参数修改对铁电薄膜相变性质的影响

在关联有效场理论的框架内, 利用微分算子技术, 详细地计算了基于横场伊辛模型描述的对称铁电薄膜系统的相变性质. 根据薄膜各层自旋平均值构成的一系列耦合方程, 推导出可以用来计算任意层的具有不同表面层的薄膜相图的解析通式方程, 讨论了参数修改对薄膜相互作用参数从FPD (铁电相占主导地位的相图)到PPD (顺电相占主导地位的相图)过渡值和参数空间中各相变区域的影响. 在与平均场近似进行比较的结果显示, 关联有效场理论所得到的铁电薄膜的铁电性在某种程度上比平均场近似下的结果减弱. 关键词： 铁电薄膜 横场伊辛模型 相图 居里温度     

Influence of surface and bulk layers on the crossover features for interaction parameters of a ferroelectric thin film

The phase diagram of a ferroelectric thin film is studied by using the usual mean-field approximation. The crossover features, from the ferroelectric-dominant phase diagram to the paraelectric-dominant phase diagram, for the physical parameters of the thin film are discussed. Special attention is devoted to the investigation of surface and bulk layers, and how to influence the crossover values of exchange interactions and transverse fields.     

外延铁电薄膜相变温度的尺寸效应

考虑外延钙钛矿型铁电薄膜内的等效应力、表面晶格变化和表面电荷引起的退极化效应等机电耦合边界条件,利用铁电薄膜系统的动态金茨堡-朗道方程(DGL),系统分析和讨论了外延铁电薄膜相变温度与临界相变厚度的尺寸效应.结果表明,铁电薄膜相变温度与临界相变厚度完全依赖于各种与薄膜厚度相关的力电耦合边界条件.也给出了BaTiO₃外延铁电薄膜相变温度在各种边界条件下随厚度的变化,从结果看出,本文的分析与结论更符合实验数据. 关键词： 尺寸效应 外延铁电薄膜 相变温度 力电耦合边界     

微结构对Eu掺杂Bi4Ti3O12铁电薄膜铁电性能的影响

采用金属有机物分解法在Pt/Ti/Si(111)基底上制备了退火温度分别为600℃,650℃,700℃的Bi_3.15Eu_0.85Ti₃O₁₂(BET)铁电薄膜,并对其结构及铁电性能进行了测试,再使用扫描探针显微镜对BET薄膜的电畴翻转进行了实时观测.BET薄膜c畴发生180°畴变的最小电压为+6V,而r畴由于其高四方性,即使极化电压增至+12V也不会发生翻转.薄膜的铁电性主要源于c畴的极化,随着退火温度的升高,c畴的区域面积增加,BET薄膜的剩余极化强度随之增大.退火温度为700℃的BET薄膜剩余极化强度达到84μC/cm². 关键词： 铁电薄膜 电畴翻转 扫描探针显微镜     

Combined effect of the transition layer and interfacial coupling on the properties of ferroelectric bilayer film

Within the framework of modified Ginzburg--Landau--Devonshire phenomenological theory, a ferroelectric bilayer film with a transition layer within each constituent film and an interfacial coupling between two materials has been studied. Properties including the Curie temperature and the spontaneous polarization of a bilayer film composed of two equally thick ferroelectric constituent films are discussed. The results show that the combined effect of the transition layer and the interfacial coupling plays an important role in explaining the interesting behaviour of ferroelectric multilayer structures consisting of two ferroelectric materials.     

Influence of lateral size on dielectric properties of ferroelectric thin films with structure transition zones

By taking into account structural transition zones near the lateral and thickness direction edges, this paper uses a modified transverse Ising model to study dielectric properties of a finite size ferroelectric thin film in the framework of the mean-field approximation. The results indicate that the influence of the lateral size on the dielectric susceptibility cannot be neglected and lateral structural transition zones could be a crucial factor that improves the mean susceptibility of the fixed size film.     

外加电场对铁电薄膜相变的影响

采用热力学非线性理论,研究了外加电场对立方基底Pb(Zr_0.3Ti_0.7)O₃(PZT)铁电薄膜相变的影响.通过数值计算,得到了"失配应变-外加电场"相图,及外加电场与极化强度的关系.当外加电场达到186 kV/cm时,能使生长在SrTiO₃ 基底上PZT铁电薄膜从单斜r相转变为c相.在实验上,采用扫描探针显微镜通过对PZT薄膜施加不同的极化电场来研究了它的电畴翻转.从得到的压电响应相图可以看出,绝大多数的电畴是清晰可 关键词： 铁电薄膜 相变 扫描探针显微镜 失配应变     

Phase transition behaviors of a ferroelectric thin film with long-range interactions

Within the framework of the mean-field approximation, the transverse-field Ising model is used to investigate the surface parameter modification of interaction constants and transverse fields on phase transition behaviors of a ferroelectric thin film with long-range interactions. The variation of Curie temperature as a function of the surface transverse field for different surface interaction constants or thickness is discussed. Meanwhile, the variation of Curie temperature as a function of the surface exchange interaction for different surface transverse fields is examined. In addition, the dependence of Curie temperature on the film thickness for different surface exchange interactions and surface transverse fields is obtained.     

Phase diagram of ferroelectric thin film with diluted surface

We study the influence of the surface of the ferroelectric films on the properties of the intrinsic ferroelectric polarization state in frame of statistical Transverse Ising Model (TIM). The quality of the surface is modelled by the dilution parameter q$q$ that reflects the relative weight of the paraelectric impurities vs. ferroelectric ions. Using the effective field approach the variation of the average value of spontaneous polarization as function of temperature for different film thicknesses has been investigated as function of dilution parameter q$q$. The phase diagram of the system and crossover from the ferroelectric to the paraelectric phase is discussed.     

Pb(Zr0.3Ti0.7)O3铁电薄膜激光感生电压效应

采用脉冲激光沉积(PLD)技术在LaSrAlTaO₃(LSATO),LaAlO₃(LAO)和SrTiO₃(STO)的单晶倾斜衬底上成功制备了Pb(Zr_0.3Ti_0.7)O₃(PZT)薄膜,在三种倾斜衬底上生长的PZT薄膜中都首次发现了LIV效应.对PZT/LSATO薄膜在a,c轴两种不同取向择优生长下的LIV效应做了研究,发现在薄膜c轴取向择优生长 关键词： 激光感生电压效应 铁电薄膜 薄膜生长取向 原子层热电堆     

The hysteresis loops of a ferroelectric bilayer film with surface transition layers

Based on the transverse Ising model in the framework of the mean field approximation,this paper discusses a ferroelectric bilayer film with the surface transition layers within each constituent slab and an antiferroelectric interfacial coupling between two slabs.The hysteresis loop of a bilayer film is investigated.The results show that the surface transition layer in a ferroelectric bilayer film plays a significant role in realizing the multiple-state memory.     

BIT/PLZT/BIT多层铁电薄膜结构设计及制备的实验研究

为了有效阻止锆钛酸铅镧(PLZT)与半导体界面发生反应和互扩散,根据锆钛酸铅镧和钛酸铋(B IT)各自的铁电性能,提出了一种新的设计思想———多层铁电薄膜.采用脉冲准分子激光淀积(PLD)方法制备了B IT/PLZT/B IT多层铁电薄膜.采用Sawyer-Tower电路测量,其剩余极化强度Pr=34μC/cm2,矫顽场Ec=40 kV/cm.这种结构吸收了锆钛酸铅镧和钛酸铋的优点,提高了铁电薄膜的铁电性能.     

铁电薄膜铁电性能与温度关系的一种实时测量实验方法

介绍了一种实时测量铁电薄膜的铁电性能与温度关系的实验方法,为进一步研究铁电薄膜的特性提供了实验基础。     

基于VO2薄膜相变原理的温控太赫兹超材料调制器

利用二氧化钒薄膜绝缘相–金属相的相变特性, 提出了一种基于超材料的温控太赫兹调制器, 研究了相变超材料在太赫兹波段的传输特性和温控可调谐特性. 当入射太赫兹波为水平偏振或垂直偏振状态时, 器件的透过率谱线在1 THz附近呈现出两个独立的、中心频率分别为1.3 THz和1.7 THz、 带宽分别为0.2 THz和0.35 THz的 透射宽带. 当温度从40℃至80℃变化时, 两宽带的透过率发生明显的降低, 在二氧化钒的相变温度(68℃)时尤其灵敏, 对入射光的二种偏振状态, 调制深度均达到60%以上, 实现了良好的调制效果. 关键词： 太赫兹超材料 2薄膜')" href="#">VO₂薄膜 调制器 相变     

Phase transitions and domain structures in thin ferroelectric films

Recent advances in technology made available high quality thin ferroelectric films and ferroelectric–paraelectric multilayers. But understanding of the properties of these systems is far from being complete. In particular, it is not clear why various anomalies observed at phase transitions here are different from those in high quality bulk systems. The aim of the paper is to discuss some specific features of ferroelectric phase transitions in thin films and multilayers which are taken into account only partially by the theory. The discussion is limited to revealing the character of ferroelectric state forming just after the transition, i.e. if it is single-domain or multi-domain, if it is single-phase or two-phase. First, thin films with electrodes and on a substrate are discussed. The role of non-ideality of electrodes in realization of one of the first pairs of possibilities is emphasized. A more recent idea is that even for ideal electrodes a domain formation is possible when some conditions on the electrode–ferroelectric interface and the material constants of the material are met. This seems to be quite possible for the considered systems. Clamping by the substrate may lead to formation of a two-phase state which is practically unexplored for very thin films on substrates. Second, ferroelectric–paraelectric multilayers are considered which are more challenging for theoretical study than the thin films. Indeed, despite periodicity in the composition the domain structures are almost never periodic along the multilayer. The non-ideality of electrodes seems to lead to practical impossibility of single-domain ferroelectric phase transition in the multilayers of the considered type.     

A numerical model for the leakage characteristics in ferroelectric thin films under ionizing radiation

A numerical model is developed to describe the leakage characteristics in ferroelectric thin films under ionizing radiation. The trap-controlled space-charge-limited conduction mechanism is modified by considering radiation-induced charge carriers and changes in the relative dielectric constant. The effect of dose rate is related to the changes in the carrier mobility. Numerical simulation using this model reveals a radiation hardness of 10 Mrad(Si) for barium strontium titanate (BST) thin films at a constant dose rate of 10 Krad(Si)/s. Differences in the leakage behavior under radiation for different conduction regions are also discussed. This model provides a useful tool in predicting the leakage behavior under ionizing radiation and estimating the radiation hardness for ferroelectric materials.     

应力作用下EuTiO3铁电薄膜电热效应的唯象理论研究

基于Laudau-Devonshire的热动力学模型, 计算了EuTiO₃铁电薄膜材料的电热效应. 结果显示在外加应力的调控下, 电极化、电热系数以及绝热温差都会随之变化. 外加垂直于表面的张应力加大, 薄膜的相变温度升高, 绝热温差增加, 最大绝热温差所对应的工作温度向高温区移动. 对于二维平面失配应变u_m =-0.005的薄膜, 当外加张应力σ₃ = 5 GPa时, 其最大电热系数为1.75×10^-3 C/m²·K, 电场变化200 MV/m 时室温下绝热温差ΔT 的最大值可达到14 K 以上, 绝热温差ΔT ≥13 K 的工作温区超过120 K, 表明可以通过调控外部应力来获取室温时较大的绝热温差. 此结果预示着铁电EuTiO₃ 薄膜在室温固态制冷方面可能具有较好的应用前景.     

PEN薄膜阻抗转变规律研究

采用真空蒸发的方法制备了PEN材料薄膜，研究了不同外电路参数下薄膜的电双稳特性.发现薄膜从高阻向低阻转变过程所需时间随电流非线性下降，此期间薄膜阻抗也呈现非线性，并对非线性规律作了数据拟合.发现整个跃变过程中存在一种能量效应，即当外加电压超过某一阈值时，该跃迁所需的能量不变. 关键词： PEN薄膜 非线性阻抗 电双稳     

The effects of uniaxial stress distribution on the ferroelectric properties of thin films with first-order phase transition

Based on the Landau theory, the first-order phase transition properties of ferroelectric thin films have been studied by taking into account uniaxial stress distribution effects. The stress is supposed to decrease from interface to surface exponentially according to the experimental results. It is shown that tensile stress decreases the polarization and the Curie temperature while compressive stress increases the polarization and the Curie temperature. A stress-driven phase transition is found at the critical stress. Our prediction is compared with the available experiment results.