Size effects on superconductivity and crystal structure in tantalum nanoparticles

• Main Authors: andywen, 陳致文
• Other Authors: Yang-Yuan Chen
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/37169738255583323288

碩士 === 輔仁大學 === 物理學系 === 93 === Tantalum has a cubic structure(α-Ta) with a superconducting transition temperature Tc = 4.48 K. Employing the technique of excimer laser ablation, we can fabricate Ta nanoparticles. By changing the pressure of the inert gas in vacuum chamber of nanoparticles with different size can be obtained. By studying specific heat and magnetic susceptibility, the correlations of superconductivity and magnetism with the size of tantalum were reported. X-ray diffraction spectra show the coexistence of two structural phases α-Ta and β-Ta in nanoparticles. β-Ta has no superconductivity with tetragonal structure. It is also observed that the content of β-Ta increases with particle size decrease. A suppression of superconductivity is revealed in heat capacity and magnetic susceptibility as size decreases, the consequence could be associated with the appearance of β-Ta and/or the quantum size effects in Ta nanoparticles. In measurements of field dependent magnetization on Ta nanoparticles, a hysteresis loop is observed. The result is conjectured to be due to the surface oxidation or it is the intrinsic property of Ta nanoparticles with a nonmagnetic -magnetic transition, the aspect needs further study.