Physical properties of the ternary borides Ni21Zn2B20 and Ni3ZnB2

JOURNAL OF ALLOYS AND COMPOUNDS

卷:550

Article

Malik, Z.¹  Grytsiv, A.¹  Michor, H.²  Rogl, G.¹  Puchegger, S.³  Mueller, H.²  Kriegisch, M.²  Bauer, E.²  Eisenmenger-Sittner, C.²  Rogl, P.¹ 

[1] Univ Vienna, Inst Phys Chem, A-1090 Vienna, Austria

[2] Vienna Univ Technol, Inst Solid State Phys, A-1040 Vienna, Austria

[3] Univ Vienna, Ctr Nanostruct Res, A-1090 Vienna, Austria

关键词: Ni21Zn2B20;    Ni3ZnB2;    Mechanical properties;    Magnetic properties;    Electrical properties;   

DOI  :  10.1016/j.jallcom.2012.09.122

来源: Elsevier

【 摘 要 】

Mechanical, electrical and magnetic properties have been determined for the compounds Ni21Zn2B20 and Ni3ZnB2, which reveal a different boron-boron aggregation and bonding due to their different boron/metal ratio. Resonant Ultrasound Spectroscopy (RUS) measurements show significantly higher elastic moduli for Ni21Zn2B20 (E = 264 GPa) with a unique cluster of a cage of 20 B-atoms nesting a Ni-metal octahedron than for Ni3ZnB2 (E = 223 GPa), which contains covalently bonded B-B chain fragments consisting of 4 B-atoms. Similarly Vickers hardness (for a load of 200 ponds) is higher for Ni21Zn2B2 (HV = 6.87 GPa) than for Ni3ZnB2 (HV = 4.99 GPa). The higher boron/metal ratio for Ni21Zn2B20 is reflected in a smaller thermal expansion coefficient alpha = 8 x 10 x 10(-6) K-1 with respect to Ni3ZnB2 with alpha = 10.4 x 10(-6) K-1 (both determined for the range 150-250 K). At elevated temperatures, the specific heat C-p of both compounds, Ni21Zn2B20 and Ni3ZnB2, is clearly dominated by the lattice contribution. Analyses of C-p in terms of Debye and Einstein models indicate that the boron related high energy Einstein modes display at similar energies with spectral weights being in clear correspondence with their boron stoichiometries. Temperature dependent magnetization measurements reveal a paramagnetic behavior for both borides suggesting almost filled 3d states of Ni by contributions from B and Zn valence electrons. Electrical resistivities attest a dominant metallic behavior for both Ni21Zn2B20 and Ni3ZnB2 yielding negative Seebeck coefficients (electrons as the majority charge carriers) in the range of a few mu V/K. (C) 2012 Elsevier B.V. All rights reserved.

【 授权许可】

Free