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.     

铈和镧掺杂对（Bi1/2Na1/2）0.94Ba0.06TiO3压电陶瓷性能的影响

采用传统陶瓷制备方法，制备出La2O3和CeO2掺杂的（Bi1/2Na1/2）0.94Ba0.06TiO3无铅压电陶瓷，研究了微量稀土元素La,Ce对（Bi1/2Na1/2）0.94Ba0.06TiO3无铅压电陶瓷微观结构、介电与压电性能的影响。XRD分析表明，La2O3和CeO2的掺杂量在0．1％～0．8％C质量分数）范围内都能形成纯钙钛矿（ABO3）型固溶体。测试了不同组成陶瓷的介电、压电性能，陶瓷材料的介电常数．温度曲线显示La2O3掺杂的陶瓷在升温过程中存在两个介电常数温度峰，而CeO2掺杂的陶瓷的低温介电常数温度峰不明显；在La2O3和CeO2掺杂量为0．3％时陶瓷的压电常数d33分别为156pC/N和160pC/N，为所研究组成中的最大值，平面机电耦合系数Kp最大值出现在La2O3和CeO2掺杂量为0．1％时，分别为0.32，0.31。     

补偿电价取代对(Bi1/2Na1/2)TiO3无铅压电陶瓷介电与压电性能的影响

采用传统陶瓷制备方法,制备出一种钙钛矿结构无铅新压电陶瓷材料(1-x)(Bi1/2Na1/2)TiO3-xBi(Mg2/3 Nb1/3)O3.研究了一种化合物Bi(Mg2/3 Nb1/3)O3中两种离子Bi3 和(Mg2/3Nb1/3)3 同时进行补偿电价取代对(Bi1/2Na1/2)TiO3陶瓷介电和压电性能的影响.X射线衍射分析表明,所研究的组成均能够形成纯钙钛矿(ABO,)型固溶体.陶瓷材料的介电常数-温度曲线显示该体系材料具有明显的弛豫铁电体特征.适量的取代能提高材料的压电性能,在x=0.7%时压电常数d33=94 pC/N,x=0.9%时厚度机电耦合系数kt=0.46,为所研究组成中的最大值.该体系陶瓷具有较大的kt值和较小的kp值,具有较大的各向异性.     

（1-y）[（Na0.96-xKxLi0.04）0.5Bi0.5]TiO3-yBa（Zr0.055Ti0.945）O3无铅压电陶瓷的压电介电特性

对（1-y）[（Na0.80K0.16Li0.04）0.5Bi0.5]TiO3-yBa（Zr0.055Ti0.945）O3无铅压电陶瓷进行了系统研究，获得压电应变常数d33高达185（pC/N）的0．94[（Na0.80K0.16Li0.04）0.5Bi0.5]TiO3-yBa（Zr0.055Ti0.945）O3压电陶瓷。还研究了该材料[（Na0.96-xKxLi0.04）0.5Bi0.5]TiO3-yBa（Zr0.055Ti0.945）O3的性质随K含量的变化．随着Ba（Zr0.055Ti0.945）O3含量的增加，该陶瓷材料的介电温谱峰值向左移动，其介电峰温度缓慢降低；与此相反，随着K掺杂量的增加，该陶瓷材料的介电温谱峰值却向右明显移动，其介电峰温度明显升高。     

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.     

Y2O3掺杂(Bi0.5 Na0.5)0.94 Ba0.06 TiO3无铅压电陶瓷的研究

采用固相合成法制备了Y2O3掺杂(Bi0.5 Na0.5)0.94 Ba0.06 TiO3无铅压电陶瓷.研究了Y2O3掺杂对(Bi0.5 Na0.5)0.94Ba0.06 TiO3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137 pC/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.     

Na-Sn掺杂Bi2O3-ZnO-Nb2O5陶瓷的性能

研究了Na+替代Bi3+、Sn4+替代Nb5+对Bi2(Zn1/3Nb2/3)2O7陶瓷烧结特性、显微结构和介电性能的影响.结果表明,替代后样品的烧结温度从1000℃降低到860℃;在-30～130℃样品出现明显的介电弛豫现象;弛豫激活能在0.3eV左右.用缺陷偶极子和晶格畸变对Na-Sn掺杂Bi2(Zn1/3Nb2/3)2O7的介电弛豫现象进行了解释.     

0.94[(Na0.96-xKxLi0.04)0.5Bi0.5]TiO3-0.06Ba(Zr0.055Ti0.945)O3无铅压电陶瓷的压电介电特性

对无铅压电陶瓷0.94[(Na0.96-xKxLi0.04)0.5Bi0.5]TiO3-0.06Ba(Zr0.055Ti0.945)O3的性质随K含量的变化进行了系统研究,获得压电应变常数d33高达185pC/N的0.94[(Na0.80K0.16Li0.04)0.5-Bi0.5]TiO3-0.06Ba(Zr0.055Ti0.945)O3压电陶瓷.随着K掺杂量的增加,该陶瓷材料的介电温谱峰值向右明显移动,其介电峰温度明显升高.     

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.     

（Na1/2Bi1/2）TiO3无铅压电陶瓷的复合离子与补偿电价取代效应研究

采用传统陶瓷制备方法，制备出两种钙钛矿结构无铅新压电陶瓷材料（1-x）（Na1/2Bi1/2）TiO3-x（Na1/2Bi1/2）（Sb1/2Nb1/2）O3和（1-y）（Na1/2Bi1/2）TiO3-yBi（Mg2/3Nb1/3）O3。研究了复合离子与补偿电价取代对（Na1/2Bi1/2）TiO3陶瓷晶体结构和压电性能的影响。）（射线衍射分析表明，在所研究的组成范围内两种陶瓷材料均能够形成纯钙钛矿固溶体．陶瓷材料的介电常数-温度曲线显示两种陶瓷体系具有明显的弛豫铁电体特征．适量的复合离子与补偿电价取代都能提高材料的压电性能，在工=0．8％时，陶瓷的压电常数d33=97pC/N，厚度机电耦合系数kr=0．50，在y=0．7％时d33=94pC/N，y=0．9％时k1=0．46，为所研究组成中的最大值。两种陶瓷体系都具有较大的‰值和较小的kp值，具有较大的各向异性，是一种优良的、适合高频下使用的超声换能材料．     

二分之一体育场

明媚操场 之所以叫做“二分之一体育场”,是因为它有着介于操场和体育场之间的特点。无论从尺度、规模,还是从形式和使用功能上来说,二分之一体育场都介于操场和体育场之间,设计师空格建筑用独特的建筑设计手法,改变了传统上学校体育场严肃、简单的刻板印象,用活泼而大胆的建筑语言,开创了全新的学校体育场的设计方式。     

Phase-transition temperatures and piezoelectric properties of (Bi1/2Na1/2)TiO3-(Bi1/2Li1/2)TiO3-(Bi1/2K1/2)TiO3 lead-free ferroelectric ceramics.

The phase-transition temperatures and piezoelectric properties of x(Bi(1/2)Na(1/2))TiO3-y(Bi(1/2)Li(1/2))TiO3-z(Bi(1/2)K(1/2))TiO3 [x + y + z = 1] (abbreviated as BNLKT100(y)-100(z)) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T(d), rhombohedraltetragonal phase transition temperature T(R-T), and dielectric-maximum temperature T(m) were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100(y)-100(z)) show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor k(33), piezoelectric constant d(33) and T(d) of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171 degrees C, and 0.590, 190 pC/N, and 115 degrees C, respectively. In addition, the relationship between d33 and Td of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high Td and high d(33), the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d(33) and T(d) of BNLKT4-28 were 135 pC/N and 218 degrees C, respectively. Moreover, this study revealed that the variation of T(d) is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a.     

Structure transformations and dielectric properties of PbY1/2Nb1/2O3 and PbHo1/2Nb1/2O3 compounds

The metastable pseudomonoclinic perovskite phases, PbY_1/2Nb_1/2O₃ and PbHo_1/2Nb_1/2O₃ were prepared under conditions of high pressures and temperatures. Investigations of structural parameters, thermal stability and some dielectric properties were carried out. The data were analyzed by comparison with corresponding data of other representatives of the PbB_1/2³⁺Nb_1/2O₃ series. The dependence of unit cell parameters on the B³⁺ rare earth cation radius for the PbB_1/2³⁺Nb_1/2O₃ perovskites was correlated with a change of electronic structure of the rare earth elements, in particular, with the 4f-shell filling.     

Spray-drying synthesis of P2-Na2/3Fe1/2Mn1/2O2 with improved electrochemical properties

Owing to its high theoretical capacity, P2-type Na_2/3Fe_1/2Mn_1/2O₂ has been considered as a kind of promising cathode material. However, the practical application is limited due to excessively high calcining temperature during traditional preparation processes. Here, we report the synthesis of P2-Na_2/3Fe_1/2Mn_1/2O₂ by using a facile spray-drying method followed by calcining at low temperature. Under the optimal conditions, the well-crystallized P2-Na_2/3Fe_1/2Mn_1/2O₂ material with excellent rate capability and cycle ability is obtained. And the sample exhibits the initial discharge capacities of 217.9, 171.3 and 117.4 mAh g⁻¹ at 0.1 C, 0.5 C and 2 C rate, respectively. The developed Na_2/3Fe_1/2Mn_1/2O₂ material, synthesized by a new spray drying-calcining procedure, may potentially be used as a suitable cathode in sodium ion batteries.     

Electrical properties of Na1/2Nd1/2TiO3 Ceramics

The polycrystalline sample of Na_1/2Nd_1/2TiO₃ was prepared by a high-temperature solid-state reaction technique. The formation of the compound was confirmed by both XRD and EDX studies. Preliminary structural analysis ofNa_1/2Nd_1/2TiO₃ using X-ray diffraction data exhibits a tetragonal phase of the material at room temperature. The dielectric permittivity and the loss tangent of the pellet sample were obtained in a wide frequency range (1 kHz to 1 MHz) at different temperatures (30 °C to 425 °C). The dielectric anomaly at 114 °C, appearance of hysteresis loop and piezoelectric properties at room temperature confirmed the ferroelectric properties of the compound. Measurements of frequency and temperature dependence of impedance over a wide frequency range (100Hz–1MHz) were carried out by complex impedance spectroscopy as a non-destructive tool and indicate that the electrical properties of the material are strongly temperature dependent. Evidence of temperature dependence of electrical relaxation phenomenon as well as the negative temperature coefficient (NTC)-type of resistance behavior of the sample has also been observed. The dc conductivity graph follows the Arrhenius law. Studies of dielectric modulus suggest the non-Debye type of relaxation in the materials, which is supported by the impedance data.     

Preparation and characterization of LiFe1/2Ni1/2VO4

A layered ceramic oxide, LiFe_1/2Ni_1/2VO₄ has been prepared using solid-state reaction technique. The preparation conditions have been optimized using thermogravimmetric analysis (TGA) studies. The formation of the material sample under the reported condition has been confirmed by X-ray diffraction (XRD) analysis. XRD analysis indicates the crystal structure to be orthorhombic with lattice parameter: a = 3.5637 Å, b = 17.7486 Å, c = 12.2884 Å. The phase morphology and surface properties studied using scanning electron microscopy (SEM), suggest a polycrystalline texture with reasonable number of the voids. Complex impedance analysis of the sample has indicated: (i) conduction due to bulk contribution at T ≤ 200 °C, (ii) the presence of grain boundary effects at T ≥ 200 °C, (iii) negative temperature coefficient of resistance (NTCR) behaviour and (iv) evidence of temperature dependent electrical relaxation phenomena in the sample. The DC conductivity (σ_DC) shows typical Arrhenius behaviour when observed as a function of the temperature. The activation energy value has been estimated to be 0.42 eV. σ_DC, as evaluated from complex impedance spectrum, shows a jump of nearly ∼4 orders of magnitude in the value at higher temperature when compared to that of the room temperature value. AC conductivity spectrum obeys Jonscher's universal power law. The results of σ_AC as a function of frequency are also discussed.     

Phase-transition temperatures and piezoelectric properties of (Bi/sub 1/2/Li/sub 1/2/)TiO/sub 3/-(Bi/sub 1/2/K/sub 1/2/)TiO/sub 3/ lead-free ferroelectric ceramics

The phase-transition temperatures and piezoelectric properties of x(Bi_1/2Na_1/2)TiO_3-y(Bi_1/2Li_1/2)TiO_3-z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y-100z) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T_d, rhombohedral-tetragonal phase transition temperature T_R-T, and dielectric-maximum temperature T_m were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100y-100z show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor &33, piezoelectric constant d₃₃ and T_d of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171degC, and 0.590, 190 pC/N, and 115degC, respectively. In addition, the relationship between d₃₃ and T_d of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high T_d and high d₃₃, the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d₃₃ and T_d of BNLKT4-28 were 135 pC/N and 218degC, respectively. Moreover, this study revealed that the variation of Td is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a.     

Depolarization temperature and piezoelectric properties of Na1/2Bi1/2TiO3-Na1/2Bi1/2(Zn1/3Nb2/3)O3 ceramics by two-stage calcination method

A new group of NBT-based lead-free piezoelectric ceramics, Na_1/2Bi_1/2TiO₃-Na_1/2Bi_1/2(Zn_1/3Nb_2/3)O₃, was synthesized using the two-stage calcination method and depolarization temperatures and piezoelectric properties were also investigated. The XRD analysis showed that the ceramics system had a morphotropic phase boundary (MPB) between the rhombohedral and the tetragonal structure. The highest piezoelectric properties of d ₃₃ = 97 pC/N and k _t = 0·46 were obtained near MPB compositions. Furthermore, the depolarization temperatures near MPB compositions were slightly decreased and the lowest T _d was maintained at 210°C.     

Dielectric and piezoelectric properties of (0.97-x) Bi1/2Na1/2TiO3-xBi1/2K1/2TiO3-0.03NaNbO3 ceramics

Ceramics of the series (0.97-x)Bi_1/2Na_1/2TiO₃-xBi_1/2K_1/2TiO₃-0.03NaNbO₃ (x = 0, 0.02, 0.06, 0.10, 0.16, 0.20, 0.30) were prepared by the conventional mixed oxide method. Influence of Bi_1/2K_1/2TiO₃ content on the crystal structure, microstructure, dielectric and piezoelectric properties were studied. All compositions showed single perovskite phase and the morphotropic phase boundary (MPB) between rhombohedral and tetragonal phase existed at the point of x = 0.16. Temperature dependences of permittivity and dissipation factor of unpoled samples revealed that permittivity increased with Bi_1/2K_1/2TiO₃ content and it reached maximum value near the MPB. At the same time, the peak value of dissipation factor increased with the addition of Bi_1/2K_1/2TiO₃. All the samples experienced two phase transitions: from ferroelectric to antiferroelectric at the first transition temperature (T_d) and from antiferroelectric to paraelectric at the temperature (T_m) corresponding to maximum value of permittivity. The phase transition from ferroelectric to antiferroelectric had relaxor characteristic and T_d shifted to lower temperature while increasing Bi_1/2K_1/2TiO₃ content. The best piezoelectric properties were obtained in 0.81Bi_1/2Na_1/2TiO₃-0.16Bi_1/2K_1/2TiO₃-0.03NaNbO₃ ceramic with a piezoelectric constant (d₃₃) of 146pC/N, planar electromechanical coupling factor (k_p) of 30.3% and thickness electromechanical coupling factor (k_t) of 53.2%. Abnormal piezoelectric properties were observed in the sample (x = 0.20), which was attributed to the co-existence of ferroelectric and antiferroelectric phases in it.