion, the total spin magnetic moment is due to 4f-unpaired electrons of the lanthanide atom [30,31]. The lanthanides can be considered as a cluster of ions, mostly trivalent, with incomplete 4f orbitals, imbedded in a cloud of free electrons.
DFT studies of thermoelectric properties of R–Au intermetallics at 300 K
2018, Journal of Rare Earths