Influence of different nano titania on microstructure and electrical properties of low voltage zinc oxide varistors

A series of check experiments showed that ZnO varistors doped with TiO₂ of different particle sizes and dispersing states have different densities, porosities and grain morphologies, which relate to their electrical properties tightly. Compared with samples added with TiO₂ dopants of others types, the varistors added with nm-TiO₂ sol exhibit large density, low porosity, big granular size, low breakdown voltage gradient and small leakage current. Hence nm-TiO₂ sol dopant is the best grain growth enhancing additive for optimizing almost all the electrical parameters.     

Effect of Gd amphoteric substitution on structure and dielectric properties of BaTiO3-based ceramics

BaTiO₃-based ceramics (doped with a small amount of Ni²⁺, Mn²⁺, Nb⁵⁺, Ca²⁺ and Zr⁴⁺) with various Gd₂O₃ concentrations were prepared by the conventional solid-state reaction method. Effects of Gd₂O₃ doping concentrations on the structure and dielectric properties were investigated. It was deduced from XRD patterns that different substitution sites of Gd³⁺ ions could be affected by Gd₂O₃ doping amount. Gd³⁺ tended to occupy Ba-site when Gd₂O₃ concentration was less than 0.25 mol%. With increasing Gd₂O₃ doping amount to 0.3 mol%, Gd³⁺ substituted into both Ba- and Ti-site which contributed to an obvious improvement on dielectric constant of BaTiO₃-based ceramics. Influences of the Gd³⁺ amphoteric substitution on the improvement of the dielectric constant were discussed based on the self-compensation mechanism.     

Structure and dielectric properties of Ca-doped (Ba0.7Sr0.3) TiO3 thin films fabricated by sol–gel method

A wide range of Ca-doped (Ba_0.7Sr_0.3)TiO₃ (BST) thin films (from 0 to 20 mol%) have been prepared on Pt/Ti/SiO₂/Si (100) substrates by sol–gel technique. The structural and dielectric properties of BST thin films were investigated as a function of Ca dopant concentration. The results showed that the microstructure and dielectric properties of the BST films were strongly dependent on the Ca contents. With the Ca dopant concentration increasing, the grain size, dielectric constant and dielectric loss of the BST thin films decreased. As the content of Ca dopant reaches 10 mol%, the dielectric constant, dielectric loss, tunability, the value of FOM and the leakage current density are 281, 0.0136, 16.7%, 12.3 and 5.5?×?10^?6 A/cm², respectively.     

Preparation and microwave properties of Mg doped barium strontium titanate (BSTO) ceramics sintered from Sol–Gel-derived powders

Studies on the Preparation and microwave properties of Mg doped barium strontium titanate (BSTO) ceramics sintered from Sol–Gel-derived powders. The crystal structure and microstructure of Ba_0.60Sr_0.40TiO₃ ceramics doped with Mg has been investigated. The microwave complex permittivity of BST ceramics doped with Mg powders is investigated in 100 MHz–6 GHz ranges by coaxial-transmission technique and the calculation of the equivalent medium theory. Experimental results showed that the typical cubic phase structure and the diffraction peaks of secondary phase that MgO phase become stronger with increasing Mg²⁺ content in the XRD pattern of the Mg doped BST ceramic sintered at 1250°C. The real part of the microwave complex permittivity of BSTM30 ceramic powders is excellent described by results of calculation of Bruggeman theory in wide powder content.     

Photoluminescence properties of a green to red-emitting Eu3+, Tb3+ co-doped CaBi2Ta2O9 ferroelectrics

The CaBi₂Ta₂O₉ bismuth layered-structure ferroelectrics doped with rare earth ions Eu³⁺ and Tb³⁺, or co-doped with Eu³⁺/Tb³⁺ were prepared by the conventional solid-state reaction method. The microstructure and photoluminescence properties of CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ were investigated. The XRD patterns demonstrate that the rare earth ions have been effectively doped into CaBi₂Ta₂O₉ host lattices. The photoluminescence properties of CaBi₂Ta₂O₉ with different activator ions are researched in details. The novel red and green light emissions were observed under the excitation of blue and near-UV light. Notably, tunable emissions and a warm-white color have been achieved in the Eu³⁺ and Tb³⁺ co-doped CaBi₂Ta₂O₉ powders. These results suggest that CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ could be novel luminescence materials. It is also expected that rare earth doped CaBi₂Ta₂O₉ ferroelectrics can find potential applications in new multifunctional photoluminescence ferroelectric devices.     

Sol-Gel Synthesis of Zn Doped MgO Nanoparticles and Their Applications

Abstract

The physicochemical properties of metal oxide nanoparticles can be significantly improved by doping. MgO and Zn²⁺ doped MgO (Zn:MgO) offers potential applications in photonic devices falling in the UV and visible region. In the present paper, sol gel method was employed to synthesize pure and Zn²⁺ doped MgO nanoparticles. XRD pattern inferred the crystalline nature of material and also the slight change in peak due to the dopant. FESEM showed the formation of nanoparticles with almost same shapes and dimensions with little agglomeration. Optical properties were studied by using UV-Vis and PL techniques. Doping of Zn²⁺ in MgO nanoparticles was verified by EDS.     

The Dopant Distribution in Ti-, Zr- and Cr-doped Y3Al5O12 Fibers Grown by the Laser Heated Floating Zone Method

Single crystal fibers of Ti-, Zr- and Cr-doped Y₃Al₅O₁₂ (YAG) were grown from polycrystalline feed rods in Ar+5%H₂, pure Ar and Ar+2%O₂ atmospheres using the laser heated floating zone method. The spatial dopant distribution and precipitation of second phases in the grown fibers has been systematically studied by means of electron probe microanalysis. A strong growth-atmosphere dependence of effective segregation coefficient and precipitate formation were seen in Ti- and Cr-doped fibers, but not in Zr-doped fibers. The highest doping of Ti into the YAG lattice was obtained in Ar+5%H₂ atmosphere, while Cr was able to be incorporated into YAG by suppression of evaporation under an Ar+2%O₂ atmosphere. The results are discussed in terms of atmosphere-dependent valence state and volatility of the dopant.     

Effect of attrition milling on the piezoelectric properties of Bi0.5Na0.5TiO3-based ceramics

Bismith sodium titanate (BNT)-based powders were prepared by conventionally mixed-oxide method using Bi₂O₃, Na₂CO₃ and TiO₂. The La₂O₃ was added as the modifier to the BNT composition for easily poling and reducing an abnormal dielectric loss at high temperatures. In this study, the investigated compositions were Bi_0.5Na_0.5TiO₃ and Bi_0.5Na_0.485La_0.005TiO₃. The powders were calcined at 900 °C for 2 h by slow heating rate at 100 °C/h. The calcined BNT-based powders were then attrition-milled for 3 h with a high speed at 350 rpm. After drying, the fine powders were uniaxially pressed and then cold-isostatically pressed (CIP) at 240 MPa for 10 min. All pressed pellets were sintered at 1000–1100 °C for 2 h in air atmosphere. The microstructure of sintered pellets was investigated by SEM. Results of dielectric and piezoelectric property measurement were also reported.     

Effect of nano-sized TiO2 powder on Ag-electrode in piezoelectric multilayer devices

The objective of this study is to present sintering shrinkage behavior of Ag-Pd electrode powders with TiO₂ nano-particle addition and the matching characteristics to a piezoelectric ceramics, Pb(Zr,Ti)O₃. The densification of the nanoparticle TiO₂-added electrode paste followed the TiO₂ solid state diffusion-controlled mechanism upon sintering process. Reaction between ceramic and electrode layers with the TiO₂ nano-particle powder allows internal stress to be reduced and mechanical bonding strength to be increased. High adhesive strength and good electrical conductivity of more than 10⁴/Ω cm could be obtained in the multilayer ferroelectric structure. In order to understand the effectiveness of the nano-TiO₂ doped electrode for multilayer device, the multilayer ceramic actuators containing Ag-based electrode without and with nano-sized TiO₂ powder were fabricated and evaluated each other. Both the samples exhibited similar piezoelectric and dielectric properties.     

Thermoelectric properties of Bi3+ substituted Co-based misfit-layered oxides

Highly densified (Ca_1?x Bi _x )₃Co₄O₉ thermoelectric ceramics with a layered structure were prepared by a sol–gel method followed by spark plasma sintering (SPS). Thermoelectric (TE) properties of the complex oxide ceramics were measured from room temperature to 700 °C. The results show that Bi³⁺ substitution leads to an increase in both electrical conductivity and Seebeck coefficient simultaneously. Bi³⁺ doped samples also show a lower thermal conductivity than undoped samples. The dimensional figure of merit ZT value of (Ca_0.95 Bi_0.05)₃Co₄O₉ samples is 0.25 at 700 °C.     

Optimizing design of the microstructure of sol–gel derived BaTiO3 ceramics by artificial neural networks

Modeling and application of artificial neural network (ANN) technique to the formulation design of BaTiO₃-based ceramics were carried out. Based on the homogenous experimental design, the results of BaTiO₃-based ceramics were analyzed using a three-layer back propagation (BP) network model. Then the influence of sintering temperatures, holding time, donor additives (La₂O₃, MnO₂, Ce₂O₃) and sintering aids (Al₂O₃–SiO₂–TiO₂ (AST)) on the average grain size (d _a), the degree of grain uniformity given by the ratio of the maximal grain size to the average grain size (d _max/d _a), and the relative density (D _r) of doped BaTiO₃ ceramics system was investigated. The optimized results and experiment data were expressed and analyzed by intuitive graphics. Based on input data and output data, the sintering behavior of BaTiO₃ nano-powder was explained well. Furthermore, the fine and uniform microstructure of sol–gel derived BaTiO₃ ceramics with d _a?≤?3 μm, d _max/d _a?≤?1.20, and D _r?≥?98% was obtained.     

Phase transition behaviors of (Na1/2Bi1/2)1−x TiPb x O3 thin films

Ferroelectric thin films of (Na_1/2Bi_1/2)_1?x TiPb _x O₃ have been synthesized via a sol–gel route. Structural changes of the films were investigated by using X-ray diffraction (XRD) and Raman spectroscopy over the composition range 0?<?x?<?0.9. There occur different nano-sized clusters in the films. More interestingly, in contrast to the previously reported results on (Na_1/2Bi_1/2)_1?x TiPb _x O₃ bulk ceramics, the ferroelectric thin films exhibit a rhombohedral–tetragonal structure change at x?=?0.4–0.5, together with a long range tetragonal symmetry at x?≥?0.8. The unique phase transition behaviors are discussed in relation to the growth of Pb²⁺TiO₃ clusters upon the substitution of Pb²⁺ for Na⁺/Bi³⁺ cations in the (Na_1/2Bi_1/2)_1?x TiPb _x O₃ films.     

Fabrication and electrical properties of barium strontium titanate thick films by modified sol–gel method

A modified sol–gel method has been developed to prepare for the barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thick films. The films were deposited on either Pd–Ag electroded alumina substrates (Pd–Ag/Al₂O₃) or silver electroded alumina (Ag/Al₂O₃) substrates by spin coating technique or screen printing technique. The thickness of the film was in the range of 2–10 μm. The key point of the process is to disperse fine-grained BST ceramic powders prepared by high energy ball mill into BST sol solution to form a slurry for spin coating and screen printing. In order to enhance the stability of the slurry and to avoid crack formation of the thick film, organic macromolecular poly-vinylpyrrolidone (PVP) was added to the sol solution. The structure and surface morphology of the films were studied by X-ray diffraction and Scanning Electron Microscope (SEM) techniques. It is revealed that the thick films exhibit pure perovskite phase and are crack-free, dense and homogeneous. The dielectric constant and loss tangent of the thick films are about 1200 and 0.01, at 10 °C and 1 KHz, respectively.     

Based on the Study on Preparation and Properties of Co(II) and La3+-Doped TiO2 Electrochromic Film

Abstract

In order to improve the optical properties and coloration effect. Co(II) and La³⁺ doped TiO₂ thin films were synthesized via a sol–gel, by using butyl titanate as precursor on the surface of ITO conductive glass substrate. Several techniques were used to characterize produces. Adopting the Sol-gel technology, [CH₃(CH₂)₃O]₄Ti, La₂O₃, CoC_l2?6H₂O as the precursor, the composite membranes with different molar ratio of Ti, Ti/La, Ti/Co to be prepared on the ITO glass substrate, the optimum technological parameters for preparation of the base material of the electro-induced discoloration glass are determined. The structure and surface morphology optical and electrochromic properties of Co(II) and La³⁺-doped TiO₂ films were examined with X-ray diffraction (XRD) analysis, energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), and ultraviolet-visible spectrophotometer (UV-vis) DTA-TG analysis. It was found that:

1. The sintering temperature coating number, [CH₃(CH₂)₃O]₄Ti content of the TiO₂ film sample, and the doping category are the main factors that affect the structure and properties of the membrane based material;

2. Using two alcohol amine as chelating agent can effectively inhibit the formation of Ti (OH)₄ precipitation;

3. The properties of the TiO₂ glass film prepared by La₂O₃ and CoCl₂·6H₂O are fine;

4. Materials based on the preparation of a radiochromic film transmittance, high cyclic reversibility, cyclic voltammetry characteristics significantly, the results of the study for the electric induced radiochromic film-based material development and application provide a theoretical and experimental basis.

     

Normal-to-relaxor ferroelectric phase transition and electrical properties in Nb-modified 0.72BiFeO<Subscript>3</Subscript>-0.28BaTiO<Subscript>3</Subscript> ceramics

Preparation and electrical properties of sintered bodies consisting of monophase cubic spinel oxides, Cr_XMn_1.5Co_(1.0-X)Ni_0.5O₄ (0 ≦ X ≦ 0.42), were investigated. Specimens with compositions within X = 0.42 were prepared as starting materials. The element of Cr was used to exchange Co³⁺ in octahedral sites (B sites) with Cr³⁺ so that the hopping mechanism can be discussed. The sintered bodies with mono cubic spinel structure were confirmed to be prepared by heat-treatment for 48 h in air at 1000 °C to convert them into a cubic spinel structure after sintering at 1400 °C. The semiconductive characteristics of the sintered bodies were determined as p-type because the Seebeck coefficients were all positive. The electrical conduction of the sintered bodies was concluded to be controlled by the small polaron hopping mechanism. In the region 0.1 ≦ X ≦ 0.42, the lattice constant increases and electrical conduction (σ) decreases linearly with increasing Cr concentration. The decrease in σ and the increase in the lattice constant corresponded to the increase in Cr concentration by which the jumping distance of electrons between Mn³⁺ and Mn⁴⁺ is lengthened.     

Effect of excess TiO2 on the phase evolution and densification of sol-gel derived (Ba,Sr)TiO3 powders

Nanoscaled (Ba_2/3Sr_1/3)Ti_{1 + x} O₃ powders have been prepared by sol-gel technique. Their phase evolution and densification behaviors have been studied by differential thermal analysis (DTA) and high temperature dilatometer, respectively. It is found the addition of 2 mol%-excess amount of TiO₂ lowers the activation energy required for the formation of the perovskite phase by about 130 kJ/mol and thus lowers the crystallization temperature of BST powders. However, the excess amount of TiO₂ makes the nano-powder difficult to sinter. Transmission electron microscopy reveals that a metastable nano-porous layer has formed on the surface of TiO₂-excess nanopowder and this may account for the slow densification rate.     

Electrical Conduction and Magnetoelectric Effect in CuFe1.8Cr0.2O4–Ba0.8Pb0.2TiO3 Composites

Magnetoelectric composites of CuFe_1.8Cr_0.2O₄– Ba_0.8Pb_0.2TiO₃ were prepared using high temperature solid-state reaction technique. X-ray structural analysis of these composites confirms the presence of both the phases in the composite. Detailed studies of dielectric properties (, tan and _ac ) as a function of frequency (100 Hz to 1 MHz) and temperature (30°C to 250°C) show that these compounds exhibit diffuse ferroelectric phase transitions. Results of ac conductivity, dc resistivity and thermoelectric power measurements show that conduction occurs by hopping of charge carriers. The magnetoelectric effect has been studied as a function of intensity of magnetic field. The electrical polarisation was induced in piezoelectric (Ba_0.8Pb_0.2TiO₃) phase as result of strain induced in the ferrite (CuFe_1.8Cr_0.2O₄) phase by the applied magnetic field. The Jahn-Teller distortion caused in the ferrite lattice by Jahn-Teller ions like Cu²⁺ and Cr³⁺ is also responsible for the elastic coupling of strain to the Ba_0.8Pb_0.2TiO₃ phase.     

Physico-chemical Properties of Nano Cr/Na-ZSM-5 Catalysts for Ethane Dehydrogenation

A series of Cr/Na-ZSM-5 catalysts for oxidative dehydrogenation of ethane reaction with different Cr contents from 2.5 wt% to 10.0 wt% were prepared by impregnation method. The analysis and testing techniques, such as XRD, CO₂-TPD, H₂-TPR and SEM, were used to characterize the physico-chemical properties of the prepared catalysts. The results show that the active component Cr₂O₃ was well dispersed on the surface of the support Na-ZSM-5. The loading of Cr₂O₃ has no influence on the structure of support Na-ZSM-5, but it can lead to the agglomeration of the catalyst when Cr content is higher than 5.0 wt%. There is an interaction between the loaded Cr₂O₃ and support Na-ZSM-5, which can affect the redox properties and result in the changing of the basicity and increasing of the basic sites.     

Low Loss Tungsten-Based Electrode Technology for Microwave Frequency BST Varactors

The electrical properties of BaO-Nd₂O₃-Sm₂O₃-TiO₂ ceramics doped with low loss glass or low melting point oxide B₂O₃ are evaluated by impedance spectroscopy. Glass or B₂O₃ is doped as liquid phase sintering aid. Doping of glass/B₂O₃ enhances both the growth in the longitudinal direction of the columnar crystal and the preferred orientation of (002). The grain size increases and grain boundary decreases with the increase of dopant. Both the grain and grain-boundary resistivities decrease with the increase of dopant. The grain boundary activation energy for charge transport is larger than that of the grain activation energy. Possible mechanisms for the electrical behavior of the liquid-phase sintered BaO-Nd₂O₃-Sm₂O₃-TiO₂ ceramics are proposed and discussed.