Effects of Mn and microstructure on the electronic transport properties of insulating Al70.5Pd21(Re1-xMnx)8.5 (0≦x≦0.3) quasicrystals
碩士 === 國立成功大學 === 物理學系碩博士班 === 94 === After studying the relationship of the microstructure and the electric conductivity of insulating Al70.5Pd21(Re1-xMnx)8.5 quasicrystals (QCs), we found that both the variation of composition caused by sample preparation process and any secondary metallic phase i...
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| Format: | Others |
| Language: | zh-TW |
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2006
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| Online Access: | http://ndltd.ncl.edu.tw/handle/63364748872529448005 |
| Summary: | 碩士 === 國立成功大學 === 物理學系碩博士班 === 94 === After studying the relationship of the microstructure and the electric conductivity of insulating Al70.5Pd21(Re1-xMnx)8.5 quasicrystals (QCs), we found that both the variation of composition caused by sample preparation process and any secondary metallic phase in the sample might affect the determined resistivity ratio
R=R(4.2K)/R(300K),and the latter may also be the main factor which leads to the non-zero conductivity of insulating QC’s at T=0K. The electric conductivity and the magnetoresistance (MR) of insulating Al70.5Pd21(Re1-xMnx)8.5 QC’S with x = 0 and x = 0.1 at low temperatures were studied in detail. We found that the electric conduction at low temperatures in these two insulating QC’s was all via variable range hopping (VRH) processes); but from electric conductivity measurements only, one cannot ascertain whether the electrons transport follows Mott VRH or Efros-Shklovskii VRH (ES VRH) law at low temperatures. By analyzing the MR data combining the MR theories of the forward interference and the wave-function shrinkage, we clearly observed that there is a crossover from Mott VRH conduction to ES VRH conduction as the temperature is lowered; and the crossover temperature is higher in the sample doped with Mn. We also found that the reason that Rapp et al. did not observe the crossover conduction was due to ignoring the negative MR contribution in analyzing the positive MR data .
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