Reinvestigation and superstructure of La3.67[Fe(C2)3]
Graphical abstract
Diffraction data reveal a superstructure with weak superstructure reflections for La3.67[Fe(C2)3] in the space group P63/m. The superstructure is caused by an ordered arrangement of La atoms along 0, 0, z with alternating short and long distances.
Introduction
Recently, the family of ternary carbides RExTyCz (RE=rare-earth metals or actinoids; T=transition metals; C=monoatomic C4− species) has been classified into two groups according to structural characteristics and the ratio (x+y)/z, i.e., carbometalates with (x+y)/z⩽2 containing complex anions and metal-rich carbides with (x+y)/z⩾4 [2]. In the search for novel carbometalates we also explored the systems RE–Fe–C. Compounds of this type have been proposed as potential hard magnet materials [3]. In spite of intensive explorations of the respective phase diagrams only a few compounds with (x+y)/z<2 have been reported: RE2FeC4 (RE=Y, Tb–Lu) [4], Sc3FeC4 [5], REFeC2 [6], ScFeC2 [7] and RE3.67FeC6 (RE=La–Nd, Sm) [1]. All these compounds contain C2-pairs as structural units instead of monoatomic carbon ligands, thus, in a strict sense they do not belong to the class of carboferrates. During our recent work in the system La–Fe–C we reinvestigated the crystal structure of La3.67FeC6, which had been described already in a previous communication by Witte and Jeitschko [1]. In the present work we report on the determination of a superstructure of this compound.
Section snippets
Preparation
All handlings were carried out in a glove box under argon atmosphere (MBraun, p(O2, H2O)<1 ppm). The title compound was prepared by arc-melting of cold pressed pellets of La (Ames, 99.99%), Fe (Alfa Aesar, 99.99%) and graphitic carbon (Chempur, 99.9%) in the molar ratios 3:1:6 and 3.67:1:6. The button specimens of about 0.6 g total mass were remelted several times to ensure compositional homogeneity. The samples were then wrapped in Fe-foils, which in turn were encapsulated in fused silica tubes,
Results and discussion
The crystal structure of La3.67FeC6 was refined in the space group P63/m (176) with residuals R1=0.044 and wR2=0.075 for 1387 unique reflections and 60 variables. The atoms are distributed on 4 La, 2 Fe and 4 C sites in the unit cell. The occupancy factors were refined in separate series of least-squares cycles as a check for partial occupancy. The refinement revealed full occupancy for all sites except those of La3 and La4. In the final cycles of the refinement the site occupancy for La3 and
Conclusion and summary
The ternary carbide La3.67[Fe(C2)3] with maximum possible La content forms a superstructure with a tripled unit cell along the c axis compared to the previously reported crystal structure [1]. The rigid host structure without any occupational disorder and with chemical composition La3FeC6 is identical for the sub- and super-structure (neglecting minimum distortions) and contains Fe(C2)3 trigonal planar groups with C2 ligands bonded end-on to the iron atoms. These complex entities are surrounded
Acknowledgments
We would like to thank Dr. Ulrich Burkhardt, Torsten Vogel, and Monika Eckert (metallographic investigations and EDXS) as well as Steffen Hückmann (X-ray powder diffraction).
References (17)
- et al.
J. Solid State Chem.
(2007) - et al.
J. Solid State Chem.
(1992) - et al.
J. Less-Common Met.
(1986) - et al.
J. Less-Common Met.
(1974) - et al.
J. Less-Common Met.
(1961) - et al.
J. Alloys Compd.
(1992) - et al.
J. Less-Common Met.
(1988) - et al.
Z. Naturforsch.
(1996)
Cited by (12)
Experimental investigation of phase transformations in the La-Fe and La-Fe-C systems
2019, Calphad: Computer Coupling of Phase Diagrams and ThermochemistryCitation Excerpt :In the work [30] the compound La3.67FeC6 with a structure P63/m was reinvestigated by X-ray powder and single crystal diffraction, and was further characterized by metallographic methods and chemical analyses. According to Ref. [30], the ternary carbide La3.67[Fe(C2)3], with a maximum possible concentration of La, forms a superstructure with a tripled unit cell along the c axis compared to the previously reported crystal structure [29]. The compound reported with the composition La3Fe20C [28] seems to be identical with a compound reported with a composition La2Fe14C [31].
Phase equilibria in the Fe-Ce-C system at 1100 °C
2018, Journal of Alloys and CompoundsCitation Excerpt :The compounds reported with the tentative compositions Ce10Fe3C17 [23] and Ce2Fe2C3 [8] seem to be identical with the carbide Ce3.67FeC6 [24]. Recently, in [25] the La3.67[Fe(C2)3] compound with a structure P63/m was reinvestigated. The compounds reported with the compositions R3Fe20C (R = La [23], Gd [22]) and R14Fe78C8 [26] seem to be identical with the composition R2Fe14C (Nd2Fe14B-structure type, P42/mnm) [27].
Alloy Systems and Compounds Containing Rare Earth Metals and Carbon
2017, Handbook on the Physics and Chemistry of Rare EarthsCitation Excerpt :Refined unit cell parameters, obtained from Guinier powder patterns using α-quartz as an internal standard, are listed in Table 3. Recently, the crystal structure of La3.67FeC6 was reinvestigated in Ref. [136]. The sample was prepared at conditions similar to those reported in Ref. [131]: arc melting followed by annealing at 900°C for 21 days.
Dy <inf>0.64</inf>{Dy <inf>5</inf>[Fe <inf>2</inf>C <inf>9</inf>]}: A complex carbide with a composite structure
2012, Journal of Solid State ChemistryCitation Excerpt :A vacancy occurs for example at Oh3 and Oh7. In the crystal structure of La3.67[Fe(C2)3] [3] the situation is similar, but not that extreme (Fig. 4(b)). Here, two octahedra filled by La alternate with one empty octahedron, while the La atoms still lying inside the octahedra.
Flux Growth of an Intermetallic with Interstitial Fluorides via Decomposition of a Fluorocarbon
2023, Inorganic Chemistry