沉积温度对Na_(0.5)Bi_(0.5)TiO_3铁电薄膜结构与性能的影响

利用脉冲激光沉积法和磁控溅射法在(001)SrTiO_3单晶基片上构架了铁电异质结电容器Pt/La_(0.5)Sr_(0.5)CoO_3/Na_(0.5)Bi_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3/SrTiO3(LSCO/NBT/LSCO/STO)。利用原子力显微镜(AFM)、X射线衍射仪(XRD)、铁电测试仪和压电力显微镜(PFM)研究了沉积温度对Na_(0.5)Bi_(0.5)TiO_3(NBT)铁电薄膜的表面形貌、微结构和电学性能的影响。AFM结果表明,NBT薄膜晶粒尺寸随着沉积温度的增加先变小后增大。XRD结果显示,不同沉积温度下生长的NBT薄膜均为(00l)择优取向结构。铁电测试仪和PFM结果表明,NBT薄膜的铁电和压电性能随着沉积温度的增加先增大后减小,650℃生长的薄膜具有最高的剩余极化强度(19.6μC/cm2)和最大的有效压电系数(146 pm/V)。     

Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3陶瓷的准同型相界与电性能

采用固相法制备了 Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3（NBT–KBT–BT–ST）陶瓷,该体系是按（1–2x）（0.8NBT–0.2KBT）–x（0.94NBT–0.06BT）–x（0.74NBT–0.26ST） （x = 0.10、0.20、0.25、0.30、0.35、0.40、0.45）组合而成的,研究了该系陶瓷的结构与电性能。结果表明：所有样品都处于三方–四方准同型相界区域。该系陶瓷在准同型相界附近表现出了优异的压电性能,压电常数 d33、机电耦合系数 kp和剩余极化强度 Pr随 x 的增加先升高后降低,其中 x=0.35 陶瓷的电性能最佳：d33= 210 pC/N,kp= 0.319,Pr= 39.3 μC/cm2,Ec= 20.2 kV/cm,是一种良好的无铅压电陶瓷候选材料。依据准同型相界组成的线性组合规律来寻找具有优异压电性能的 NBT–KBT–BT–ST 陶瓷准同型相界组成是可行的。     

Pt/Na_(0.5)Bi_(0.5)TiO_(3)/La_(0.5)Sr_(0.5)CoO_(3)电容器的结构和铁电疲劳特性EI北大核心CSCD

采用偏轴磁控溅射法,以单晶钛酸锶(001)SrTiO_(3)(STO)为衬底,不同沉积温度下外延生长了La_(0.5)Sr_(0.5)CoO_(3)(LSCO)氧化物底电极。X射线衍射仪(XRD)和原子力显微镜(AFM)结构表征以及四探针方阻测试结果表明:LSCO薄膜外延(00l)取向最优温度沉积条件为550℃。此外,利用脉冲激光沉积法,以LSCO/STO异质结为模板,构架了Pt/Na_(0.5)Bi_(0.5)TiO_(3)(NBT)/LSCO/STO铁电电容器。XRD和AFM结构表征表明:NBT薄膜为(00l)外延结构。电流密度-电压测试曲线结果表明,室温变为70℃时,Pt/NBT/LSCO异质结漏电流密度有所增加,但未改变导电机制:低压下为欧姆导电和高压下为陷阱的空间电荷限制电流导电。在5 V驱动电压下,室温和70℃时,Pt/NBT/LSCO电容器具有饱和的电滞回线和保持特性,且经过10^(10)翻转后,均未产生疲劳。     

Mg掺杂对Ba0.5Sr0.5TiO3薄膜介电性能的影响

用醋酸盐和钛酸四丁酯为原料,采用sol-gel工艺在Pt/TiO/SiO/Si基片上制备了含有Mg元素的Sr0.5Ba0.5-xMgxTiO3薄膜,其退火处理温度为750℃.通过X射线衍射和扫描电镜分析技术研究了薄膜的相结构和形貌.采用美国HP Angilent 4294A阻抗分析仪测试了以Pt为底电极、Ag为上电极的MFM电容器的介电性能.实验结果表明:掺镁Sr05Ba05.xMgxTiO3薄膜较未掺杂的Ba05Sr0.5TiO3薄膜相对介电常数高、介电损耗低.介温谱表明在居里温度附近发生了弥散型相变,且居里温度有向低温方向漂移的趋势.     

热处理工艺对Sol-gel法制备BST薄膜性能的影响

以醋酸锶、醋酸钡和钛酸四丁酯为前驱体原料,采用溶胶-凝胶(Sol-gel)法,利用旋转涂覆工艺,采用不同的热处理工艺制备了组分为Ba/Sr=0.65/0.35的Ba0.65Sr0.35TiO3薄膜.采用XRD、SEM和阻抗分析仪分析薄膜的结晶、表面形貌和介电性能.研究了不同热处理工艺对BST薄膜晶化行为、结构和性能的影响.结果表明,最佳热分解温度和时间为400 ℃和30 min,最佳升温速率为0.5～1 ℃;经650 ℃热处理后,BST薄膜已基本形成ABO3型钙钛矿结构,随着热处理温度的提高,薄膜的结晶程度提高,且沿(110)晶面择优取向.经750 ℃热处理的BST薄膜表面光滑致密无裂纹,颗粒均匀分布,晶粒发育较好,且介电性能最佳.     

溶胶-凝胶法制备BaTiO_3-Bi_(0.5)Na_(0.5)TiO_3无铅PTCR陶瓷

新型高温无铅PTCR(Positive temperature coefficient of resistance)陶瓷是一种重要的功能材料。以BaC_4H_6O_4、Bi C_6H_9O_6、NaC_2H_3O_2、YC_6H_9O_6、C_(16)H_(36)O_4Ti为原料,通过溶胶-凝胶法制备了Y施主掺杂90mol%BaTiO_3-10mol%Bi_(0.5)Na_(0.5)TiO_3(简写为90BT-10BNT)陶瓷粉体,并且在低温下烧结成无铅PTCR陶瓷。利用XRD测试了粉体的相结构,利用SEM观察了粉体的形貌,并且测试了PTCR陶瓷的介电温度谱和电阻温度特性。研究表明,溶胶-凝胶法制备的新型90BT-10BNT无铅PTCR陶瓷的居里温度达到了195℃,但电阻突跳不高,小于1个数量级。     

Bi(Zr0.5Zn0.5)O3-PbTiO3高温压电陶瓷的结构与相变温度研究

采用传统固相反应法制备了(1-x)Bi(Zn0.5 Zr0.5) O3-xPbTiO3(BZZPTx)陶瓷,并利用XRD、SEM,介温等方法分析表征样品.XRD测试结果显示,当x＞O.67时,可获得单一四方相钙钛矿结构的BZZPTx陶瓷,通过XRD精修数据计算出BZZPTx体系陶瓷具有较大的四方畸变度(c/a＞1.1);介温测试表明BZZPTx体系的居里温度均超过500℃,最高的居里温度组分为BZZPPT0.67,Tc～668℃;实验表明该压电陶瓷体系的弱压电活性跟较大的四方畸变有关系.     

含Ti-Al阻挡层的硅基Na_(0.5)Bi_(0.5)TiO_3电容器的结构与电学性能

通过射频磁控溅射法和脉冲激光沉积法,以Ti-Al为阻挡层,在(001)Si衬底上制备了La0.5Sr0.5CoO_3(LSCO)/Na_(0.5)Bi_(0.5)TiO_3(NBT)/LSCO(LSCO/NBT/LSCO)异质结铁电电容器。研究了Na_(0.5)Bi_(0.5)TiO_3铁电薄膜的结构和物理性能。结果表明:Ti-Al阻挡层为非晶结构,NBT薄膜结晶质量良好。在1 500 k V/cm驱动电场下,LSCO/NBT/LSCO电容器呈现饱和的电滞回线,具有较大的剩余极化强度(47.9μC/cm2)和较小的脉宽依赖性,而且抗疲劳特性和保持特性良好。此外,漏电机制研究表明:当外加电场小于400 k V/cm时,LSCO/NBT/LSCO电容器满足欧姆导电机制,在电场大于400 k V/cm时,满足空间电荷限流传导机制。     

高温无铅PTC的研制

利用NBT作为居里温度移动剂制备了高温无铅PTC。研究了NBT掺杂比例对无铅高温PTC阻温性质的影响。结果表明NBT有效提高了PTC的居里温度,NBT比铅的移动效果大大提高,样品性能较好,但是掺杂比例超过0.5%后,PTC半导化困难。无氧环境以及较低的烧成温度有助于改善其半导化程度。     

拓扑化学反应制备片状Na0.5Bi0.5TiO3粉体的研究

通过熔盐法制备出具有铋层结构的前驱体Na0.5Bi4.5Ti4O15,其取向度f值(Lotgering factor法)高达0.9.粉体Na0.5Bi4.5Ti4O15再与NaaCO3和TiO2发生拓扑化学反应,铋层状结构的Na0.5Bi4.5Ti4O15完全转变成钙钛矿结构的Na0.5Bi0.5TiO3(NBT),所得到NBT粉体保留了NBIT的层状形貌,其厚度约0.4μm,长度为5-10μm,显示出较高的各向异性.研究了烧成温度对前躯体NBIT微粒形态的影响.通过SEM分析,固相法,熔盐法和拓扑反应合成的NBT粉体微观结构显示出巨大的差异.     

Piezoelectric K0.5Na0.5NbO3 Ceramics Textured Using Needlelike K0.5Na0.5NbO3 Templates

Improved performance by texturing has become attractive in the field of lead‐free ferroelectrics, but the effect depends heavily on the degree of texture, type of preferred orientation, and whether the material is a rotator or extender ferroelectric. Here, we report on successful texturing of K_0.5Na_0.5NbO₃ (KNN) ceramics by alignment of needlelike KNN templates in a matrix of KNN powder using tape casting. Homotemplated grain growth of the needles was confirmed during sintering, resulting in a high degree of texture parallel to the tape casting direction (TCD) and the aligned needles. The texture significantly improved the piezoelectric response parallel to the tape cast direction, corresponding to the direction of the strongest <001>_pc orientation, while the response normal to the tape cast plane was lower than for a nontextured KNN. In situ X‐ray diffraction during electric field application revealed that non‐180° domain reorientation was enhanced by an order of magnitude in the TCD, compared to the direction normal to the tape cast plane and in the nontextured ceramic. The effect of texture in KNN is discussed with respect to possible rotator ferroelectric properties of KNN.     

Thermally-stable large strain in Bi(Mn0.5Ti0.5)O3 modified 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 ceramics

(1-x)[0.8Bi_0.5Na_0.5TiO₃-0.2Bi_0.5K_0.5TiO₃]-xBi(Mn_0.5Ti_0.5)O₃ (x = 0–0.06, BNKMT100x) lead-free ferroelectric ceramics were prepared via solid state reaction method. Bi(Mn_0.5Ti_0.5)O₃ induces a structure transition from rhombohedral-tetragonal morphotropic phases to pseudo-cubic phase. Moreover, the wide range of compositions within x = 0.03–0.055 exhibit large strain of 0.31%–0.41% and electrostrictive coefficient of 0.027–0.041 m⁴/C². Especially, at x = 0.04, the large strain and electrostrictive coefficient are nearly temperature-independent in the range of 25–100 °C. The impedance analysis shows the large strain and electrostrictive coefficient originate from polar nanoregions response due to the addition of Bi(Mn_0.5Ti_0.5)O₃.     

Dielectric properties of some low-lead or lead-free perovskite-derived materials: Na0.5Bi0.5TiO3–PbZrO3, Na0.5Bi0.5TiO3–BiScO3 and Na0.5Bi0.5TiO3–BiFeO3 ceramics

Na_0.5Bi_0.5TiO₃ (NBT) and its modifications are known to be new lead-free ferroelectric materials and are promising for environment friendly devices. The systems under investigation were (i) NBT (trigonal/ferroelectric)–PbZrO₃ (orthorhombic/antiferroelectric); (ii) NBT (trigonal/ferroelectric)–BiScO₃ (trigonal/paraelectric); and (iii) NBT (trigonal/ferroelectric)–BiFeO₃ (trigonal/antiferromagnetic).The lattice parameters change as expected from the respective ionic radii values. For NBT–PZ, the dielectric permittivity shows a large frequency and temperature dispersion suggesting a relaxor-like behaviour dependent on the thermal annealing of the samples. For NBT–BS, the Curie temperature increases with BS content as well as the diffuseness of the phase transition, connected with the introduced disorder. For NBT–BF, the overall behaviour of the permittivity of NBT is maintained up to 50% BF but anomalies of the permittivity appeared close to 600 °C, which might be connected with the onset of magnetic influence for high BF content.     

K0.5Na0.5NbO3-BaCu0.5W0.5O3无铅压电陶瓷的结构与性能

以传统固相法工艺制备(1-x)K0.5Na0.5NbO3-xBaCu0.5W0.5O3[(1-x)KNN-xBCW]无铅压电陶瓷,研究不同BCW掺量(x=0％,0.1％,0.25％,0.5％,1.0％,摩尔分数,下同)对KNN陶瓷的晶体结构和电性能的影响,结果表明:x＜0.5％时,KNN陶瓷的相结构没有改变,仍为正交相...     

Electrical properties and relaxor phase evolution of Nb-Modified Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 lead-free ceramics

In this work, the crystalline phase, domain structure, and electrical properties of [Bi_0.5(Na_0.84K_0.16)_0.5]_0.96Sr_0.04Ti_1-xNb_xO₃ (x = 0.010–0.030) ceramics are investigated. Increasing the Nb content induces the phase transition from coexistent rhombohedral and tetragonal phases to a single pseudo-cubic phase, and the lamellar ferroelectric domains evolve into polar nanoregions. Decreased ferroelectric-to-relaxor transition temperature and enhanced frequency dispersion are found in the temperature-dependent dielectric constant and loss, implying a transition from the non-ergodic to ergodic relaxor state. The Nb substitution significantly degrades the long-range ferroelectric order with sharply decreased piezoelectric coefficients from ? 140 to ? 1 pC/N. However, a large strain of 0.32% at 5 kV/mm (normalized strain of 640 pm/V) is obtained around the critical composition of x = 0.0225. The composition of x = 0.030 shows good temperature insensitivity of the strain response, characterized by 308 pm/V with less than 15% reduction from 25 °C to 125 °C.     

Enhanced pyroelectric response from domain-engineered lead-free (K0.5Bi0.5TiO3-BaTiO3)-Na0.5Bi0.5TiO3 ferroelectric ceramics

Enhanced pyroelectric response is achieved via domain engineering from [001] grain-oriented, tetragonal-phase, lead-free 0.2(2/3K_0.5Bi_0.5TiO₃-1/3BaTiO₃)-0.8Na_0.5Bi_0.5TiO₃ (KBT-BT-NBT) ceramics prepared by a templated grain growth method. The [001] crystallographic orientation leads to large polarization in tetragonal symmetry; therefore, texturing along this direction is employed to enhance the pyroelectricity. X-ray diffraction analysis revealed a Lotgering factor (degree of texturing) of 93 % along the [001] crystallographic direction. The textured KBT-BT-NBT lead-free ceramics showed comparable pyroelectric figures of merit to those of lead-based ferroelectric materials at room temperature (RT). In addition to the enhanced pyroelectric response at RT, an enormous enhancement in the pyroelectric response (from 1750 to 90,900 μC m^?2 K^?1) was achieved at the depolarization temperature because of the sharp ferroelectric to antiferroelectric phase transition owing to coherent 180° domain switching. These results will motivate the development of a wide range of lead-free pyroelectric devices, such as thermal sensors and infra-red detectors.     

Enhanced energy storage properties of BiAlO3 modified Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 lead-free antiferroelectric ceramics

Lead-free (1−x)(0.75Bi_0.5Na_0.5TiO₃–0.25Bi_0.5K_0.5TiO₃)–xBiAlO₃ (BNT–BKT–100xBA, x=0–0.10) ceramics were prepared by two-step sintering method and their phase structure, micro morphology and electrical properties were systematically investigated. X-ray diffraction analysis indicates a pure perovskite phase for x≤0.06 as well as a structural evolution from a tetragonal toward a pseudocubic phase. Transmission electron microscopy study of the x=0.04 composition reveals the existence of antiferroelectric phase with a⁰a⁰c⁺ oxygen octahedron tilting which is in the form of nano-domains. Polarization-electric field and current-electric field hysteresis loops demonstrate that the increase of BA concentration destroys the ferroelectric order and strengthens antiferroelectric order. A much enhanced energy storage density of 1.15 J/cm³ and efficiency of 73.2% is achieved under 105 kV/cm at x=0.06. In addition, its energy storage property is found to depend weakly on temperature within the measurement range of 25–150 °C.     

Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3系无铅压电陶瓷的极化工艺研究

主要研究了极化电场,极化时间和极化温度等工艺参数对Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3系无铅压电陶瓷介电和压电性能的影响。结果表明:极化电场和极化温度对压电陶瓷的介电、压电性能影响较大,而极化时间则影响较小。适宜的极化电场是3～3.5kV/mm,极化温度70～80℃,极化时间为10～15min。     

CeO2掺杂钛酸铋钠钾陶瓷的制备工艺与介电性能

为了进一步探索合成工艺对钛酸铋钠系无铅材料的结构及介电特性的影响,本文以甘氨酸为燃料,利用固相-燃烧法制备了CeO2掺杂的Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 (BNKT)陶瓷.XRD表明,在固相合成工艺中引入燃烧法制备BNKT陶瓷,比传统固相法降低预烧温度150 ℃,掺杂的CeO2扩散进入了BNKT钙钛矿的晶格,且当掺杂量为0%~0.3%时,形成纯的钙钛矿相结构;SEM表明,CeO2掺杂使晶粒尺寸趋于平均,对晶粒生长有抑制作用;介电温谱表明,随着CeO2掺杂量增加,介电常数εr和退极化温度Td、相转变温度Tm降低,介电反常峰逐渐弱化,且室温至300 ℃,介电损耗tanδ始终在0.3%以下,并从微结构缺陷空位形成机制角度,结合铁电畴壁运动状态,分析讨论了对材料介电特性的作用规律.     

Raman spectroscopy of Na0.5Bi0.5TiO3

We have measured the Raman spectra of bismuth sodium titanate in its rhombohedral, tetragonal, and cubic phases, with special attention paid to the phase transitions at 584K and 837K (heating). Both transitions appear to be order-disorder and strongly first order, with large thermal hysteresis. The phonon spectra at temperature slightly below the tetragonal phase are remarkably similar to BaTiO₃ with A₁(To) modes at 130, 269, and 541 cm^-1 (compared with 170, 270, 520 cm^-1 in BaTiO₃) and an E(TO) at 52 cm^-1.