Effects of S-doping on the lattice thermal expansion and magnetoresistive characteristics of BiOCuSe
| Autor: | Shih-Bin Liu, 劉仕彬 |
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| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 This article reports on the observations of lattice thermal expansion, magnetoresistive characteristics, and magnetic properties in layered oxychalcogenide BiOCuSe1-xSx powder, through the x-ray diffraction, electric transport, ac magnetic susceptibility, and magnetization measurements. In those powder compounds, crystallizes still into a tetragonal P4/nmm symmetry, but the lattice constants will be suppressed by substituting the sulfur for selenium in BiOCuSe. An alterable lattice thermal expansion is achieved mainly by tuning the sulfur doping level, and this exceptional small thermal expansion will be detected when x = 0.1. Partially electronic charge transfer between (Bi2O2)2+ and (Cu2Se2)2- layers will produce the minimal thermal expansion at this special sulfur composition. The temperature dependences of resistivity R can be described by the 3D variable range hopping conduction, except the data of x = 0.3 sample. A vicissitude of magnetoresistance (MR) can be observed from positive to negative by altering the sulfur composition, and there is significant relation with the variability of electron distribution near Cu and O ions. R(T) and MR(T) curves both can be classified into two types with the sulfur composition. This borderline between the two regions is at 30 %. We suppose this phenomenon can conjunction with the S-doping effect of conduction band and valence band. The changed energy gap leads to the variation of transport and magnetoresistive characteristics. No apparent magnetism is observed of BiOCuSe1-xSx samples. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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