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.     

A位复合铁电陶瓷Bi0.5(Na0.82K0.18 )0.5TiO3-BiCrO3 的介电弛豫

采用固相反应法制备了A位复合铁电陶瓷(1-x)Bi0.5(Na0.82K0.18)0.5TiO3-xBiCrO3(BNKT-BCx). 研究了该陶瓷在室温至500℃温度范围内的介电性能. 结果表明该陶瓷的介电温谱存在两个介电反常峰和一个介电损耗峰,低温介电反常峰温度附近具有明显的介电常数频率依赖性,但居里峰随频率增加基本不变,与典型弛豫铁电体的特征不同. 将弛豫铁电体分为本征弛豫和非本征弛豫铁电体,通过分析极化前和极化后陶瓷的介电温谱,发现该体系低温介电反常峰温度附近的介电频率依赖性为空间电荷和缺陷偶极子极化引起的非本征弛豫.     

驰豫型铁电体的宏观介电性能与极化机制研究

驰豫型铁电体是很重要的功能材料,其介电性能和极化机制一直是研究的热点。作者通过对掺钛铌镁酸铅系列铁电陶瓷介电、铁电、热电等宏观性能和微观结构详细、系统的实验研究,提出铁电微畴为三方相畸变结构散布于立方钙钛矿母相中,通过类马氏体预相变的位移型形核过程,实现顺电—驰豫型铁电态的弥散相变,进一步通过类马氏体相变,完成驰豫型铁电态无序态分布的微畴向正常铁电态长程序铁电宏畴转变;提出T_1可调整A(B′B″)O_3型复合钙钛矿铁电体B′和B″离子价态和离子半径等不同所产生的内电场和弹性场,使立方母相所承受切应力发生变化,诱发极性微区、铁电微畴随组成变化表现不同活性。对弛豫型铁电体介电谱分析与计算表明,其在介电常数峰值温度Tm附近的介电弛豫过程连续变化,不对应结构突变的相变过程,较接近偶极介质。通过铌锌酸铅基系列铁电陶瓷在准同型相界附近异常特性的研究,进一步揭示弛豫型铁电体中结构特征决定宏观行为的必要性,反映出铁电材料由微观到介观、再到宏观的有趣规律性。在此基础上,对复合钙钛矿弛豫型铁电体偏压介电行为、电致伸缩特性、介电老化行为等进行了系统研究,合理解释了一系列新的实验现象和结果;并对钨青铜结构铌酸锶钡弛豫型铁电陶瓷复介电响应进行了详细的对比分析和讨     

La2O3掺杂（Na0．5 Bi0．5）0．94 Ba0.06 TiO3无铅压电陶瓷的介电弛豫研究

采用固相合成法制备了La2O3掺杂(Na0.5Bi0.5)0.94Ba0.06TiO3无铅压电陶瓷.研究了La2O3掺杂对(Na1/2Bi1/2)TiO3陶瓷晶体结构、介电性能与介电弛豫行为的影响.XRD分析表明,在所研究的组成范围内陶瓷材料均能够形成纯钙钛矿固溶体.材料的介电常数-温度曲线显示陶瓷具有两个介电反常峰Tf和Tm.修正的居里-维斯公式较好的描述了陶瓷弥散相变特征,弥散指数随La2O3掺杂量的增加而增加.掺杂量较低的陶瓷仅在低温介电反常峰Tf附近表现出明显的频率依赖性,随掺杂量的增加,陶瓷材料在室温和低温介电反常峰Tf之间都表现出明显的频率依赖性.并根据宏畴-微畴转变理论探讨了该体系陶瓷介电弛豫特性的机理.     

A位复合铁电陶瓷Bi0.5(Na0.82K0.18)0.5TiO3-BiCrO3的介电弛豫

采用固相反应法制备了A位复合铁电陶瓷(1-x)Bi_0.5(Na_0.82K_0.18)_0.5TiO₃-xBiCrO₃(BNKT-BCx). 研究了该陶瓷在室温至500℃温度范围内的介电性能. 结果表明该陶瓷的介电温谱存在两个介电反常峰和一个介电损耗峰, 低温介电反常峰温度附近具有明显的介电常数频率依赖性, 但居里峰随频率增加基本不变, 与典型弛豫铁电体的特征不同. 将弛豫铁电体分为本征弛豫和非本征弛豫铁电体, 通过分析极化前和极化后陶瓷的介电温谱, 发现该体系低温介电反常峰温度附近的介电频率依赖性为空间电荷和缺陷偶极子极化引起的非本征弛豫.     

BaNb2O6掺杂Na1/2Bi1/2TiO3无铅压电陶瓷的介电弛豫

采用传统陶瓷制备方法,制备了无铅新压电陶瓷材料Na1/2Bi1/2TiO3-xBaNb2O6.研究了BaNb2O6掺杂对(Na1/2Bi1/2)TiO3陶瓷晶体结构、介电性能与介电弛豫行为的影响.XRD分析表明,在所研究的组成范围内陶瓷材料均能够形成纯钙钛矿固溶体.材料的介电常数-温度曲线显示陶瓷具有两个介电反常峰Tf和Tm,修正的居里一外斯公式较好的描述了陶瓷弥散相变特征,弥散指数随BaNb2O6掺杂量的增加而增加.该体系陶瓷表现出与典型弛豫铁电体明显不同的弛豫行为,低掺杂量的陶瓷仅在低温介电反常峰Tf附近表现出明显的频率依赖性,而高掺杂的陶瓷材料在室温和Tf之间都表现出明显的频率依赖性.并根据宏畴一微畴转变理论探讨了该体系陶瓷产生介电弛豫的机理.     

Y2O3掺杂（Bi0．5Na0．5）0．94Ba0．06TiO3无压电陶瓷的研究铅

采用固相合成法制备了Y2O3掺杂（Bi0．5Na0．5）0．94Ba0．06TiO3无铅压电陶瓷。研究了Y2O3掺杂对（Bi0．5Na0．5）0．94Ba0．06TiO3陶瓷晶体结构、介电与压电性能的影响。XRD分析表明,在所研究的组成范围内陶瓷均能够形成纯钙钛矿固溶体。介电常数-温度曲线显示陶瓷具有弛豫铁电体特征,陶瓷的弛豫特征随掺杂的增加更为明显。在Y2O3掺杂量为0．5％时陶瓷的压电常数d33分别为137pC／N,为所研究组成中的最大值,掺杂量为0．1％时,机电耦合系数kp与kt最大值为0．30,0．47。     

细晶Ba0.6Sr0.4TiO3(BST)陶瓷材料的制备与介电性能

采用改进的Sol-gel工艺和传统烧结技术制备了晶粒尺寸在0.15～10μm的Ba0.6Sr0.4TiO3(BST)陶瓷,观察了样品的显微结构,并对样品的介电性能进行了测试,分析了晶粒尺寸对材料介电性能的影响.实验结果表明:改进的Sol-gel工艺和两步烧结法可以有效地控制Ba0.6Sr0.4TiO3(BST)陶瓷的晶粒尺寸.晶粒尺寸的降低,材料的介电常数也随之下降,介电峰呈现明显的铁电-顺电弥散相变;但当陶瓷的晶粒尺寸＜1 μm,介电常数出现峰值,铁电相变温区变窄.     

(Na0.5Bi0.5)TiO3基弛豫铁电体相变的研究进展

钛酸铋钠((Na0.5Bi0.5)TiO3,NBT)是一种典型的A位复合钙钛矿结构弛豫铁电体,具有复杂的相变序列,介电温度峰呈现明显的弛豫性.总结了NBT弛豫铁电体的相变及NBT基复合铁电体准同型相界的研究进展;从晶体结构出发,通过与B位复合型钙钛矿结构弛豫铁电体类比,对A位复合型NBT的弛豫机理进行了探讨,提出NBT弛豫性来源于其A位离子有序-无序引起的B位离子位移的变化.     

La替代对Bi2O3-ZnO-Nb2O5陶瓷介电性能的影响

研究了A位La^3＋替代对Bi2O3-ZnO-Nb2O5（BZN）陶瓷结构和介电性能的影响。当La替代量X〈0．5时，陶瓷相结构为单一的立方焦绿石相。随着La替代量的增加，陶瓷样品的晶粒尺寸和密度逐渐减小。低温下的介电弛豫现象随着La替代量的增加也发生有规律的变化，介电常数逐渐减小，弛豫峰峰形逐渐宽化，峰值温度向低温方向移动。与La替代量为0．1、0．15、0．3和0．5相对应的弛豫峰的峰值温度分别为-95℃、-99℃、-109℃和-112℃。     

Enhanced room temperature multiferroic behaviour of Ni-doped Na0.5Bi0.5TiO3 ceramics

In this paper, room temperature multiferroic behaviour in Ni (Nickel)-doped NBT (Na_0.5Bi_0.5TiO₃) ceramics synthesized using solid state reaction technique have been investigated. Structural, dielectric, ferroelectric, magnetic and magneto-dielectric properties were consistently probed with the increment in transition metal doping. XRD peaks were indexed for the monoclinic Cc phase. SEM micrographs clearly depicted the reduction of grain size with addition of Ni content. Ferroelectric polarization (P) vs applied electric field (E) hysteresis curves shows an increase in lossy behaviour with an increase in Ni content. The room temperature magnetization (M) vs applied magnetic field (H) curves depict the weak ferromagnetic ordering on increasing the Ni doping. Enhanced magneto-dielectric change of 1.26% was observed in 25% Ni-doped NBT ceramic, which may be useful in the development of novel non-volatile lead-free multiferroic memory devices.

     

(Bi0.5Na0.5)0.935Ba0.065TiO3-xBiScO3陶瓷储能及应变性能研究

本研究采用BiScO₃组分对固相烧结工艺制备的(1-x)(Bi_0.5Na_0.5)_0.935Ba_0.065TiO₃-xBiScO₃(BNBT-xBS)无铅陶瓷进行改性, 考察了BiScO₃掺杂含量对陶瓷的微观结构、储能、场致应变和介电等性能的影响。结果表明: 随着BiScO₃掺杂含量的增加, BNBT-xBS陶瓷的相结构由三方相与四方相共存演变为伪立方相, 无杂相形成, 且平均晶粒尺寸略有增大; BiScO₃组分的引入破坏了BNBT陶瓷铁电畴的长程有序, 表现出弱极化, 且伴随有铁电相到弛豫铁电相的相变过程。BiScO₃组分提高了储能和应变性能, 在70 kV/cm电场下其最大储能密度为0.46 J/cm³, 电致应变达到0.25%。介电常数随着掺杂含量的增加逐渐降低, 其介电行为也表明陶瓷具有弛豫铁电体特征; BNBT-xBS陶瓷表现出负温度系数效应, 且在450℃以下具有较好的绝缘性。     

Effect of La and K on the microstructure and dielectric properties of Bi0.5Na0.5TiO3-PbTiO3

Small amounts of lanthanum and potassium dopants could modify the microstructure and dielectric properties of 0.90Bi_0.5Na_0.5TiO₃-0.10PbTiO₃ and 0.88Bi_0.5Na_0.5TiO₃-0.12PbTiO₃ solid solutions. La lowered both phase transition temperatures of ferroelectric to antiferroelectric and antiferroelectric to paraelectric. It also decreased the maximum value of relative dielectric permittivity of the composition. In contrast, K shifted the first phase transition to the lower temperature but insignificantly affected the Curie temperature and raised the maximum dielectric permittivity. Furthermore, K influenced the microstructure in the way to enhance the long grains of this solid solution but La inhibited this effect.     

Pb(Ni1/3Nb2/3)O3-PbTiO3系统准同型相界附近的介电异常

用两步合成法制备了(1-x)Pb(Ni1/3Nb2/3)O3-xPbTiO3(x=0.300.40)陶瓷,对其相结构和介电性能进行了研究. XRD分析表明,准同型相界在PT含量x=0.340.38范围内. 介电性能研究结果表明,组成在准同型相界处的试样, 其介电常数呈现最大值.同时还发现,准同型相界处的陶瓷出现介电双峰,其中一个为弛豫型?铁电相向顺电相转变的相变峰;另一个介电峰处于130150C的高温区, 可能是由镍离子变价、相结构变化等缺陷引起的松弛极化产生的.     

Ferroelectric, electromechanical, and dielectric properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 co-doped MnO2 and La2O3 lead-free ceramics

The modified (Na_0.5Bi_0.5)_0.94Ba_0.03La_0.02Ti_0.995Mn_0.005O₃ lead-free ceramics were prepared using a traditional solid-state reaction process, and their structures were characterized by X-ray diffraction, scanning electron microscope, and Raman spectroscopy, respectively. A double-like P–E loop was discussed at the room temperature for the co-doped ceramics by reason of the appearance of the anti-ferroelectric. The ferroelectric hysteresis loop and field-induced strain were studied at different temperatures. A large strain (S ₃₃ = 0.33 %, E = 50 kV/cm at 120 °C) was observed due to the transformation between ferroelectric and anti-ferroelectric phase at the phase transition temperature. Also, the depolarization temperature (T _d) of the co-doped ceramics was determined from the pyroelectric current density versus temperature plots, which was consistent with the result from the position of dielectric loss’s peak as a function of temperature.     

Microstructure, dielectric and piezoelectric properties of lead-free Bi 0·5 Na 0·5 TiO 3 −Bi 0·5 K 0·5 TiO 3 −BiMnO 3 ceramics

To improve the piezoelectric properties of Bi _0·5Na _0·5TiO ₃-based ceramics, a new perovskite-type lead-free piezoelectric (1 –  x –  y)Bi _0·5Na _0·5TiO ₃??xBi _0·5K _0·5TiO ₃??yBiMnO ₃ system has been fabricated by a conventional solid–state reaction method and their microstructure, dielectric and piezoelectric properties have been investigated. The results of X-ray diffraction (XRD) analysis reveal that the addition of small amounts of BiMnO ₃ did not cause a remarkable change in crystal structure, but resulted in an evident evolution in microstructure. An obvious secondary phase was observed in samples with high Bi _0·5K _0·5TiO ₃ content. It is found from dielectric constant curves that low-temperature hump disappeared with increasing y and it appeared again with increasing x. The piezoelectric properties significantly increase with increasing Bi_0·5K_0·5TiO₃ and BiMnO ₃ content. The piezoelectric constant and electromechanical coupling factor attain maximum values of d ₃₃?=?182 pC/N at x = 0·21(y = 0·01) and k _p = 0·333 at x = 0·18 (y = 0·01), respectively.     

Effect of Sintering Temperature on the Microstructure,Electrical, and Magnetic Properties of Bi 0 . 8 5 Eu 0 . 1 5 FeO 3 Ceramics

Polycrystalline Bi _0.85Eu _0.15FeO ₃ ceramics were synthesized by solid-state reaction method with rapid liquid phase sintering process at various sintering temperatures. The dependence of structural, microstructural, electrical, and magnetic properties on sintering temperature was systematically investigated. X-ray diffraction measurements reveal that single perovskite phase is developed in Bi _0.85Eu _0.15FeO ₃ ceramics sintered at 850 and 870^° C, while secondary phases can be detected in the samples sintered at 890^° C due to the volatilization of Bi ³⁺ ions, and the crystallinity increases with increasing sintering temperature from 850 to 890 °C. The scanning electron microscopy investigation has suggested that the grain size increases with increasing sintering temperature from 855 t o 890^° C; while the pore size decreases with increasing sintering temperature from 850 to 870^° C and then increases with a further increase of sintering temperature. The electrical and magnetic measurements show that the leakage current, dielectric constant, dielectric loss, and magnetic properties are strongly dependent on the sintering temperature. The Bi _0.85Eu _0.15FeO ₃ ceramics sintered at 870^° C have the lower leakage current, higher dielectric constant, and lower dielectric loss. The room temperature magnetization increases with increasing sintering temperature from 850 to 890 °C. The possible reason for all the above observations was discussed.     

Enhanced tunable characteristics of the Na0.5Bi0.5TiO3-NaTaO3 relaxor-type system

We have investigated the voltage-tunable characteristics of the Na(0.5)Bi(0.5)TiO(3)-NaTaO(3) homogeneity region, for which samples were prepared using a conventional solid-state reaction. The highest value of the relative tunability (n(r)) was obtained for the sample with 5 mol% of NaTaO(3), i.e., 47% at 1 MHz and a 70 kV/cm dc bias field. This sample also showed the highest value of the dielectric losses (tan delta) and temperature coefficient of the dielectric constant (tau(epsilon)), i.e., 0.05 and 4478 ppm/K, respectively. As the concentration of NaTaO(3) increased up to 90 mol% n(r), tan delta, and tau(epsilon) gradually decreased toward 22%, 0.0002 and -899 ppm/K, respectively. The dielectric constant of the samples varied in a similar manner between 662 and 130. At microwave frequencies, the dielectric losses of the samples substantially increased due to their relaxor-type nature. The lowest value was obtained for the samples with 90 mol% of NaTaO(3), i.e., 0.002. The tunable characteristics of the samples are related to the ferroelectric and dielectric properties, and it appears that the dielectric tunability of the Na(0.5)Bi(0.5)TiO(3)-NaTaO(3) system originates from its relaxor-type behavior.     

Dielectric and impedance characteristics of Ba(Bi0.5Nb0.5)O3 ceramics

A lead free polycrystalline material Ba(Bi_0.5Nb_0.5)O₃ was prepared using a high-temperature mixed oxide technique using high purity ingredients. The formation of the material in monoclinic crystal structure was confirmed by an X-ray structural analysis at room temperature. The nature and texture of microstructure by scanning electron microscopy show that the compound has well defined grains uniformly distributed throughout the surface of the sample. Detailed studies of dielectric and impedance properties of the material, carried out in the frequency range of (1 kHz–1 MHz) at different temperatures (30 °C to 475 °C), have shown many interesting properties. Dielectric study showed an existence of diffuse phase transition around 317 °C. The temperature dependence of impedance parameters (impedance, modulus etc.) of the material exhibits a strong correlation of its micro-structure (i.e., bulk, grain boundary, etc.) with the electrical parameters. An existence of negative temperature coefficient of resistance (NTCR) type behavior in the material similar to that of semiconductors was also observed. The complex electric modulus analysis indicates the existence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law. The temperature dependent pre-exponential factor (A) shows peak and frequency exponent (n) possesses a minimum at transition temperature.     

Effects of La occupation site on the dielectric and piezoelectric properties of [Bi0.5(Na0.75K0.15Li0.10)0.5]TiO3 ceramics

The crystal structure, phase transition and ferroelectric (FE)/piezoelectric properties were investigated for three types of La-doped [Bi_0.5(Na_0.75K_0.15Li_0.10)_0.5]TiO₃ ceramics. The dielectric measurements showed that the transition between FE and antiferroelectric (AFE) phases near 180 °C became pronounced by La addition, and the maximum permittivity was observed at 360 °C in La-doped samples, whereas at 290 °C in non-doped samples. Normal FE and excellent piezoelectric properties were observed by P–E hysteresis loop and piezoelectric measurements in samples without vacancy. However, when the A-site or B-site vacancies were formed, the temperature range of AFE phase extended even appeared at room temperature, which resulted in the presence of deformed P–E curves and decrease of piezoelectric properties. It was suggested that the AFE phase originated from the decoupling effect between BO₆ octahedra in ABO₃ perovskites due to the A-site and/or B-site vacancies.