弛豫铁电体弥散相变与热滞效应的伊辛模型  

Diffuse phase transition and thermal hysteresis in relaxor ferroelectrics from modified Ising model

作　　者：黄建邦 南虎 张锋[1] 张佳乐 刘来君[2] 王大威[1] Huang Jian-Bang;Nan Hu;Zhang Feng;Zhang Jia-Le;Liu Lai-Jun;Wang Da-Wei(School of Microelectronics,Faculty of Electronics and Information Engineering,Xi’an Jiaotong University,Xi’an 710049,China;Key Laboratory of New Processing Technology for Nonferrous Metals and Materials,Ministry of Education,Guangxi Key Laboratory of Optical and Electronic Materials and Devices,College of Materials Science and Engineering,Guilin University of Technology,Guilin 541004,China)

机构地区：[1]西安交通大学电子与信息学部微电子学院,西安710049 [2]桂林理工大学,有色金属及材料加工新技术教育部重点实验室,广西光电材料与器件重点实验室,桂林541004

出　　处：《物理学报》2021年第11期16-25,共10页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11974268,11574246);广西自然科学基金(批准号:AA138162,AA294014,GA245006)资助的课题。

摘　　要：弛豫铁电体材料在通讯、传感、超声、能量转换、航空航天等领域具有重要的应用.与正常铁电体不同,弛豫铁电体在冷却过程中出现弥散相变,体系的宏观极化不会突然产生,而是出现纳米极性微区,体系的宏观晶体对称性没有明显的变化.如何理解弥散相变及其与内部机制之间的相互影响是一个重要的问题.本研究基于伊辛模型(Ising model),对自旋变量(在研究中视为电偶极子)引入能量势阱的作用,并计算了这一系统的相变过程.结果表明这一改进的伊辛模型使极化率的相变曲线显著变缓,呈现出具有弥散相变的弛豫体特性.研究显示,弛豫体现象出现的一个重要原因是系统内部偶极子受到势阱限制而出现反转受阻,从而使极化率偏离常规铁电体.利用这一改进的伊辛模型进一步研究了弛豫铁电体的热滞效应,分析了热滞的起源,并与实验结果进行了对比分析,明确了弛豫体弥散相变和热滞的物理机制.Relaxor ferroelectric is a very special type of ferroelectric material,which has important applications in communication,sensor,ultrasound,energy conversion,and aerospace industry.Unlike normal ferroelectric,a relaxor undergoes a diffuse phase transition in the cooling process,and its macroscopic polarization does not occur suddenly,but polar nano region appears while the macro-symmetry does not change significantly.As the transition from the paraelecric to the ferroelectric phase is a gradual process with a broad dielectric peak,relaxor ferroelectric has no definite Curie temperature(TC),and the temperature corresponding to the maximum dielectric constant(Tm)and the Burns temperature(TB)are often used as their characteristic temperatures.Here,in order to understand the diffuse phase transition and its internal mechanism,we build a modified Ising model by introducing an energy potential well that affects the spin variable(which is regarded as electric dipole in this research)and simulate the phase transition process using this model,which results in significantly smoothed phase transition with respect to temperature,exhibiting relaxor characteristics with diffuse phase transitions.More precisely,it is found that by applying the energy potential well to the dipoles in the system,the ferroelectric phase transition can be significantly broadened,that is,a diffused phase transition appears,showing strong relaxation characteristics that,as the temperature gradually increases,the average electric dipole moment does not change abruptly while the peak value of its permittivity decreases with the energy potential well.Moreover,at a temperature much higher than the transition temperature of the usual Ising model,the system can still maintain a certain polarization,which is in line with relaxor characteristics.By comparing to a previously proposed statistical model,it is found that the relaxation phenomenon is due to the fact that dipoles in the system are constrained by the given potential well,therefore difficult to flip,

关 键 词：弛豫铁电体 伊辛模型 弥散相变 蒙特卡罗模拟 

分 类 号：TM221[一般工业技术—材料科学与工程]