Study on Electrical Conductivity and Hall Effect Spectra in a Non-Cuprate High-Tc Superconductive Oxide

本文研究了高温超导相非铜酸盐超导氧化物Ba1-xKxBiO3的半导体-超导体转变机制、电导、电子态和电子结构。本论文的研究内容包括：(1)单晶的合成与表征；(2)电导、霍尔效应、光学光谱、磁学性质、光电导和磁场效应等方面的研究。1.通过改变覆盖熔体的气氛中水蒸气的量，采用成分(X)控制的电化学方法合成了从半导体相到超导相的宽组成范围内几乎没有缺钾的Ba1-xKxBiO3单晶。通过在晶体生长过程中采用这种x控制技术，我们将研究扩展到成功地制备了全部由Ba1-xKxBiO_3组成的隧道结构。2.从…通过对超导体Ba1-xKxBiO3(x=0.42)中霍尔效应的详细分析，阐明了电子的光学声子散射在电导机制中的重要性。首次在半导体相(x&lt；0.3)中研究了霍尔效应的温度依赖性。对于0*x*0.19，观察到了正空穴密度的活化型行为。结果表明，正孔的质量非常大。当x=0.19时，在200K以上观察到明显的电子对电导的贡献。首次在半导体Ba1-xKxBiO3中观察到光导信号。为了更详细地研究这一现象，进一步的研究正在进行中。通过对已报道的声子谱和XPS实验结果的离子有效电荷的分析，观察到BaBiO_3的共价性比能带计算所预期的要大得多。因此，我们再次肯定了BaBiO_3的半导性和相关超导体的半导性相的解释，而不是3D-CDW形成的由Bi(6S)-O(2p)组成的宽带的分裂。较少

The present study was performed with the aim of investigating the mechanisms of semiconductor-superconductor transition and electrical conductivity, electronic state and electronic structure in a non-cuprate superconductive oxide Ba_1-xKxBiO_3 with high-Tc (Tc_<max>=32K) in the superconducting phase. The study includes (1) synthesis and characterization of single crystals and (2) studies of electrical conductivity, Hall effect, optical spectroscopy, magnetic property and photoconductivity and the magnetic field effect.1.Single crystals of Ba_1-xKxBiO_3 with little potassium deficiency in wide composition range covering from semiconductive to superconducting phases were synthesized by an electrochemical method with a composition (x) control technique by changing the amount of water vapor in atmosphere covering melt. We extended our studies to the successful fabrication of tunnel structure all composed of Ba_1-xKxBiO_3 by adopting this x control technique during the crystal growth.2.From … More the detailed analysis of the Hall effect in superconductive Ba_1-xKxBiO_3 (x=0.42), we clarified the importance of optical phonon scattering of electrons in the mechanism of conductivity. Temperature dependence of the Hall effect has been for the first time studied in the semiconductive phase (x<0.3). Activation type behavior of positive hole density was observed for 0*x*0.19. It was found that mass of positive hole is extremely heavy. For x=0.19, the contribution of electrons to conductivity is clearly observed above 200K.Photoconductive signal has been observed for the first time in semiconductive Ba_1-xKxBiO_3. In order to investigate the phenomenon in details, further research is on progress. By analyzing effective charges of ions from the previously reported experimental results of phonon spectrum and XPS,a much more covalent character of BaBiO_3 than expected by the band calculation has been observed. Thus, we reconfirmed that semiconductive nature of BaBiO_3 and semiconductive phase of related superconductors should be explained without the scenario of split-off by 3D-CDW formation of the wide band composed of Bi (6s) -O (2p). Less