【作者】 崔岩；

【导师】 高春晓；

【作者基本信息】 吉林大学 ， 凝聚态物理， 2024， 硕士

【摘要】 偏钒酸盐,AVO₃（A=K,Rb,Cs）是一种被广泛应用于发光、催化、能源等领域的多功能材料,而电学性质是决定其性能的重要因素之一。通过对晶体中原子间距离施加压力,可以微调其结构和特性,并且能够触发在一般气压下无法显现的效应。在本论文中,我们选定KVO₃为研究对象,利用阻抗谱分析和拉曼光谱技术,并配合第一性原理的计算,对高压环境下KVO₃的电子迁移以及结构进行深度研究。旨在挖掘压强对导电特性的作用和导电机制与结构之间的内在关系,期望可以观察到KVO₃全新的电子迁移行为。通过研究,得到如下结论:（1）正交相碱金属钒酸盐具有12个拉曼活性模式(Γ=2A_1g+4B_1g+B_2g+5E_g)。在常压下,我们能观察到其中的9个拉曼峰。随着压强的升高,拉曼峰发生蓝移。与其它具有钒酸盐结构的稀土化合物类似,KVO₃的拉曼光谱在500-800cm^-1区间内表现出明显的频率间隙,通常可以分为低频和高频两个区域,其中高频区主要归属于VO₄四面体的内部振动,而低频区域则与四面体的弯曲振动模式有关。当压强增加到3.5 GPa时,拉曼光谱出现了一些新峰,在75 cm^-1的拉曼峰发生劈裂,可以说明KVO₃开始由正交相变为单斜相。随着压强的持续增加,原有的正交相特征拉曼峰强度减弱,继续增加压强到9.3 GPa时,正交相的拉曼峰已经基本消失,表明单斜相成为主导。（2）通过第一性原理计算,得到了KVO₃在高压下的能带结构、态密度和电子局域函数。计算结果表明KVO₃为直接带隙半导体。在0-4.0 GPa范围内,带隙随压强的增加而增大。对于价带来说O原子起主导作用,而对于导带来说则V原子起主要作用,V-O原子间距离会对相对介电常数产生一定的影响。（3）通过高压原位交流阻抗谱的测量,发现在0-15.0 GPa范围内,KVO₃表现出离子传导行为;当压强高于15.0 GPa时,表现为纯电子导电行为。离子导电变为电子导电,电导率开始急剧增加,驰豫频率的变化规律与电导率基本一致,说明电导率的变化主要受载流子迁移速率的影响。其介电特性表现在结构相变的压强点发生了不连续变化。通过KVO₃的总电阻、晶粒电阻、晶界电阻可知,当压强处于2.5-5.0 GPa时,总电阻急剧上升,晶界电阻比晶粒电阻大2-3个数量级,所以晶界电阻在输运过程中占主导。当压强小于5.0 GPa时,KVO₃的相对介电常数ε_r在Pbcm相中随压强增大而增大,这意味着极化得到加强。更多还原

【Abstract】 Metavanadates,AVO₃（A=K,Rb,Cs）,are multifunctional materials widely used in luminescence,catalysis,and energy sectors with electrical properties being one of the key determinants of their performance.By exerting pressure on the interatomic distances in the crystal,it’s possible to finely adjust their structure and properties,and trigger effects that could not be revealed under normal pressure.In this paper,we have selected KVO₃ as our research subject and using impedance spectroscopy and Raman spectroscopy techniques,in conjunction with first-principles calculations,we have conducted an in-depth study on the electron migration and structure of KVO₃ under high-pressure conditions.The aim is to explore the role of pressure on the conductive properties and the intrinsic relationship between the conduction mechanism and structure,with an expectation for observing a novel electron migration behavior in KVO₃.Through our research,we arrived at the following conclusions:（1）The alkali metal vanadate perovskites possess 12 Raman active modes(Γ=2A_1g+4B_1g+B_2g+5E_g).Under normal pressure,we can observe nine Raman peaks which shifted blue with increased pressure.Much like other lanthanide compounds with similar vanadate structure,KVO₃’s Raman spectra display significant frequency gaps in the 500-800 cm^-1range,which can typically be divided into low-frequency and high-frequency areas.The high-frequency area is mainly attributed to the internal vibrations of the VO₄ tetrahedron,while the low-frequency area is related to the bending vibration modes of the tetrahedron.With the pressure increase to 3.5 GPa,new peaks appeared in the Raman spectra and the Raman peak at 75 cm^-1split,exemplifying KVO₃’s orthorhombic to monoclinic phase change.As pressure continued to increase,the original olivine phase feature Raman peak intensity weakened,and by 9.3 GPa,the olivine phase Raman peaks had virtually disappeared,indicating monoclinic phase dominance.（2）Through first-principles calculations,we obtained the band structure,density of states,and electron localization function of KVO₃ under high pressure.The results revealed KVO₃ as a direct bandgap semiconductor-within the 0-4.0 GPa range,the bandgap increased with increasing pressure.O atoms play a dominant role for the valence band,and the V atoms play a substantial role for the conduction band-the distance between the V-O atoms can have certain impacts on the relative permittivity.（3）In-situ AC impedance spectroscopy measurements showed ionic conductive behavior for KVO₃ in the 0-15.0 GPa pressure range;when the pressure exceeded 15.0GPa,it exhibited purely electronic conductive behavior.The transition from ionic to electronic conduction caused a sharp increase in conductivity.Relaxation frequency changes were consistent with conductivity changes,implying that the variation in conductivity was mainly affected by carrier migration rates.Its dielectric characteristic exhibited discontinuous changes at the structural phase transition pressure point.Total resistance,grain resistance,and grain boundary resistance of KVO₃ showed that total resistance sharply increased when the pressure was between 2.5-5.0 GPa.The grain boundary resistance was 2-3 orders of magnitude greater than the grain resistance so grain boundary resistance dominated during transmission.When the pressure was less than 5.0 GPa,the relative permittivityε_r of KVO₃ increased with the increasing pressure in the Pbcm phase,suggesting intensified polarization.更多还原