Preparation of ferroelectric Pb(Zr0.52 Ti0.48)O3 thin films by sol-gel processing

Ferroelectric Pb(Zr_0.52 Ti_0.48)O₃ thin films were prepared by sol-gel processing on the Pt/Ti/SiO₂/Si(100) substrates. Effects of the concentration (0.2–0.8 M) of the starting solution (Pb/Zr/Ti= 1.1/0.52/0.48) and the sintering temperature (500–700 ‡C) on crystallinity, microstructure and electrical properties of PZT thin films were investigated. For the thin film prepared at 0.4 M starting solution, the highest crystallinity appeared at a sintering temperature of 650 ‡C. The average grain size of the PZT thin films was about 0.17 Μm. The film thickness was about 0.2 Μm. The relative dielectric constant and the dissipation factor of the film measured at 1 kHz were about 750 and 4.3%, respectively. The remnant polarization (Pr) and coercive field (Ec) of the film measured at the applied voltage of 5 V were about 49 ΜC/cm² and 134 kV/cm, respectively.     

The anisotropic conductivity of ferroelectric La2Ti2O7 ceramics

Ferroelectric ceramics with perovskite-like layered structure (PLS) have good potential for high temperature piezoelectric applications due to their high Curie point (T_c). The electrical conduction behaviour of these materials is a critical parameter to consider for practical applications. In this study, we prepared textured ceramics of the typical PLS ferroelectric La₂Ti₂O₇ using spark plasma sintering and investigated the electrical properties using impedance spectroscopy and Seebeck measurements. The results reveal that the bulk resistivity along the parallel direction is much higher than that along the perpendicular direction. The activation energy for conduction (E_a) along the parallel direction is 1.45 eV, which is close to half of the optical band gap and much higher than the 0.67 eV along the perpendicular direction. Electrical conduction along both the directions is dominated by p-type hole conduction. No appreciable contribution of oxide ion conduction to the measured conductivity is observed.     

Fabrication of La2Zr2O7 ceramic fibers via electrospinning method using different La2O3 precursors

Despite La₂Zr₂O₇ ceramic fiber has been fabricated by electrospinning method, the effects of thermal pyrolysis process on the microstructures and properties of the fibers have seldom been considered. Three La₂O₃ precursors were used to prepare La₂Zr₂O₇ ceramic fibers. Phase transformation of La₂Zr₂O₇ ceramic fibers were characterized by XRD and Raman spectra. The influence of the decomposition process on the microstructure of the fibers was studied by TG/DSC, XPS and SEM. The results show that slow weight loss leads to smaller grain size which could obtain higher strength fibers while fast weight loss could develop pores which are benefit to the decrease of the thermal conductivity.     

Fabrication and properties of transparent Tb2Ti2O7 magneto-optical ceramics

Transparent Tb₂Ti₂O₇ magneto-optical ceramics were fabricated from co-precipitated nano-powders by vacuum pre-sintering with hot isostatic pressing (HIP) post-treatment. The formation of pyrochlore phase, decomposition of the precursor, and the morphology of powders calcined at different temperatures were investigated. The in-line transmittance of Tb₂Ti₂O₇ ceramics, which were pre-sintered at 1350 ℃ for 2 h with HIP post-treatment at 1450 ℃ for 3 h and subsequently annealed at 800 ℃ for 20 h in NH₃ atmosphere, reaches 65.5 % at 1064 nm. The Verdet constant of Tb₂Ti₂O₇ ceramics is −229.0 ± 0.6 rad·T⁻¹ m⁻¹ at the wavelength of 633 nm, which is 71 % higher than that of the commercial Tb₃Ga₅O₁₂ crystals. Tb₂Ti₂O₇ magneto-optical ceramics show a promising application for Faraday rotators.     

A new sol-gel route to prepare dense Al2O3 thin films

Anew sol-gel route has been applied to synthetize dense Al₂O₃thin films from aluminum isopropoxide (Al(OPri)₃)as raw precursor material. The results show that, in the solution, acetylacetone (AcAc) and aluminum form a complex compound which effectively suppresses the growth of colloidal particles and makes the sol very stable. Al₂O₃thin films fabricated by spin-coating method and calcined at 500 °C for 3 h possess an amorphous structure and exhibit a highly homogeneous surface texture without evidence of holes or cracks throughout the film. Moreover, the prepared films display a low leakage current and a high transmittance. This new sol-gel route appears to be a highly promising method to synthetize dense Al₂O₃ thin films from Al(OPrⁱ)₃, and could provide a wide range of optical and electric applications.     

Dip-coated La2Ti2O7 as a buffer layer for growth of Bi3.25La0.75Ti3O12 films with enhanced (0 1 1) orientation

Thin-films of La₂Ti₂O₇ were obtained by dip-coating process using a precursor salt in nitric acid solution. The effects of solution concentration, withdrawal speed, post-annealing duration and temperature were investigated both on grain size and orientation of the La₂Ti₂O₇ thin layers. In addition, a target with the required stoichiometry for PVD deposition of La-substituted Bi₄Ti₃O₁₂ (BLT) was successfully sintered by spark plasma sintering (SPS) at 750 °C. Finally (0 1 1)-oriented BLT ferroelectric films have been grown by RF sputtering on (1 1 0)-oriented La₂Ti₂O₇ polycrystalline thin-film. A preferential orientation of BLT thin films has been obtained after annealing at a temperature lower than 650 °C.     

Photocatalytic Water Splitting over La2Ti2O7 Synthesized by the Polymerizable Complex Method

Highly donor-doped (110) layered perovskite materials, La₂Ti₂O₇, with high surface areas were synthesized by the polymerizable complex (PC) method. Relative to La₂Ti₂O₇ prepared by the solid state reaction (SSR) method, PC catalysts showed higher surface areas, crystallization at lower temperatures, higher phase purity, more uniform morphology and better-distributed nickel on the outer surface of La₂Ti₂O₇. All these factors led to higher photocatalytic activity for overall water splitting under UV irradiation. The quantum yield of the reaction over La₂Ti₂O₇ prepared by the PC method was as high as 27%, which was about twofold greater than that over La₂Ti₂O₇ prepared by the SSR method.     

Fabrication of CaLa4(Zr0.05Ti0.95)4O15 thin films by RF magnetron sputtering

Crystalline CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films deposited on n-type Si substrates byRF magnetron sputtering at a fixed RF power of 100 W, an Ar/O₂ ratio of 100/0, an operating pressure of 3 mTorr, and different substrate temperatures were investigated. The surface structural and morphological characteristics analyzed by X-ray diffraction and atomic force microscopy were sensitive to the deposition conditions, such as the substrate temperature. The diffraction pattern showed that the deposited films had a polycrystalline microstructure. As the substrate temperature increased, the quality of the CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films improved, and the kinetic energies of the sputtered atoms increased, resulting in a structural improvement of the deposited CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films. A high dielectric constant of 16.7 (f=1 MHz), a dissipation factor of 0.19 (f=1 MHz), and a low leakage current density of 3.18×10⁻⁷ A/cm² at an electrical field of 50 kV/cm were obtained for the prepared films.     

MOCVD growth of epitaxial pyrochlore Bi2Ti2O7 thin film

Growth of Bi₂Ti₂O₇ films on the substrates having cubic-structure was investigated by metal organic chemical vapor deposition (MOCVD). (1 0 0), (1 1 0) and (1 1 1)SrTiO₃ single crystals, (1 1 1)-oriented Pt- and SrRuO₃-coated (1 1 1)SrTiO₃ were used as substrates together with (1 1 1)Pt/TiO₂/SiO₂/Si. Peaks originated to Bi₂Ti₂O₇ phase were not detected on (1 0 0), (1 1 0) and (1 1 1)SrTiO₃ substrates. On the other hand, (1 1 1)-oriented Bi₂Ti₂O₇ phase was ascertained to be prepared on (1 1 1)Pt//(1 1 1)SrTiO₃ and (1 1 1)Pt/TiO₂/SiO₂/Si substrates in spite of the almost the same lattice parameters of SrRuO₃ and SrTiO₃ with Pt. From the pole figure measurement, Bi₂Ti₂O₇ films prepared on the (1 1 1)Pt//(1 1 1)SrTiO₃ substrates were ascertained epitaxial grown, (1 1 1)Bi₂Ti₂O₇//(1 1 1)Pt//(1 1 1)SrTiO₃, while that on the (1 1 1)Pt/TiO₂/SiO₂/Si were (1 1 1)-one-axis-oriented Bi₂Ti₂O₇ with in-plain random. The easy growth of (1 1 1)-oriented Bi₂Ti₂O₇ film on (1 1 1)Pt layer can be explain by the existence of the sub-unit in (1 1 1)Pt plane consist of three Pt atoms.     

Fabrication and characterization of intergrown Bi4Ti3O12-based thin films using a metal-organic precursor solution

Ferroelectric intergrowth-structured Bi₄Ti₃O₁₂-based thin films have been fabricated by chemical solution deposition. Bi₄Ti₃O₁₂–SrBi₄Ti₄O₁₅ (BiT–SBTi) and SrBi₂Nb₂O₉–Bi₄Ti₃O₁₂ (SBN–BiT) precursor films crystallized in the desired intergrown BiT–SBTi and SBN–BiT structures on Pt/TiO_x/SiO₂/Si substrates by optimizing the processing conditions. Synthesized BiT–SBTi and SBN–BiT thin films exhibited ferroelectric P–E hysteresis loops. The BiT–SBTi thin films crystallized at 750 °C showed a 2P_r value approximately 20 μC/cm². Although a little smaller P_r value was observed for the SBN–BiT thin films, the squareness of a P–E hysteresis loop was superior to that of BiT–SBTi thin films. Also, the SBN–BiT thin films had a smoother surface morphology compared with BiT–SBTi thin films.     

Piezoelectric and dielectric properties of Ce substituted La2Ti2O7 ceramics

The ferroelectric and dielectric properties of cerium (Ce) substituted La₂Ti₂O₇ (LTO) have been investigated. Single phase, dense La_2?xCe_xTi₂O₇ (x = 0.15, 0.25, 0.35) ceramics were prepared by spark plasma sintering. The solubility limit of Ce in La_2?xCe_xTi₂O₇ was found to be between 0.35 and 0.5. The a-, b- and c-axes of the unit cell decrease with increasing Ce substitution. The Curie point (Tc) of La_2?xCe_xTi₂O₇ (x = 0, 0.15, 0.25, 0.35) decreases and dielectric constant and loss increase with increasing Ce substitution. Cerium can increase the d₃₃ of La₂Ti₂O₇. The highest d₃₃ was 3.9 ± 0.1 pC/N for La_1.85Ce_0.15Ti₂O₇ textured ceramic.     

Thermal oxidation of oxynitride films as a strategy to achieve (Sr2Ta2O7)100-x(La2Ti2O7)x based oxide perovskite films with x = 1.65

• •This study concerns STLTO compounds of the ferroelectric (Sr₂Ta₂O₇)_100-x(La₂Ti₂O₇)_x solid solution. The purpose is to produce the STLTO composition x = 1.65 as thin films by thermal oxidation of the corresponding oxynitride composition. Indeed, the combination of an STLTO oxide target with a dioxygen-rich reactive atmosphere during the sputtering deposition leads to Sr-deficient oxide thin films, shifting composition and structure from the perovskite to the tetragonal tungsten bronze type. An alternative synthesis pathway is to first deposit, under nitrogen-rich atmosphere, stoichiometric oxynitride films and produce, by thermal annealing under air, the stoichiometric oxide. For low oxidation temperatures ([550–600 °C]), samples remain intact and display an oxide character but still contain a significant amount of nitrogen, they could be described as intermediate phases containing nitrogen-nitrogen pairs as demonstrated by Raman. Dielectric characteristics of these original film materials are of interest with a tunability value of 26 % at 30 kV/cm (10 kHz).

     

Natural-superlattice structured CaBi2Nb2O9-Bi4Ti3O12 ferroelectric thin films

Natural-superlattice-structured/intergrowth CaBi₂Nb₂O₉-Bi₄Ti₃O₁₂ (CBNO-BIT) ferroelectric thin films were successfully prepared via a magnetron sputtering process. XRD and TEM analysis revealed the [Bi₂O₂-(CaNb₂O₇)-Bi₂O₂-(Bi₂Ti₃O₁₀)]_n intergrowth structure of the film, as well as a (200)/(020) texture. XPS and EDS results confirmed that the film composition is close to the chemical stoichiometry. With its microstructure being successfully tailored at the nanoscale, the CBNO-BIT film exhibits good electrical properties, including a large dielectric constant (ε_r ∼390), a high piezoelectric coefficient (d₃₃ ∼90 pm/V) as well as a high energy storage density (W_E ∼76 J/cm³). Finally, the intergrowth nature of the film was verified by the measured temperature-dependent dielectric response (C-T).     

烧结条件对La_2Ti_2O_7陶瓷铁电性的影响

本文通过传统固相法制备La_2Ti_2O_7陶瓷,研究不同烧结温度和时间对La_2Ti_2O_7陶瓷的铁电性影响,通过XRD和铁电测试手段分别对其晶体结构和铁电性进行表征,并对影响机理作了初步探讨,以探索最佳的制备工艺。结果表明:当烧结温度为1400℃及烧结时间为24 h时,La_2Ti_2O_7陶瓷的铁电性较好,漏电流最小,其剩余极化Pγ为3.96μC/cm~2,矫顽场Ec为27.8 k V/cm。     

Preparation and electrical properties of Sm-doped Bi2Ti2O7 thin films prepared on Pt (111) substrates

Crack-free Sm-doped Bi₂Ti₂O₇ (Sm:BTO) thin films with strong (111) orientation have been prepared on Pt (111) substrates using a chemical solution deposition (CSD) method. The structural properties and crystallizations were studied by X-ray diffraction. The surface morphology and quality were examined using atomic force microscopy (AFM). The insulating and dielectric properties were also evaluated at room temperature. The results demonstrate that the Sm:BTO films exhibit improved electrical performances as compared to the pure Bi₂Ti₂O₇ thin films and suggest a strong potential for utilization in microelectronics devices.     

Magnetic behavior of Ga doped yttrium iron garnet ferrite thin films deposited by sol-gel technique

Yttrium Iron Garnet (YIG) ferrites thin films having compositional formula Y₃Ga_xFe_5-xO₁₂, where (x = 0, 1, 2, 3, 4) are synthesized by sol gel dip coating technique. XRD, SEM and VSM characterizations are employed to explore structural, morphological and magnetic properties, respectively. XRD showed that Ga is completely doped in YIG and not formed any cluster or other phase with YIG. SEM confirmed the formation of agglomeration of YIG particles. Magnetic parameters like coercivity, remnant squareness, saturation magnetization, magnetic moment, anisotropy constant, initial permeability Y–K angles and microwave frequency were calculated of these films. The coercivity and moderate magnetization suggested that fabricated ferrite films are highly applicable in electromagnetic microwave absorption and frequency agile antenna for wireless communication.     

湿化学法制备石榴石型固态电解质Li7La3Zr2O12

锂电池因能量密度高、循环寿命长、绿色清洁等特点被广泛应用,但其液态电解质易泄漏、挥发,且隔膜易被锂枝晶刺穿造成短路,引发危险。固态电解质大多是不具燃烧性的无机材料,室温下离子电导率较高、电化学窗口宽且适用温度范围广。因此,采用固态电解质替代液态电解质具有十分重要的意义。相对于其他类型固态电解质,石榴石型氧化物Li₇La₃Zr₂O₁₂（LLZO）具有离子电导率高、电化学窗口宽（>5V vs. Li/Li⁺）、对锂稳定性好和热稳定性高等特点,是非常具有发展潜力的无机固态电解质。本文采用溶胶-凝胶法和低温燃烧法两种湿化学法合成LLZO粉末,对应的电解质片在40℃时的离子电导率分别为1.22×10^-5S/cm和3.87×10^-6S/cm,活化能分别为0.34eV和0.32eV。从实验结果综合比较,溶胶-凝胶法为最佳制备方法。     

Mechanical properties and thermal shock in thin ZrO2–Y2O3–Al2O3 films obtained by the sol-gel method

Thin multilayer coatings of ZrO₂–Y₂O₃–Al₂O₃ were prepared using the sol-gel method and dip-coating technique in order to advance in the study of what influence the incorporation of Al₂O₃ has on films of Y₂O₃-doped ZrO₂, investigating its role in the synthesis of the solutions and in the characteristics and properties of the coatings. After the characterization of the solutions used in the process, the microstructure of the films was studied and their mechanical behaviour and resistance to thermal shock were determined so as to optimize the characteristics and functionality of these coatings. With increased alumina content, 3YSZ-Al₂O₃ (20 mol%), the cubic phase of the zirconia disappeared completely at the sintering temperature used (700 °C), resulting in the tetragonal phase with Al in solution. There was also a decrease in the coatings' hardness and Young's modulus, and an increase in toughness and resistance to thermal shock. These results allow guidelines to be established for the design of multilayer structures that are, tougher, more resistant, and have improved surface properties.     

Optimizing the processing conditions of sodium potassium niobate thin films prepared by sol-gel spin coating technique

In the present study, potassium sodium niobate (KNN) thin films were synthesized by means of sol-gel spin coating method. Along with the synthesis, the effects of annealing temperature and various number of coating layers on both the structural and electrical properties were looked into. The results of the study revealed that the annealing temperature had a great impact on the properties of KNN. In addition, the XRD diffractograms and texture coefficient of the synthesized films confirmed that a highly oriented orthorhombic perovskite structure was obtained at 650 °C, whereas at a relatively higher temperature (700 °C), a spurious phase of K₄Nb₆O₁₇ was evolved. In addition, the growth of KNN at 650 °C exhibited a reasonable resistivity value for piezoelectric applications. Looking into the results, it was discovered that the KNN thin films also found to be dependent on a number of coating layers. Field emission scanning electron microscopy (FESEM) showed that KNN with five coating layers was highly crystalline, cracks-free, and had significantly more homogenous surface morphology and the size of grains being uniform, the resistivity of KNN thin films improved with the increasing number of coating layers i.e., up to five.