Syntheses and Crystal Structures of CaCuGe, CaAuIn, and CaAuSn - Three Different Superstructures of the KHg2 Type

Abstract

The intermetallic compounds CaCuGe, CaAuIn, and CaAuSn can be prepared from the elements in sealed tantalum tubes or in glassy carbon crucibles in a high‐frequency furnace. Their crystal structures were determined from single crystal X‐ray data. The three compounds crystallize with the same subcell structure (KHg2), however, they form three clearly perceptible superstructures with different unit cells, but all in space groups Pnma: a = 2124.9(6) pm, b = 436.0(2) pm, c = 749.4(5) pm, Z = 12, wR2 = 0.0789, 1303 F2 values, 56 variables for CaCuGe (own structure type), a = 738.2(1) pm, b = 459.4(1) pm, c = 839.4(2) pm, Z = 4, wR2 = 0.0651, 656 F2 values, 20 variables for CaAuIn (TiNiSi type), a = 3690.3(3) pm, b = 470.5(1) pm, c = 813.6(2) pm, Z = 20, wR2 = 0.1294, 1730 F2 values, 92 variables for CaAuSn (new structure type). The three structures may be considered as superstructures of the KHg2 type with an ordered arrangement of the transition metal and germanium (indium, tin) atoms on the mercury position. Each calcium atom in the structures of CaCuGe, CaAuIn, and CaAuSn has an distinctly ordered near‐neighbor environment of six transition metal (T) and six p element (X) atoms in the form of two counter‐tilted T3X3 hexagons. All known superstructures of the KHg2 type are described in terms of a group‐subgroup scheme.

Crystal structure of calcium silver germanium, CaAg0.98Ge1.02

“…The intermetallic compound CaAg 0.98 Ge 1.02 is isostructural with its Cu and Cu-Sn homologues CaCuGe [1], and CaCuSn [2]. It crystallizes in asuperstructure of the KHg 2-type [3] with an almost complete ordering of the Ag and Ge atoms on the Hg positions.…”

Gold-Tin Ordering in SrAu2Sn2

“…Tin shows an excellent wettability for many transition metals, and especially the stannides of the electron-rich transition metals are important materials in microelectronics as solder/metal interfaces [2]. The most relevant stannides are Cu 6 Sn 5 , Cu 3 Sn, and Ni 3 Sn 4 , but presently the gold stannides Au 5 Sn, AuSn and AuSn 4 have become very important in high-quality devices with corrosion-resistant gold supply cables.…”

“…So far only the stannides MgAuSn [3], CaAuSn [4], Ca 14 Au 46 Sn 5 [5], the icosahedral quasicrystal approximants Ca 3 Au 14.36 Sn 4.38 and Ca 13 Au 47.2 Sn 28.1 [6], SrAuSn [7], SrAuSn 2 [8], the solid solutions SrAu x Sn 4−x (1.3 ≤ x ≤ 2.2) [9], and BaAuSn [7] have been reported. Gold-tin ordering in such stannides is driven by the formation of strong covalent Au-Sn bonds with lengths close to the sum of the covalent radii for gold and tin of 274 pm [10].…”

“…Gold-tin ordering in such stannides is driven by the formation of strong covalent Au-Sn bonds with lengths close to the sum of the covalent radii for gold and tin of 274 pm [10]. Examples are CaAuSn (273 -278 pm) [4] or SrAuSn (279 -286 pm) [7]. Within the small range of the solid solutions SrAu x Sn 4−x (1.3 ≤ x ≤ 2.2), such a goldtin ordering is possible for the composition SrAu 2 Sn 2 .…”

LiBC – Synthesis, Electrochemical and Solid-state NMR Investigations

“…The lithium pieces were mixed with the boron lumps and the carbon flakes in an atomic ratio of 3 : 1 : 1 under flowing argon and then arc-welded in a niobium ampoule under an argon pressure of about 700 mbar. The niobium tube was then placed in the water-cooled sample chamber of an induction furnace [24]. The sample was rapidly heated to 1800 K and held at that temperature for 15 min.…”