Erbium diboride
| Names | |
|---|---|
| Other names
Erbium boride | |
| Identifiers | |
| Properties | |
| ErB2 | |
| Molar mass | 188.88 g/mol |
| Density | 8.94 g/cm3 |
| Structure | |
| Hexagonal, aluminium diboride type | |
| P6/mmm, No. 191 | |
a = 0.32725 nm, c = 0.37845 nm | |
Formula units (Z) |
1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Erbium diboride is an inorganic compound of erbium and boron with the chemical formula ErB2. It crystallizes in the hexagonal aluminium diboride structure type and is a metallic rare-earth diboride. At low temperature, ErB2 undergoes a ferromagnetic transition near 14 K and exhibits a sizeable magnetocaloric effect.[1][2]
Preparation
[edit]Erbium diboride can be prepared by reaction of elemental erbium and boron:
- Er + 2 B → ErB2
Polycrystalline material may be produced by arc melting erbium and boron under an inert atmosphere.[3]
Unlike many congruently melting compounds, ErB2 forms by a weakly peritectic reaction. The liquid endpoint of the peritectic lies near 65 at.% boron and about 2185 °C, only slightly removed from the 66.7 at.% boron composition of stoichiometric ErB2.[3]
This behavior allows large single crystals to be grown using a traveling-solvent floating-zone method. In one procedure, stoichiometric ErB2 feed and seed rods were used while the molten zone self-adjusted toward the boron-poorer peritectic composition. Growth was performed under high-pressure argon at temperatures above 2000 °C.[3]
Earlier single-crystal platelets were grown from an erbium-rich molten flux at about 1750 °C.[4]
Properties
[edit]Crystal structure
[edit]ErB2 crystallizes in the hexagonal crystal system, space group P6/mmm (No. 191), with the AlB2 structure type.[3]
A modern Rietveld refinement gives lattice parameters a = 3.2725(2) Å and c = 3.7845(3) Å.[1]
The structure consists of alternating layers of erbium atoms and planar hexagonal boron nets. Er occupies the (0,0,0) position, while the boron atoms occupy the (1⁄3,2⁄3,1⁄2) and (2⁄3,1⁄3,1⁄2) positions.
Magnetic properties
[edit]ErB2 undergoes a ferromagnetic transition at about 14 K.[1] Measurements of single crystals show strong magnetic anisotropy, with the basal plane acting as the magnetically easy plane.[3][2]
Above the ordering temperature, the magnetic susceptibility follows approximately Curie–Weiss behavior. The effective magnetic moment is close to that expected for free Er3+ ions, indicating that the magnetism is dominated by localized erbium 4f moments.[3]
Pressure measurements up to 5.6 GPa show that the magnetic ordering temperature increases with pressure, indicating stabilization of the ordered state as the lattice contracts.[2]
Magnetocaloric properties
[edit]ErB2 displays a pronounced low-temperature magnetocaloric effect around its ferromagnetic transition.[1]
For a magnetic-field change of 5 T, the peak magnetic entropy change reaches about 26.1 J kg−1 K−1 near 14 K. The corresponding peak adiabatic temperature change is about 8.6 K.[1]
The magnetocaloric response is characteristic of a second-order ferromagnetic transition, with the specific-heat anomaly shifting and broadening toward higher temperature under an applied magnetic field.[1]
Electrical transport
[edit]ErB2 is metallic. Its electrical resistivity shows a clear anomaly near the magnetic ordering temperature, reflecting the reduction in magnetic scattering on entering the ordered state.[2]
Under quasi-hydrostatic pressure, the resistivity anomaly moves to higher temperature, consistent with the pressure-induced increase in the ferromagnetic transition temperature.[2]
References
[edit]- 1 2 3 4 5 6 Terashima, Kensei; Baptista de Castro, Pedro; Saito, Akiko Takahashi; Yamamoto, Takafumi D.; Matsumoto, Ryo; Takeya, Hiroyuki; Takano, Yoshihiko (2023). "Experimental exploration of ErB2 and SHAP analysis on a machine-learned model of magnetocaloric materials for materials design". Science and Technology of Advanced Materials: Methods. 3 (1) 2217474. doi:10.1080/27660400.2023.2217474.
- 1 2 3 4 5 Tong, A.; Nuzhina, D.; Resch, C.; Benka, G.; Bauer, A.; Pfleiderer, C. (2025). "Electrical resistivity of ErB2 under pressure". Journal of Physics: Condensed Matter. 37 (19) 195806. Bibcode:2025JPCM...37s5806T. doi:10.1088/1361-648X/adc77a. PMID 40164105.
- 1 2 3 4 5 6 Bauer, Andreas; Benka, Georg; Neubauer, Andreas; Regnat, Alexander; Engelhardt, Alexander; Resch, Christoph; Wurmehl, Sabine; Blum, Christian G. F.; Adams, Tim; Chacon, Alfonso; Jungwirth, Rainer; Georgii, Robert; Senyshyn, Anatoliy; Pedersen, Björn; Meven, Martin; Pfleiderer, Christian (2022). "Compositional Studies of Metals with Complex Order by means of the Optical Floating-Zone Technique". Physica Status Solidi (B). 259 (5) 2100159. arXiv:2111.09764. Bibcode:2022PSSBR.25900159B. doi:10.1002/pssb.202100159.
- ↑ Castellano, R. N. (1972). "Crystal growth of TmB2 and ErB2". Materials Research Bulletin. 7 (4): 261–265. doi:10.1016/0025-5408(72)90202-4.