Tau-borides (Mn_x{Ru,Os,Ir}_1-x)23B₆: X-ray single crystal and TEM data, physical properties

Autor(en)

Gerda Rogl, Georg Binder, Herwig Michor, Jiří Buršík, Markus Eiberger, Andriy Grytsiv, Gerald Giester, Peter Franz Rogl

Abstrakt

Investigation (electron microprobe and X-ray powder and single crystal diffraction analyses) of the phase relations in the Mn-rich corner (> 45 at% Mn) of the systems Mn-{Ru,Os,Ir}-B, prompted in all three systems a ternary compound with formula (Mnx{Ru,Os,Ir}_1-x)₂₃B₆. For the systems Mn-Ru-B, Mn-Ir-B phase equilibria have been determined at 950^◦C (Ru), 900^◦C (Ir) revealing in both cases a small homogeneity region at constant B-content (Mn_1-xRu_x)₂₃B₆ (0.29 < x < 0.37); (Mn_1-xOsx)₂₃B₆ (0.33 < x < 0.37), as well as (Mn_1-xIr_x)₂₃B₆ (0.29 < x < 0.34). The crystal structure of the three compounds was determined from single crystal and X-ray powder intensity data analyses to be isotypic with the Cr₂₃B₆-type (so-called tau-phase, space group Fm3m, No. 225). In all cases Mn atoms fully occupy the 4a site (0,0,0) at the origin of the unit cell. For the 8c site (¼,¼,¼) we observed a random distribution of Mn_1-x(PM)x with decreasing PM content (PM stands for a platinum group metal atom) going from Ru to Os and Ir, where Mn atoms fully occupy 8c. Whereas the remaining sites (48h, 32f)
show various ratios of the two metal species, boron atoms fully occupy the centers (24e site) of the Archimedean metal atom antiprisms. A transmission electron microscopic study confirms the absence of superstructures related to these metal atom disorder, thus Mn and PM atoms randomly share their sites. The latter is well reflected in the behavior of the electrical resistivity of these compounds, which is dominated by disorder scattering.
For (Mn_0.6{Ru,Os}_0.4)₂₃B₆, temperature dependent dc magnetization studies reveal distinct antiferromagnetic-like anomalies at T_N ≅ 72 K and 114 K, respectively. Low field dc and ac magnetic susceptibility data of (Mn_0.7Ir_0.3)₂₃B₆ display a distinct ferromagnetic-like transition at T_C = 280 K, consistent with a pronounced specific heat anomaly and a rather continuous temperature dependent evolution of magnetic anisotropy effects. Mechanical properties (hardness) characterize the tau phases among rather hard and brittle intermetallics (about 5–6 GPa).

Organisation(en)

Institut für Materialchemie, Institut für Mineralogie und Kristallographie

Externe Organisation(en)

Technische Universität Wien, Czech Academy of Sciences, Universität Wien

Journal

Journal of Alloys and Compounds

Band

993

ISSN

0925-8388

DOI

https://doi.org/10.1016/j.jallcom.2024.174604

Publikationsdatum

07-2024

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 104011 Materialchemie, 105113 Kristallographie

Schlagwörter

ASJC Scopus Sachgebiete

Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry

Link zum Portal

https://ucris.univie.ac.at/portal/de/publications/tauborides-mnxruosir1x23b6-xray-single-crystal-and-tem-data-physical-properties(8fdf7893-c405-4e2e-a7b9-ec096af67af7).html