Effects of excess Bi2O3 on grain orientation and electrical properties of CaBi4Ti4O15 ceramics

A CaBi₄Ti₄O₁₅ (CBTO) ceramic in which the Bi₂O₃ concentration was controlled from 0 to 10 wt% was fabricated using a solid-state reaction method. Structural analysis by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) indicated differences in the preferred grain orientation and size of the plate-like grains according to the Bi₂O₃ concentration. The orientation of plate-like grains was also found to vary with the Bi₂O₃ concentration. There was no noticeable change trend of dielectric properties with different Bi₂O₃ concentrations. Relatively low dielectric constants (about 135) were exhibited by the CBTO ceramic with 1 wt% Bi₂O₃ and CBTO ceramic with 10 wt% Bi₂O₃ only, and similar values (about 150) were exhibited by the other ceramics. The dielectric loss exhibited a low value in the range of 0.01–0.09 for all samples (frequency range of 1–100 kHz). Regarding the ratio changes of the piezoelectric coefficient (d₃₃) and the ratio of a-axis orientation of plate-like grains, the trends of these two values were shown to be similar. These results suggest that the addition of Bi₂O₃ greatly influences the microstructure of CBTO ceramics, including the grain size and orientation of plate-like grains. In particular, the change in the preferred grain orientation is closely related to the change in the piezoelectric properties.     

Effect of amorphous TiO2 buffer layer on the phase formation of CaBi4Ti4O15 ferroelectric thin films

Amorphous buffer layers of TiO₂ were introduced between CaBi₄Ti₄O₁₅ thin films and Pt bottom electrodes through chemical solution deposition techniques. Several tens of nanometers thick alkoxy-derived TiO₂ layers were found to be critical for acceleration of the phase transition in the thin films. Unlike thin film crystallized directly onto a highly (111) oriented Pt bottom electrode, the thin film on an amorphous TiO₂ layer was almost single phase perovskite and showed random orientation. The crystallinity of the CaBi₄Ti₄O₁₅ thin film was much higher than that crystallized directly onto the Pt bottom electrode. The dielectric and ferroelectric properties of the CaBi₄Ti₄O₁₅/TiO₂ stacked thin films on Pt coated Si substrates are evaluated, leading to the potential of the amorphous buffer layer for the integrated devices being clarified. PACS 77.84.-s; 68.37.-d; 81.15.-z     

Microstructure and dielectric properties of pulsed-laser-deposited CaCu 3 Ti 4 O 12 thin films on LaNiO 3 buffered Pt/Ti/SiO 2 /Si substrates

CaCu₃Ti₄O₁₂ (CCTO) thin films have been prepared by a pulsed-laser-deposition method on LaNiO₃ buffered Pt/Ti/SiO₂/Si substrates, and their microstructure and dielectric properties have been compared with those of the films deposited directly on Pt/Ti/SiO₂/Si substrates. The crystalline structure and the surface morphology of the CCTO thin films were markedly affected by the bottom electrodes. Both the films show temperature-independent dielectric properties in a wide temperature range, which is similar to those properties obtained in single-crystal or epitaxial thin films, while the room-temperature dielectric constant of the 350-nm-thick CCTO films on LaNiO₃/Pt/Ti/SiO₂/Si substrates at 100 kHz was found to be 2300, which was increased significantly compared with that obtained in the films on Pt/Ti/SiO₂/Si substrates. Using the impedance spectroscopy technique, it has been suggested that the high dielectric constant response of the CCTO thin films originates from the grain boundary layer mechanism as found in internal barrier layer capacitors. PACS 77.55.+f; 81.15.Fg; 68.55.-a     

Enhanced ferroelectric,piezoelectric and dielectric properties of (1-x)CaBi2Nb2O9-xBaZr0.2Ti0.8O3 high-temperature piezoelectric composite ceramics

Among Aurivillius layer-structured materials, CaBi₂Nb₂O₉ is a best potential candidate for ultrahigh-temperature applications because of its highest Curie temperature of about 940 °C. In this paper, (1-x)CaBi₂Nb₂O₉-xBaZr_0.2Ti_0.8O₃ composite ceramics were prepared by conventional solid-state sintering method. The dielectric results show that the introduction of BaZr_0.2Ti_0.8O₃ not only increases the permittivity of the material, but also reduces its dielectric loss. The optimum electrical properties were obtained in the x = 0.01 sample with piezoelectric coefficient (d₃₃) of 15.1 pC/N and high ferroelectric remnant polarization (P_r) of 9.9 μC/cm². Furthermore, the composite samples show good thermal depoling performance, the d₃₃ of the x = 0.01 sample is 13.8 pC/N, which is about 91% of the initial value after depoling at 800 °C. Therefore, (1-x)CaBi₂Nb₂O₉-xBaZr_0.2Ti_0.8O₃ is one of the candidates for high temperature piezoelectric materials.     

Improved electrical properties in La- and V-co-doped Na0.5Bi4.5Ti4O15 thin films

Ferroelectric La- and V-co-doped Na_0.5Bi_4.5Ti₄O₁₅ (NLBTV) thin film was prepared on Pt(111)/Ti/SiO₂/Si substrates by using a chemical solution deposition method and annealed at 750?°C under oxygen atmosphere. Crystal structure of the thin film was investigated by X-ray diffraction and Raman scattering. Surface morphology of the thin film was investigated by scanning electron microscopy. The NLBTV thin film capacitor exhibited better ferroelectric properties such as larger remnant polarization and smaller coercive electric field than Na_0.5Bi_4.5Ti₄O₁₅ (NBT) thin film capacitor. Reduced leakage current was observed in the NLBTV thin film capacitor compared to the NBT thin film capacitor. Almost no polarization fatigue was observed up to 1.44×10¹⁰ switching cycles.     

Structural and dielectric properties of barium-modified SrBi4Ti4O15 ceramics

Barium-modified strontium bismuth titanate ceramics with chemical formula Sr_1?xBa_xBi₄Ti₄O₁₅ (x = 0.00, 0.02, 0.06, 0.08 and 0.1) (SBBT) have been prepared by means of solid-state reaction technique and their structural and electrical properties were investigated. X-ray diffraction data confirm that all the compositions show orthorhombic structure without any deleterious phase. Scanning electron micrographs show plate like grain morphology with random orientation of platelets. The temperature-dependent dielectric study shows that the phase transition temperature decreases, but the dielectric constant increases with increase in Ba content. Complex impedance plots show that both grain and grain boundary effect on the resistance mechanisms in all the compositions. The values of the activation energy confirm that the oxygen vacancies play an important role in the conduction. The ac conductivity of SBBT ceramics increases as a function of frequency due to relaxation phenomenon which arises due to mobile charge carriers.     

Mo掺杂SrBi4Ti4O15陶瓷的铁电介电性能

用传统的固相烧结工艺,制备了钼掺杂铁电陶瓷样品SrBi4Ti4O15(SBTi)铁电陶瓷SrBi4-2x/3Ti4-xMoxO15(x=0.00,0.003,0.012,0.03,0.06,0.09).X射线衍射的结果表明,样品均为单一的层状钙钛矿结构相,Mo掺杂未改变SBTi的晶体结构.通过扫描电子显微镜观测发现,样品晶粒为片状,随掺杂量的增加,晶粒逐渐变小.铁电测量表明,Mo掺杂使SBTi的铁电性能得到较大改善.随掺杂量x的增加,样品的剩余极化(2Pr)呈现出先增大,后减小的规律.在x=0.06时,2Pr达到最大值26.5 μC/cm2,与SrBi4TiO15(2Pr=12.2 μC/cm2)相比,提高117%.材料的矫顽场Ec在掺杂后增加仅为20%左右.SBTi的居里温度受掺杂的影响甚微,说明Mo对SrBi4Ti4O15的掺杂基本未影响材料原有的良好的热稳定性.     

Structure and magnetic properties of annealed metastable FeAg/Pt films

FeAg and FeAg/Pt films were prepared by dc magnetron sputtering at room temperature. The effects of Ag volume fraction in FeAg films and postannealing temperature and time on structure and magnetic properties of FeAg and FeAg/Pt films have been investigated. The results show that the as-deposited FeAg films are metastable. After annealing at 300°C, the phase separation of metastable FeAg films happened and the highest coercivity is obtained in Fe₅₀Ag₅₀/Pt film. With increasing annealing temperature, the ordering and the magnetic properties of the Fe₅₀Ag₅₀/Pt films were improved. When the Fe₅₀Ag₅₀/Pt films are annealed at 600°C for different annealing times, a long annealing time enhances the ordering of the metastable Fe₅₀Ag₅₀/Pt films and affects the orientation development. When the films are annealed for a long time, the grain size and the magnetic domain size also increase, which lead to an increase of correlation length due to the growth of FePt grains.     

Studies of structural and electrical properties on four-layers Aurivillius phase BaBi4Ti4O15

BaBi₄Ti₄O₁₅ (BBT) ceramic was synthesized using mixed oxide route and the structural and electrical properties were investigated systematically. The structural studies confirmed it to be an n=4 member of the Aurivillius oxide. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed. The dielectric relaxation obeyed the Vogel–Fulcher relation wherein f₀=8.37E+14 Hz, E_a=0.13 eV, and T_f=608.18 K. The diffuseness parameter γ established the relaxor nature and it was attributed to the A-site cationic disorder. The specimen exhibited the excellent reproducibility in the measurements of displacement current, a remnant polarization of 5.4 μC/cm², and a coercive field of 4.03 MV/m. The room temperature piezoelectric coefficient d₃₃ was found to be 23 pC/N and the field-induced strain S was about 0.018% at the 8 MV/m electric field.     

Structure and piezoelectric properties of microporous polyvinylidene fluoride films

A method to produce microporous polyvinylidene fluoride films characterized by a high content of a piezoactive crystalline phase and a developed relief surface is elaborated. The porous films are obtained in the process based on melt extrusion with subsequent isometric annealing and uniaxial extension. It is found that the samples have an oriented lamellar structure containing both α- and β-modifications of the crystallites. The effect of temperature and degree of uniaxial extention of the annealed films on the characteristics of the porous samples, that is, the content of the piezoactive crystalline β-phase, overall porosity, breakdown voltage and the piezoelectric modulus is studied.

     

La掺杂SrBi4Ti4O15铁电材料性能研究

按x=0 0 0 ,0 10 ,0 2 5 ,0 5 0 ,0 75和 1 0 0 ,采用固相烧结工艺 ,制备了不同La掺杂量的SrBi4-xLaxTi4O1 5的陶瓷样品 .用x射线衍射对其微结构进行了分析 ,并测量了铁电、介电性能 .结果发现 ,La掺杂未改变SrBi4Ti4O1 5的晶体结构 .随掺杂量的增加 ,样品的矫顽场 (Ec)下降 ,剩余极化 ( 2Pr)先增大 ,后减小 .在x =0 2 5时 ,2Pr 达到极大值 ,为2 4 2 μC·cm- 2 ,这时Ec=60 8kV·cm- 1 ,与SrBi4Ti4O1 5相比 ,2Pr 增加了近 5 0 % ,而Ec 下降了近 2 5 % ,材料铁电性能显著提高 .SrBi4-xLaxTi4O1 5的相变温度Tc 随x的增加逐渐降低 ,x =0 2 5时 ,Tc=45 1℃ .在x =0 75 ,1 0 0时 ,样品出现弛豫铁电体的典型特征     

B位等价掺杂SrBi4Ti4O15铁电材料的性能研究

采用了传统的固相烧结工艺,制备了不同Zr和Hf掺杂量的SrBi₄Ti_4-xZr_xO₁₅（x=000,003, 006,010,020）和SrBi₄Ti_4－xHf_xO₁₅（x=000,0005, 0015,0030,0060）的陶瓷 关键词： 4Ti_4-xZr_xO₁₅')" href="#">SrBi₄Ti_4-xZr_xO₁₅ 4Ti_4－xHf_xO₁₅')" href="#">SrBi₄Ti_4－xHf_xO₁₅ 铁电性能 介电性能     

Microstructure,dielectric, and piezoelectric properties of Ce‐modified Na0.5Bi4.5Ti4O15 high temperature piezoceramics

The cerium modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that the cerium modified NBT ceramics have a pure four‐layer Aurivillius phase structure. The piezoelectric activity of NBT ceramics was found significantly improved by the modification of cerium. The Curie temperature T_c, and piezoelectric coefficient d₃₃ for the NBT ceramics with 0.50 wt% cerium modification were found to be 655 °C, and 28 pC/N respectively. The Curie temperature gradually decreased from 668 °C to 653 °C with the increase of cerium modification. The dielectric spectroscopy showed that the samples possess stable piezoelectric properties, demonstrating practical potential that for high temperature applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric properties of Bi4Ti3O12–SrBi4Ti4O15 intergrowth ceramics synthesized by a modified oxalate route

In this study, Bi₄Ti₃O₁₂–SrBi₄Ti₄O₁₅ (BIT–SBTi) intergrowth ferroelectric ceramics was synthesized by a modified oxalate route. The phase formation behaviour, structure, morphology and electrical properties of the intergrowth ceramics were also investigated. The phase formation takes place through intermediate phases like SrBi₂O₄ and Bi₁₂TiO₂₀. The precursor mostly changes to Bi₄Ti₃O₁₂ at 600°C and to BIT–SBTi intergrowth at 800°C. Rietveld analysis of the X-ray diffraction pattern showed that the structure of the intergrowth compound was orthorhombic with lattice parameters a = 5.4408(3), b = 5.4505(1) and c = 74.0851(4) Å. The intergrowth ferroelectrics showed a phase transition at 610°C and a frequency-stable permittivity and dielectric loss behaviour. The intergrowth ferroelectrics also showed a larger 2P_r than their constituents BIT and SBTi.     

Dielectric and piezoelectric properties of the Ba0.92Ca0.08Ti0.95Zr0.05O3 thin films grown on different substrate

Lead free Ba_0.92Ca_0.08Ti_0.95Zr_0.05O₃ (BCZT) thin films were deposited on Pt/Ti/SiO₂/Si and LaNiO₃(LNO)/Pt/Ti/SiO₂/Si substrates by a sol–gel processing technique, respectively. The effects of substrate on structure, dielectric and piezoelectric properties were investigated in detail. The BCZT thin films deposited on LNO/Pt/Ti/SiO₂/Si substrates exhibit (100) orientation, larger grain size and higher dielectric tunability (64%). The BCZT thin films deposited on Pt/Ti/SiO₂/Si exhibit (110) orientation, higher Curie temperature (75 °C), better piezoelectric property (d₃₃ of 50 pm/V) and lower dielectric loss (0.02). The differences in dielectric and piezoelectric properties in the two kinds of oriented BCZT films should be attributed to the difference of structure, in-plane stress and polarization rotation in orientation engineered BCZT films.     

(Bi, La)4Ti3O12-Sr(Bi, La)4Ti4O15共生结构铁电材料性能研究

采用固相烧结工艺,制备了不同La掺杂量(x=0.00,0.25,0.50,0.75,1.00,1.25和1.50)的(Bi, La)4Ti3O12-Sr(Bi, La)4Ti4O15 (SrBi8-xLaxTi7O27)共生结构铁电陶瓷样品.用x射线衍射对其进行微结构分析,并测量铁电、介电性能.结果发现,La掺杂未改变Bi4Ti3O12-SrBi4Ti4O15共生结构铁电材料的晶体结构.随掺杂量的增加,样品的矫顽场(Ec)略有增加,剩余极化(2Pr)先增大,后减小.在x＝0.50时,2Pr达到极大值,为25.6 μC*cm-2,与Bi4Ti3O12-SrBi4Ti4O15相比,2Pr增加了近60%,而Ec仅增加约10%.随La掺杂量的增加,样品的居里温度TC逐渐降低,x＝0.50时,TC=556 ℃.在x=1.50时,样品出现弛豫铁电体的典型特征.     

Structure and properties of ultrafast-quenched Sn-Bi foils

The effect of bismuth on the microstructure of ultrafast-quenched foils of Sn-Bi alloys has been investigated. Bismuth phase precipitation is observed in alloys containing more than 2 at % Bi. With an increase in the bismuth concentration to 8 at %, most precipitates acquire a needle-like shape. Cross-sectional inhomogeneity of the initial foils is revealed. It is found that addition of bismuth leads to an increase in the foil microhardness by a factor of 2.5.     

Quartz crystal microbalance measurements of O/Ti and CO/Ti atom ratios on very thin Ti films

The adsorption of O₂ and CO on Ti films with thicknesses in the range 0–200 Å was investigated by quartz crystal microbalance (QCM) measurements. The O/Ti and CO/Ti ratios in the limit of zero film thickness was determined to be 1.5 and 0.5 respectively using the film thickness as a parameter. This result suggests that the oxide formed is Ti₂O₃. The Ti + O₂ results are discussed in a model where the thinnest metal films are assumed to consist of metal islands. From the model an “oxidation depth” of ≈10 Å is estimated.     

Enhanced piezoelectric properties of sodium bismuth titanate (Na0.5Bi4.5Ti4O15) ceramics with B‐site cobalt modification

The piezoelectric properties of the cobalt‐modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics were investigated. The piezoelectric properties of NBT ceramics were significantly enhanced by cobalt modification. The Curie temperature T_C and piezoelectric constant d₃₃ for the 0.3 wt% cobalt‐modified NBT ceramics (NBT‐C3) were found to be 663 °C and 30 pC/N, respectively. Thermal annealing studies presented that the cobalt‐modified NBT ceramics possess stable piezoelectric properties, demonstrating that the cobalt‐modified NBT‐based ceramics are promising candidates for high temperature piezoelectric applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and magneto-optical properties of Co/Pt multilayered films

Both experimental and computer-simulated magneto-optical (MO) and optical spectroscopies of Co/Pt multilayered films (MLF) with a nearly constant Pt sublayer thickness and variable Co sublayer thickness, as well as pure Co and Pt, and Co_0.51Pt_0.49 alloy films, have been performed in the energy range 1.1–4.7 eV. The simulations were achieved by solving the multireflection task for various models of the MLF. The comparison between experimental and computer-simulated optical properties of the Co/Pt MLF allowed us to evaluate the thickness of the interfacial regions with the alloyed components. The diagonal and off-diagonal components of the optical conductivity tensor were calculated not only for the pure Co and Co_0.51Pt_0.49 alloy films, and the whole Co/Pt MLF, but also for the spin-polarized Pt layers in the Co/Pt MLF.