Fe13Ga9 intermetallic in bcc-base Fe–Ga alloy
Introduction
Fe−Ga alloys, often referred to as Galfenols, attract considerable interest as rare-earth free magnetostrictive material. The most attractive properties have been reported around 18 at.% and 27 at.% Ga [[1], [2], [3]], whereby, the achievable magnetostrictive constants depend strongly on the heat treatment applied. This suggests a role of changes of the atomic structure and microstructure due to phase transformations in the solid state caused by temperature and composition dependent phase stabilities.
According to current phase diagrams [[4], [5], [6], [7], [8], [9], [10]], Fe−Ga alloys exist in bcc-related (body-centred cubic) crystal structures up to about 50 at.% Ga at elevated temperatures, with composition and thermal history-dependent occurrence of A2 (disordered W type terminal solid solution) and partially ordered B2 (CsCl type) and D03 (BiF3 or binary Heusler type) phases, the latter two being superstructures of A2. At low temperatures formation various non-bcc structures have been reported, with hexagonally close packed (hcp) based D019 and face centred cubic (fcc) based L12 type ordered phases being equilibrium phases occurring around the “Fe3Ga” composition (25 at.% Ga). Their formation, however, requires some heat-treatment time, see e.g. Ref. [11]. Due to the strong heat-treatment dependence, metastable versions of the phase diagram have been formulated, depicting e.g. only the type of ordering in bcc-type structures [4,9]. An equilibrium phase diagram according to Kubaschewski [7] focusing on the solid phases in an intermediate compositional range is depicted in Fig. 1.
In the course of attempts to better understand the phase transformation behavior upon heat treating bcc-based Fe–Ga alloys by extending the experimental basis to alloys with >30 at.% Ga, initially unaccountable reflections were encountered in powder X-ray diffraction data of as-cast Fe-38.4 at%Ga alloy. In the present work it is shown that these reflections originate from a Fe13Ga9 intermetallic phase of Ni13Ga9-type [12] crystal structure. That Fe13Ga9 phase most likely corresponds to a metastable phase reported previously [4] and which had been suggested (in the passing) to have such a Ni13Ga9 crystal structure [4]. While the present paper addresses the characteristics of the crystal structure, formation mechanism and thermodynamics of the Fe13Ga9 phase, the way how formation of this phase affects magnetostricitive behavior has to remain topic of future research.
Section snippets
Experimental
Alloy preparation followed a procedure described in Refs. [13]. The investigated Fe–Ga alloy has a nominal composition of Fe-38at.%Ga and was inductively melted (Indutherm MC-20 V mini furnace) from pure Fe (commercial purity) and pure Ga (99.99%) in a ceramic crucible under protective high-purity argon gas and cast into a copper mould of inner dimension of 4 × 16 × 60 mm3.
The alloy composition was determined on a polished cross section by energy dispersive X-ray spectroscopy as Fe-(38.4 ± 0.1)
DFT calculations
The DFT calculations, basically pertaining to the situation at 0 K, imply that a Ni13Ga9-type Fe13Ga9 has ferromagnetic ordering with 2.0–2.3 μB for the different Fe sites. The Ga also attain small moments (−0.12 - −0.14 μB) due to hybridisation between Fe and Ga and the procedure of local magnetic moment calculation in the VASP code. Fe13Ga9 phase has a negative energy of formation of Ef = −0.170 meV/atom, which implies its stability with respect to the pure elements of Fe and Ga. The refined
Atomic structure of Fe13Ga9
The crystal structure of Fe13Ga9 belongs to the group of Ni2In/NiAs-based structures (Strukturbericht designations B82/B81) [23]. In these structures, main group metal B atoms form an hcp like arrangement, which has, for the currently relevant structures, a characteristically small axial ratio ch/ah of the order of 1.225; see below, where the index h refers to the hexagonal unit cell pertaining to the hcp structure. In this hcp arrangement, transition metal atoms T(1) usually occupy all
Conclusions
The crystal structure of an intermetallic phase with the formula Fe13Ga9, earlier proposed in the passing [4], has been determined on the basis of powder X-ray and neutron diffraction data on as-cast Fe-38.4 at.%Ga alloy. The alloy consists of bcc phase likely with A2 type order, from which this phase has developed in agreement with [4,6]. The crystal structure is a Ni2In/NiAs-based superstructure referred previously to as the Ni13Ga9 or Pt4In3/Pt13In9 type. The following points can be
Declaration of competing interest
We declare lack of competing interest.
Acknowledgements
ISG, IAB, and AMB are indebted to the Russian Science Foundation for the support (project 19-72-20080). The alloys were produced by A.K. Mohamed, National University of Science and Technology “MISIS”, Russia, who also commented on the manuscript. The authors also thank Dr. T.N. Vershinina for her help with neutron data analysis.
References (43)
- et al.
Structural investigations of Fe–Ga alloys: phase relations and magnetostrictive behavior
Acta Mater.
(2008) - et al.
Phase equilibria and stability of ordered b.c.c. phases in the Fe-rich portion of the Fe–Ga system
J. Alloys Compd.
(2002) - et al.
The Fe–Ga phase diagram: Revisited
J. Alloys Compd.
(2020) - et al.
Time-Temperature-Transformation from metastable to equilibrium structure in Fe-Ga
Mater. Lett.
(2020) - et al.
Kristallstruktur von Ni13Ga9 und zwei Isotypen
J. Less Common Met.
(1969) - et al.
Cooling rate as a tool of tailoring structure of Fe-(9–33%)Ga alloys
Intermetallics
(2019) Recent advances in magnetic structure determination by neutron powder diffraction
Physica B
(1993)- et al.
Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set
Comput. Mater. Sci.
(1996) - et al.
Understanding migration barriers for monovalent ion insertion in transition metal oxide and phosphate based cathode materials: a DFT study
Comput. Mater. Sci.
(2018) - et al.
A survey of superstructures in intermetallic NiAs-Ni2In-type phases
J. Solid State Chem.
(1995)
The monoclinic lattice distortion of η′-Cu6Sn5
J. Alloys Compd.
An orthorhombic D022-like precursor to Al8Mo3 in the Al–Mo–Ti system
J. Alloys Compd.
Strukturuntersuchungen in einigen mischungen T-B3-B4 (T=Mn,Fe,Co,Ir,Ni,Pd; B3= Al,Ga,Tl; B4=Si,Ge)
J. Less Common Met.
Kristallstruktur von Ni4GaGe2
J. Less Common Met.
Crystal structure of Pd13Pb9.r
J. Less Common Met.
An ordered ω-phase in the rapidly solidified Zr-27 at.%Al alloy
Acta Metall.
Determination of the stretch tensor for structural transformations
J. Mech. Phys. Solid.
Omega phase in materials
Prog. Mater. Sci.
Mechanical instabilities in the b.c.c. lattice and the beta to omega phase transformation
Acta Metall.
Thermodynamics of intermetallic phases with the triple-defect B2 structure
Acta Metall.
Ordering processes in Fe-Ga alloys studied by positron annihilation lifetime spectroscopy
Mater. Lett.
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