Electrical,dielectric and pyroelectric behavior of neodymium substituted barium zirconium titanate

Neodymium (Nd) substituted barium zirconium titanate with nominal composition (Ba_1−xNd_x)(Zr_0.52Ti_0.48)O₃ [x = 0.1, and 0.2] were synthesized using solid state reaction method. X-ray analysis confirmed the formation of perovskite structure along with minor pyroclore phase of neodymium. The change in grain size revealed the influence of Nd-ions on the microstructure. The sintered samples exhibited negative temperature coefficient of resistance (NTCR) and superior semiconducting behavior. Addition of Nd³⁺varies the room temperature resistivity of Ba(Zr_0.52Ti_0.48)O₃. As the concentration of Nd-ion increased, the value of temperature dependent dielectric constant decreased whereas the Curie temperature of the ceramics shifted toward higher temperature side showing diffuse phase transition. This is attributed to decrease in average grain size. Temperature dependent pyroelectric current exhibited combination of primary and secondary pyroelectric effect.     

Fabrication and characterization of cerium doped barium titanate/PMMA nanocomposites

The cerium doped barium titanate (BaTiO₃:Ce)/poly methyl methacrylate(PMMA) polymer nano-composites (PNC) were successfully fabricated via solvent evaporation method with microwaves (2.4 GHz) heating. The X-ray diffraction measurements confirm the formation of barium titanate (BT) with crystallite size ranges from 55 to 62 nm. Differential scanning calorimetry study shows that the glass transition temperature (T_g) directly affected by microwaves heat treatment and particle size of filler. The broadband dielectric spectroscopy was employed to investigate the frequency and temperature dependence of the dielectric properties of the nanocomposites in a frequency range from 75 kHz to 5 MHz and temperature range 80–400 K. The introduction of different BT fillers in PMMA enhance the dielectric constant of PNCs drastically and give a smooth response in frequency range mentioned above. The loss factor of the composite can be suppressed by using cerium doped barium titanate filler rather than pure barium titanate filler.     

Detection of up-conversion in nano-structure BaTiO<Subscript>3</Subscript> co-doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> ions

Nano-structure pure barium titanate BaTiO₃ (BT) and (BT) co-doped with constant concentration of Er³⁺ ions and different concentrations of Yb³⁺ ions were prepared using sol–gel method. XRD results confirmed that the pure sample was found to crystallize in tetragonal phase by sintering at 750 °C for 1 h. All major peaks corresponding to perovskite BT phase appeared. Efficient infrared-to-visible up-conversion is reported in the doped samples. The conversion process and results in the generation of visible emissions are discussed. Up-conversion efficiency for red emission predominates in doped samples. Results illustrate the large potential of this class of materials for photonic applications in optoelectronics devices.     

Dielectric and optical properties of BaTiO<Subscript>3</Subscript> thin films prepared by low-temperature process

Barium titanate (BaTiO₃) thin films have been prepared by low temperature processing on Pt/Ti/SiO₂/Si substrates using sol-gel-hydrothermal (SGHT) technique, which combined the conventional sol-gel process and hydrothermal method. X-ray diffraction analysis showed that the barium titanate thin films are polycrystalline. As-reacted barium titanate films grown on Pt(111)/Ti/SiO₂/Si(100) substrates had a dielectric constant (ε) and loss tangent (tanδ) of 80 and 0.05 at 1 MHz, respectively. The optical constants including refractive index n, extinction coefficient k, and absorption coefficient α of the barium titanate thin films in the wavelength range of 2.5–12.6 μm were obtained by infrared spectroscopic ellipsometry.     

Effect of ZnO on sintering and microwave dielectric properties of 0.5CaTiO3-0.5 (Li0.5La0.5) TiO3 ceramics

The novel calcium titanate-lithium lanthanum titanate doped with zinc oxide (0.10, 0.30, and 0.50 mol. %) ceramic samples were prepared by solid-state reaction route. The phase formation, microstructure, densification, and microwave dielectric properties were investigated. It was found that the doping with zinc oxide led to a decrease in sintering temperature by 25 ^oC as compared with pure calcium titanate lithium lanthanum titanate due to the liquid phase effect. Also, the calcium titanate lithium lanthanum titanate (10ZCTLLT&30ZCTLLT)) doped with lower zinc oxide (0.10 and 0.30 mol. %) led to higher densification parameter. This was followed by increasing the zinc oxide doping up to (0.50 mol. %) which resulted in a decrease in densification and microwave dielectric properties which may be attributed to increase in porosity and grain growth upon the evaporation of zinc and oxygen vacancy. This led to the increase in dielectric loss (≈10 × 10^?4) value with 50ZCTLLT. Hence, the best result of microwave dielectric characteristics was obtained for 0.5CaTiO₃–0.5(Li_0.5La_0.5)TiO₃ with (0.10 and 0.30 mol. % ZnO) 10ZCTLLT and 30ZCTLLT ceramic samples sintered at 1175 ^oC/2h, with low dielectric constant (ε_r) = 4.4–10.5, very low dielectric loss = 1.07-2.23 × 10^?4 and high quality factor (Q x ?) ≈59-55 × 10⁴ at 8 GHz. Consequently, they can be used not only in wireless satellite communications technology but also can be used in the fifth-generation telecommunication 5G technology construction.     

Preparation and Pyroelectric Properties of Poly(pentafluorostyrene)-r-Poly(4-vinylaniline) Copolymer Films

Abstract: In this study poly(pentafluorostyrene)-ran-poly(4-vinylaniline) (PPFS-r-PVA) was synthesized by solution polymerization with AIBN utilized as an initiator. The dilute THF solution of the resultant copolymer was spin-coated onto clean Ag/Si(100) substrates, and then the copolymer film was electrically poled at 85 °C for 30 min using a plane poling method with a poling voltage of 7.0 kV. The pyroelectric coefficient was determined by a digital integral method and carried out with a charge integral instrument. It was observed that the average pyroelectric coefficient of the resultant PPFS-r-PVA was 20.4 µC/cm²K in the range of 20–45 °C, and the average dielectric loss is about 0.2298 between 3.2 × 10⁴–1.0 × 10⁶ Hz.     

Dielectric relaxation behavior of C5+ (70 MeV) swift heavy ion irradiated polyetheretherketone (PEEK) using TSDC technique

The dielectric relaxation characteristics of polyetheretherketone (PEEK) irradiated with C⁵⁺ (70 MeV) ion, have been investigated in the temperature range 60–230° as a function of poling temperature T _P (50, 100, 150, and 200°C), poling field E _P (200, 300, 400, and 500 kV/cm), and storage time t _s (2, 24, 48, and 120 h), using thermally stimulated discharge current (TSDC) technique. The TSDC spectra show a prominent maximum around glass transition temperature (T _g ～ 143°C) named as α-peak. This peak is attributed to the movement of ketone dipoles linked with the main chain. It is observed that the magnitude of α-peak increases with the increase in poling temperature and poling field. The peak current and area under the α-peak are found to be diminished with the increase of storage time t _s for electrets. The β-peak (space charge peak) is absent in irradiated PEEK samples as compared to pristine PEEK samples. The results obtained, in the present studies, are compared with the results on pristine samples. The activation energies and pre-exponential factor for PEEK samples determined using Bucci plot method.     

Characterization and physical properties of Li2O-CaF2-P2O5 glass ceramics with Cr2O3 as a nucleating agent—Physical properties

In this paper, studies on various physical properties, viz., dielectric properties (dielectric constant, loss tan δ, a.c. conductivity σ) over a wide range of frequency and temperature, optical absorption, ESR at liquid nitrogen temperature and magnetic susceptibility at room temperature of Li₂O-CaF₂-P₂O₅: Cr₂O₃ glass ceramics, have been reported. The optical absorption, ESR and magnetic susceptibility studies indicate that the chromium ions exist in Cr⁵⁺, Cr⁴⁺ and Cr⁶⁺ states in addition to Cr³⁺ state in these samples. The dielectric constant and loss variation with the concentration of Cr₂O₃ have been explained on the basis of space charge polarization mechanism. The dielectric relaxation effects exhibited by these samples have been analysed by a graphical method and the spreading of dielectric relaxation has been established. The a.c. conductivity in the high-temperature region seems to be connected both with electronic and ionic movements.     

From Synthesis to Applications: Copper Calcium Titanate (CCTO) and its Magnetic and Photocatalytic Properties

Investigations focusing on electrical energy storage capacitors especially the dielectric ceramic capacitors for high energy storage density are attracting more and more attention in the recent years. Ceramic capacitors possess a faster charge-discharge rate and improved mechanical and thermal properties compared with other energy storage devices such as batteries. The challenge is to obtain ceramic capacitors with outstanding mechanical, thermal and storage properties over large temperature and frequencies ranges. ABO₃ as a type of perovskites showed a strong piezoelectric, dielectric, pyroelectric, and electro-optic properties useful as energy storage and environmental devices. CaCu₃Ti₄O₁₂ (CCTO) perovskite with cubic lattice (Im3 symmetry) was discovered to have a colossal dielectric constant (10⁴) that is stable over a wide range of frequencies (10 Hz–1 MHz) and temperature independence (100–300 K). The origin of this high dielectric constant is not fully established, specially because it is the same for single crystal and thin films. In this review, the history of CCTO will be introduced. The synthesis and the sintering approaches, the dopant elements used as well as the applications of CCTO will be reported. In addition to dielectrical properties useful to energy storage devices; CCTO could serve as photocatalytic materials with a very good performance in visible light.     

The electrical properties of chemically obtained barium titanate improved by attrition milling

Barium titanate ceramics were prepared using the nanopowder resulting from a polymeric precursor method, a type of modified Pechini process. The obtained nanopowder was observed to agglomerate and in order to de-agglomerate the powder and enhance the properties of the barium titanate the material was attrition milled. The impact of this attrition milling on the electrical properties of the barium titanate was analysed. The temperature dependence of the relative dielectric permittivity showed three structural phase transitions that are characteristic for ferroelectric barium titanate ceramics. The relative dielectric permittivity at the Curie temperature was higher for the attrition-treated sample than for the non-treated barium titanate. The dielectric losses were below 0.04 in both barium titanate ceramics. The grain and grain-boundary contributions to the total resistivity were observed using impedance analyses for both ceramics. A well-defined ferroelectric hysteresis loop and piezoelectric coefficient d₃₃ = 150 pC/N were obtained for the ceramics prepared from the de-agglomerated powder. In this way we were able to demonstrate that by attrition milling of chemically obtained powders the ferroelectric and piezoelectric properties of the ceramics could be enhanced.     

Liquid-phase synthesis of barium acetatotitanyl and barium oxalatotitanyl as intermediates for preparing nanosized barium titanate

Liquid-phase methods (an oxalate process in aqueous solution and a semialkoxide sol-gel process in anhydrous acetic acid) were used to prepare barium acetatotitanyl (BAT) and barium oxalatotitanyl (BOT), which are potential fillers for electrorheological liquids, and to prepare barium titanate during heat treatment of the aforementioned intermediates at 1200°C. The materials were characterized using electron microscopy, FTIR spectroscopy, and thermal analysis. The particle size was 80 to 100 nm for BAT powders and 20 to 50 nm for BOT powders. X-ray spectra of the powders dried at 120°C contain reflections from a barium titanate phase. The dielectric spectra of the materials synthesized were studied for suspensions in PMS-20 silicone oil over the frequency range from 25 to 10⁶ Hz up to 4 kV/mm. The dielectric parameters of BOT suspensions decrease hyperbolically with rising alternate current frequency, whereas BAT suspensions give rise to a relaxation dielectric spectrum with relaxation times on the order of 10⁻³ s.     

Preparation and Properties of Nb-Coated Barium Titanate Composite Particles by Surface Modification with Nb Alkoxide in Hydrophobic Solvent

Chemical processing for the preparation of Nb-coated barium titanate composite particles was investigated using surface modification technology, hydrolyzing Nb ethoxide on the surface of barium titanate particles dispersed in hydrophobic solvent.It was confirmed from the measurements of specific surface area and zeta potential as well as SEM, TEM and EDX observations of the resulting composite particles that the original barium titanate particles were coated uniformly with hydrolysis product of Nb ethoxide.Barium titanates coated with 1 wt% of Nb as oxide were well sintered at 1200–1300°C. The dielectric constants of the sintered barium titanates showed flattened temperature dependence, but it depended upon the average particle size of original barium titanate. The sintered bodies of Nb-coated barium titanate powders with average particle size of 0.2 m gave dielectric constants of 2000–3000 and those of barium titanate with average particle size of 0.5 m showed dielectric constants of 3000–4000 at room temperature.The microstructure of the sintered barium titanate coated with Nb oxide consisted of grains of about 1 m, smaller than those of sintered original barium titanate.     

Structural and Electrical Properties of Iron-Containing Aluminosilicate Gel-Derived Pellets

Aluminosilicate pellets containing 10 mol% of Fe₂O₃, prepared by the sol-gel method, have been investigated. Electrical conductivity, dielectric constant, X-ray diffraction, scanning electron microscopy and electron paramagnetic resonance have been used to characterize the evolution of the samples with the heat-treatment temperature and atmospheric conditions. Results show that iron is present in the air heat-treated samples as Fe³⁺, goethite and hematite particles. Metallic iron and magnetite were identified in the samples heat-treated under reducing conditions. The d.c. conductivity decreases with increasing heat-treatment temperature of the samples indicating a variation, with the temperature, of the electrical free charges. However, in the case of the dielectric constant the samples heat-treated in air and under reducing conditions do not present the same behaviour. This variation was related with the microstructural evolution of the samples.     

Sol-gel synthesis of cerium dioxide nanoparticles coated with stimuli-responsive components and the application for conversion of <Emphasis Type="SmallCaps">d-</Emphasis>(−)-fructose into platform molecules

Barium zirconium titanate (Ba(Zr _x Ti_1?x)O₃, BZT) super smooth thin films are synthesized through modified sol-gel dip coating route on fluorine-doped tin oxide substrates with a suitably low calcination temperature. The Fourier tranformed infrared spectroscopy proves that impurities and starting materials are completely removed in the calcination process. Crystallographic phases of the samples are identified by the X-ray diffractometry and confirms that all samples are crystallized into a single perovskite phase. Introducing zirconium into the structure causes a reduction in dielectric constant of barium titanate. The optical properties of the films are also investigated. The results indicate that all samples are highly transparent and zirconium reduces the absorption coefficient. Moreover, the band gap energy of barium titanate increases when doped with zirconium and the highest band gap energy of about 3.71?eV along with the lowest dielectric constant of 850 at frequency of 100?kHz are obtained in 15 at.% zirconium-doped sample.

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聚苯乙烯—钛酸钡复合材料介电性能的研究

以聚苯乙烯与化学沉淀法钛酸钡陶瓷为基本组成，采用溶液共混，溶液聚合，表面处理后溶液聚合三种方法进行复合，发现后两种复合的钛酸钡颗粒表面发生界面变化，形成活性界面，使得溶液聚合法和表面处理后溶液聚合所得到的材料具有较低的介电损耗，在高频下能保持较高的介电系数。     

Electrical properties and initial permeability of Cu–Mg ferrites

A series of polycrystalline spinel ferrites with composition Cu_1−xMg_xFe₂O₄ where 0.0 ≤ x ≤ 1 are prepared by the standard ceramic method. The single-phase cubic spinel structure of all the samples has been confirmed from X-ray diffraction analysis. The lattice constant increases linearly with increasing magnesium content obeying Vegard's law. The electrical properties (ɛ′, and σ) of the prepared samples are measured at different temperatures as a function of applied frequency ranging from 100 kHz up to 5 MHz. The general trend of ɛ′, and σ is decreased with increasing Mg²⁺ and increases with increasing temperature. The observed variation of dielectric properties is explained on the basis of Cu²⁺/Cu¹⁺ ionic concentration as well as the electronic hopping frequency between Fe²⁺ and Fe³⁺ ions in the present samples. The data of initial permeability is also discussed.     

Visible Up-Conversion Luminescence in Ho3+: BaTiO3 Nano-Crystals Prepared by Sol Gel Technique

Visible up-conversion emissions at (435, 545, 580, 675 and 690 nm) and (437, 547 575 and 675 nm) have been observed from the sol-gel derived nano-crystalline Ho³⁺: BaTiO₃ powders and thin films respectively, under 808 nm laser diode excitation emissions. Combined with the energy level structure of Ho³⁺ ions and the kinetics of the visible emissions, the up-conversion mechanism has been analyzed and explained. The blue, green and red emissions of both samples has been attributed to the ground state-directed transition from (⁵F₁), (⁵S₂) and (⁵F₅), which are populated through excited state absorption (ESA) for 808 nm excitation. Nano-structure pure barium titanate and doped with different concentrations of Ho³⁺ ions in the from of powder and thin film have been prepared by sol-gel technique, using barium acetate (Ba(Ac)₂), and titanium butoxide (Ti(C₄H₉O)₄), as precursors. The thin films were prepared by sol-gel spin coating method. The as-grown thin films and powders were found to be amorphous, which crystallized to the tetragonal phase after heating at 750°C in air for 30 minutes. The crystallite sizes of the thin film and powder both doped with 4% Ho³⁺ ions was found to be equal to 11 and 16 nm, respectvely.     

Preparation of Barium Titanate Nanopowder through Thermal Decomposition of Peroxide Precursor and Its Formation Mechanism

H₂TiO₃ was dissolved in the mixture of hydrogen formed peroxide and ammonia under the pH range of 8–10 with a transparent yellow solution formed. When an equivalent mole of Ba²⁺ solution was added into the yellow solution, the precipitate produced was the peroxide precursor of barium titanate. The cubic nanopowder of barium titanate was obtained when the precipitate was washed, stoved, and then calcined at 600°C for 1 h. The peroxide precursor of barium titanate and barium titanate nanopowder prepared were characterized to be BaTi(H₂O₂)₂O₃ by TGA‐DTA, XRD, TEM, SEM, and XREDS. The peroxide precursor of barium titanate was determined to be BaTi(H₂O₂)₂O₃. The particle size of the barium titanate nanopowder, the calcined product of BaTi(H₂O₂)₂O₃, was in the range of 20–40 nm. A formation mechanism of the barium titanate nanopowder through thermal decomposition of its peroxide precursor was proposed and then validated.     

Complex dielectric constant and relaxation parameters of aqueous solutions of barium nitrate

Microwave dielectric properties of aqueous solutions of barium nitrate are studied as a function of concentration at frequencies from 3.4 to 23.5 GHz and temperatures from 283 to 313 K. The following dielectric parameters of the solutions are determined: static dielectric constant ε_s, dielectric relaxation time τ, and enthalpy of activation of dielectric relaxation ΔH _ε ⁺⁺ . In transfer from water to the solutions, the static dielectric constant decreases for all test solutions. Decreases in τ and ΔH _ε ⁺⁺ are induced by the increasing mobility of water molecules in ion hydration shells. The ionic effect disappears as temperature increases.