Layered Manganese Bismuth Tellurides with GeBi4Te7– and GeBi6Te10–type Structures: Towards Multifunctional Materials

Abstract

<p>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<i>P</i>-GeBi4Te7 (space group <i>P</i>3<i>m</i>1) and 51<i>R</i>-GeBi6Te10 (space group <i>R</i>3<i>m</i>) structure types they adopt. Modified compositions Mn1–<i>x</i>Bi4+2<i>x</i>/3Te7 (<i>x </i>= 0.15 – 0.2) and Mn1–<i>x</i>Bi6+2<i>x</i>/3Te10 (<i>x </i>= 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 [M2Te3] and septuple-layer [M3Te4] slabs (M = mixed occupied by Bi and Mn) with 1:1 sequence (12<i>P </i>stacking) in Mn0.85Bi4.10Te7 and 2:1 sequence (51<i>R </i>stacking) in Mn0.81Bi6.13Te10 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 MnII oxidation state and point at predominantly ferromagnetic coupling in both compounds. The thermoelectric figures of merit of n-type conducting Mn0.85Bi4.10Te7 and Mn0.81Bi6.13Te10 reach <i>zT </i>= 0.25 at 375 °C and <i>zT </i>= 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.</p>

Hybridization-induced gapped and gapless states on the surface of magnetic topological insulators

“…In fact, MnBi2Te4 belongs to the ternary van der Waals compound series (MnBi2Te4)m(Bi2Te3)n with [Te-Bi-Te-Mn-Te-Bi-Te] septuple (S) layers ([MnBi2Te4], SLs) and [Te-Bi-Te-Bi-Te] quintuple (Q) layers ([Bi2Te3], QLs) alternately stacking along the c axis [45,46]. While MnBi2Te4 has been extensively studied recently , its sister compounds with higher n number such as MnBi4Te7 (n = 1) and MnBi6Te10 (n = 2), remain less explored [47][48][49][50][51][52][53][54][55][56][57][58].…”

Tuning Fermi Levels in Intrinsic Antiferromagnetic Topological Insulators MnBi2Te4 and MnBi4Te7 by Defect Engineering and Chemical Doping

“…The Mn deficiencies were estimated to be 15%-20% in MnBi4Te7 and 19%-25% in MnBi6Te10. [14,21,30] Such high defect densities not only affect the Fermi level but could also influence the magnetic and topological properties. For example, a high density of magnetic defects may affect the surface magnetism and the opening of the surface energy gap.…”

Magnetic field tuning of the spin dynamics in the magnetic topological insulators (MnBi$_{2}$Te$_{4}$)(Bi$_{2}$Te$_{3}$)$_{n}$

“…the crystallographic c axis and held together by weak van der Waals forces [13,14]. In MnBi 4 Te 7 , the magnetic SLs are separated from each other by additional nonmagnetic QLs forming a joint SL-QL-SL-QL-SL... stack [11,[15][16][17].…”