Low-dimensional lithium ion conductors

低维锂离子导体

• 批准号: 166864354
• 负责人: Professor Dr. Paul Heitjans
• 金额: --
• 依托单位: Arbeitsgruppe Anorganische Chemie/ Festkörperchemie
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2016-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/166864354?language=en
• 关键词: Low; dimensional; lithium; ion; conductors

The project is concerned with the study how Li diffusion is influenced by dimensionality effects. The investigations are to be performed on selected single-crystalline and polycrystalline materials which feature structurally confined diffusion pathways. To this end NMR techniques will be employed which are sensitive to both the mobility of the Li ions and the dimensionality of the diffusion process.One and two dimensional diffusion can be distinguished by means of temperature dependent and frequency dependent 6,7Li NMR spin-lattice relaxation (SLR) measurements. Both 1D and 2D lithium-ion conductors show a characteristic asymmetry of the diffusion-induced SLR NMR rate peak. Furthermore, the rates reveal a characteristic dependence on the Larmor frequency ω0 in the so-called high temperature limit where the mean jump rate 1/τ is much larger than ω0. Typically, at common magnetic field strengths, the frequency ω0/2π(7Li) ranges from 10 to 300 MHz. In the case of 1D diffusion appropriate relaxation models predict a square root dependence of the rate on ω0 and a logarithmic dependence in the case of 2D diffusion. Analogously, the same holds true for SLR measurements performed in the rotating frame of reference where the Larmor frequency is replaced by the locking frequency ω1 being of the order of several kHz. In this case jump processes are covered which are 1000 times slower than those usually probed in the laboratory frame of reference. Even lower jump rates are directly accessible by NMR spin-alignment echo (SAE) measurements which do not require a model to convert decay rates into Li jump rates. The SAE NMR technique is per se sensitive to the geometry of the elementary jump process, and thus to its dimensionality.Besides NMR techniques, for which polycrystalline materials are sufficient, macroscopic methods can be employed in the case of single crystalline samples. Here, the dimensionality of the transport process is reflected by the anisotropy of the mass or charge transport. Macroscopic techniques include impedance spectroscopy, mass tracer measurements and field gradient NMR spectroscopy.

该项目关注的是维度效应如何影响Li扩散的研究。调查将在选定的单晶和多晶材料上进行，这些材料具有结构限制的扩散途径。为了达到这个目的，我们采用了对Li离子的迁移率和扩散过程的维数都很敏感的NMR技术，通过依赖于温度和频率的6，7 Li NMR自旋晶格弛豫（SLR）测量可以区分一维和二维扩散。1D和2D锂离子导体都显示出扩散诱导的SLR NMR速率峰的特征不对称性。此外，速率揭示了在所谓的高温极限中对拉莫尔频率ω0的特征依赖性，其中平均跳跃速率1/τ远大于ω0。通常，在普通磁场强度下，频率ω0/2π（7 Li）的范围为10至300 MHz。在1D扩散的情况下，适当的弛豫模型预测速率对ω0的平方根依赖性和在2D扩散的情况下的对数依赖性。类似地，这同样适用于在旋转参考系中执行的SLR测量，其中拉莫尔频率由几kHz量级的锁定频率ω1代替。在这种情况下，跳跃过程是1000倍，比通常在实验室的参考系探测慢。甚至更低的跳跃率可以通过NMR自旋对准回波（SAE）测量直接获得，其不需要模型来将衰变率转换为Li跳跃率。SAE NMR技术本身对基元跳跃过程的几何形状敏感，因此对它的维数敏感。除了NMR技术，多晶材料就足够了，宏观方法也可以用于单晶样品。在这里，传输过程的维度由质量或电荷传输的各向异性反映。宏观技术包括阻抗谱、质量示踪剂测量和场梯度NMR谱。