复合BaTiO3的Li0.5La0.5TiO3固体电解质的制备和性能

采用高温固相法合成具有高离子电导率的固体电解质Li0.5La0.5TiO3,并以Li0.5La0.5TiO3为母体,通过复合高介电纳米BaTiO3制得一系列不同复合量的复合电解质。对样品进行XRD、SEM分析,并应用交流阻抗技术测试其电导率。母体钛酸镧锂(LLTO)为存在超结构的立方晶体,30℃时晶粒电导率为1.1×10-3S/cm。在复合样品中,LLTO与BaTiO3形成具有棒状结构的钙钛矿型固溶体(Li、La、Ba)TiO3。在低的复合量下(小于10%),复合样品的晶粒电导率比纯样晶粒电导率高。120℃时,母体与复合5%样品的晶粒电导率分别为0.84×10-2、2.39×10-2S/cm,活化能分别为0.22、0.40eV。     

Characteristic of grain oriented (Bi0.5Na0.5)TiO3-BaTiO3 ceramics

Dielectric and piezoelectric properties of grain oriented (Bi_0.5Na_0.5)TiO₃-BaTiO₃ ceramics were investigated in a process that the templated grain growth and hot pressing methods were employed. A ceramic composition in Bi-based perovskite structure family, (Bi_0.5Na_0.5)TiO₃-BaTiO₃, was chosen as a matrix material and plate shaped SrTiO₃ as a template. To examine the combined process effect on piezoelectric properties, three processes, conventional solid reaction, templated grain growth and the combine treatment of templated grain growth and hot-pressing, were compared. Specimen processed by templated grain growth and hot pressing methods exhibited better piezoelectric coefficient, d ₃₁ (−79.6 pC/N) and electromechanical coefficient, k ₃₃ (0.35) than those of the other specimens, fabricated by solid reaction and templated grain growth, respectively. The improved properties were attributed to reduction of pore existing in matrix, which is related to abnormal grain growth from SrTiO₃ template and its resultant heterogeneous shrinkage.     

K0.5Na0.5NbO3掺杂对BaTi03陶瓷介电性能的影响

采用固相反应法制备了（K0.5Na0.5）Nb03-BaTiO3。体系陶瓷。借助XRD、SEM和阻抗分析仪研究了掺杂（K0.5Na0.5）Nb03（简写为KNN）对陶瓷微结构及介电性能的影响。结果表明,掺杂KNN的陶瓷均呈单一的钙钛矿结构;掺杂KNN能促进陶瓷的烧结和提高陶瓷的致密度。,BaTiO,陶瓷在高温端的电容变化率随KNN量的增加显著减小。陶瓷晶粒尺寸随KNN的增加（KNN掺杂量≤3m01％）逐渐变小。掺杂3mol%6和5m01％KNN的BaTiO3陶瓷满足EIAX7R特性。     

Processing and properties of nanocrystalline Pb(Sc0.5Ta0.5)O3, Pb(Sc0.5nb0.5)O3 and Pb(Mg1/3Nb2/3)O3 films produced by RF-sputtering from ceramic targets

Abstract

Nanocrystalline thin films of different relaxor materials, namely Pb(Sc_0.5Ta_0.5)O₃ (PST), Pb(Sc_0.5Nb_0.5)O₃(PSN), Pb(Mg_1/3Nb_2/3)O₃(PMN) have been produced by RF-sputtering to investigate whether it will affect their dielectric properties if their grain size is reduced to the dimensions known from their nanodomains. The XRD shows that the amorphous film crystallizes in pyrochlore structure at lower temperatures and short times. Annealing at higher temperatures and far longer time intervals leads to an increasing amount of perovskite phase with a grain size in the nanometer range. These results including dielectric measurements will be presented and discussed.     

Preparation of Perovskite Pb(B0.5Nb0.5)O3 (B = Rare-Earth Elements)

Pb(B_0.5Nb_0.5)O₃ (B = Sc, Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) powders were prepared from mixed nitrate solutions by a chemical coprecipitation method. This method produced very small particles (30 nm) with good compositional homogeneity. These powders were highly reactive upon calcination. The powders of the systems (B = Sc, Tm, Yb and Lu) yielded 100% perovskite phase after calcination between 800C and 1000C for 1 h. For the system with B = Er, 93% perovskite phase was formed at 900C for 1 h. For the other systems of the elements (B = Y, Nd, Sm, Eu, Gd, Tb, Dy and Ho) with a larger ionic size, perovskite compounds were not formed up to 1100C. The stability and the possible formation of the compounds with a perovskite structure for the Pb(B_0.5Nb_0.5)O₃ series were discussed.     

Study on growth,optical and dielectric properties of ‘Nd’ DOPED NBT-BT (0.94(Na0.5Bi0.5tio3)-0.06batio3) relaxor ferroelectric single crystals

Journal of Electroceramics - The present work describes the effect of Neodymium (Nd) in the NBT-BT (0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-BT (94/06))?+?xNd (x?=?0, 0.4, 0.6,...     

The resistance degradation of (Ba0.5Sr0.5)TiO3 thin films

Abstract

The leakage current and dielectric properties of (Ba_0.5Sr_0.5)TiO₃(BST) thin films prepared by pulsed laser deposition (PLD) were investigated. It was found that leakage currents for positive bias voltage were higher than that for negative bias voltage, which was attributed to the lattice mismatch between bottom Pt electrode and BST thin film. The time-dependent breakdown process under positive voltage was observed, which was interpreted as the increase of the internal electric field in the film near the bottom electrode. However, the internal electric field can be decreased and eventually recovered by applying negative bias voltage. It was found that internal electric field near the interface can influence the capacitance of the BST thin film capacitor. An explanation for the thickness effect of BST thin films was given.     

CHARACTERIZATIONS OF W-DOPED (Ba0.5Sr0.5)TiO3 THIN FILMS USING LaNiO3 ELECTRODE

ABSTRACT

The (Ba_0.5Sr_0.5)TiO₃ thin films were deposited onto LaNiO₃ by RF-magnetron sputtering at 550°C. The influence of W content on microstructure and electrical properties of BST films were investigated. The surface and grain size become smoother and smaller as the W content increased. Besides, the dielectric constant, tunability, dissipation factor, and leakage current decreased when the W content increased. The 1% W is the optimal doping concentration. The resultant BST film, with proper dielectric constant and leakage current, has a tunability of 32%, a dissipation factor of 0.006, a FOM value of 53.3 under applied field of 450 kV/cm.     

Effect of La3+ substitution on microwave dielectric properties of (Pb0.5Ca0.5)(Fe0.5Nb0.5)O3 ceramics

Microwave dielectric properties of the [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ and [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics were investigated as a function of La³⁺ content $ {\left( {0.0 \leqslant \times \leqslant 0.2} \right)} $ . A single perovskite phase was detected in [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃, while Pb₃Nb₄O₁₃ were detected as a secondary phase in [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ beyond x?=?0.05 due to the excess of unbalanced charge. The amount of Pb₃Nb₄O₁₃ was proportional to the unbalanced charge. Qf value of [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ decreased remarkably with La³⁺ substitution due to the increase of oxygen vacancy. For [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics, dielectric constant and Qf value increased with La³⁺ content up to x?=?0.03 due to an increase of density and grain size. Temperature coefficient of resonant frequency (TCF) was depended on B-site bond valence in single perovskite phase.     

High-temperature stable dielectrics in Mn-modified (1-x) Bi0.5Na0.5TiO3-xCaTiO3 ceramics

In the current work, the bulk (1-x) Bi_0.5Na_0.5TiO₃-xCaTiO₃ [BNCT100x] system was synthesized via solid-state route. CaTiO₃ in solid solution with Bi_0.5Na_0.5TiO₃ was observed to decrease the dielectric constant at higher temperature and raise the dielectric constant at lower temperature. Polarization hysteresis measurements indicated that the ferroelectricity of Bi_0.5Na_0.5TiO₃ was weakened with an increase of CaTiO₃, resulted in the shift of the depolarization temperature (T _d) toward lower temperatures. X-ray diffraction analysis revealed that TiO₂ was produced as a secondary phase due to the losses of Bi and Na during milling and sintering processes. Moreover, the addition of Ca promoted the segregation of Ti out of BNT grains. Dielectric properties of BNCT12 ceramics with different dopant levels of Mn were characterized as a function of temperature for potential use of high-temperature capacitors. Modification of BNCT12 materials with Mn improved the temperature characteristic of capacitance (?55°C to 250°C, △C/C_25°C ≤ ±15%). Finally, by doping 1.5 wt% Mn, the dielectric constant at room temperature could reach over 900, with a low dielectric loss below 1% and a high insulation resistivity about 10¹² Ω?cm. Furthermore, a small amount of Mn influenced the microstructure in the way to inhibit the long grains and grain growth of BNCT solution ceramics. However, excess Mn caused abnormal grain growth, and therefore, rectangle grains appeared again.     

SYNTHESIS AND CHARACTERIZATION OF SB-SUBSTITUTED (K0.5Na0.5)NbO3 PIEZOELECTRIC CERAMICS

ABSTRACT

Lead-free piezoelectric ceramics (K_0.5Na_0.5)(Nb_1-xSb_x)O₃+0.5 mol.%MnO₂, where x = 0 ÷ 0.10, with single phase structure and rhombohedral symmetry at room temperature were prepared by conventional ceramic technology. The optimal sintering temperatures of compositions were within 1100°–1140°C. MnO₂ functions as a sintering aid and effectively improves the densification. The samples reached density from 4.26 g/cm³ for undoped (K_0.5Na_0.5)NbO₃ to 4.40 g/cm³ for Mn/Sb⁵⁺ co-doped ceramics. The co-effects of MnO₂ doping and Sb⁵⁺ substitution lead to significant improvement in dielectric and piezoelectric properties: ε at the T_c increased from 6000 (KNN) to 12400 (x = 0.04), d₃₃ = 92 ÷ 192 pC/N, k_p = 0.32 ÷ 0.46, k_t = 0.34 ÷ 0.48.     

Ferroelectric phase transition and electrical properties of Ba(Bi0.5Ta0.5)O3

A lead free polycrystalline material Ba(Bi_0.5Ta_0.5)O₃ was prepared by a standard high-temperature solid-state technique (calcination temperature?=?1180 °C and sintering temperature?=?1200 °C) using high-purity ingredients. The room temperature X-rays diffraction analysis of the material has confirmed its formation in the monoclinic crystal system. The study of microstructure using scanning electron microscopy (SEM) shows 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 were carried out in a wide frequency range (1 kHz ?1 MHz) at different temperatures (30 °C to 490 °C). Dielectric study shows that the material has ferroelectric properties with diffuse-phase transition around 315 °C. Complex impedance spectroscopic analysis establishes some correlation between the microstructure and electrical properties of the material. The frequency dependence of ac conductivity follows the Jonscher’s power law. The dc conductivity, calculated from the ac conductivity spectrum, shows the negative temperature coefficient of resistance behavior similar to that of a semiconductor. The temperature dependent pre-exponential factor shows peak, and frequency exponent possesses a minimum at transition temperature.     

Low-temperature sintering and electrical properties of (1−x)Pb(Zr0.5Ti0.5)O3-xPb(Cu0.33Nb0.67)O3 ceramics

Electrical properties and sintering behaviors of (1 − x)Pb(Zr_0.5Ti_0.5)O₃-xPb(Cu_0.33Nb_0.67)O₃ ((1 − x)PZT-xPCN, 0.04 ≤ x ≤ 0.32) ceramics were investigated as a function of PCN content and sintering temperature. For the specimens sintered at 1050^∘C for 2 h, a single phase of perovskite structure was obtained up to x = 0.16, and the pyrochlore phase, Pb₂Nb₂O₇ was detected for further substitution. The dielectric constant (ε _r), electromechanical coupling factor (K_p) and the piezoelectric coefficient (d ₃₃) increased up to x = 0.08 and then decreased. These results were due to the coexistence of tetragonal and rhombohedral phases in the composition of x = 0.08. With an increasing of PCN content, Curie temperature (T_c) decreased and the dielectric loss (tanδ) increased. Typically, ε_r of 1636, K_p of 64% and d₃₃ of 473pC/N were obtained for the 0.92PZT-0.08PCN ceramics sintered at 950^∘C for 2 h.     

STRESS CONTROLLED FERROELECTRIC (BA0.5Sr0.5)TiO3 THIN FILMS PREPARED ON GD2O3/SRTiO3(001) BY A PULSED LASER DEPOSITION

ABSTRACT

Stress controlled epitaxial ferroelectric Ba_0.5Sr_0.5TiO₃ (BST) films have been deposited on Gd₂O₃/SrTiO₃ by pulsed laser deposition with oxygen background pressure of 200 mTorr at the deposition temperature of 750°C. In order to control the stress in BST films, oxygen pressures for Gd₂O₃ buffer layers have been varied from 0.1 to 100 mTorr, while that of BST films have been fixed at 200 mTorr. It has been found that the lattice parameters of the BST films deposited on Gd₂O₃ were changed. Furthermore, microwave properties of co-planar waveguide (CPW) fabricated on BST films were investigated by a HP 8510C vector network analyzer from 1–20 GHz. Large dielectric tunabilities were observed from the CPW's fabricated on BST films deposited on Gd₂O₃ layers deposited at low and high oxygen pressures, 0.1 and 100 mTorr, respectively.     

Electro-Optic Properties of Heteroepitaxial Pb(Zr,Ti)O3/La0.5Sr0.5CoO3 Film Structures

Vertical ferroelectric Pb(Zr,Ti)O₃ (PZT) 1 μm thick film capacitor was fabricated by pulsed laser deposition technique (PLD) onto conducting La_0.5Sr_0.5CoO₃(LSCO) 100 nm thick bottom electrode on both side polished YAlO₃ + 1% Nd₂O₃ (Nd:YAlO₃) single crystal substrate to operate as a Pockels cell optical modulator. On top of the PZT film, semitransparent 30 nm thick Au electrode was deposited by thermal evaporation. Intensity of the chopped 670 nm polarized laser radiation transmitted through the Au/PZT/LSCO/Nd:YAlO₃ cell was measured at various temperatures and bias voltage applied. Applying 20 V (200 kV/cm) across the capacitive cell, modulation of the transmitted light as high as 3% was achieved while the voltage tunability measured at 1 kHz from C-V characteristics was about 70%. Thermo-optical measurements performed for PZT/Nd:YAlO₃ sample in the range up to 400°C showed the phenomenon of critical opalescence in the vicinity of Curie temperature at 208°C. Optical transmission through the PZT film biased with electric field was studied in the range 400 to 1000 nm. Film thickness, refraction index and absorption coefficient have been determined from the interference pattern observed in the PZT transmission spectrum. A simple model yields the dispersion relation for the electro-optic coefficient.     

Thermal Expansion Behavior of (Bi0.5Na0.5)Zr1-x Ti x O3 Ceramics

(Bi_0.5Na_0.5)Zr_1-xTi_xO₃ with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 ceramics were fabricated by a conventional sintering technique at 850–950°C for 2 h. From X-ray diffraction study, three regions of different phases were observed in the ceramic system; i.e., orthorhombic phase region (0 ≤ x ≤ 0.2), mixed-phase region (0.3 ≤ x ≤ 0.4), and rhombohedral phase region (0.5 ≤ x ≤ 0.6). The thermal expansion coefficient data indicated the phase transition in the temperature range from 100°C–150°C of the ceramics. The thermal strain curve of all compositions suggested a decrease of local polarization with temperature increment up to the Burns temperature.     

层状的LiNi_(0.5)Mn_(0.5)O_2合成及其电化学性能

采用超声波辅助溶胶-凝胶法合成层状的锂离子电池的正极材料LiNi0.5Mn0.5O2,并用热重分析、X射线衍射(XRD)、扫描电子显微镜(SEM)对材料的结构与形貌进行了研究,电化学性能采用循环伏安法(CV)、交流阻抗和充放电测试进行表征.结果表明,在950℃灼烧12 h的材料结晶度比较好,其晶胞参数a=0,287 9 nm,c=1.431 nm,结构比较理想.当材料在2.8～4.2 V间进行充放电时,其首次放电容量为170 mAh/g,50次循环后容量的保持率为89%.