La substitution in four-layers Aurivillius phase SrBi4Ti4O15

Ceramics with the nominal composition of SrBi_4−xLa_xTi₄O₁₅ have been prepared within the range of 0≤x≤1.8, and the dielectric properties are investigated. Single phase SrBi_4−xLa_xTi₄O₁₅ solid solution exists until the secondary phase of La_2/3TiO₃ appears at x=1.6. The Curie temperature is 520 °C for pure SrBi₄Ti₄O₁₅, and it shifts to low temperature with increasing x, which is due to the smaller structural distortion caused by La³⁺ substitution. In addition, the dielectric constant anomaly is suppressed with the substitution. No dielectric relaxation behavior is observed. When x≥1.2, the paraelectric state is attained in the present ceramics. La³⁺ substitution effects on the SrBi₄Ti₄O₁₅ ceramics are also compared with the previous work on Bi_4−xLa_xTi₃O₁₂.     

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.     

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.     

CaCu3Ti4O12陶瓷的微观结构和电学性能

利用传统的固相反应工艺,在不同的烧结温度下制备了一系列的CaCu3Ti4O12陶瓷样品,考察了其微观结构以及介电和复阻抗方面的电学性质.研究发现这些样品在微观结构方面可分为三种类型,高介电性与微观结构有着密切的关联性.室温下,样品的低频介电常数随陶瓷晶粒尺寸的增大而提高.随着测试温度的升高,不同微观结构类型的样品呈现出不同的电学性质的变化,但其中也存在着一些相同的特征.高温下,介电频谱呈现出一个低频介电响应和两个类Debye型弛豫色散,复阻抗谱呈现出三个Cole-Cole半圆弧.将实验上观测到的电学性质的起因归于陶瓷多晶微结构中的晶畴、晶界和晶粒内的缺陷.     

Magnetic,dielectric and optical properties of five-layered Aurivillius phase Bi6Fe2Ti3O18-based ceramics

The structural, magnetic, dielectric and optical properties of Aurivillius Bi₆Fe₂Ti₃O₁₈-based ceramics were investigated in detail. The replacement of Co for Fe/Ti ions obviously varies the grain morphology. Compared with Bi₆Fe₂Ti₃O₁₈ (BFTO) with antiferromagnetic ordering, a spin glass state can be observed in Bi_5.25La_0.75Fe₂Ti₃O₁₈ ceramic, while other samples exhibit the ferromagnetic behavior. The specimen Bi₆Fe₂Ti₂(NbCo)_0.5O₁₈ (BFTNCO) represents the largest remanent magnetization M_r of 0.93emu/g among all the samples, which can be attributed to the combination of a short lattice parameter c and a large lattice distortion as well as more magnetic ions in a unit cell. The room-temperature dc conductivity of BFTNCO is one order magnitude lower than that of BFTO. In addition, the band gaps of Co-doped samples are about 0.2eV smaller than these of Co-free samples. This work provides a promising path forward to tailor the multiferroic and optical properties in five-layered Aurivillius compounds.     

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     

Structure and ferro-/piezoelectric properties of bimorph-shape CaBi4Ti4O15 films on Pt foils

In-plane c-axis oriented CaBi₄Ti₄O₁₅ (CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The a/b-axis orientation of the ferroelectric films was affected by the preferred orientation of Pt foil, which is associated with the thickness. The 500 nm-thick CBTi144 films showed good ferro- and piezoelectric properties on 0.010 mm-thick Pt foils. The Pr and Ec were 26 C/cm² and 230 kV/cm, respectively, at an applied voltage of 75 V. The d₃₃ was characterized as 25–34 pm/V by piezoresponse force microscopy. The values enhanced compared to those of the CBTi144 thin film with random orientation. The polar-axis oriented CBTi144 films would open for novel devices as Pb-free piezoelectric materials. PACS 77.84.-s; 68.37.-d; 81.15.-z     

(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.     

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     

Influence of B2O3 on electrical properties and phase transition of lead-free Ba(Ti0.9Sn0.1)O3 ceramics

The phase transition and electrical properties of Ba(Ti_0.9Sn_0.1)O₃ ceramics with B₂O₃ added were investigated to explore the effect of B₂O₃ addition on enhanced densification and dielectric constant of these ceramics. With increasing B₂O₃ content, a linear reduction of ferroelectric to paraelectric transition temperature was observed. In addition, higher B₂O₃ concentrations enhanced a ferroelectric relaxor behavior in the ceramics. Changes in this behavior were related to densification, second-phase formation and compositional variation of the ceramics.     

Some aspects of electrical properties and structural phase transition in p-diiodobenzene

The A.C. conductivity and complex dielectric constant (relative permittivity) as function of temperature 300<T<500?K measured at different frequencies (f?=?5, 10, 15, 20 and 100?kHz) for polycrystalline samples of p-diiodobenzene (hereafter p-DIB) are presented. The main feature of the behavior of electrical parameters clarified that, the compound undergoes a structural phase transition at ≈?327?K. The interpretation of the behavior of the obtained parameters is outlined and correlated to the crystal structure of the two phases.     

Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu₃Ti₄O₁₂ (CCTO) ceramics. For this purpose, neutron and X-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T. At low temperatures the dielectric constant shows a minor but significant dependence on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.     

Effect of Al3+ substitution on structural,cation distribution,electrical and magnetic properties of CoFe2O4

We present the structural, cation distribution, electrical and magnetic studies of CoAl_xFe_2−xO₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8) ferrites. The Rietveld-fitted X-ray diffraction (XRD) patterns confirm the formation of single-phase cubic spinel structures with $Fd\overline{3}m$ space group for all the samples. A comprehensive analysis of XRD-based cation distribution has been performed to see the effect of Al³⁺ ions substitution on various structural parameters such as site ionic radii, edge length, bond length and interionic distances. The dielectric constant and direct current (DC) conductivity decreases with increasing Al³⁺ substitution up to x = 0.4. However, with further increase in Al³⁺ substitution, both the dielectric constant and the DC conductivity increase. The presentation of dielectric data in the complex electric modulus form reveals the presence of a non-Debye-type relaxation behaviour in the considered ferrites. The power law behaviour of alternating current (AC) conductivity indicates a strong correlation among electrons in these systems. The isothermal magnetisation versus applied field curves with high-field slope and significant coercivity suggest that the studied materials are highly anisotropic with canted spin structures. The samples exhibit ferrimagnetic behaviour at 300 K and the magnetisation decreases with increasing Al³⁺ concentration. The as-prepared samples are promising candidates for various industrial applications.     

Synthesis and phonon properties of nanosized Aurivillius phase of Bi2MoO6

Nanosized crystallites Bi₂MoO₆ of a platelet shape were synthesized by a mild hydrothermal crystallization process. The effect of particle size on the structure and properties of Bi₂MoO₆ was studied by X‐ray diffraction, transmission electron microscopy, as well as Raman and infrared (IR) spectroscopies. Moreover, temperature‐dependent Raman spectra were collected for bulk and nanocrystalline Bi₂MoO₆. These studies showed that the thickness of the smallest crystallites is about 8–11 nm. Raman and IR studies have revealed that the damping and the intensity of Raman and IR bands are significantly modified with decreasing particle size and temperature. Moreover, some bands experience significant shifts both towards lower and higher wavenumbers. The obtained results indicate that, similar to the isostructural Bi₂WO₆, the orthorhombic distortion decreases with decreasing particle size. However, the structure of nanocrystalline Bi₂MoO₆ remains orthorhombic and noncentrosymmetric, and the structural changes are not the same as those observed in Bi₂WO₆. Copyright © 2010 John Wiley & Sons, Ltd.