Praseodymium induced symmetry switching and electrochemical characteristics of LaCoO3 nanostructures

IF 4.3 3区 材料科学 Q2 CHEMISTRY, MULTIDISCIPLINARY
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Abstract

A comparative study of the crystal structures and electrochemical characteristics of bulk and nanoscale La1-xPrxCoO3 (x = 0, 0.3 and 0.6) perovskites is made using synchrotron x-ray diffraction, cyclic voltammetry, and galvanostatic charge/discharge methods. It is shown that the sol-gel synthesized nano structures and bulk LaCoO3 exhibit different crystal structures, viz., rhombohedral [a = b = 5.4401 Å, c = 13.134 Å (on hexagonal axes), Z = 6, R 3 c] and monoclinic [am = 5.3865 Å, bm = 5.4482 Å, cm = 7.6365 Å, βm = 89.010°, Z = 4, I2/a], respectively. The evidence for CoO6 octahedra distortion in bulk LaCoO3 is also gathered from the three distinct Raman active modes at 518, 646, and 688 cm−1 emerging due to the Jahn-Teller effect, which, in-turn, reduces the crystal symmetry for achieving structure stabilization. This amounts to changes in Co–O bond lengths and Co–O–Co bond angles with promotion of t2g electron to eg level simultaneously for Co3+(3d6) to attain an intermediate spin state (S = 1) or higher. However, Pr-insertion induces phase transition to orthorhombic in both but with space group Pnma in nanostructures and equivalent Pbnm in bulk. The substitution effect on the specific capacitance (C) is opposite in nature, i.e., while ‘C’ decreases from 149 to 12 F/g in nano structures, it increases from 0.4 to 4 F/g in bulk with increase in Pr-content from x=0 to 0.6. A galvanostatic charge-discharge test of pristine nano LaCoO3 performed at a constant scan rate of 50 mVs−1 reveals electrode electrochemical stability by retaining 96 % of specific capacitance ∼82.5 F/g for 2000 cycles at least. The variation in the crystal structure and bond length and/or angle plays a key role in controlling the electrochemical performance of Pr-substituted LaCoO3 perovskites.
镨诱导的 LaCoO3 纳米结构的对称转换和电化学特性
利用同步辐射 X 射线衍射、循环伏安法和电静态充放电法,对块状和纳米级 La1-xPrxCoO3(x = 0、0.3 和 0.6)包晶石的晶体结构和电化学特性进行了比较研究。结果表明,溶胶-凝胶合成的纳米结构和块状 LaCoO3 呈现出不同的晶体结构,即、分别为斜方晶系[a = b = 5.4401 Å, c = 13.134 Å(六方轴), Z = 6, R 3‾ c]和单斜晶系[am = 5.3865 Å, bm = 5.4482 Å, cm = 7.6365 Å, βm = 89.010°, Z = 4, I2/a]。由于贾恩-泰勒效应(Jahn-Teller effect),在 518、646 和 688 cm-1 处出现了三种不同的拉曼活性模式,这也是块状 LaCoO3 中 CoO6 八面体变形的证据。这相当于改变了 Co-O 键长度和 Co-O-Co 键角度,同时将 t2g 电子提升到 eg 级,使 Co3+(3d6) 达到中间自旋态(S = 1)或更高。然而,Pr 的插入会诱导两者的相变,但在纳米结构中空间群为 Pnma,而在块体中则相当于 Pbnm。取代对比容(C)的影响是相反的,即在纳米结构中,"C "从 149 F/g 下降到 12 F/g,而在块体中,随着镨含量从 x=0 增加到 0.6,"C "从 0.4 F/g 增加到 4 F/g。在 50 mVs-1 的恒定扫描速率下对原始纳米 LaCoO3 进行的电静态充放电测试表明,电极的电化学稳定性很好,至少在 2000 次循环中保持了 96% 的比电容 ∼ 82.5 F/g。晶体结构、键长和/或角度的变化在控制镨取代的 LaCoO3 包晶石的电化学性能方面起着关键作用。
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来源期刊
Journal of Physics and Chemistry of Solids
Journal of Physics and Chemistry of Solids 工程技术-化学综合
CiteScore
7.80
自引率
2.50%
发文量
605
审稿时长
40 days
期刊介绍: The Journal of Physics and Chemistry of Solids is a well-established international medium for publication of archival research in condensed matter and materials sciences. Areas of interest broadly include experimental and theoretical research on electronic, magnetic, spectroscopic and structural properties as well as the statistical mechanics and thermodynamics of materials. The focus is on gaining physical and chemical insight into the properties and potential applications of condensed matter systems. Within the broad scope of the journal, beyond regular contributions, the editors have identified submissions in the following areas of physics and chemistry of solids to be of special current interest to the journal: Low-dimensional systems Exotic states of quantum electron matter including topological phases Energy conversion and storage Interfaces, nanoparticles and catalysts.
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