Understanding the Role of Ferroelastic Domains on the Pyroelectric and Electrocaloric Effects in Ferroelectric Thin Films

Temperature‐ and electric‐field‐induced structural transitions in a polydomain ferroelectric can have profound effects on its electrothermal susceptibilities. Here, the role of such ferroelastic domains on the pyroelectric and electrocaloric response is experimentally investigated in thin films of the tetragonal ferroelectric PbZr_0.2Ti_0.8O₃. By utilizing epitaxial strain, a rich set of ferroelastic polydomain states spanning a broad thermodynamic phase space are stabilized. Using temperature‐dependent scanning‐probe microscopy, X‐ray diffraction, and high‐frequency phase‐sensitive pyroelectric measurements, the propensity of domains to reconfigure under a temperature perturbation is quantitatively studied. In turn, the “extrinsic” contributions to pyroelectricity exclusively due to changes between the ferroelastic domain population is elucidated as a function of epitaxial strain. Further, using highly sensitive thin‐film resistive thermometry, direct electrocaloric temperature changes are measured on these polydomain thin films for the first time. The results demonstrate that temperature‐ and electric‐field‐driven domain interconversion under compressive strain diminish both the pyroelectric and the electrocaloric effects, while both these susceptibilities are enhanced due to the exact‐opposite effect from the extrinsic contributions under tensile strain.     

反铁电材料中负电卡效应的研究进展

电卡效应是指电介质材料中由于施加或去除电场导致的材料温度变化的现象, 包括正电卡效应和负电卡效应两种类型。电卡效应作为一种高效率、无噪音、环境友好的制冷效应, 在固态制冷特别是集成电路制冷领域显示出广阔的应用前景, 在过去的几十年中吸引了科研人员广泛的研究兴趣。研究表明, 通过结合正负电卡效应, 可以显著提高电卡效应的制冷能力。与正电卡效应不同, 负电卡效应因其独特的物理起源, 调控手段极为有限。本文以负电卡效应为中心, 重点介绍反铁电材料中负电卡效应的最新研究进展, 具体内容包括以下四个部分: 首先, 从电卡效应的研究历史出发, 介绍了电卡效应的制冷原理, 介绍了一个典型的能将正、负电卡效应结合的双制冷循环; 其次, 介绍了基于Maxwell关系的负电卡效应间接测试方法, 以及几种负电卡效应直接测试方法, 并讨论了不同方法的适用条件和优缺点; 再次, 以典型的负电卡效应材料——反铁电材料为例, 着重介绍了负电卡效应的物理起源, 综述了反铁电薄膜和反铁电块体材料中的负电卡效应, 并对其它铁电材料中的负电卡效应做了简要介绍; 最后, 对负电卡效应的研究进行了总结和展望。     

Electrocaloric Materials for Solid‐State Refrigeration

The electrocaloric effect (ECE) in dielectric materials has great potential in realizing solid‐state cooling devices with compact size and high efficiency, which are highly desirable for a broad range of applications. This paper presents the general considerations for dielectric materials to achieve large ECE and reviews the experimental efforts investigating ECE in various polar dielectrics. For practical cooling devices, an ECE material must possess a large isothermal entropy change besides a large adiabatic temperature change. We show that polar dielectrics operated at temperatures near order–disorder transition have potential to achieve large ECE due to the possibility of large change in polarization induced by electric field and large entropy change associated with the polarization change. We further show that indeed the ferroelectric poly(vinylidene fluoride–trifluoroethylene)‐based polymers display a large ECE, i.e., an isothermal entropy change of more than 55 J (kgK)^?1 and an adiabatic temperature change of more than 12 °C, at temperatures above the order–disorder transition.     

Cu2O薄膜的制备方法

氧化亚铜（Cu2O）薄膜在太阳能电池及其它光电器件上有重要应用,它具有无毒、制备成本低、材料广泛易得等优点。制备Cu2O薄膜的方法主要有热蒸发、溅射、化学气相沉积和电化学沉积等,本文对Cu2O薄膜的制备方法进行了综述与展望。     

金属-绝缘体颗粒膜的巨霍尔效应研究进展

介绍了金属-绝缘体颗粒膜巨霍尔效应的研究背景及样品的制备与测量，总结了近年来该领域的研究进展和应用前景，最后对研发应用中存在的问题和趋势提出了自己的看法。     

Highly Crystalline Y3Fe5O12 Thin Films by Cictric Spray Pyrolysis

Ethylene glycol solution of mixed-metal Y(III)-Fe(III) citric complexes has been used as a starting material for a spray pyrolysis deposition of Y₃Fe₅O₁₂ (YIG) thin films on silica and on single crystal Y₃Al₅O₁₂ (YAG) substrates heated up to 500°C. O₂ was used as a carrier gas. A post-deposition thermal annealing at 800–1100°C was applied. Films of 0.1–1.2 m in thickness were obtained. Their composition, binding energies, crystal structure, morphology, and magnetic properties were studied. Phase homogeneous polycrystalline or highly textured YIG films were obtained on silica or YAG substrates at annealing temperatures of 860° and 960°C, respectively. The crystallite grain sizes of both type of layers were 80 nm along the (400) plane. A columnar structure of the films with the column diameter of 400–500 nm might be supposed following the atomic force microscopy data. Saturation and permanent magnetizations along the easy axis of 1545 Gs and 816 Gs, respectively, and coercive force along the same axis of 4 Oe were measured.     

Interfacial Coupling Boosts Giant Electrocaloric Effects in Relaxor Polymer Nanocomposites: In Situ Characterization and Phase‐Field Simulation

The electrocaloric effect (ECE) refers to reversible thermal changes of a polarizable material upon the application or removal of electric fields. Without a compressor or cooling agents, all‐solid‐state electrocaloric (EC) refrigeration systems are environmentally benign, highly compact, and of very high energy efficiency. Relaxor ferroelectric ceramics and polymers are promising candidates as EC materials. Here, synergistic efforts are made by composing relaxor Ba(Zr_0.21Ti_0.79)O₃ nanofibers with P(VDF‐TrFE‐CFE) to make relaxor–relaxor‐type polymer nanocomposites. The ECEs of the nanocomposites are directly measured and these relaxor nanocomposites exhibit, so far, the highest EC temperature change at a modest electric field, along with high thermal stability within a broad temperature range span to room temperature. The superior EC performance is attributed to the interfacial coupling between dipoles across the filler/polymer interfaces. The thermodynamics and kinetics of interfacial coupling are investigated in situ by piezoresponse force microscopy while the real‐time evolution of interfacial coupling is simulated and visualized by phase‐field modeling.     

V2O5薄膜的电学性质及其应用

综述了Ｖ２Ｏ２薄膜材料的结构、电学性质及其在电学中的应用。     

V2O5干凝胶薄膜的制备及应用

综述了V2O5干凝胶（VXG）薄膜的结构组成特性，介绍了VXG薄膜的制备方法及其在电压开关、气体传感器、湿度传感器、智能窗和锂电池等领域的应用，指出了该研究存在的问题和发展前景。     

MOD法制备的Bi3.25Nd0.75Ti3O12薄膜的铁电各向异性行为

采用金属有机分解法(MOD)在(111)Pt／Ti／SiO2／Si衬底上制备了含(117)成分的c轴择优取向和α轴择优取向的Bi3.25Nd0.75Ti3O12(BNT)薄膜．实验发现，BNT薄膜的品型结构主要依赖于预退火条件．电学性能测试表明，α轴择优取向的BNT薄膜具有高的剩余极化和矫顽场，较高的介电常数和介电损耗，以及较大的电容调谐率；而c轴择优取向的则相反．BNT薄膜具有同Bi4Ti3O12(BIT)薄膜相似的铁电各向异性行为．     

In2O3薄膜及纳米颗粒制备进展

主要介绍了In2O2薄膜及其纳米颗粒的制备方法和特点,并比较了它们的优缺点。     

Giant Barocaloric Effect at the Spin Crossover Transition of a Molecular Crystal

The first experimental evidence for a giant, conventional barocaloric effect (BCE) associated with a pressure‐driven spin crossover transition near room temperature is provided. Magnetometry, neutron scattering, and calorimetry are used to explore the pressure dependence of the SCO phase transition in polycrystalline samples of protonated and partially deuterated [FeL₂][BF₄]₂ [L = 2,6‐di(pyrazol‐1‐yl)pyridine] at applied pressures of up to 120 MPa (1200 bar). The data indicate that, for a pressure change of only 0–300 bar (0–30 MPa), an adiabatic temperature change of 3 K is observed at 262 K or 257 K in the protonated and deuterated materials, respectively. This BCE is equivalent to the magnetocaloric effect (MCE) observed in gadolinium in a magnetic field change of 0–1 Tesla. The work confirms recent predictions that giant, conventional BCEs will be found in a wide range of SCO compounds.     

Y元素对Sr_(0.5)Ba_(0.5-y)Y_yTiO_3薄膜结构与性能影响的研究

为了研究掺杂BarSr1-xTiO3介电薄膜材料的性能,采用阻抗分析仅等测试方法研究了微量元素钇对Sr0.5Ba0.5-yYyTiO3薄膜介电性能的影响。当Y元素的掺量为0-0.030mol时,相对介电常数εr和tanδ分别为74.2和0.067;最大介电常数温度点Tm(居里温度点)逐渐移向低温;在所测试频率范围内,Y元素的掺量为0.010、0.0150mol(Y2、Y3)时,εr、tanδ均能表现出较好的频散特性。采用XRD、TEM等测试方法分析了薄膜的结构特征。薄膜的矿物组成为四方钙钛矿结构,但Y的溶入改变了晶胞参数的c/a比,减小了薄膜的颗粒尺寸,提高了薄膜的致密度;晶粒的生长为取向一致和无取向生长两种方式。     

铁基巨磁阻抗薄膜的研究

溅射方法制备的非晶Fe68Cu0 .5Cr4 V5Si13 .5B9薄膜 ,通过适宜的退火处理得到具有纳米α Fe(Si)和非晶母相的混合结构和最佳的软磁性能 ,相应的巨磁阻抗值最高可达 72 %。本文着重研究了热处理条件、薄膜组织结构、软磁性能以及驱动电流频率对Fe68Cu0 .5Cr4 V5Si13 .5B9薄膜磁致阻抗的影响。