Non-stoichiometry is the key to single-phase layered compounds in the system Mn/Bi/Te, which is essential to evaluate their multifunctional properties.
During the production
of molybdenum, the first reduction step of
molybdenum trioxide to molybdenum dioxide is crucial in directing
important product properties like particle size and oxygen content.
In this study, the influence of heating rate, hydrogen flow, and potassium
content on the reduction of MoO3 has been investigated via
in situ X-ray powder diffraction. For
low heating rates, a molybdenum bronze H
x
MoO3 could be confirmed as an intermediate, while γ-Mo4O11 can only be observed at high heating rates.
Molybdenum formation at temperatures as low as 873 K can be controlled via hydrogen flow. The potassium content of reactants has
a direct influence on the amount of Mo4O11 formed
during the reaction as well as rates of Mo4O11 and MoO2 formation.
<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>
Two new mixed nickel-gallium chalcogenides, Ni9.39Ga2S2, Ni5.80GaTe2, and a new mixed nickel-indium telluride, Ni5.78InTe2, have been synthesized by a high-temperature ampoule route with an addition of iodine, and characterized from...
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