Phase evolution,dielectric, ferroelectric,and piezoelectric properties of Bi(Mg0.5Hf0.5)O3–modified BiFeO3–BaTiO3

Bi(Mg_0.5Hf_0.5)O₃–modified BiFeO₃–BaTiO₃ ternary solid solutions of (0.725-x)BiFeO₃-0.275BaTiO₃-xBi(Mg_0.5Hf_0.5)O₃ (0 < x ≤ 0.05, abbreviated as BFO-BTO-xBMHO) were prepared for lead-free piezoelectrics. The addition of BMHO delivers a rhombohedral (R3c, denoted as R-phase) to tetragonal (P4mm, denoted as T-phase) phase transition at x = 0.05, giving the coexistence of R- and T-phase in intermediate compositions: R-phase dominated in x = 0.01–0.02 and T-phase dominated in x = 0.03–0.04. The increment of BMHO tunes the grain size, lowers the ferroelectric transition temperature (T_C) and dielectric loss (tanδ), and drives a gradually ferroelectric to relaxor transition. The morphotropic phase boundary between the R-and T-phases, together with the homogeneous morphology, results in the best performance for x = 0.04 case with piezoelectric d₃₃ of 130 pC/N, K_p of 0.286, Q_m of 58.993, electrostrain S_max of 0.18%, and T_C of 428 °C, showing potential applications for lead-free piezoelectric ceramics at considerably high temperature.     

Preparation and optical–electrical properties of Al-doped ZnO films

Among the various semiconducting metal oxide materials, ZnO thin films are highly attractive in the development of materials area. In this paper, Al-doped ZnO thin films were prepared by sol–gel dipping and drawing technology and their composition, structure and optical–electrical properties were investigated. XRD results shows that the Al-doped ZnO thin film is of polycrystalline hexagonal wurtzite structure, and the (002) face of the thin film has the strongest orientation at the annealing temperature of 550 °C. The surface resistance of Al-doped ZnO thin film firstly drops and then increases with the increase in annealing temperature. Al doping concentration is also an important factor for improving the conductivity of modified ZnO thin films, and the surface resistance has the tendency to drop at first and then to increase when the Al concentration is increasing. The surface resistance of modified ZnO thin films drops to the lowest point of 139 KΩ sq^?1 when the Al concentration is 1.6 at% and the annealing temperature is 500 °C. The light transmission measurements show that the doping concentration has little influence on light transmittance. The transmittance at the visible region of films is all over 80 %, and the highest value is up to 91 %.     

The structural and electric properties of the perovskite system BaTiO3–Ba(Fe1/2Ta1/2)O3

Compounds in the pseudo-binary BaTiO₃–Ba(Fe_1/2Ta_1/2)O₃ system have been synthesized at 1500°C in air and characterized by X-ray and electron diffraction as well as impedance analysis and Mössbauer spectroscopy. The symmetry of Ba(Fe_1/2Ta_1/2)O₃ is found to be trigonal with the space group P3m1. Two solid solutions exist in the BaTi_1−xFe_x/1Ta_x/1O₃ system at room temperature. The first (SS1) is in the composition range 0⩽x⩽0.07 and is tetragonal, P4mm, while the second broader solid solution, (SS2) 0.12⩽x⩽1, is trigonal and has the space group P3m1. The conductivity becomes higher with reduced amount of Ti in the structure. The activation energy of conductivity differs between the two solid solutions, 0.80 eV for SS1 and 0.30 eV for SS2, which indicates different mechanisms. The maximum of the real part of the permittivity recorded for compounds in SS1 decreases towards room temperature with increasing amount of Fe/Ta doping and a high dielectric constant of around 7000 is found for BaTi_0.94Fe_0.03Ta_0.03O₃.     

Effect of Tb content on microstructure and ferroelectric properties of Bi4−x Tb x Ti3O12 thin films grown by sol–gel method

The effects of Tb substitution on the structural and electrical properties of ferroelectric Bi₄Ti₃O₁₂ (BTO) thin films grown on Pt/TiO₂/SiO₂/Si substrates by a sol–gel process have been reported. X-ray diffraction indicated A-site Tb substitutions did not change the polycrystalline bi-layered Aurivillius structure of the BTO, but a lattice distortion was observed. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current density decreased from 10^?2 to 10^?4 A/cm² with the increase of x under 150 kV/cm. The remnant polarization (2P _r ) and dielectric constant (ε _r) increase firstly and then decreases with the increase of the Tb content. We observed a substantial increase in the remnant polarization (2P _r ) with Tb substitution and obtained a maximum value of~60 μC/cm² at an applied electric field of 500 kV/cm for x = 0.4. Moreover, this BTT-0.4 capacitor did not show fatigue behaviors after 1.0 × 10¹⁰ switching cycles, suggesting an anti-fatigue character.     

Luminescence and dielectric properties of c-axis oriented (Bi1.90Eu0.10)(V1−zMoz)O5.5 ferroelectric thin films

(Bi_1.90Eu_0.10)(V_1−zMo_z)O_5.5 (z = 0, 0.05, 0.10, 0.15 and 0.20) thin films with c-axis oriented were prepared on Pt(111)/Ti/SiO₂/Si substrates by using chemical solution deposition method. The effect of Mo⁶⁺ concentration on the structure, luminescence properties and dielectric properties of the thin films were characterized systematically. X-ray diffraction data indicates that the thin films with low Mo⁶⁺-doping content can remain Bi₂VO_5.5 structure. When the Mo⁶⁺-doping content z reaches to 0.15, the thin films are a mixture of diphase with the main phase Bi₂VO_5.5 and secondary phase Bi₂MoO₆. Under UV irradiation, all the thin films emit a bright red or orange emission which origin from Eu³⁺. With increasing Mo⁶⁺-doping content z, the relative intensity of the Red and Orange emissions show obviously change. The value of Red/Orange ratio first decrease, and it reached minimum when z is 0.15, then it recover to the initial value. The variation trend of the Red/Orange ratio reflects the change of the lattice symmetry. Dielectric constant of the thin films increased with the increasing of the Mo⁶⁺ concentration while dielectric loss decreased. The decrease of the quantities of oxygen vacancies and the generation of Bi₂MoO₆ phase are responsible for the improvement of electric properties. These results explain that Eu³⁺ion can be used as an effective luminescent probe in (Bi_1.90Eu_0.10)(V_1−zMo_z)O_5.5 (z = 0, 0.05, 0.10, 0.15 and 0.20) thin films, and the electric properties of the thin films can be improved by Mo⁶⁺ doping.     

Fabrication and properties of xBiFeO3-(1 − x)Bi4Ti3O12 system by sol–gel process

The thin films of mixture of xBiFeO₃-(1 − x)Bi₄Ti₃O₁₂ (x = 0.4, 0.5, and 0.6) system were prepared by a sol–gel process. The thicknesses of the thin films were 540, 500, and 570 nm, respectively. The crystal structure of all thin films annealed at 650 °C was analyzed by X-ray diffraction. It was found that the thin films at x = 0.4 and 0.5 mainly consisted of a Bi₄Ti₃O₁₂ phase while Bi₅Ti₃FeO₁₅ was the major phase of the thin film at x = 0.6. The thin film (x = 0.6) showed better ferroelectric properties in remnant polarization and polarization fatigue than those observed in the thin films (x = 0.4 and 0.5). The values of remnant polarization 2P _r and coercive field 2E c of the thin film at x = 0.6 were 36 μC/cm² and 192 kV/cm at an applied electric field of 260 kV/cm, respectively. There was almost no polarization fatigue up to 10¹⁰ switching cycles. Also weak ferromagnetism was observed in the thin film at x = 0.6.     

Structural and electrical properties of chemical solution deposited (Bi0.9Tb0.1)(Fe0.975 TM 0.025)O3±δ (TM = Ni, Mn and Ti) thin films

Effects of Tb and transition metal (TM = Ni, Mn and Ti) ions co-doping on the structural, electrical and ferroelectric properties of the BiFeO₃ thin films prepared by using a chemical solution deposition method were reported. From X-ray diffraction and Raman scattering analyses, distorted rhombohedral perovskite structures were observed for all thin films. Improved electrical and ferroelectric properties were observed for the co-doped thin films. Among the thin films, the lowest leakage current density of 2.67 × 10^?6 A/cm² (at 100 kV/cm), large remnant polarization (2P _r ) of 82.2 μC/cm² and low coercive field (2E_c) of 680 kV/cm (at 1,036 kV/cm) were measured for the (Tb, Mn) co-doped thin film.     

Sintering, microstructures and dielectric properties of Ba1−xPbx(Ti1−xLix)O3−3xF3x ferroelectric ceramics

Various compositions (1−x)BaTiO₃ + xPbF2 + xLiF were prepared, shaped to pellets then sintered at 900°C for 2 h in gold sealed tubes. The purity and the symmetry of the obtained samples were checked by X-ray diffraction. A new solid solution with Ba_1−x Pb _x (Ti_1−x Li _x ) O_3−3x F_3x formula occurs in the composition range 0 ≤ x ≤ 0.20. SEM observations were performed on polished and fractured ceramics. The complex permittivity was measured as a function of temperature (−120°C ≤ T ≤ 250°C) and frequency (50 Hz ≤ f ≤ 4 × 10⁷ Hz). The dielectric performances are the best for ceramic Ba_0.97Pb_0.03(Ti_0.97Li_0.03)O_2.91F_0.09. The real component ε′, exhibits a maximum of approximately 7500 at the ferroelectric Curie temperature T _C ≈ -18°C, the dielectric losses tan δ value being 0.012. At room temperature, the relaxation frequency f _r is around 40 MHz for this ceramic. This novel ferroelectric oxifluoride is a promising material for applications, in particular in the field of Z5U multilayer capacitors.      

Dielectric,piezo and ferroelectric properties of microwave sintered PbTiO3 synthesized by sol–gel method

Journal of Sol-Gel Science and Technology - Of all the piezoelectric ceramics, lead titanate (PbTiO3) has an important place as an electromechanical transducer. In the present article PbTiO3...     

Structure and optical properties of [Ba1–xY2x/3](Zr0.25Ti0.75)O3 powders

[Ba_1–xY_2x/3](Zr_0.25Ti_0.75)O₃ powders with different yttrium concentrations (x = 0, 0.025 and 0.05) were prepared by solid state reaction. These powders were analyzed by X-ray diffraction (XRD), Fourier transform Raman scattering (FT-RS), Fourier transform infrared (FT-IR) and X-ray absorption near-edge (XANES) spectroscopies. The optical properties were investigated by means of ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurements. Even with the addition of yttrium, the XRD patterns revealed that all powders crystallize in a perovskite-type cubic structure. FT-RS and FT-IR spectra indicated that the presence of [YO₆] clusters is able to change the interaction forces between the O–Ti–O and O–Zr–O bonds. XANES spectra were used to obtain information on the off-center Ti displacements or distortion effects on the [TiO₆] clusters. The different optical band gap values estimated from UV–vis spectra suggested the existence of intermediary energy levels (shallow or deep holes) within the band gap. The PL measurements carried out with a 350 nm wavelength at room temperature showed that all powders present typical broad band emissions in the blue region.     

Phase evolution and electrical properties of BaO–SrO–TiO2–SiO2–Al2O3-based glass ceramics prepared by sol–gel process

Crystallization of BaO–SrO–TiO₂–SiO₂–Al₂O₃-based glass ceramics, prepared by sol–gel process, was evaluated in terms of the effect of sintering temperature on phase evolution and electrical properties. The characterization of the samples was performed by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) studies and impedance spectroscopy analysis. The XRD results demonstrate that fresnoite phase starts to crystallize at 700 °C and perovskite phase appears at 900 °C. The glass ceramic samples sintered at high temperatures contained three crystalline phases, including perovskite, feldspar and fresnoite. In addition, SEM observation showed that the average grain size increased and the porosity decreased with increasing sintering temperature. Furthermore, the measurement of impedance spectroscopy suggests that there is a minimum value of the activation energy associated with the sintering temperature of the glass ceramics. The possible explanation of the sintering temperature dependence was discussed.     

Influences of preferred orientation growth on electrical properties of ZnO:Al films by sol–gel method

Using different precursor preparation, heating methods, and initial layers, this work investigated the relation between the micro-structural and electrical properties of ZnO:Al (AZO) films prepared by sol–gel method on glass and silicon substrates. It was found that adding monoethanolamine (MEA), using initial layers, or an intentionally produced steep temperature gradient obviously promoted film growth along the (002) direction. However, the carrier mobility rose only a little while the carrier concentration was not affected or even reduced. Generally speaking, the film conductivity was not evidently improved. It could be concluded that all three methods are advantageous for enhancing the crystallographic quality and therefore the mobility of the AZO films, but the major reason for the poor conductivity of the sol–gel derived ZnO films was the low activation of the dopant, which is the key factor for further improvements and should be solved first.     

Optical,electrical, and thermochromic properties of polyazothiophene Langmuir–Blodgett films

The conductivity and luminescence of conjugated polymers may be combined with the photoisomerization capability of azobenzene materials to achieve unique properties for a variety of applications, particularly if conjugated polymers with azobenzene side chains are processed as nanostructured films. In this study, we report on Langmuir–Blodgett (LB) films of a polythiophene-bearing azobenzene moieties, which displayed photoluminescence, thermochromism, electroactivity, and photoinduced birefringence. The latter three properties were enhanced in the LB films, as compared to spin-coated films of the polyazothiophene, and this has been attributed to differences in film morphology that could be probed with atomic force microscopy.     

Visible-light photoresponsive heterojunctions of (Nb–Ti–Si) and (Bi/Bi-O) nanoparticles

The increasing motivation to seek alternative sources of clean and sustainable energy has intensified, due to a growing awareness that fossil fuels are finite in quantity, and that the combustion products of such fuels contribute to global warming. Solar energy is considered one of the most readily available alternatives, but materials which are able to harness this form of energy need to be developed. This study details the development of a novel composite material, of the form of Bi/Bi-O nanoparticles supported on a (Nb–Ti–Si) oxide. Characterized using electrochemical and other methods, this material generates a photocurrent, and is capable of photo-oxidizing airborne-styrene in a fluidized-bed photoreactor when exposed to visible-light.