title: Manganese Tetraboride, MnB4: High-Temperature Crystal Structure, p-n Transition, (55)Mn NMR Spectroscopy, Solid Solutions, and Mechanical Properties.
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 P2(1)/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. (55)Mn NMR measurements revealed an isotropic chemical shift of -1315 ppm, confirming an oxidation state of Mn close to I. Solid solutions of Cr(1-x)Mn(x)B4 (two phases in space groups Pnnm and P2(1)/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.
authors.affiliation: Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Technische Universität Darmstadt, Alarich-Weiss-Strasse 12, 64287 Darmstadt (Germany).
authors.forename: Arno
authors.initials: A
authors.lastname: Knappschneider
authors.affiliation: Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Technische Universität Darmstadt, Alarich-Weiss-Strasse 12, 64287 Darmstadt (Germany).|present address: Chemische Fabrik Budenheim KG, Rheinstrasse 27, 55257 Budenheim (Germany).
authors.forename: Christian
authors.initials: C
authors.lastname: Litterscheid
authors.affiliation: Materials Department and Materials Research Laboratory, University of California Santa Barbara, Santa Barbara CA 93106 (USA).
authors.forename: Jakoah
authors.initials: J
authors.lastname: Brgoch
authors.affiliation: Materials Department and Materials Research Laboratory, University of California Santa Barbara, Santa Barbara CA 93106 (USA).
authors.forename: Nathan C
authors.initials: NC
authors.lastname: George
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS (UK).
authors.forename: Sebastian
authors.initials: S
authors.lastname: Henke
authors.affiliation: Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS (UK).
authors.forename: Anthony K
authors.initials: AK
authors.lastname: Cheetham
authors.affiliation: Materials Department and Materials Research Laboratory, University of California Santa Barbara, Santa Barbara CA 93106 (USA).
authors.forename: Jerry G
authors.initials: JG
authors.lastname: Hu
authors.affiliation: Materials Department and Materials Research Laboratory, University of California Santa Barbara, Santa Barbara CA 93106 (USA).
authors.forename: Ram
authors.initials: R
authors.lastname: Seshadri
authors.affiliation: Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Technische Universität Darmstadt, Alarich-Weiss-Strasse 12, 64287 Darmstadt (Germany). albert@ac.chemie.tu-darmstadt.de.
authors.forename: Barbara
authors.initials: B
authors.lastname: Albert
keywords: boron; chromium; manganese; phase transitions; solid solutions