Effect of Ce and La substitution on dielectric properties of bismuth titanate ceramics

Effect of Ce and La substitution on the microstructure and dielectric properties of bismuth titanate (BT) ceramics was investigated. Bismuth titanate ceramics (Bi_4−xA_xTi₃O₁₂) (A = Ce or La; x = 0, 0.5, 1) were processed by sintering of pressed pellets, prepared from nanopowder synthesized by the modified sol-gel method. Pure and La modified bismuth titanate ceramics have single Bi₄Ti₃O₁₂ phase of Aurivillius type, whereas a small amount of Bi₂Ti₂O₇ pyrochlore phase appears in Ce modified bismuth titanate ceramics. In the same time addition of La and Ce improved sinterability of BT ceramics. The results of the measurement of dielectric constant and loss tangent at different frequencies (100 Hz-1 MHz) as a function of temperature reveal that Ce modified ceramics has a diffuse phase transition. Temperature T_m, corresponding to the maximum value of the dielectric constant, is shifted to higher temperature and the maximum value of the dielectric constant is decreased with increasing frequency, which indicate that relaxor behavior is caused by Ce substitution.     

Crystal structure and electrical properties of bismuth sodium titanate zirconate ceramics

Lead-free bismuth sodium titanate zirconate (Bi_0.5Na_0.5Ti_1-xZr_xO₃ where x = 0.20, 0.35, 0.40, 0.45, 0.60, and 0.80 mole fraction) [BNTZ] ceramics were successfully prepared using the conventional mixed-oxide method. The samples were sintered for 2 h at temperatures lower than 1,000°C. The density of the BNTZ samples was at least 95% of the theoretical values. The scanning electron microscopy micrographs showed that small grains were embedded between large grains, causing a relatively wide grain size distribution. The density and grain size increased with increasing Zr concentration. A peak shift in X-ray diffraction patterns as well as the disappearance of several hkl reflections indicated some significant crystal-structure changes in these materials. Preliminary crystal-structure analysis indicated the existence of phase transition from a rhombohedral to an orthorhombic structure. The dielectric and ferroelectric properties were also found to correlate well with the observed phase transition.     

Enhancement of dielectric properties and energy storage density of bismuth and lithium co-substituted strontium titanate ceramics

Polycrystalline Bismuth and Lithium Co-Substituted Strontium Titanate Sr _(1-x)(Bi,Li)xTiO₃, was prepared using the solid-state method with microwave assisted heating of initial materials. The effect of Bi³⁺ and Li⁺ concentration on the crystal structure, microstructure, and permittivity and energy storage properties of SrTiO₃ ceramics are investigated. The phase and structure have been confirmed by XRD along with Rietveld refinement studies. Morphological investigations have been carried out using FESEM. Frequency and temperature dependence of dielectric permittivity was investigated using impedance spectroscopy. The sample with x?=?0.02 has shown dielectric relaxation behavior. The activation energy of relaxation is found to be 1.2?eV and relaxation time equals 1.12 $\times$ 10^?7 sec. The room temperature P-E loop has been investigated, and the result confirms that there is no signature of the ferroelectric phase in all samples. The energy storage density was theoretically estimated in the present study using a P-E loop. The results showed an astonishing ten-time increase in energy storage density with 8% co-substitution. With increasing x, the grain size steadily decreased, and dielectric breakdown strength increased, yielding a higher energy storage density. The obtained results herald a promising future in the development of electrical capacitors for energy storage applications.     

pH对低温镀铁组织形貌及性能的影响

介绍了低温镀铁的工艺配方及流程.利用扫描电镜观察了镀层的组织形貌,利用硬度计测试了镀层硬度,利用锉刀法和热震法检验了镀层的结合强度,考察了pH对沉积速率、显微硬度和耐蚀性能的影响.结果表明,所得镀层结合力良好,pH为1.0时,沉积速率最高,耐蚀性能最好;镀层硬度随pH的升高而增大,最大值为587.43 HV.     

Vanadium doping effects on microstructure and dielectric properties of barium titanate ceramics

V-doped barium titante ceramics were prepared by conventional solid state reaction method. XRD patterns show that V⁵⁺ ions have entered into the tetragonal perovskite structure of solid solution to substitute for Ti⁴⁺ ions on the B sites. Addition of vanadium accelerates grain growth of BTO ceramics and there is abnormal grain growth of barium titanate ceramics with higher vanadium concentration. Vanadium doping can increase the Curie temperature and decrease the dielectric loss of barium titanate ceramics. As vanadium concentration increases, the remnant polarization of V-doped BTO ceramics begins to increase and reaches the maximum and then decreases. The coercive electric field for V-doped barium titanate ceramics decreases with the increasing of vanadium concentration. As temperature rises, the remnant polarization and the coercive electric field of V-doped barium titanate ceramics decrease simultaneously.     

Relations on synthesis,crystal structure and microwave dielectric properties of SrZnP2O7 ceramics

Different experimental conditions were applied to investigate the optimum sintering properties of SrZnP₂O₇ ceramics, and its crystal structure and microstructure were investigated by X-ray powder diffraction and scanning electron microscope, respectively. The microwave dielectric properties were measured using a network analyzer. In calcination process, SrZnP₂O₇ powders were synthesized at different temperatures. The sintering characterizations and electric properties of the SrZnP₂O₇ ceramics prepared from the different calcined SrZnP₂O₇ powders were studied systematically. Better microwave dielectric properties can be obtained when using well calcined powders and optimum sintering conditions.     

Crystallization behavior,microstructure and dielectric properties of lead titanate glass ceramics in the presence of Bi2O3 as a nucleating agent

The crystallization behavior of PbO–TiO₂–B₂O₃–SiO₂ glasses in the presence of Bi₂O₃ as a nucleating agent were studied utilizing XRD, DTA, SEM. The glass samples heat treated in the range of 557–630 °C for different soaking times, all developed PbTiO₃ (PT) with perovskite structure. It was found that the addition of 0.5–1.0 mol% Bi₂O₃ resulted in the formation of homogenous, nano-structured glass ceramics with a mean crystallite size of 20–25 nm and PbTiO₃ as the major crystalline phase. The dielectric constant and dissipation factors for the prepared glass ceramics were in ～140–400 and ～0.04–0.4 ranges respectively.     

Enhancement of the dielectric permittivity and magnetic properties of Dy substituted strontium titanate ceramics

Structural, dielectric and magnetic properties of dense Dy-substituted strontium titanate ceramics are investigated. In the Sr_1-1.5xDy_xTiO₃ system, incorporation of Dy onto the Sr site is confirmed by a linear decrease of the lattice parameter up to x = 0.05. Dielectric spectroscopy analysis of Sr_1-1.5xDy_xTiO₃ ceramics reveals four relaxations. Two relaxations observed below 55 K are attributed to dipoles formed by off-centre displacement of Dy³⁺ ions on the Sr sites. Other two dielectric relaxations found at higher temperatures are attributed to the oxygen vacancy related mechanisms. As result, very high dielectric permittivity of ～33500 at 28 K and of ～9600 around room temperature at moderate dissipation factor of ～0.02 are obtained for Sr_0.985Dy_0.01TiO₃ ceramics, making it a promising material for capacitor electronic applications. Paramagnetic behaviour observed for Sr_1-1.5xDy_xTiO₃ as well as for Sr_1-xDy_2xTi_1-xO₃ ceramics indicates impossibility to induce a magnetic order and hence magnetoelectric coupling in strontium titanate by Dy substitution.     

Influence of fuel on phase formation,morphology, electric and dielectric properties of iron oxides obtained by SCS method

Nanopowders of iron oxides were obtained by Solution Combustion Synthesis (SCS) method from sol-gel compositions containing iron nitrates and soluble organic reducing agents (glycine, urea, citric acid). The synthesis processes and their intensity depending on the type of fuel and fuel/oxidizer ratio (?) were investigated. It was established that the combustion regime affects the phase formation of the obtained powders, their morphology, the color of the final Fe₂O₃ powders, dielectric properties and etc. It was shown that iron oxides with a preferred morphology and high dielectric properties (ε = 44.5 at ? = 0.6 vs ε = 4.0 at ? = 1.4 using urea as fuel) could be produced by the SCS method.     

Effects of glass additions on the microstructure and dielectric properties of barium strontium titanate (BST) ceramics

Commercial glass frits (lead borosilicate glasses) were employed as the sintering aids to reduce the sintering temperatures of BST ceramics. The effects of the glass content and the sintering temperature on the microstructures, dielectric properties and tunabilities of BST ceramics have been investigated. Densification of BST ceramics of 5 wt% glass content becomes significant from sintering temperature of 1000 °C. The glass content shows a strong influence on the Curie temperature T_c, permittivity and the diffuse transition. X-ray results show all BST ceramics exhibit a perovskite structure and also the formation of a secondary phase, Ba₂TiSi₂O₈. The shift of BST diffraction peaks towards higher angle with increasing the glass content indicates the substitution of Pb²⁺ in Ba²⁺ site, which mainly accounts for the diffuse transition observed in these BST ceramics. BST ceramics with 10 wt% glass additives possess the highest tunability at all four sintering temperatures. A tunability of 12.2% at a bias field of 1 kV/mm was achieved for BST ceramics with 10 wt% glass content sintered at 900 °C.     

Effect of zirconium deficiency on structure characteristics,morphology and microwave dielectric properties of Li2Mg3Zr1-xO6 ceramics

To suppress the impurity phases and porous microstructure caused by lithium volatilization, the Li₂Mg₃ZrO₆ and Zr-deficiency Li₂Mg₃Zr_1-xO₆ (x = 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were successfully synthesized via the solid-state method assisted with atmosphere-controlled sintering. The influences of non-stoichiometric on structure characteristics, morphology and microwave dielectric properties of Li₂Mg₃Zr_1-xO₆ ceramics were investigated. The XRD and SEM results proved that the Zr-deficiency restrained the formation of impurity phases and remarkably improved the densification of Li₂Mg₃Zr_1-xO₆ samples. The variation trend of dielectric constant (ε_r) was explained by the relative density and theoretical dielectric polarizability. The quality factor (Q × f) was strongly associated with the impurity phases and relative density. Additionally, the temperature coefficient of resonant frequency (τ_f) showed the same trend as the total bond energy E_total, indicating the bond energy might play vital roles in thermal stability of Li₂Mg₃Zr_1-xO₆ samples. Typically, the Li₂Mg₃Zr_1-xO₆ sample obtained at x = 0.06 possessed remarkable dielectric performances: ε_r = 13.13, Q × f = 116,400 GHz (10.14 GHz) and τ_f = ?26.30 ppm/°C.     

Effects of titanate coupling agent on the dielectric properties of NiZn ferrite powders–epoxy resin coatings

During ferrite powder–polymer resin slurry preparation, the ferrite particles tend to hold together, forming agglomerates, which lead to the formation of micro-structural defects in the ferrite powder–polymer coatings. These defects affect the quality of magnetic devices. In this study, the titanate coupling agent effects on the NiZn ferrites powder dispersion in an epoxy resin and solvent system and the electromagnetic properties of NiZn ferrite powders–epoxy resin composite coatings are investigated. It was observed that the dispersion of NiZn ferrite powders and the affinity of NiZn ferrites and epoxy resin can be substantially enhanced by coating a titanate coupling agent onto the ferrite powder surfaces. This coating promotes mixing homogeneity and increases the dielectric constants at low frequencies (below 100 Hz) due to the increase in phase boundary between the NiZn ferrite powders and epoxy resin.     

Effect of magnesium content on structure and dielectric properties of cubic bismuth magnesium niobate pyrochlores

Structure and dielectric properties of cubic pyrochlore Bi_1.5Mg_NNb_2.5−NO_8.5−1.5N (BMN) compositions with N=0.6–1.3 have been studied. X-ray diffraction (XRD), infrared reflectivity spectra and Raman spectra were employed to analyze the crystal structures and phonon vibration modes of BMN compositions. The vibration spectra were sensitive to the content of Mg²⁺ ions, which is caused by the randomness of Mg²⁺ ions partially filling both the cubic pyrochlore A and B sites. The intensity of A3O stretching vibrations became stronger with increasing Mg²⁺ content, but B3O stretching vibrations were quite opposite. With the increase of Mg²⁺ content, the dielectric constant and loss tangent both increased. Temperature dependent dielectric constant was observed in the samples with N>0.8. The tendency of the dielectric constant with the increasing temperature showed a quick drop in the samples with higher Mg²⁺ content, which seems to be associated with the disorder in the A₂O′ network.     

Influence of interface structure on microstructure and dielectric properties of bismuth magnesium niobate thin films

Bismuth magnesium niobate (Bi_3/2MgNb_3/2O₇, BMN) thin films were prepared on bare SiO₂/HR-Si and Pt/TiO₂/SiO₂/HR-Si substrates by using sol-gel spin coating technique followed by rapid thermal annealing process. The influence of the interface on crystalline structure and tunable dielectric properties of the two types of BMN films were investigated. It was found that the BMN films prepared on SiO₂/Si substrate with a BMN/SiO₂ interface structure had higher orientation and better crystallinity. The deposited BMN thin films with a BMN/SiO₂ interface structure exhibited superior tunability of 52.5%, while it showed a relative small tunability value of the film with BMN/Pt interface structure. It suggests that the interface state between the films and substrates, electric field distribution, and orientation degree are responsible for the impacts on the microstructure and tunable dielectric properties of the BMN thin films.     

Effect of La and Ni substitution on structure,dielectric and ferroelectric properties of BiFeO3 ceramics

In this communication, we present the results on Bi_1−xLa_xFe_1−yNi_yO₃ (x=0.0, 0.1; y=0.0, 0.05) samples processed by solid-state reaction route in order to study crystalline and electronic structure, dielectric and ferroelectric properties. The best refinement was achieved by choosing rhombohedral structure (R3c) for BiFeO₃ and Bi_0.9La_0.1FeO₃ samples. Whereas, the XRD pattern of BiFe_0.95Ni_0.05O₃ and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ samples were refined by choosing rhombohedral (R3c) and cubic (I23) structure. Raman scattering measurement infers nine Raman active phonon modes for all the as prepared samples. The substitution of Ni ion at Fe-site in BiFeO₃ essentially changes the modes position i.e. all the modes are observed to shift to lower wave number. Dielectric constant (ε′) and dielectric loss (tan δ) as a function of frequency have been investigated and they decreases with increasing frequency of the applied alternating field and become constant at high frequencies. This feature is a characteristic of Maxwell Wagner type of interfacial polarization. The remnant polarization (P_r) for Bi_0.9La_0.1FeO_3, BiFe_0.95Ni_0.05O₃, and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ are 0.08, 0.11, 0.69 μC/cm², respectively and the value of coercive field for Bi_0.9La_0.1FeO_3, BiFe_0.95Ni_0.05O₃, and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ are 0.53, 0.67, 0.68 kV/cm, respectively. X-ray absorption spectroscopy (XAS) experiments at Fe L₂,₃ and O K-edges are performed to investigate the electronic structure of well-characterized Bi_1−xLa_xFe_1−yNi_yO₃ (x=0.0, 0.1; y=0.0, 0.05) samples. The presence of reasonable ferroelectric polarization at room temperature in Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ ceramics makes it suitable for technological applications.     

Crystal structure,infrared spectra and microwave dielectric properties of novel extra low-temperature fired Eu2Zr3(MoO4)9 ceramics

A new kind of low-temperature fired Eu₂Zr₃(MoO₄)₉ ceramic was fabricated by conventional solid-state reaction method. The mixed powders was calcined at 600 ℃ and the samples were sintered at 500 ℃ –700 ℃ for 4 h. X-ray diffraction analysis and Rietveld refinement indicated that Eu₂Zr₃(MoO₄)₉ belonged to a trigonal system with space group R-3c. Bond ionicity, lattice energy and bond energy of the ceramic were calculated by the complex chemical bond theory. Microwave dielectric properties were determined at microwave frequencies of 9.7–14.7 GHz by a network analyzer. Far infrared spectra indicated the main contribution to polarization for Eu₂Zr₃(MoO₄)₉ ceramics was the absorption of structural phonon oscillation. The ceramic sintered at 600 ℃ for 4 h exhibited the best dielectric properties with a relative permittivity (ε_r) of 10.75, a quality factor (Q·f) of 74,900 GHz and a temperature coefficient of resonance frequency (τ_f) of -8.88 ppm/℃.     

Intrinsic correlation between structure,vibration spectrum and microwave dielectric properties of ferroelectric-dielectric composite ceramics

A novel series of (1-x)Ba_0.45Sr_0.55TiO₃-xMgGa₂O₄ (x = 0, 10, 30, 50, 70 wt%) ceramics was prepared by a solid-state method to investigate the relationship between their dielectric properties and ion diffusion, composition effect, and lattice vibration. XRD refinement and DFT calculations of Ba_0.45Sr_0.55TiO₃ (BST45) revealed that the substitution of Ga³⁺ and Mg²⁺, both of which have small polarizability for Ti⁴⁺, reached the saturation state at x = 10 wt%, thus decreasing the quality factor (Q value). In contrast, the addition of MgGa₂O₄ (MG) with x > 10 wt% significantly reduced the relative permittivity and improved the Q value owing to the compositional effect. The vibration spectra (Raman and FT-IR) confirmed that the Q value initially decreased owing to ion diffusion at x < 10 wt% and then increased with increasing MG content according to the composition effect. Therefore, the Q value was remarkably improved in the Ba_0.45Sr_0.55TiO₃-MgGa₂O₄ composites, with good tunability and low relative permittivity.     

Effects of pH on formation and morphology of barium titanate powders prepared by coprecipitation process

Abstract

The effects of pH on the formation and microstructure of barium titanate (BaTiO₃) prepared by a coprecipitation process have been investigated. After calcination of the precipitates at 800°C, pure BaTiO₃ was formed in samples prepared from oxalic solutions with pH in the range 5-7, and the powders obtained exhibited spherical shape with a size range of 5-10 μm. In contrast, small particles (around 0·1 μm) with Ti enriched phases (BaTi₃O₇, BaTi₄O₉) were produced at pH 1, and BaCO₃ with irregular shape appeared at pH 10. The phases and morphologies of the calcined powders markedly influenced the sintering behaviour and dielectric properties of BaTiO₃. After sintering at 1350°C, densified ceramics with high dielectric constants were derived from the calcined powders containing pure BaTiO₃ phase. These results show that close control of the pH of the oxalic solutions is required to produce BaTiO₃ powders with high sinterability and high dielectric constant.     

Ultra-fast synthesis and properties of high dielectric constant calcium copper titanate (CCT) ceramics synthesized by electric discharge assisted mechanical milling in oxygen and argon plasma

Synthesis of high dielectric constant calcium copper titanate (CCT) was carried out using the novel approach of electric discharge assisted mechanical milling (EDAMM) under oxygen and argon atmospheres. X-ray diffraction revealed complex structural changes associated with processing for different periods and under the different atmosphere. Morphology and grain size were investigated by field emission scanning electron microscopy and transmission electron microscopy. CCT was found to form directly by EDAMM processing in oxygen, while EDAMM processing in argon resulted in formation of intermediated nanostructure phases. Both the oxygen and argon EDAMM processed samples were sintered in air at 900 °C, and coarsen to produce CCT microstructures. The oxygen processed samples were found to have the larger grain size. Dielectric properties of the prepared samples were investigated using an LCR meter. The highest reported dielectric constant of CaCu₃Ti₄O₁₂ (CCT) was found for the oxygen EDAMM processed and annealed sample, a dielectric constant of 48,000 measured at room temperature. This is the highest value ever reported for CCT materials which are not in nano-powder form.