Na0.5 Bi0.5 TiO3-K0.5 Bi0.5 TiO3系铁电体的相变研究

研究了(Na1-xKx)0.5Bi0.5TiO3体系x分别为0、0.08、0.16和0.20时陶瓷不同频率下的介电温谱,发现材料为弛豫型铁电体,材料的介电谱在室温到500℃的温度范围内存在一个介电常数-温度"台阶",一个介电常数-温度峰和一个介电损耗-温度峰,通过分析陶瓷不同温度下的电滞回线验证陶瓷在升温过程中产生了铁电-反铁电-顺电相变,采用铁电体成分起伏理论和内电场理论解释了这类弛豫型铁电体相变的原因.     

脉冲激光沉积Ba0.5Sr0.5TiO3、Pb0.5Ba0.5TiO3和Pb0.5Sr0.5TiO3薄膜及其介电性质

采用脉冲激光沉积法,在Pt／Ti／SiO2／Si基底上分剐制备厚度为350nm的Ba0.5Sr0.5TiO3(BST)、Pb0.5Ba0.5TiO3(PBT)和Pb0.5Sr0.5TiO3(PST)薄膜并研究了它们的介电性质。XRD显示,在相同的制备条件下三者具有不同的择优取向,PST具有(110)择优取向,PBT具有(111)择优取向,而BST则是混合取向。SEM显示三者样品表面均匀致密,颗粒尺寸大约在50nm至150nm之间。PST与BST、PBT相比有更高的介电常数,在频率为10kHz时,分别为874、334和355,而损耗都较低,分别为0．0378、0．0316和0．0423,同时PST漏电流也是最小的。测量薄膜的C-V特性扣铁电性能表明室温下BST呈现的是顺电相,PST和PBT则呈铁电相。本文也测量了薄膜在不同频率下的介电温度特性,BST、PBT和PST均表现出频率弥散现象,即随着频率的降低．居里温度降低而介电常数会升高。并测得BST和PST的居里温度分剐为-75和150℃。而PBT的居里温度在250℃以上。本文研究表明：与BST相比较,PBT的介电常数与之相近,漏电流较大;而PST具有高介电常数,较小的漏电流和较大的电容-电压调谐度,在相关半导体器件中的应用将有很大的潜力。     

Na0.5K0.5NbO3 and 0.9Na0.5K0.5NbO3–0.1Bi0.5Na0.5TiO3 nanocrystalline powders synthesized by low-temperature solid-state reaction

Nanocrystalline powders of K_0.5Na_0.5NbO₃ (KNN) and 0.9Na_0.5K_0.5NbO₃–0.1Bi_0.5Na_0.5TiO₃ (KNN–BNT) have been prepared using a low-temperature solid-state reaction. Phase development of the powders incurred during various calcination temperatures was examined by X-ray diffraction (XRD). Crystallite size and particle morphology of KNN powders were examined by XRD and transmission electron microscopy, respectively. Perovskite phase was formed at the temperature as low as 500 °C, and the average crystallite size of KNN powders depended on calcination temperature. In addition, the crystalline structure of KNN powders tended to change from tetragonal symmetry to orthorhombic symmetry with increase in crystallite size. Similar results were obtained in KNN–BNT system. The developed method is well suited for the mass production of niobate nanocrystalline powders due to its simplicity and low cost.     

Structure and piezoelectric properties of K0.5Na0.5NbO3–Bi0.5Li0.5TiO3 lead-free ceramics

Lead-free (1−x) K_0.5Na_0.5NbO₃–xBi_0.5Li_0.5TiO₃ + 1 mol% MnO₂ piezoelectric ceramics have been prepared by a conventional ceramic technique and their structure and piezoelectric properties have been studied. Our results reveal that Bi_0.5Li_0.5TiO₃ diffuse into K_0.5Na_0.5NbO₃ lattices to form a solid solution with a perovskite structure. The addition of Bi_0.5Li_0.5TiO₃ to the K_0.5Na_0.5NbO₃ solid solution decreases the paraelectric cubic-ferroelectric tetragonal phase transition temperature (T _C) slightly, but shifts the ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperature (T _O−T) significantly to low temperatures. As a result, coexistence of the orthorhombic and tetragonal phases is formed at 0.01 < x < 0.03 near room temperature, leading to a significant improvement in the piezoelectric properties of the ceramics. The ceramic with x = 0.025 exhibits a relatively high T _C (392 °C) and optimum piezoelectric properties: d ₃₃ = 191 pC/N, k _p = 51.5% and k _t = 45.5%. The ceramic also exhibit a good thermal stability of piezoelectric properties.     

Piezoelectric and dielectric properties of Bi0.5Na0.5TiO3–Bi0.5Li0.5TiO3 lead-free ceramics

(1 − x)Bi_0.5Na_0.5TiO₃–xBi_0.5Li_0.5TiO₃ lead-free ceramics have been prepared by a conventional solid-state reaction method, and their piezoelectric and dielectric properties have been studied. X-ray diffraction studies reveal that Li⁺ diffuses into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure. The addition of Bi_0.5Li_0.5TiO₃ effectively lowers the sintering temperature of the ceramics and greatly assists in the densification of the ceramics. The ceramic with x = 0.075 possesses the optimum piezoelectric properties: piezoelectric coefficient d ₃₃ = 121 pC/N and planar electromechanical coupling factor k _P = 18.3%. After the partial substitution of Li⁺ for Na⁺ in the A-sites of Bi_0.5Na_0.5TiO₃, the ceramics exhibit more relaxor characteristic, which is probably resulted from the cation disordering in the 12-fold coordination sites. The depolarization temperature T _d shifts to low temperature with the substitution level x of Li⁺ for Na⁺ increasing.     

Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷的制备与性能

采用传统的干压成型法制备了Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷,研究了不同K0.5Bi0.5TiO3含量对Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3陶瓷的微观结构与电性能的影响规律.结果表明,Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷随K0.5Bi0.5TiO3含量增加,晶格常数增大,密度减小,晶粒尺寸减小,压电常数先增大后减小,介电常数增大,介电损耗增加,机械品质因数下降,而居里温度不断升高,在200℃附近存在由铁电相向反铁电相转变的一个相变点,组分为0.84 Na0.5Bi0.5TiO3-0.16 K0.5Bi0.5TiO3的陶瓷位于准同型相界附近,具有最佳的压电性能.     

水热法制备K0.5 Bi0.5 TiO3纳米粉体

以Bi(NO3)3·5H2O、Ti(OC4H9)4、KOH为原料,研究和分析了水热条件下纳米K0.5Bi0.5TiO3(KBT)粉体和影响KBT晶体生长与形成的各个影响因素,并利用XRD、TEM、ED等分析方法对所得粉体的晶相、微观形貌、分散性等性质进行了表征.结果表明,反应温度为180℃,保温时间为24h,KOH浓度为4～12mol/L时能制备出纯净的、结晶完整、分散性良好、钙钛矿型的纳米K0.5Bi0.5TiO3晶体,其颗粒尺寸为15～75nm.     

熔盐法合成Na0.5K0.5NbO3粉体

采用熔盐法在K2CO3和Na2CO3的熔盐（K2CO3／Na2CO3=45／55）中800℃并保温2h的条件下制备出了单相、纯钙态矿型结构的Na0.5K0.5NbO3粉体,运用XRD以及SEM技术对所得粉体进行了相组成及显微结构分析。结果表明：随着盐含量的增加,晶体结构从正交相转变为四方相,晶粒大小先增加而后稍微减小,并且获得较好的介电压电性：ε33^T／ε0（1kHz）=45-264,tgδ=1．5％～2．6％,Tc=402℃,Tτ-o=202℃,d33=88-98pC／N,Qm=465-574,Kp=29．09%～30．47％,在10kHz频率下,介电损耗有一点改变。NKN将有可能成为用于高频下的无铅压电陶瓷之一。     

La0.5Ba0.5CoO3中的Pr掺杂效应

用固相反应法制备了La0.5-xPrxBa0.5CoO3系列化合物，系统研究了Pr不同含量时材料的磁性和电输运特性，结果表明：Pr掺杂没有改变Co的3d电子的巡游特性。随Pr掺杂量增加，材料的分子磁矩单调下降，其原因是当Pr逐渐取代La时，Co离子的3d电子逐渐由中间自旋态向低自放态转变。随Pr含量增加，材料的居里温度逐渐下降，这是由于稀土离子的尺寸效应，电阻测量表明：在所研究的温度范围内，居里温度以下，所有掺Pr材料的导电机制为热扩散型。居里点以上，导电机制为变程跳跃导电。     

Structure and electrical properties of the Ho2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics

Ho₂O₃ (0–0.7?wt%)-doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The effects of Ho₂O₃ on the microstructure and electrical properties were investigated. X-ray diffraction data shows that Ho₂O₃ in an amount of 0.1–0.7?wt% can diffuse into the lattice of the BNKT18 ceramics and form the pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain sizes of BNKT18 ceramics decrease with the increase of Ho₂O₃ content; in addition, the modified ceramics have the clear grain boundary and a uniformly distributed grain size. At room temperature, the electrical properties of the BNKT18 ceramics have been improved with the addition of Ho₂O₃, and the BNKT18 ceramics doped with 0.3wt.% Ho₂O₃ have the highest piezoelectric constant (d ₃₃?=?137?pC/N), the highest remnant polarization (P _r?=?26.9?μC/cm²), the higher relative dielectric constant (ε _r?=?980) and lower dissipation factor (tanδ?=?0.046) at a frequency of 10?kHz. The BNKT18 ceramics doped with 0.1?wt% Ho₂O₃ have the highest planar coupling factor (k _p?=?0.2426).     

(Na0.5Bi0.5)TiO3-BaTiO3的合成与压电性能

合成了具有单一钙钛矿结构的(Nao.5Bi0.5)1-xBaxTiO3超细粉料,研究其陶瓷的压电性能.结果表明,柠檬酸与金属离子的摩尔比(C/Mn )和前驱体溶液的pH值是影响溶胶与凝胶形成的主要因素,凝胶在600℃下热处理1 h后可形成单一钙钛矿结构的(Nao.5Bi0.5)1-xBaxTiO3超细粉料.用柠檬酸盐法合成粉料的颗粒细小、化学成分均匀,有利于提高(Na0 5Bi0.5)1-xBaxTiO3陶瓷的压电性能.在准同质相界附近的组分存在较多的自发极化取向,因而表现出优良的压电性能.x=0.06时,柠檬酸盐法制备陶瓷样品的压电常数d33达到180 pC/N.     

Crystallographic textured evolution in 0.85Na0.5Bi0.5TiO3–0.04BaTiO3–0.11K0.5Bi0.5TiO3 ceramics prepared by reactive-templated grain growth method

0.85Na_0.5Bi_0.5TiO₃–0.04BaTiO₃–0.11K_0.5Bi_0.5TiO₃ (BNBK) lead-free piezoelectric ceramics with extensive [001]_pc (pc: pseudo cubic) texture were fabricated by the reactive-templated grain growth method using anisotropic Bi₄Ti₃O₁₂ (BIT) particles as templates. The degree of grain orientation increased with increasing heat treatment temperature (600–1,200 °C). The obtained textured ceramics showed dense and brick-wall like microstructure, giving a Lotgering factor of 0.6. A physical understanding of interaction between BIT templates and matrix powders and the mechanism of texture evolution were proposed and confirmed by experimental evidences of X-ray diffraction patterns, scanning electron microscope images and density measurements. The piezoelectric response was enhanced by the grain orientation, and the piezoelectric constant (d₃₃) of the textured ceramics sintered at 1,170 °C attained a value of 254 pC/N, which was 41 % higher than random ceramics (180 pC/N).     

Origin of the large strain response in tenary SrTi0.8Zr0.2O3 modified Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 lead-free piezoceramics

The perovskite oxides (1 ? x)Bi_0.5(Na_0.9K_0.1)_0.5TiO₃–xSrTi_0.8Zr_0.2O₃ (SZT1000x, x = 0, 0.2, 0.4, 0.6, 0.8, and 1 %) were prepared via the conventional solid-state reaction method. The room temperature ferroelectric P–E loops coordinate with polarization current density J–E curves illustrated the changes of ferroelectric domains and polar nanoregions under different driving fields exhaustively. The composition and electric field dependent strain behavior of this system were investigated to develop a lead-free piezoelectric material with a large strain response at a lower electric field. A large strain of 0.44 % (S _max/E _max = 744 pm/V) at an applied field of 50 kV/cm was obtained at the composition of 0.6 mol% SZT. Temperature-dependent hysteresis measurements reveal the primary origin of the large strain is due to the presence of a nonpolar phase at a zero field. Upon the application of an electric field, the nonpolar phase that can easily transform into a long-range ferroelectric phase, and then brings the system back to its unpoled state once the applied electric field is removed. Notably, the electric field required to deliver large strains is reduced to 40 kV/cm while the S _max/E _max reached up to 717 pm/V, indicating that the developed material is highly promising for actuator applications.     

Nd3+A位置换对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能的影响

研究了Nd³⁺离子A位置换改性(Pb_0.5Ca_0.5)(Fe_0.5Nb_0.5)O₃陶瓷的微波介电性能.[(Pb_0.5Ca_0.5)_1-xNd_x](Fe_0.5Nb_0.5)O₃(PCNFN)陶瓷的微波介电性能得到改善是由于少量过剩的Nd³⁺与(Pb,Ca)²⁺的固溶能够消除氧空位.当x=0.02时,能够形成单相的钙钛矿相,随着Nd³⁺置换量的增加,过剩的Nd³⁺将导致第二相焦绿石的形成,焦绿石会恶化PCNFN的微波介电性能.PCNFN介电性能随x的增加而下降是由于焦绿石相随x增加的结果.当x=0.02-0.05,PCNFN陶瓷有很好的微波介电性能,介电常数K>100,Qf值为5385-5797GHz,频率温度系数TCF随Nd³⁺含量的增加从正的变为负的.     

Sr_(0.5)Ba_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3双层薄膜的微观结构

采用脉冲激光沉积法在(001)LaAlO_3衬底上制备了Sr_(0.5)Ba_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3薄膜,利用透射电子显微镜对薄膜的微观结构进行了研究。结果表明,底电极La_(0.5)Sr_(0.5)CoO_3在LaAlO_3衬底上外延生长并形成立方-立方取向关系。不同于块体结构,LSCO薄膜发生了结构转变,形成一种氧缺位有序调制结构。整个薄膜由大量取向畴组成,其中包含一些层错与反相畴界等缺陷。生长温度为500℃时,Sr_(0.5)Ba_(0.5)TiO_3薄膜为柱状多晶结构;当温度升高至820℃时,薄膜为缺陷较少的单晶结构。     

Structures and electrical properties of (Na0.5K0.5)NbO3–Li(Ta0.5Nb0.5)O3 lead-free piezoelectric ceramics

Solid solutions of (Na_0.5K_0.5)NbO₃ (NKN) and Li(Ta_0.5Nb_0.5)O₃ (LTN) were investigated as a potential candidate of lead-free piezoelectric ceramics. It was found that the Curie temperature of solid solutions increases slightly with increasing the LTN content and simultaneously the polymorphic phase transition temperature linearly decrease till below room temperature. An orthorhombic to tetragonal phase transformation at room temperature, or a morphotropic phase boundary, in NKN is induced by ~7 at% LTN addition, where the best dielectric, piezoelectric and electromechanical properties are achieved. The 0.94NKN–0.07LTN ceramics possess a dielectric constant of 765, a loss tangent of 0.04 at 1 kHz, a piezoelectric constant d₃₃ of 253 pC/N and an electromechanical coupling factor k_p of 48%.     

Studies on the structural,electrical and magnetic properties of LaCrO3, LaCr0.5Cu0.5O3 and LaCr0.5Fe0.5O3 by sol–gel method

The structural, electrical and magnetic properties of LaCr_0.5M_0.5O₃ (M = Cr³⁺, Cu²⁺ and Fe³⁺) synthesized by a sol–gel technique were studied. The X-ray diffraction pattern shows the structure to be orthorhombic and the size of the particles is around 100 nm as seen from the TEM images. The effects of Cu²⁺ and Fe³⁺ on the electrical properties of LaCrO₃ were studied using impedance spectroscopy at room temperature (RT). The properties of LaCr_0.5Cu_0.5O₃ were studied over a wide range of temperature from RT to 533 K. A maximum conductivity of 1.7 × 10^?3 S cm^?1 was observed for LaCr_0.5Cu_0.5O₃ at a measured temperature of 533 K. The impedance spectra indicate a negative temperature coefficient of resistance (NTCR) and also imply the conduction is through bulk of the material. The magnetic studies performed using a SQUID magnetometer interpret the antiferromagnetically ordered LaCrO₃ to behave ferromagnetically on the addition of Cu²⁺ and Fe³⁺, and the magnetization was found to be enhanced in the LaCr_0.5Fe_0.5O₃.     

Na0.5Bi0.5TiO3-BaTiO3陶瓷的介电和压电性能研究

研究了Ｎａ_０．５Ｂｉ_０．５ＴｉＯ_３和（Ｎａ_０．５Ｂｉ_０．５）_０．９４Ｂａ_０．０６ＴｉＯ_３陶瓷的电滞回线、压电性能和热滞现象·得到（Ｎａ_０．５Ｂｉ_０．５）_０．９４Ｂａ_０．０６ＴｉＯ_３陶瓷的剩余极化Ｐ_ｒ＝１９ｕＣ／ｃｍ^２、矫顽场Ｅ_ｃ＝４．７ｋＶ／ｍｍ．发现用适量的Ｂａ^２＋取代（Ｎａ_０．５Ｂｉ_０．５）^２＋尽管压电性能有所提高,但同时使得材料的温度稳定性大大降低．