New Quaternary Chalcogenides BaLnMQ3 (Ln - Rare Earth; M = Cu, Ag; Q = S, Se): I. Structures and Grinding-Induced Phase Transition in BaLaCuQ3

✍ Scribed by Amy E. Christuk; Ping Wu; James A. Ibers

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 397 KB
• Volume: 110
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1994.1176

✦ Synopsis

The new quaternary compounds (\mathrm{BaLaCu}{3}(Q=\mathrm{S}), Se) have been synthesized by the reaction of the constituent binary chalcogenides and elements at (1000^{\circ} \mathrm{C}). The crystal structures have been determised by X-ray diffraction techniques. Crystal data: BaLa (\mathrm{CuS}{3})-space group (D_{2 h}^{16})-Pnma, (M=435.97, Z=4, a=11.316(2)), (b=4.236(1), c=11.724(2) \AA(T=115 \mathrm{~K}), V=562.0(2) \AA^{3}), (R_{w}\left(F^{2}\right)=0.059) for 1051 observations and 38 variables, (R(F)=) 0.019 for 1037 observations having (F_{0}^{2}>2 \sigma\left(F_{0}^{2}\right)); BaLa (\mathrm{CuSe}{3})-space group (D{2 h}^{16}-\mathrm{Pnma}, M=576.67, Z=4, a=11.111) (4), (b=4.293(2), c=13.830(4) \AA(T=115 \mathrm{~K}), V=659.7(4) \AA^{3}), (R_{w}\left(F^{2}\right)=0.129) for 1385 observations and 38 variables, (R(F)=) 0.050 for 1313 observations having (F_{0}^{2}>2 \sigma\left(F_{0}^{2}\right)). The BaLaCuS structure has a three-dimensional framework with channels that accommodate barium ions. The lanthanum atoms have monocapped trigonal prismatic coordination and the copper atoms have tetrahedral coordination. (\mathrm{BaLaCuSe}{3}) crystallizes into two phases, an (\alpha) phase that is isostructural with (\mathrm{BaLaCuS}{3}) and a layered (\beta) phase that is isostructural with (\mathrm{Eu}{2} \mathrm{CuS}{3}). The layers, which are separated by (\mathrm{Ba}^{2+}) ions, consist of edge-sharing octahedral chains and corner-sharing tetrahedral chains. The two structures are closely related and (\beta)-BaLaCuSe ({ }{3}) undergoes a phase transformation to (\alpha)-BaLaCuSe ({ }{3}) upon mechanical grinding. The reverse phase transition occurs when (\alpha)-BaLaCuSe ({ }_{3}) is annealed at elevated temperatures. 1994 Academic Press, Inc.