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@article{1733456,
author = {Yan, Xinlin and Brož, Pavel and Vřešťál, Jan and Vlach, Jiří and Buršík, Jiří and Mazalová, Martina and Pavlů, Jana and Smetana, Bedřich and Rogl, Gerda and Eiberger, Markus and Grytsiv, Andriy and Michor, Herwig and Müller, Herbert and Giester, Gerald and Rogl, Peter},
article_location = {Lausanne},
article_number = {June},
doi = {http://dx.doi.org/10.1016/j.jallcom.2021.158715},
keywords = {Intermetallics; crystal structurephase diagrams; thermodynamic modeling; magnetic measurements; thermal analysis},
language = {eng},
issn = {0925-8388},
journal = {Journal of Alloys and Compounds},
title = {On the Constitution and Thermodynamic Modeling of the Phase Diagrams Nb-Mn and Ta-Mn},
url = {https://doi.org/10.1016/j.jallcom.2021.158715},
volume = {865},
year = {2021}
}
TY - JOUR
ID - 1733456
AU - Yan, Xinlin - Brož, Pavel - Vřešťál, Jan - Vlach, Jiří - Buršík, Jiří - Mazalová, Martina - Pavlů, Jana - Smetana, Bedřich - Rogl, Gerda - Eiberger, Markus - Grytsiv, Andriy - Michor, Herwig - Müller, Herbert - Giester, Gerald - Rogl, Peter
PY - 2021
TI - On the Constitution and Thermodynamic Modeling of the Phase Diagrams Nb-Mn and Ta-Mn
JF - Journal of Alloys and Compounds
VL - 865
IS - June
SP - "158715"
EP - "158715"
PB - Elsevier Science SA
SN - 09258388
KW - Intermetallics
KW - crystal structurephase diagrams
KW - thermodynamic modeling
KW - magnetic measurements
KW - thermal analysis
UR - https://doi.org/10.1016/j.jallcom.2021.158715
L2 - https://doi.org/10.1016/j.jallcom.2021.158715
N2 - The constitution of the two phase diagrams Nb-Mn and Ta-Mn has been determined from light optical and transmission and scanning electron microscopy (LOM, TEM and SEM) with energy dispersive (EDX) as well as wavelength dispersive (WDX) X-ray spectroscopy, X-ray powder (XPD) and single crystal diffraction (XSCD), differential thermal analysis (DTA) and/or differential scanning calorimetry (DSC). The Laves phases NbMn2 and TaMn2 are the only binary compounds in these systems. High-temperature differential thermal analyses revealed congruent melting for NbMn2 with T,(NbMn2) = 1515 +/- 15 degrees C, whereas TaMn2 melts incongruently with T-m(TaMn2)= 1797 +/- 40 degrees C close to a depleted peritectic reaction. Both Laves phases engage in eutectic reactions l <-> (Mn) + Nb(Ta)Mn-2 (T-eut = 1220 +/- 10 degrees C at 4.9 at% Nb and T-eut = 1234 +/- 10 degrees C at 0.7 at% Ta, respectively). NbMn2 also forms a eutectic with (Nb): l <-> (Nb) + NbMn2 at T-eut = 1493 +/- 15 degrees C and 53.2 at% Nb. Mn shows remarkably large maximum solid solubilities of 19.4 at% Mn in (Nb) as well as of 21.3 at% Mn in (Ta). Detailed atom site distribution has been established for the Laves phases by means of temperature dependent X-ray single crystal data (both C14 - MgZn2-type). Combined data from XPD, EDX/WDX and SEM microstructure indicate that for both Laves phases extended homogeneity regions exist: Nb1+xMn2+x (62.5-73.0 at% Mn at 950 degrees C: -0.19 <= x <= 1.125) and Ta1+xMn2-x (59.5-68.5 at % Mn: -0.055 <= x <= 1.215). Density functional theory (DFT) calculations favor Nb(Ta)/Mn antisite occupation rather than defects. The phases, "NbMn" and "TaMn", adopted earlier in the literature as binary system inherent compounds, were shown (TEM, WDX electron microprobe data and X-ray Rietveld refinements) to be oxygen stabilized phases of the Ti4Ni2O type (so-called eta(eta)-phases) with modified Nb(Ta)/Mn site substitution to comply with the formula Nb(Ta)(3-x)Mn3+xO1-y (defect eta-W3Fe3C-type). From magnetic susceptibility and magnetization measurements, both oxide stabilized eta phases eta-Nb3Mn3O1-y and eta-Ta3Mn3O1-y were found to order ferromagnetically below T-c similar to 77 K, but the Laves phases NbMn2, TaMn2 reveal weakly temperature dependent paramagnetism. No trace of the rhombohedral kyphase (W6Fe7-type) has been encountered in our investigation of the two binary phase diagrams. Thermodynamic and transport properties (specific heat, electrical resistivity and magnetic susceptibility/magnetization) classify the Laves phases with metallic behavior whilst mechanical properties (elastic moduli from DFT and nanoindentation as well as hardness and thermal expansion) group both Laves phases among rather hard and brittle intermetallics. Based on (i) the experimentally derived constitution of the Nb-Mn and Ta-Mn systems, and (ii) on new own DFT data of the energy of formation of the Laves phases, a CALPHAD (CALculation of PHAse Diagrams) calculation of both systems was made providing a complete set of optimized thermodynamic data. Furthermore, the DFT calculations provided information on the instability of the eta-Ta3Mn3 structure and the atom-site specific stabilization effect of oxygen.
ER -
YAN, Xinlin, Pavel BROŽ, Jan VŘEŠŤÁL, Jiří VLACH, Jiří BURŠÍK, Martina MAZALOVÁ, Jana PAVLŮ, Bedřich SMETANA, Gerda ROGL, Markus EIBERGER, Andriy GRYTSIV, Herwig MICHOR, Herbert MÜLLER, Gerald GIESTER and Peter ROGL. On the Constitution and Thermodynamic Modeling of the Phase Diagrams Nb-Mn and Ta-Mn. \textit{Journal of Alloys and Compounds}. Lausanne: Elsevier Science SA, 2021, vol.~865, June, p.~''158715'', 19 pp. ISSN~0925-8388. Available from: https://dx.doi.org/10.1016/j.jallcom.2021.158715.
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