期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 21, 期 22, 页码 8177-8181出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201406631
关键词
boron; chromium; manganese; phase transitions; solid solutions
资金
- ConvEne IGERT Program of the National Science Foundation [DGE 0801627]
- MRSEC Program of the NSF [DMR 1121053]
- California Nanosystems Institute (NSF) [CNS-0960316]
- Hewlett-Packard
- MRL
- Feodor Lynen Fellowship
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 650K. The material remained semiconducting after the transition, but its behavior changed from p-type to n-type. Mn-55 NMR measurements revealed an isotropic chemical shift of -1315ppm, confirming an oxidation state of Mn close to I. Solid solutions of Cr1-xMnxB4 (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 37GPa obtained by DFT calculations.
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