Manganese Tetraboride,MnB4: High‐Temperature Crystal Structure,p–n Transition, 55Mn NMR Spectroscopy,Solid Solutions,and Mechanical Properties |
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| Authors: | Dr Arno Knappschneider Dr Christian Litterscheid Dr Jakoah Brgoch Dr Nathan C George Dr Sebastian Henke Prof Anthony K Cheetham Dr Jerry G Hu Prof Ram Seshadri Prof?Dr Barbara Albert |
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| Institution: | 1. Eduard‐Zintl‐Institute of Inorganic and Physical Chemistry, Technische Universit?t Darmstadt, Alarich‐Weiss‐Strasse 12, 64287 Darmstadt (Germany);2. present address: Chemische Fabrik Budenheim KG, Rheinstrasse 27, 55257 Budenheim (Germany);3. Materials Department and Materials Research Laboratory, University of California Santa Barbara, Santa Barbara CA 93106 (USA);4. Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3?0FS (UK) |
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| Abstract: | The structural and electronic properties of MnB4 were studied by high‐temperature powder X‐ray diffraction and measurements of the conductivity and Seebeck coefficient on spark‐plasma‐sintered samples. A transition from the room‐temperature monoclinic structure (space group P21/c) to a high‐temperature orthorhombic structure (space group Pnnm) was observed at about 650 K. The material remained semiconducting after the transition, but its behavior changed from p‐type to n‐type. 55Mn NMR measurements revealed an isotropic chemical shift of ?1315 ppm, confirming an oxidation state of Mn close to I. Solid solutions of Cr1?xMnxB4 (two phases in space groups Pnnm and P21/c) were synthesized for the first time. In addition, nanoindentation studies yielded values of (496±26) and (25.3±1.7) GPa for the Young’s modulus and hardness, respectively, compared to values of 530 and 37 GPa obtained by DFT calculations. |
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| Keywords: | boron chromium manganese phase transitions solid solutions |
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