A free web page under the name MAGNDATA, which provides detailed quantitative information on more than 400 published magnetic structures, has been made available at the Bilbao Crystallographic Server (http://www.cryst.ehu.es). It includes both commensurate and incommensurate structures. In the first article in this series, the information available on commensurate magnetic structures was presented [Gallego, Perez-Mato, Elcoro, Tasci, Hanson, Momma, Aroyo & Madariaga (2016). J. Appl. Cryst. 49, 1750–1776]. In this second article, the subset of the database devoted to incommensurate magnetic structures is discussed. These structures are described using magnetic superspace groups, i.e. a direct extension of the non-magnetic superspace groups, which is the standard approach in the description of aperiodic crystals. The use of magnetic superspace symmetry ensures a robust and unambiguous description of both atomic positions and magnetic moments within a common unique formalism. The point-group symmetry of each structure is derived from its magnetic superspace group, and any macroscopic tensor property of interest governed by this point-group symmetry can be retrieved through direct links to other programs of the Bilbao Crystallographic Server. The fact that incommensurate magnetic structures are often reported with ambiguous or incomplete information has made it impossible to include in this collection a good number of the published structures which were initially considered. However, as a proof of concept, the published data of about 30 structures have been re-interpreted and transformed, and together with ten structures where the superspace formalism was directly employed, they form this section of MAGNDATA. The relevant symmetry of most of the structures could be identified with an epikernel or isotropy subgroup of one irreducible representation of the space group of the parent phase, but in some cases several irreducible representations are active. Any entry of the collection can be visualized using the online tools available on the Bilbao server or can be retrieved as a magCIF file, a file format under development by the International Union of Crystallography. These CIF-like files are supported by visualization programs like Jmol and by analysis programs like JANA and ISODISTORT.

MAGNDATA: towards a database of magnetic structures. I. The commensurate case

Intermetallic compounds with the equiatomic composition CeTX that crystallize with the orthorhombic TiNiSi-type structure can be synthesized with electron-rich transition metals (T) and X = Zn, Al, Ga, Si, Ge, Sn, As, Sb, and Bi. The present review focusses on the crystal chemistry and chemical bonding of these CeTX phases and on their physical properties, ¹¹⁹Sn and ¹²¹Sb Mossbauer spectra, high-pressure effects, hydrogenation reactions and the formation of solid solutions in order to elucidate structure–property relationships. This paper is the final one of a series of four reviews on equiatomic intermetallic cerium compounds [Part I: Z. Naturforsch. 2015, 70b, 289; Part II: Z. Naturforsch. 2015, 70b, 695; Part III: Z. Naturforsch. 2016, 71b, 165].

Cerium intermetallics with TiNiSi-type structure

The equiatomic CeXX′ phases (X and X′ = elements of the 3ʳᵈ, 4ᵗʰ, or 5ᵗʰ main group) extend the large series of CeTX intermetallics (T = electron-rich transition metal). These phases crystallize with simple structure types, i.e. ZrNiAl, TiNiSi, CeScSi, α-ThSi₂, AlB₂, and GdSi₂. In contrast to the CeTX intermetallics one observes pronounced solid solutions for the CeXX′ phases. The main influence on the magnetic ground states results from the absence of d electrons. All known CeXX′ phases show exclusively trivalent cerium and antiferro- or ferromagnetic ordering at low temperatures. The crystal chemical details and some structure-property relationships are reviewed.

Equiatomic cerium intermetallics CeXX′ with two p elements

Abstract The Sn rich ternary intermetallic compounds Li3Cu6Sn4 (CSD-427097) and Li2CuSn2 (CSD-427098) were synthesized from the pure elements by induction melting and annealing at 400°C. Structural investigations were performed by powder- and single-crystal XRD. Li3Cu6Sn4 crystallizes in space group P6/mmm; it is structurally related to but not isotypic with MgFe6Ge6 (a = 5.095(2) Å, c = 9.524(3) Å; wR2 = 0.059; 239 unique F2-values, 17 free variables). Li3Cu6Sn4 is characterized by two sites with a mixed Cu:Sn occupation. In contrast to all other Cu-Li-Sn compounds known so far, any mixed occupation was found for Cu-Li pairs only. In addition, one Li site is only half occupied. The second Sn rich phase is Li2CuSn2 (space group I41/amd, a = 4.4281(15) Å, c = 19.416(4) Å; wR2 = 0.033; 213 unique F2-values, 12 atom free variables); it is the only phase in the Cu-Li-Sn system which is noted for full ordering. Both crystal structures exhibit 3D-networks which host Li atoms in channels. They are important for understanding the lithiation mechanism in Cu-Sn electrodes for Li-ion batteries.

S. Capelli

Papers

Neutron powder diffraction study of the ternary RMgSn (R¼Ce-Nd, Tb-Tm, Yb) compounds

Magnetic properties and magnetic structures of the CeScSi-type RMgPb (R¼Ce-Nd, Sm, Gd-Tm) compounds

Magnetic properties of MgFe6Ge6