Study on disordered structure and ionic diffusion in amorphous solids with non linear ultrasonic resonance

迄今为止，锂钴氧化物已被用作锂离子可再充电电池的阴极材料，并且期望有具有更高充电/放电性能的先进阴极材料。在这项研究中，我们的目的是获得新的见解的结构变化和离子扩散的非晶态类锂化合物，通过使用飞-AIRS-Al铣削（MM）方法来控制晶体结构的无序。基于单离子跳跃过程，用Delve模型分析了球磨钴酸锂的电阻率。结果表明，在MM法制备的钴酸锂中，中等的MM条件和较短的球磨时间有利于锂离子通过缺陷的扩散，而过量球磨条件下球磨时间过长会导致锂离子的扩散，因为过量球磨会导致大量的缺陷有效地切断了锂离子在钴酸锂中迁移的扩散通道，使^7Li NMR谱的谱线宽度减小， ...更多信息 随着研磨时间的增加而变宽。MM过程改变了CoO_6八面体中钴的低自旋磁态，从而使谱线展宽归因于MM引起的钴的T磁矩引起的磁宽。另一方面，球磨数小时的压电材料LiNbO_3和LiTaO_3在室温下表现出^7 Li-NMR谱线的动态变窄。这意味着无序的晶体结构在这些材料中引起快速的离子扩散。分解谱分析表明，材料中有百分之几的锂发生了扩散，其扩散激活能为0.3eV，远低于未球磨LiNbO_3的原始扩散激活能1.6eV，由窄谱和宽谱组成。用双脉冲声子回波技术测量了从室温到500 K温度范围内SiO_2粒子中传播波的T_2。T_2值与温度无关，因此SiO_2可以作为一种标准物质来检测颗粒与其它细粉样品接触时的能量损失。SiO_2粒子的声子回波受细粒子混合的强烈影响。在室温空气中，LiNbO_3细粉的加入量仅为0.5mol%时，由于湿的LiNbO_3细粉阻止了SiO_2颗粒的振动，从而抑制了声子回波强度。细粉在393 K下脱水使SiO_2颗粒振动更好，声子回波强度增加。然而，大量的混合细粉末即使在高温下也抑制了声子回波强度，使得声子回波的消失不仅仅取决于湿度。进一步的研究将计划研究混合粒子系统中声子回波消失的原因。少

lithium cobalt oxide has been used as a cathode material of lithium ionic rechargeable battery so far and advanced cathode material with higher charge/discharge properties has been expected. In this study, our aim is to obtain new insights into structural change and ionic diffusion in amorphous like lithium compounds by using fly-AIRS-Al milling (MM) method to control disorder of crystal structure. Electrical resistivity of milled lithium cobalt oxide is analyzed by a Delve model on the basis of a single ion hopping process The results indicate that in lithium cobalt oxide prepared by MM the moderate MM condition with short milling time stimulates the lithium ionic diffusion through the defects, while the excessive MM condition with long milling time degrades the lithium ionic diffusion becalm a large number of defects induced by excessive MM effectively cut off diffusion path fir migrating lithium ions In lithium cobalt oxide, it hind that the NMR line width of ^7Li NMR spectrum becom … More es broader with increasing milling time. The MM process changes magnetic state of cobalt which is primitively a low spin configuration in the CoO_6 octahedron so that the line broadening is ascribed to the magnetic width due to tee magnetic moment of cobalt induced by MM.On the other hand, piezoelectric material LiNbO_3 and LiTaO_3 milled fir several hours show the motional narrowing of ^7Li-NMR line width at mom temperature. This means that disordered crystal structure induces a fast ionic diffusion in these materials. From the NMR spectrum analysis by decomposing spectrum, it hind that several percent of lithium in the materials would diffuse with much lower activation energy of 0.3 eV than primitive activation energy of 1.6 eV in non-milled LiNbO_3 from the analysis by decomposing NMR spectrum, consisting of a narrow and broad spectrum.Echo decay time, T_2 of propagating wave in a SiO_2 particle was measured over the temperature range from room temperature to 500 K by two-pulse phonon echo technique. The values of T_2 are temperature independent so that SiO_2 might be a standard material to detect energy loss out of particles contacting other fine powder samples. Phonon echo of SiO_2 particles is strongly affected by mixing fine particles. Only 0.5 mol% of LiNbO_3 fine powder suppresses phonon echo intensity at room temperature in the air, because the wet fine powder prevent from vibration of SiO_2 particles. Phonon echo intensity increases due to dehydrating fine powder at 393K because it makes vibration of SiO_2 particles better. However, a large amount of mixed fine powder has suppressed phonon echo intensity even at high temperatures so that disappearance of phonon echo does not depend only on humidity. A further study will plan to study an origin of disappearance of phonon echo in mixed particle system. Less