Intervalence charge transfer and electronic transport in molten salts containing tantalum and niobium complexes of mixed valency
Intervalence charge transfer and electronic transport in molten salts containing tantalum and niobium complexes of mixed valency
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DOI：
10.1039/a904648h
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发表时间：
1999
影响因子：
3.3
通讯作者：
U. Stöhr;W. Freyland
中科院分区：
文献类型：
--
作者：
U. Stöhr;W. Freyland
我们报告的测量电子电导率和部分的电子迁移率和光学吸收光谱在碱金属卤化物熔体中含有钽或铌的氯化物和氯氧化合物在不同的氧化态。电化学阻抗谱和Wagner-Hebb极化方法已在不同的氧化还原电位和温度高达1000 K。在所有体系中，电子电导率在平衡氧化还原电位附近都呈现近似抛物线的电位依赖关系，在Ta（IV）-Ta（V）平衡附近σe最大，为0.1 Ω-1cm-1，而在含铌体系中相应的氧化还原平衡值较低。阻抗和极化实验的结果在2倍内一致。在含钽熔体中的电子扩散系数已被确定从在极化实验中的电流瞬变和典型值的10-2 cm 2 s-1被发现在830 K与活化能约为0.7 eV的830 μ T/K的10 - 980。一个简单的两个网站的电子跳跃和价间电荷转移在这些熔体中的模型进行了讨论，定性地解释了所观察到的抛物线电位依赖的电子电导率和温度依赖性。
We report measurements of the electronic conductivity and partly the electronic mobility and optical absorption spectra in alkali halide melts containing tantalum or niobium chloride and oxychloride complexes in different oxidation states. Both electrochemical impedance spectroscopy and the Wagner–Hebb polarization method have been employed at various redox potentials and temperatures up to 1000 K. In all systems a nearly parabolic potential dependence of the electronic conductivity around the equilibrium redox potential is observed with a maximum of σe∽0.1 Ω-1 cm-1 near the Ta(IV)–Ta(V) equilibrium and lower values for the respective redox equilibria in the niobium containing systems. Results from impedance and polarization experiments agree within a factor of 2. The electronic diffusion coefficients in the tantalum containing melts have been determined from the current transients in the polarization experiments and typical values of ∽10-2 cm2 s-1 are found at 830 K with an activation energy of about 0.7 eV for 830⩽T/K⩽980. A simple two site model for electron hopping and intervalence charge transfer in these melts is discussed which qualitatively explains the observed parabolic potential dependence of the electronic conductivity and its temperature dependence.