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

Abstract

Ag 0.98 CaGe 1.02 ,orthorhombic, Pnma (no. 62), a =21.5602(5) Å, b =4.5625(2) Å, c =7.8713(2) Å, Source of materialThe air-sensitive single crystals of the title compound were obtained from amixture of the elements (Ca granules (99.5 %), Ag powder (99.9 %) and Ge powder (99.999 %), all from ABCR) with the molar ratio Ca :Ag:Ge=5:4:4,heated in aNbampoule at 1253 Kfor one hour and then slowly cooled at arate of 6K/h to room temperature. The crystals were selected in an Argon-filled glove-box and mounted in asealed capillary and transferred for X-ray diffraction data collection. Experimental detailsThe refinement, after all atomic positions were located by direct methods, revealed an electron density hole on the Ag1 position with relatively large ADPs. The possibility of Ag/Ge mixed occupancy was then checked for all atomic positions, but it was significant only at the Ag1 position (0.052(5) occupancy for Ge in the final refinement) where the hole was originally detected, yielding slightly lower residuals than the fully ordered model.

Calcium platinum aluminium, CaPtAl

“…ordering of the atomic sites (Ponou & Lidin, 2008;Ponou, 2010). This phase has previously been reported by Merlo et al (1996) in the KHg 2 structure type with Ag and Ge atoms randomly distributed on the Hg site.…”

“…For structural systematics and properties of the TiNiSi structure type, see: Kussmann et al (1998);Hoffmann & Pö ttgen (2001); Nuspl et al (1996); Evers et al (1992). For related compounds of the TiNiSi structure type, see: Ponou & Lidin (2008); Ponou (2010); Banenzoué et al (2009). For atomic radii, see: Pauling (1960).…”

On a TiNiSi‐Type Superstructure: Synthesis, Crystal and Electronic Structures of CaAgGe and Its Mn‐Substituted Derivative

“…Furthermore, when using aluminium as substituting element, we found that the superstructure is suppressed and a random Ag/Al mixing is observed in the solid solution CaAg 1-x Al x Ge with x close to 0.5 as expected from the Zintl concept. [29] 4. Experimental Section 4.1.…”

“…This procedure yielded the phase Ca 3 Mn 0.21(1) Ag 2.79(1) Ge 3 with lower than expected Mn content from the refinement of the data from single-crystal X-ray diffraction, and confirmed by EDS analysis. Further attempts to increase the Mn content by either larger amount of Mn in the reaction mixtures or higher reaction temperature were unsuccessful, as their resulted in roughly similar refined composition (within 3σ standard deviation) and, in the formation of other phases like the solid solution Ca 3 Mn 0.43 Ag 0.87 Ge 2.70 [29] with the Sc 3 NiSi 3 type [30] and CaMnGe as the major phase. [31] Previous endeavours to prepare the hypothetical Mg-substituted charge-balanced phase Ca 3 MgAg 2 Ge 3 were also elusive, and always produced phases with higher Mg content, CaMg 1-x Ag x Ge (x Ͻ 0.15) in the simple TiNiSi type subcell.…”

“…Recently, we reported the phase CaAg 0.98 Ge 1.02 in an isomorphic superstructure of the TiNiSi type with a tripling of the a-axis (i 3 , minimal isomorphic subgroup of index 3) and, an almost complete ordering of the atomic sites. [15] The occurrence of the superstructure in this structural family is well known, like for instance EuAuGe and CaPdGe (i 2 , space group Imm2), [16] YPdSi [7] (i 2 , S.G. Pmmn), as well as CaCuGe (i 3 , S.G. Pmna) and YbAuSn (i 3 , S.G. Imm2), or even CaAuSn (i 5, S.G. Pmna). [6] But, the origin of the superstructure has been scarcely discussed.…”