Indium Flux-Growth of Eu₂AuGe₃: A New Germanide with an AlB₂ Superstructure

Abstract

The germanide Eu(2)AuGe(3) was obtained as large single crystals in high yield from a reaction of the elements in liquid indium. At room temperature Eu(2)AuGe(3) crystallizes with the Ca(2)AgSi(3) type, space group Fmmm, an ordered variant of the AlB(2) type: a = 857.7(4), b = 1485.5(10), c = 900.2(4) pm. The gold and germanium atoms build up slightly distorted graphite-like layers which consist of Ge(6) and Au(2)Ge(4) hexagons, leading to two different hexagonal-prismatic coordination environments for the europium atoms. Magnetic susceptibility data showed Curie-Weiss law behavior above 50 K and antiferromagnetic ordering at 11 K. The experimentally measured magnetic moment indicates divalent europium. The compound exhibits a distinct magnetic anisotropy based on single crystal measurements and at 5 K it shows a metamagnetic transition at ∼10 kOe. Electrical conductivity measurements show metallic behavior. The structural transition at 130 K observed in the single crystal data was very well supported by the conductivity measurements. (151)Eu Mössbauer spectroscopic data show an isomer shift of -11.24 mm/s at 77 K, supporting the divalent character of europium. In the magnetically ordered regime one observes superposition of two signals with hyperfine fields of 26.0 (89%) and 3.5 (11%) T, respectively, indicating differently ordered domains.

Phase Relations and Crystal Structures in the Ternary Systems Sr‐{Ag, Au}‐{Si, Ge}

“…τ 1 crystallizes with AlB 2 type as defined by the Rietveld refinement in Figure 10 of the X-ray powder pattern of the alloy with nominal composition Sr 30 Au 16.5 Ge 53.5 . The formation of an ordered superstructure with 2:1:3 composition, as suggested by Sebastian et al, [42] was not observed during this investigation but cannot be excluded to exist at another temperature. Besides τ 1 the alloy also contains small quantities of τ 2 and (Ge) according to the location of the sample in the three-phase field.…”

“…Similar to the high temperature modification, β-K 4 ᮀ 2 P 6 type (see also [40] General descriptions of the AlB 2 family including the ordered 2:1:3 superstructures are given in an review article of Hoffmann and Pöttgen [41] and further discussions on 2:1:3 superstructure formations can be found in the article of the isotypic compound Eu 2 AuGe 3 . [42] With all distances Si-(Au,Si) and (Au,Si)-(Au,Si) being smaller than 2.50 Å, we may count on strong covalent bonding within the planar Au,Si networks in Sr 2.00 Au 1.01 Si 2.82 ᮀ 0.18 . As has been pointed out earlier, [42] direct Au-Au (d 10 -d 10 ) contacts are the driving force for the formation of puckered hexagonal layers, which so far have not been found in 2:1:3 compounds.…”

“…[42] With all distances Si-(Au,Si) and (Au,Si)-(Au,Si) being smaller than 2.50 Å, we may count on strong covalent bonding within the planar Au,Si networks in Sr 2.00 Au 1.01 Si 2.82 ᮀ 0.18 . As has been pointed out earlier, [42] direct Au-Au (d 10 -d 10 ) contacts are the driving force for the formation of puckered hexagonal layers, which so far have not been found in 2:1:3 compounds. [42] Although the results from Rietveld refinement and single crystal refinement on Sr 2 Au 1 Si 3 differ concerning the mixed sites and the position of the defect, the resulting composition is almost the same (composition from SC: Sr 2.00 Au 1 Crystal structure and homogeneity range of τ 2 -SrAu 2+x Si 2-x were investigated by EPMA and XPD after annealing at 800°C and by XSCD.…”

Structural and magnetic properties of Nd2NiGe3

“…The origins of these wide ranges of fascinating and anomalous physical properties are associated with the interplay of interactions between the localized 4f (or 5f) electrons of the rare earth atoms and the delocalized conduction electrons of the transition metal atoms. Among the RE-T-X (RE = rare earths, T = transition metals, X = p-block elements) intermetallics, compounds having general the formula RE 2 TX 3 are extensively studied for their interesting structural and physical properties [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. These compounds generally crystallize in the AlB 2 structure type and its ordered superstructures [24].…”

Synthesis of Ce2Rh3Ge5 Crystals from a Bismuth Flux

“…Several examples are summarized in [4]. Indium on the other hand seems to be a good candidate for a non-reactive flux, as recently shown for the synthesis of DyNiGe 2 [12], Eu 2 AuGe 3 [13] and Yb 5 Ni 4 Ge 10 [14] crystals. Good results have also been obtained with bismuth fluxes for the phosphides RERh 6 P 4 (RE = Sc, Yb, Lu) [15], and this has been applied to the germanide CeRh 6 Ge 4 [16].…”