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

锂钴氧化物是目前锂离子二次电池的正极材料，人们期待具有更高充放电性能的正极材料。在本研究中，我们的目的是利用Fly-AIRS-Al Mloing(MM)方法来控制晶体结构的无序，从而对类非晶态锂化合物的结构变化和离子扩散有新的认识。在单离子跃迁过程的基础上，用Delve模型分析了球磨过程中锂钴氧化物的电阻率。结果表明，在MM法制备的锂钴氧化物中，适当的MM条件和较短的球磨时间促进了锂离子通过缺陷的扩散，而过多的MM条件和较长的球磨时间使锂离子的扩散变差，因为过量的MM导致大量的缺陷有效地切断了锂钴氧化物中锂离子的扩散路径，这表明7Li的核磁共振谱的线宽变成了…随着球磨时间的增加，Es越宽。MM过程改变了CoO_6八面体中钴的低自旋构型的磁性状态，从而使谱线展宽归因于MM诱导的钴的磁矩所致的磁宽度。另一方面，在MoM温度下，压电材料LiNbO_3和LiTaO_3球磨数小时后，表现出^7Li-核磁共振线宽的动态变窄。这意味着无序的晶体结构导致了离子在这些材料中的快速扩散。从分解谱的核磁共振谱分析可以看出，材料中的几个百分比的锂会以0.3 eV的活化能扩散，比未球磨的LiNbO_3的原始活化能1.6 eV低得多，由窄而宽的谱组成。用双脉冲声子回波技术测量了从室温到500K的温度范围内SiO_2颗粒中传播波的回波衰减时间T_2。T_2值与温度无关，因此SiO_2有可能成为测量颗粒与其他细粉样品接触时能量损失的标准材料。SiO_2颗粒的声子回波受细颗粒混合的强烈影响。在室温空气中，只有0.5mol%的LiNbO_3微粉抑制了声子回波强度，这是因为湿的微粉阻止了SiO_2颗粒的振动。在393K时，细粉脱水使SiO_2颗粒振动增强，声子回声强度增大。然而，即使在高温下，大量的混合细粉也抑制了声子回声强度，因此声子回声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。较少

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