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

目前，钴酸锂作为锂离子可充电电池的正极材料已得到广泛应用，具有更高充放电性能的新型正极材料已成为人们的期待。在本研究中，我们的目的是通过fly-AIRS-Al milling （MM）方法来控制晶体结构的无序性，从而获得非晶类锂化合物结构变化和离子扩散的新见解。基于单离子跳变过程，采用Delve模型对磨矿钴酸锂的电阻率进行了分析。结果表明，在MM法制备的钴酸锂中，适度的MM条件和较短的磨矿时间促进了锂离子通过缺陷的扩散；长磨矿时间下过量的MM条件会降低锂离子的扩散速率，过量MM引起的大量缺陷有效地切断了迁移锂离子在钴酸锂中的扩散路径，并且随着磨矿时间的增加，^7Li核磁共振谱的谱线宽度变得更宽。MM过程改变了钴在CoO_6八面体中的原始低自旋结构的磁态，使谱线的增宽归因于MM引起的钴的三通磁矩引起的磁宽。另一方面，经过几小时研磨的压电材料LiNbO_3和LiTaO_3在一定温度下表现出^7Li-NMR谱线宽度的动态变窄。这意味着无序的晶体结构在这些材料中引起了快速的离子扩散。从分解谱分析可知，材料中有百分之几的锂会扩散，其活化能为0.3 eV，远低于未研磨LiNbO_3的原始活化能1.6 eV，由窄谱和广谱组成。用双脉冲声子回波技术测量了SiO_2粒子在室温至500k范围内传播波的回波衰减时间T_2。T_2的值与温度无关，因此SiO_2可以作为检测颗粒接触其他细粉样品的能量损失的标准材料。SiO_2粒子的声子回波受细粒子混合的强烈影响。仅0.5 mol%的LiNbO_3细粉就能抑制室温下空气中的声子回波强度，这是由于湿的LiNbO_3细粉阻止了SiO_2颗粒的振动。细粉在393K时脱水使SiO_2颗粒的振动性增强，声子回波强度增大。然而，即使在高温下，大量混合的细粉也会抑制声子回波强度，因此声子回波的消失并不仅仅取决于湿度。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