The determination of the crystal structure of the σ phase in the iron–chromium and iron–molybdenum systems

Bergman, G.; Shoemaker, David P.

doi:10.1107/s0365110x54002605

Cited by 187 publications

(80 citation statements)

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“…This feature is very similar to that of phase structure found in the Fe Cr and Fe Mo systems. 17 The FeCr has a tetragonal structure with lattice parameters of a = 0.880 nm and c = 0.454 nm. Note that the value a = 0.880 nm of FeCr is closely similar to the lattice parameter a = 0.882 nm of Nd2Fe14B.…”

Section: During the Course Of The Preparation Of This Manuscriptmentioning

confidence: 99%

Permanent magnet materials based on the rare earth-iron-boron tetragonal compounds

Sagawa¹,

Fujimura²,

Yamamoto³

et al. 1984

IEEE Trans. Magn.

748

188

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Structural and metallographic studies were carried out on the Nd Fe B alloy system as well as the Nd Fe B tetragonal compound on which record high energy mag nets have been developed using a powder metallurgical technique. The study on the new magnet has also been extended to other R Fe B compounds containing various rare earths R and to R Fe Co B alloys. The results are as follows:1 The sintered Nd Fe B magnet is composed of mainly three phases, the Nd2Fe14B matrix phase plus Nd rich phase and B rich phase ~Nd2Fe7B6 as minor phases.2 Nd2Fe14B has the space group of P42/mnm. The crystal structure of this phase can be described as a layer structure with alternate stacking se quence of a Nd rich layer and a sheet formed only by Fe atoms. The sheet of Fe atoms has a structure similar to the phase found in Fe Cr and Fe Mo systems.3 The Nd rich phase containing more than 95 atoms Nd, 3~5 atoms Fe and a trace of B has fcc structure with a = 0.52 nm. This phase is formed around grain boundaries of the matrix phase. Nd2Fe7B6 phase has an one dimensional incommensurate structure with a = ao and c 8co, based on a tetragonal structure with ao = 0.716 nm and co = 0.391 nm.4 In the as sintered Nd15Fe77B8 alloy periodic strain contrasts are observed along grain boundaries, which disappear after annealing at 870 K. This may be related to the enhancement of the intrinsic coercivity of the sintered mag net by post sintering heat treatment.5 Stable R2Fe14B phases are formed by various rare earths except La. Of all the R2Fe14B com pounds, Nd2Fe14B has the maximum saturation magnetization as high as 1.57 T. Dy and Tb form R2Fe14B phases with the highest anisotropies. Small additions of these elements greatly en hance the coercive force of the Nd2Fe14B base magnet.6 Partial replacement of Fe by Co raises the Curie temperature of the Nd2Fe14B compound, which improves the temperature coe cient of the remanence of the magnet. But the intrinsic co ercive force is decreased by the Co addition.

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Section: During the Course Of The Preparation Of This Manuscriptmentioning

confidence: 99%

Permanent magnet materials based on the rare earth-iron-boron tetragonal compounds

Sagawa¹,

Fujimura²,

Yamamoto³

et al. 1984

IEEE Trans. Magn.

748

188

View full text Add to dashboard Cite

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“…A detailed description of this structure based on the early work of Shoemaker & Bergman (1950), Bergman & Shoemaker (1951, 1954, Dickins, Douglas & Taylor (1951)and Kasper, Decker & Belanger (1951), and also an account of its physical properties, have been given by Sinha (1972).…”

Section: And 15 (G)mentioning

confidence: 99%

The ordering of the σ phases Cr₂Ru and Cr₂Os

Veiga¹,

Costa²,

Almeida³

et al. 1980

Acta Crystallogr Sect B

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Two a-phase structures, Cr2Ru and Cr2Os, have been studied using X-ray single-crystal diffraction techniques. The ordering determined has been compared with those of other a phases and A15 structures. Although atoms of both kinds occupy every atomic position, a significant departure from complete disorder was detected. This is particularly important in the 14-fold J atomic positions which are associated with bond angles of 180°: the marked preference of the smaller Cr atoms for these sites indicates that their occupancy appears to be determined by the electronic A.]

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“…The crystal data for the K phase are compared with those for the o phase (Bergman & Shoemaker, 1954) and the 6 phase (Shoemaker & Shoemaker, 1963) in Table 1. The 6 phase is pseudo-tetragonal and its cell dimensions are similar to those of the o phase, except for an approximate doubling of the c axis.…”

Section: Structure Model For the Subcellmentioning

confidence: 99%

The crystal structure and superstructure of the K phase, Mn77Fe4Si19

Shoemaker¹,

Shoemaker²

1977

Acta Crystallogr Sect B

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The K phase, Mn77Fe4Si~9, is monoclinic, a = 13.362 (1), b = 11.645 (1), c = 8.734 (1) × 2 ,~,,/~ = 90-53 (1) °, 110 x 2 atoms per unit cell, space group C2 (C~). Reflections with odd / are quite weak, indicating that the full cell represents a superstructure. The structure model for the substructure was derived from the aspects of the diffraction pattern that resemble the o-FeCr and the 6-MoNi patterns, and with the help of a threedimensional Patterson function. It was refined by full-matrix anisotropic least squares with Mo Kc~ diffractometer data to R(F) = 0.13 (all 3244 reflections) or 0-06 (1932 reflections with I > 2o). The substructure has rumpled layers and is entirely 'tetrahedrally close-packed' (tcp), with Mn(Fe) in the positions of coordination numbers (CN) 16, 15, and 14, and with mixtures of Mn(Fe) and Si in the positions of CN 12. Since the substructure did not show evidence of 'elongated atoms' (marked apparent thermal anisotropies) the superstructure was assumed to be substitutional in regard to occupancy of CN 12 sites by Mn(Fe) or Si. The superstructure was solved with the aid of a Patterson function calculated with superstructure data only, and with least-squares refinement of site occupancies for the CN 12 atoms. Different CN 12 sites were found to be occupied by Mn(Fe) atoms, Si atoms, or mixtures of Mn(Fe) and Si. The alteration between the two subcells is such as to allow Si atoms to be everywhere coordinated only by Mn(Fe). In this the K phase resembles the v phase, Mn82Si~8, and the X phase, MN45Co40Sils, with plane-layered tcp structures, but differs from the D phase, MnsSi 2, with a somewhat 'non-ideal' tcp structure in which there are a few Si-Si contacts.

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The determination of the crystal structure of the σ phase in the iron–chromium and iron–molybdenum systems

Cited by 187 publications

References 1 publication

Permanent magnet materials based on the rare earth-iron-boron tetragonal compounds

Permanent magnet materials based on the rare earth-iron-boron tetragonal compounds

The ordering of the σ phases Cr₂Ru and Cr₂Os

The crystal structure and superstructure of the K phase, Mn77Fe4Si19

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The determination of the crystal structure of the σ phase in the iron–chromium and iron–molybdenum systems

Cited by 187 publications

References 1 publication

Permanent magnet materials based on the rare earth-iron-boron tetragonal compounds

Permanent magnet materials based on the rare earth-iron-boron tetragonal compounds

The ordering of the σ phases Cr2Ru and Cr2Os

The crystal structure and superstructure of the K phase, Mn77Fe4Si19

Contact Info

Product

Resources

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The ordering of the σ phases Cr₂Ru and Cr₂Os