Dielectric and Electromechanical Properties of Textured Niobium-Doped Bismuth Titanate Ceramics

Textured Nb-doped bismuth titanate ceramics (Bi₄Ti_{3− x /5}- Nb _{x /5}O₁₂, where x = 0.02) were fabricated by templated grain growth. It was found that the use of a fine precursor powder led to enhanced densification of the ceramic, while Nb doping reduced electrical conduction and dielectric loss, which enabled poling at high temperatures and high electric fields. Sintered tapes showed anisotropic dielectric and piezoelectric properties when measured parallel and perpendicular to the casting plane (e.g., the remanent polarization differed by more than a factor of 15 in the two directions). The piezoelectric constant parallel to the casting plane of the tape was ∼30 pC/N, or ∼77% of the single-crystal value. Thermal depoling studies demonstrated that high-temperature piezoelectric applications are possible up to ∼450°C in textured, doped bismuth titanate.     

Structure,electrical and dielectric properties of Ca substituted BaTiO3 ceramics

BaTi_1-xCa_xO_3-x [BTC100x] ceramics were synthesized via solid-state reaction method. Effect of Ca substitution on the structure, electrical and dielectric properties of BTC100x ceramics was systematically investigated. Calcined BTC100x powders were in tetragonal phase when x?≤?0.01, whereas transformed to cubic at x?>?0.01. Additionally, the diffraction peak (200) shifted to lower angles with increasing x, indicating increased unit cell volume. Meanwhile, Ba_0.97Ca_0.03TiO₃ [BC3T] ceramic was prepared and studied, to compare with BaTi_0.97Ca_0.03O_2.97 (BTC3). It was found that pure BaTiO₃ [BT] and BC3T ceramics had the similar structural and dielectric properties, whereas BTC3 ceramic showed much difference,XRD patterns, Raman spectrum, impedance spectra and dielectric-temperature spectra provided strong evidence of Ca²⁺ substitution at Ti site in BT lattice. Finally, BTC100x ceramics were produced and dielectric properties were investigated. With increasing x, the Curie temperature decreased from 128?°C (BT) to 42?°C (BTC5).     

Sintering and dielectric properties of perovskite SrTaO2N ceramics

Single-phase perovskite oxynitride SrTaO₂N ceramics were prepared by pressureless sintering at 1400 °C under a nitrogen atmosphere, using 5 wt% of SrCO₃ or La₂O₃ as a sintering additive. In contrast, SrTaO₂N bulks without additives contained TaC and Ta₃N₅ impurities. Sintering in nitrogen led to oxygen/nitrogen deficiencies in the oxynitride, while post annealing in flowing ammonia was effective to eliminate the anion vacancies. The introduction of additives significantly improved the sinterability of SrTaO₂N ceramics. A relative density of >90% in the bulk was achieved with a highly dense microstructure with smaller grain sizes. The SrTaO₂N bulk with SrCO₃ additive exhibited superior dielectric performance with a high relative permittivity (?_r = 1.0 × 10⁴) and dissipation factor (tan δ = 0.039) at a frequency of 1 MHz.     

Effect of Potassium Concentration on the Grain Orientation in Bismuth Sodium Potassium Titanate

Bi_0.5(Na_{1- x} K _x )_0.5TiO₃ (BNKT) bulk ceramics with a preferred <100> orientation were prepared using the reactive templated grain-growth method with platelike Bi₄Ti₃O₁₂ particles as templates for BNKT. The potassium concentration ( x value) had a large effect on the degree of orientation, and highly oriented ceramics were obtained for the specimens with x = 0.10 and x = 0.15, whereas the specimen with x = 0.00 had a small degree of orientation. Increased potassium concentration from x = 0.00 to x = 0.15 decreased the grain-growth rate and changed the grain shape from irregular to cubic. These factors were responsible for the increased degree of orientation.     

Effect of yttrium (Y) substitution on the structure and dielectric properties of BaTiO3

As the rate of application of multilayer ceramic capacitors (MLCCs) in small electronic devices increases, the use of the raw material barium titanate (BaTiO₃) with a small particle size and excellent dielectric properties becomes needed. Due to the size effect, small-sized BaTiO₃ generally has a cubic phase structure with a low dielectric constant, which limits its use in MLCCs. We report the preparation of small cubic phase Y-doped BaTiO₃ (BYT) nanoparticles by a hydrothermal method and the preparation of highly dielectric tetragonal phase BYT ceramics based on this method. XRD and Raman analysis showed that the BYT nanoparticles are in substable cubic phases. The particle size of the BYT nanoparticles, measured by TEM, XRD, and BET, was approximately 35 nm. The dielectric properties of the BYT ceramics were tested by an impedance analyzer, and the dielectric constant of the BYT ceramics was 7547 when the Y³⁺ doping amount was 0.5 mol%. In addition, the substitution mechanism of Y³⁺ doping in BaTiO₃ crystals was proposed from XPS and EPR analysis. The results demonstrate for the first time that the 50 nm cubic phase BaTiO₃ powder can meet the needs of next-generation high-capacity MLCCs. This work provides a reference for small cubic phase BaTiO₃ as a dielectric material for high-capacity MLCCs.     

Synthesis,characterization, and dielectric properties of low loss LaBO3 ceramics

The preparation, sintering behaviour, and dielectric properties of low loss LaBO₃ ceramics have been investigated. Single-phase LaBO₃ powder was synthesized by the conventional solid-state ceramics route and dense ceramics (relative density >96%) with uniform microstructure (grain size ～30 μm) were obtained by sintering at 1300 °C in air. The electrical conductivity of LaBO₃ follows the Arrhenius law and the related activation energies for electrical conduction of bulk and grain boundary are 0.62 eV and 0.90 eV, respectively. The LaBO₃ ceramics sintered at 1300 °C exhibit excellent microwave dielectric properties with a relative permittivity, ?_r ～ 11.8, a quality factor, Q × f₀ value ～76,869 GHz (at ～15 GHz), and a negative temperature coefficient of resonant frequency τ_f ～ ?52 ppm/°C.     

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.     

Formation mechanisms and electrical properties of perovskite mesocrystals

Mesocrystals are oriented polycrystals with superstructures consisting of crystallographically ordered nanocrystals. They usually show the electron diffraction behaviour of a single crystal owing to the high order of the nanoscale building units. Mesocrystals have potential applications in many processes such as catalysis, sensing, energy storage and conversion. Perovskite mesocrystals are a novel class of mesocrystalline dielectric nanomaterials that exhibit synergistic properties and anomalous electrical properties; so they have been extensively studied in various fields. This review investigates the chemical formation processes, formation mechanisms and mechanisms that affect performance of perovskite mesocrystals. Moreover, the formation mechanisms of perovskite mesocrystals, namely topochemical mesocrystal conversion mechanism is discussed. Understanding and application of these mechanisms are important for the design and preparation of advanced structural and functional materials. Most importantly, mesocrystal-derived functional materials can be designed by combining orientation, strain, and domain engineering. The potential applications of perovskite mesocrystals as structural and functional materials in piezoelectric, ferroelectric, dielectric, and catalytic devices as well as perovskite solar cells are discussed. This investigation not only develops the chemistry of mesocrystals and proposes new routes for the design of oriented film and ceramic materials, but also provides theoretical support for future applications of perovskite mesocrystals in material science.     

掺杂三氧化二锑的钛酸铋钠钾陶瓷的显微结构和电学性能

采用固相合成工艺制备了（1–x）[0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3]–xSb2O3（BNKT–xSb）压电陶瓷,研究了Sb2O3掺杂对BNKT陶瓷的显微结构和电学性能的影响规律。研究表明：Sb2O3掺杂量x小于0.020时,不改变基体的钙钛矿结构,且Sb具有可变化合价,能形成＂施主＂和＂受主＂2种掺杂而起到＂软化＂或＂硬化＂的作用。当Sb2O3掺杂量x≤0.005时,其压电系数d33随Sb2O3掺杂量的增加而增大,此时Sb2O3表现出了＂软化＂的特征;当Sb2O3掺杂量x〉0.005时,d33降低,从而又表现出了＂硬化＂的特性;当Sb2O3掺杂≥0.010时,诱使陶瓷室温下反铁电微畴的形成,导致铁电性和压电性的骤减。     

Effect of neodymium ion on the structural,electrical and magnetic properties of nanocrystalline nickel ferrites

NiNd_xFe_2-xO₄ nanoferrites with different compositions of x?=?0.01, 0.03, 0.05, 0.07 and 0.09 were prepared using the sonochemical method. The structural, optical and morphological properties of the prepared nanoferrites were characterized by X-ray diffraction, ultra violet-diffuse reflectance spectroscopy, scanning electron microscopy and X-ray fluorescence techniques. The X-ray diffraction analysis of the prepared nanoferrites confirmed the presence of a cubic spinel structure. The average crystallite sizes of the prepared nanoferrites were 52, 49, 46, 44 and 40?nm for x?=?0.01, 0.03, 0.05, 0.07 and 0.09, respectively. The particle size of the prepared NiNd_xFe_2-xO₄ nanoferrites was in the range 60–40?nm. The dielectric parameters ranged from 2.9?GHz to 5.6?GHz. Decrease in the dielectric constant was observed with an increase in Nd³⁺ ions in the prepared NiNd_xFe_2-xO₄ nanoferrites. However, a reverse trend was observed in the dielectric loss. An impedance analysis of the prepared nanoferrites was carried out to explore the pseudo-capacitance behavior. The saturation magnetization and remnant magnetization values of the prepared nanoferrites decreased with an increase in the concentration of Nd³⁺ ions in NiNd_xFe_2-xO₄ nanoferrites.     

Ferroelectric,dielectric, magnetic,structural and photocatalytic properties of Co and Fe doped LaCrO3 perovskite synthesized via micro-emulsion route

In the present investigation, La_1-xCo_xCr_1-yFe_yO₃ (x,y = 0.0, 0.12, 0.36, 0.60) perovskite was fabricated via a facile micro-emulsion route. The synthesized perovskites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques to examine the effect of Co and Fe ions on the physico-chemical properties. The ferroelectric, dielectric, and magnetic properties of La_1-xCo_xCr_1-yFe_yO₃ were changed significantly as a function of dopants contents (Co and Fe ions). Outcomes revealed that the dielectric, ferroelectric and magnetic properties of LaCrO₃ perovskite can be tuned significantly via Co and Fe doping and La_0.40Co_0.60Cr_0.40Fe_0.60O₃ have potential for photocatalytic dye removal under (visible) light expoure. The photocatalytic activity (PCA) of the pristine LaCrO₃ and La_0.40Co_0.60Cr_0.40Fe_0.60O₃ photocatalyst was evaluated under (visible) light irradiation for crystal violet (CV) dye. Experimental results revealed that La_0.40Co_0.60Cr_0.40Fe_0.60O₃ photocatalyst degrdae almost 77.21% CV dye with the rate constant value of 0.01475 min^?1. In the presence of isopropyl alcohol (IPA) scavenger, the PCA of the La_0.40Co_0.60Cr_0.40Fe_0.60O₃ photocatalyst and rate constant value of the photocatalytic reaction decreased to 32.5% and 0.00491 min^?1, suggesting the superoxide as main active specie. Results revealed that Co and Fe doping doped material is efficient for photocatalytic presentations under solar light expoure.     

Influence of Mn-substitution on the structure and low-temperature electrical conduction properties of PrCoO3

Rare earth cobalt perovskite oxide (LnCoO₃) is one kind of complex metal oxides and has a wide variety of applications. The performance of LnCoO₃ is controlled by its electrical conduction, and therefore it is essential to study the behaviour of electrical conduction in LnCoO₃ and elucidate the corresponding conduction mechanism. In this work, a series of PrCo_1−xMn_xO₃(x = 0, 0.05, 0.1, 0.15, 0.2) were prepared by sol-gel method. The structures and low-temperature electrical conduction properties of these samples were investigated using x-ray diffraction, infrared spectra and alternating current impedance spectroscopy. All samples crystallized in an orthorhombic perovskite structure. Structural refinements reveal that the lattice parameters increased, while the orthorhombility decreased with Mn substitution. Further investigation of infrared spectrum indicates that the stretching vibration bands of Co-O bonds shifted towards lower wavenumbers followed by an increase of the population of Co³⁺ ions with intermediate spin state. These variations led to a reduced bandwidth of e_g band which could be the dominant reason for the abrupt decrease of bulk semi-conduction and the increase of activation energies for small polaron hopping conduction in PrCo_1−xMn_xO₃.     

Effect of Mn-doping on the structure and electrical properties of (Pb0.325Sr0.675)TiO3 ceramics

Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics (x?=?0, 0.001, 0.005, 0.01, and 0.05) were successfully prepared by traditional solid-state reaction method. It was found that the lattice constant calculated through Rietveld refinement initially increased and then decreased with increasing Mn content, which was attributed to the variation in valence state of Mn and Ti ions. The microstructure gradually varied from the coexistence of large grains and fine grains for x?=?0 to the uniform grain for x?=?0.05 by increasing the doping Mn ions. With increasing Mn content from x?=?0 to x?=?0.05, the Curie temperature (Tc) dramatically decreased from 25?°C to ??40?°C and dielectric maximum decreased from 27,100 to 13,200. Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics with x?=?0.001 showed the lowest dielectric loss of 0.006 with a relatively high dielectric peak value of ~ 21,000. The grain boundaries resistance obtained from the complex impedance decreased with the increase of Mn content. The decrease in resistance was ascribed to oxygen vacancies and electronics produced by the change of ionic valence state. X-ray photoemission spectroscopy revealed that Ti ions were Ti⁴⁺ and the valences of Mn ions were deduced to be mainly in the form of Mn²⁺ and/or Mn³⁺ for ceramics with low content of Mn, while the Ti ions were in the form of Ti³⁺ and Ti⁴⁺ and Mn ions were diverse valence states with the coexistence of Mn²⁺, Mn³⁺, and Mn⁴⁺ for ceramics with x?=?0.01 and 0.05.     

Effects of Ni doping on structural,optical and dielectric properties of ZnO

Structural, optical and dielectric properties of Ni doped ZnO samples prepared by the solid state route are presented. X-ray diffraction confirmed the substitution of Ni on Zn sites without changing the hexagonal structure of ZnO. NiO phase appeared for 6% Ni doping. Fourier transform infrared measurements were carried out to study phonon modes in Ni doped ZnO. Significant blueshift with Ni doping was observed in UV–visible studies, strongly supported by photoluminescence spectra that show a high intensity UV emission peak followed by the low intensity green emission band corresponding to oxygen vacancies and defects. The photoluminescence analysis suggest that doping of Ni can affect defects and oxygen vacancies in ZnO and give the possibility of band gap tuning for applications in optoelectronic devices. High values of dielectric constant at low frequency and a strong dielectric anomaly around 320 °C were observed.     

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.     

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.     

Zinc substitution effect on the structural,spectroscopic and electrical properties of nanocrystalline MnFe2O4 spinel ferrite

This paper reports the structural, morphological, spectroscopic, dielectric, ac conductivity, and impedance properties of nanocrystalline Mn_1-xZn_xFe₂O₄. The nanocrystalline Mn–Zn ferrites were synthesized using a solvent-free combustion reaction method. The structural analysis using X-ray diffraction (XRD) pattern reveals the single-phase of all the samples and the Rietveld refined XRD patterns confirmed the cubic-spinel structure. The calculated crystallite size values increase from 8.5 nm to 19.6 nm with the Zn concentration. The surface morphological analysis using field emission scanning electron microscopy and the transmission electron microscopy confirms the nano size of the prepared ferrites. X-ray photoelectron spectroscopy was used to study the ionic state of the atoms present in the samples. Further, the high-resolution Mn 2p, Zn 2p, Fe 2p, and O 1s spectra of Mn_1-xZn_xFe₂O₄ does not result in the appearance of new peaks with Zn content, indicating that the Zn substitution does not change the ionic state of Mn, Zn, Fe, and O present in nanocrystalline Mn_1-xZn_xFe₂O₄. The investigated electrical properties show that the dielectric constant, tan δ and ac conductivity gradually decrease with increasing Zn substitution and the sample Mn_0·2Zn_0·8Fe₂O₄ has the lowest value of conductivity at 303 K. The ac conductivity measured at different temperatures shows the semiconducting nature of the ferrites. The impedance spectra analysis shows that the contribution of grain boundary is higher compared with the grain to the resistance. The obtained results suggest that the Zn substituted manganese ferrite nanoparticles can act as a promising candidate for high-frequency electronic devices applications.     

Influence of a metal–polymer interfacial interaction on dielectric relaxation properties of polyurethane

The influence of metal–polymer interaction on dielectric relaxation properties of polyurethane (PU), prepared from poly(oxypropylene)diol and hexamethylendiisocyanate, was investigated by means of dielectric relaxation spectroscopy in the frequency domain on the dependence of the thickness of the PU layer and electrode material (gold and steel). Strong electrostatic part of an adhesion interaction between steel substrate and PU results in changes of the -, β-, γ- and Maxwell–Wagner–Sillars relaxation of the PU, as compared to a gold substrate. The effect of the metal–polymer double layer results in the complication of the cooperative and local motions in the polymer. The influence of metal–polymer interaction on the relaxation parameters becomes pronounced at a thickness of less than 60 μm for the steel substrate. For the gold substrate the relaxation characteristics hardly depend on the thickness.     

Effect of Gd doping on structural,optical properties,photoluminescence and electrical characteristics of CdS nanoparticles for optoelectronics

Synthesis of pure and 0.1 to 5?wt.% Gd-doped CdS nanoparticles (NPs) was achieved through a modified domestic microwave-assisted route in a short timespan at 700?W power. The formation of hexagonal CdS NPs was verified via X-ray diffraction analysis, and no structural variation was observed except for lattice variation. The size of the crystallites (D), dislocation concentration, and lattice strain were calculated, and the D was in the range of 3–6?nm. Fourier transform-Raman analysis confirmed the presence of 1LO, 2LO, and 3LO modes at 294.76, 590, and 890?cm^?1, respectively, in all the synthesized nanostructures, with minute variations in their positions due to doping; however, no new mode was observed. The position of the vibration modes was red shifted compared to that of the bulk material, indicating a confinement effect. Scanning electron microscopy (SEM) mapping/energy-dispersive X-ray spectroscopy revealed homogeneous doping of Gd and the presence of all the constituents in the final products. The morphology of the synthesized materials was tested via field-emission SEM, which revealed spherical NPs with small dimensions. Additionally, high-resolution transmission electron microscopy was performed to visualize the shape and size of the prepared 0.1% Gd:CdS NPs. The energy gap was calculated using the Kubelka–Munk theory and found to be in the range of 2.31–2.41?eV. The photoluminescence emission spectra exhibited two green emission peaks at 516?±?2?nm and 555?±?2?nm and showed the reduction of defects with Gd doping in terms of intensity quenching. The dielectric constant (${\epsilon }^{\text{'}}$), loss, and alternating-current electrical properties were studied in the high-frequency range. The values of ${\epsilon }^{\text{'}}$ were in the range of 17–27. An enhancement of these values was observed for CdS when it was doped with Gd. The electrical conductivity exhibited frequency power law behavior.     

Effect of Ag on the microstructure and electrical properties of ZnO

Various amounts of silver particles, 0.08–7.7 mol%, are mixed with zinc oxide powder and subsequently co-fired at 800–1200 °C. The effects of Ag addition on the microstructural evolution and electrical properties of ZnO are investigated. A small Ag doping amount (<0.76 mol%) promotes the grain growth of ZnO; however, a reversed trend in grain growth is observed for a relatively larger Ag addition (>3.8 mol%). It is evident that a tiny amount of Ag (0.08 mol%) may dissolve into the ZnO lattice. High-resolution TEM observations give direct evidences on the segregation of Ag solutes at the ZnO grain boundaries. The grain boundary resistance of ZnO increases 35-fold with the presence of Ag solute segregates. The Ag-doped ZnO system exhibits a nonlinear electric current–voltage characteristic, confirming the presence of an electrostatic barrier at the grain boundaries. The barrier is approximately 2 V for a single grain boundary.