[Zurück]

P. Rogl, V.V. Romaka, Jiri Bursik, H. Michor, M. Reissner, G. Giester, V. Homolova:
"Structure and properties of a novel boride (V_0.92FeV_0.08)V₂FeBV₂ with partially ordered U₃Si₂-type";
Journal of Alloys and Compounds, 746 (2018), S. 638 - 647.

X-ray single-crystal structure analysis was performed for the novel compound V_1.84Fe_1.16B₂ ≡ (V_1-xFe_x)₂FeB₂ at x = 0.08 (P4/mbm; a = 0.555931(9) nm, c = 0.306781(5) nm; U₃Si₂-type). Consequently, structural identity is obvious between (V_0.92Fe_0.08)₂FeB₂ and the precipitates V_∼2Fe_∼1B₂ earlier identified in the UGISTAB 215-XH permanent magnet. Magnetic and ⁵⁷Fe Mössbauer studies of (V_0.92Fe_0.08)₂FeB₂ reveal a magnetically ordered ground state with T_C∼110 K. Mössbauer spectra point towards a ferrimagnetic spin arrangement.

Enthalpy of formations (DFT calculations) for (Fe,V), VB, V₃B₂, and the hypothetical solution V_3-xFe_xB₂ (x<1.5) clearly document that the tie-line between (Fe,V) and VB is more stable than the continuous solid solution of the U₃Si₂-type phase. This explains the experimental observation that (i) binary V₃B₂ only dissolves a minor amount of Fe (replacing V), and that (ii) binary V₃B₂ and isotypic V_1.84Fe_1.16B₂ appear as independent phases in the ternary phase diagram.

Calculation of the electron localization function elf yielded a very high value (ϒ ∼0.75) between boron atoms documenting strong covalent bonding. The Young's modulus E (from nano-indentation) for V_1.84Fe_1.16B₂ is 442 GPa. The higher anisotropy in the ternary boride V₂FeB₂ is concluded from the significantly higher difference between C₁₁ and C₃₃ in V₂FeB₂ (192.1 GPa) with respect to V₃B₂ (117.0 GPa).

Transition metal alloys and compounds, Precipitation, Crystal structure, Magnetic measurements

http://dx.doi.org/10.1016/j.jallcom.2018.02.323