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Manganese Tetraboride, MnB 4 : High‐Temperature Crystal Structure, p–n Transition, 55 Mn NMR Spectroscopy, Solid Solutions, and Mechanical Properties
Author(s) -
Knappschneider Arno,
Litterscheid Christian,
Brgoch Jakoah,
George Nathan C.,
Henke Sebastian,
Cheetham Anthony K.,
Hu Jerry G.,
Seshadri Ram,
Albert Barbara
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201406631
Subject(s) - monoclinic crystal system , orthorhombic crystal system , crystallography , materials science , crystal structure , manganese , nanoindentation , seebeck coefficient , analytical chemistry (journal) , chemistry , thermal conductivity , metallurgy , composite material , chromatography
The structural and electronic properties of MnB 4 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 P 2 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 B 4 (two phases in space groups Pnnm and P 2 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.