Incommensurately modulated Nowotny Chimney-ladder phases: Cr 1- x Mo x Ge ∼1.75 with x = 0.65 and 0.84

✍ Scribed by Rohrer, F. E.; Lind, H.; Eriksson, L.; Larsson, A.-K.; Lidin, S.

• Book ID: 120631386
• Publisher: Oldenbourg Wissenschaftsverlag
• Year: 2001
• Tongue: English
• Weight: 368 KB
• Volume: 216
• Category: Article
• ISSN: 2194-4946
• DOI: 10.1524/zkri.216.4.190.23255

✦ Synopsis

Abstract

The crystal structures of two new ternary, incommensurately modulated phases in the Cr/Mo/Ge system, Cr~1-~~x~Mo~x~Ge~∼1.75~with__x= 0.65 and 0.84, have been refined using the same composite approach as for the earlier reported compounds, (Mo/Rh)~11~Ge~18~and (Mo/Rh)~13~Ge~22~, from the Mo/Rh/Ge system. The composite model consists of a rather stable diamond-like transition metal substructure and a helical main group element arrangement. The same super space group pair,W:P__4/nnc: q1̅q1__P:I__4~1~/amd: 11̅ss, the same positions and modulation waves were used. The refinements of the new phases in the Cr/Mo/Ge system converged rapidly to__R-values below 5% with GOF of 2.53 and 3.71, respectively. Each structure is built by two sub lattices with the parameters -a,c~x~and the modulation vector__q~x~- for Ge and__a,c~T~and q~T~for the transition metals. The refined data for__x= 0.65 are found to be__a__= 5.935(2),c~x~= 2.770(1),c~T~= 4.839(1),q~x~= 0.428 [001]*,q~T~= 0.253 [001]* and for__x__= 0.84,a= 5.963(1),c~x~= 2.786(1),c~T~= 4.875(1),q~x~= 0.430 [001]*,q~T~= 0.264 [001]*. It is clearly shown the composite approach is applicable to different chimney-ladder compounds, even though they have quite different compositions and henceq-vectors.