Layered manganese bismuth tellurides with GeBi4Te7- and GeBi6Te10-type structures: towards multifunctional materials. Issue 32 (30th July 2019)

• Record Type: Journal Article
• Authors: Souchay, Daniel; Nentwig, Markus; Günther, Daniel; Keilholz, Simon; de Boor, Johannes; Zeugner, Alexander; Isaeva, Anna; Ruck, Michael; Wolter, Anja U. B.; Büchner, Bernd; Oeckler, Oliver
• Is Part Of: Journal of materials chemistry. Volume 7:Issue 32(2019)
• Page Start: 9939
• Page End: 9953
• Publication Date: 2019-07-30
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c9tc00979e
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Non-stoichiometry is the key to single-phase layered compounds in the system Mn/Bi/Te, which is essential to evaluate their multifunctional properties. Abstract : The crystal structures of new layered manganese bismuth tellurides with the compositions Mn0.85(3) Bi4.10(2) Te7 and Mn0.73(4) Bi6.18(2) Te10 were determined by single-crystal X-ray diffraction, including the use of microfocused synchrotron radiation. These analyses reveal that the layered structures deviate from the idealized stoichiometry of the 12 P -GeBi4 Te7 (space group P 3̄ m 1) and 51 R -GeBi6 Te10 (space group R 3̄ m ) structure types they adopt. Modified compositions Mn1− x Bi4+2 x /3 Te7 ( x = 0.15–0.2) and Mn1− x Bi6+2 x /3 Te10 ( x = 0.19–0.26) assume cation vacancies and lead to homogenous bulk samples as confirmed by Rietveld refinements. Electron diffraction patterns exhibit no diffuse streaks that would indicate stacking disorder. The alternating quintuple-layer [ M 2 Te3 ] and septuple-layer [ M 3 Te4 ] slabs ( M = mixed occupied by Bi and Mn) with 1 : 1 sequence (12 P stacking) in Mn0.85 Bi4.10 Te7 and 2 : 1 sequence (51 R stacking) in Mn0.81 Bi6.13 Te10 were also observed in HRTEM images. Temperature-dependent powder diffraction and differential scanning calorimetry show that the compounds are high-temperature phases, which are metastable at ambient temperature. Magnetization measurements are in accordance with a Mn II oxidation state and point at predominantly ferromagnetic coupling in both compounds. The thermoelectric figures of merit of n-type conducting Mn0.85 Bi4.10 Te7 and Mn0.81 Bi6.13 Te10 reach zT = 0.25 at 375 °C and zT = 0.28 at 325 °C, respectively. Although the compounds are metastable, compact ingots exhibit still up to 80% of the main phases after thermoelectric measurements up to 400 °C.