Thin film fabrication of nano-porous 12CaO·7Al2O3 crystal and its conversion into transparent conductive films by light illumination

Thin film fabrication of crystalline 12CaO·7Al₂O₃ (C12A7) with zeolitic structure was examined, and their electrical and optical properties were measured. Polycrystalline thin films were prepared by post-annealing of amorphous films in oxygen atmosphere at temperatures above 800 °C. Choice of substrates was crucial for obtaining single-phase thin films. Although various oxide substrates (single crystals of Al₂O₃, Y-stabilized ZrO₂, MgO and silica glass) were examined, single-phase films were obtained only for MgO substrates and the other substrates reacted with the CaO component in the films during post-annealing. The optical band gap of C12A7 was evaluated to be 5.9 eV. Hydride ions were incorporated into the film by a thermal treatment in a hydrogen atmosphere at 1200 °C. The resulting transparent thin films were converted into transparent persistent electronic conductors exhibiting an electrical conductivity 6.2×10⁻¹ S cm⁻¹ at 300 K by ultraviolet light illumination. This is the first example of transparent conductive thin film in which conductive areas can be patterned directly by light.     

Synthesis of Tb3Al5O12 (TAG) transparent ceramics for potential magneto-optical applications

Tb₃Al₅O₁₂ transparent ceramics have been prepared by solid state reaction and vacuum sintering. The optical quality and the microstructure of the samples were investigated. The sample sintered at 1650 °C possessed relatively good optical transparency from 400 nm to 1600 nm. The Verdet constant measured at 632.8 nm of the quasi-pore-free Tb₃Al₅O₁₂ transparent ceramic was −172.72 rad T⁻¹ m⁻¹, which was close to the counterpart of Tb₃Al₅O₁₂ single crystal. The thermal conductivity of the sample was also measured. To the best of our knowledge, this is the first time that Tb₃Al₅O₁₂ transparent ceramic with relatively good optical quality and magneto-optical property has been reported.     

Growth of Al2O3 thin film by oxidation of resistively evaporated Al on top of SnO2, and electrical properties of the heterojunction SnO2/Al2O3

Aiming for the investigation of insulating properties of aluminum oxide (Al₂O₃) layers, as well as the combination of this oxide with tin dioxide (SnO₂) for application in transparent field effect transistors, Al thin films are deposited by resistive evaporation on top of SnO₂ thin films deposited by sol–gel dip-coating process. The oxidation of Al films to Al₂O₃ are carried out by thermal annealing at 500 °C in room conditions or oxygen atmosphere. X-ray diffraction data indicate that tetragonal Al₂O₃ is indeed obtained. A simple device and electric circuit is proposed to measure the insulating properties of aluminum oxide and the transport properties of SnO₂ as well. Results indicate a fair insulation when four layers or Al₂O₃ are grown on the tin dioxide film, concomitant with thermal annealing between each layer. The current magnitude through the insulating layer is only 0.2% of the current through the semiconductor film, even though the conductivity of the SnO₂ alone is not very high (the average resistivity is 2 Ω cm), because no doping is used. The presented results are a good indication that this combination may be useful for transparent devices.     

La-substitution Bi2Ti2O7 thin films grown by chemical solution deposition

(La_0.05Bi_0.95)₂Ti₂O₇ (LBTO) thin films had been successfully prepared on P-type Si substrate by chemical solution deposition method. The structural properties of the films were studied by X-ray diffraction. The phase of (La_0.05Bi_0.95)₂Ti₂O₇ is more stable than the phase of Bi₂Ti₂O₇ without La substitution. The films exhibited good insulating properties with room temperature resistivities in the range of 10¹²-10¹³ Ω cm. The dielectric constant of the film annealed at 550 °C at 100 kHz was 157 and the dissipation factor was 0.076. The LBTO thin films can be used as storage capacitors in DRAM.     

Enhanced tunable dielectric properties of Ba0.5Sr0.5TiO3/Bi1.5Zn1.0Nb1.5O7 multilayer thin films by a sol-gel process

Ba_0.5Sr_0.5TiO₃(BST)/Bi_1.5Zn_1.0Nb_1.5O₇(BZN) multilayer thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol-gel method. The structures and morphologies of BST/BZN multilayer thin films were analyzed by X-ray diffraction (XRD) and field-emission scanning electron microscope. The XRD results showed that the perovskite BST and the cubic pyrochlore BZN phases can be observed in the multilayer thin films annealed at 700 °C and 750 °C. The surface of the multilayer thin films annealed at 750 °C was smooth and crack-free. The BST/BZN multilayer thin films annealed at 750 °C exhibited a medium dielectric constant of around 147, a low loss tangent of 0.0034, and a relative tunability of 12% measured with dc bias field of 580 kV/cm at 10 kHz.     

Transparent magnetic oxide thin films of Fe3O4 on glass

Transparent magnetic oxide (TMO) thin films of magnetite (Fe₃O₄) were grown on top of a (Zn,Al)O transparent conducting oxide on a glass substrate. The polycrystalline magnetite thin films show the typical Raman spectrum of Fe₃O₄, a sharp Verwey transition at 120 K and hysteretic behavior. The highest achieved average transmittance in the visible range (400-800 nm) for the entire multilayer was slightly below 80%. TMOs permit the inclusion of magnetic functionalities into transparent electronics. Our results show that TMOs can be successfully used to add magnetic functionalities to transparent conducting oxides.     

Properties of tungsten-doped Bi4Ti3O12-SrBi4Ti4O15 intergrowth ferroelectrics

Ferroelectric and dielectric properties of tungsten-doped Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅ ceramics were investigated. A pure phase of all the samples is confirmed by X-ray diffraction patterns. The remanent polarization (2P_r) of the samples increases initially and reaches its maximum value of 43.2 μC/cm² when W content is 0.03, which is over twice as large as that of non-doped one, then decreases with further doping. The coercive field (E_c) shows a weak tungsten content dependency. It is considered that the enlarged 2P_r could be mainly attributed to the restraint of oxygen vacancies as well as the weakening of their mobility. The Curie temperature decreases a little with increasing doping content, which indicates the good thermal stability is not deteriorated by tungsten doping.     

Enhancement of remnant polarization in multilayered Bi4Ti3O12/(Bi3.25La0.75)Ti3O12 films obtained by chemical solution deposition

Enhancement of remnant polarization was observed in artificially multilayered Bi₄Ti₃O₁₂ (BT)/(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) films_. The multilayer were prepared on platinum coated silicon substrate by chemical solution deposition and compared with the single-phase BT, BLT and (Bi_3.5La_0.5)Ti₃O₁₂ films_. The multilayered film with a stacking periodicity of 60 nm BLT/30 nm BT shows a remnant polarization (2Pr) of about 61 μC/cm², which is much higher than those of the single-phase films. In addition, the multilayered films show a good fatigue-endurance character. After post-annealing the multilayered films at 700 °C for a long time (20 h), its remnant polarization decreased to a value close to the corresponding uniform film. Some possible mechanisms behind the polarization enhancement were proposed.     

Phase equilibria in the system Li2O-TiO2

The system Li₂O-TiO₂ contains four stable phases: Li₄TiO₄, Li₂TiO₃, Li₄Ti₅O₁₂ and Li₂Ti₃O₇, and one metastable phase, H. Li₂TiO₃ undergoes an order-disorder phase transition at 1215°C. High Li₂TiO₃ forms an extensive range of solid solution between ～44 and 66 mole % TiO₂ and low Li₂TiO₃ forms a more limited range of solid solution between ～47 and 51% TiO₂. The temperature of the order-disorder transition decreases to either side of the Li₂TiO₃ composition. The spinel phase Li₄Ti₅O₁₂, has an upper limit of stability at 1015 ± 5°C, above which it decomposes to high Li₂TiO₃ ss and Li₂Ti₃O₇. Li₂Ti₃O₇ has a lower limit of stability at 957 ± 20°C, below which it decomposes to Li₄Ti₅O₁₂ and rutile. During this decomposition of Li₂Ti₃O₇, phase H, a metastable phase of unknown composition, forms as an intermediate. Li₂Ti₃O₇ forms a short range of solid solutions between ～74 and 76% TiO₂. A phase diagram for the system Li₂O-TiO₂ has been constructed using a combination of results determined here and those reported by GICQUEL, MAYER and BOUAZIZ. X-ray powder diffraction data are given for Li₂Ti₃O₇, Li₄Ti₅O₁₂ and phase H.     

Structure and lithium ion conductivity of garnet-like Li5La3Sb2O12 and Li6SrLa2Sb2O12

Oxides with the nominal chemical compositions Li₅La₃Sb₂O₁₂ and Li₆SrLa₂Sb₂O₁₂ were prepared by solid-state reaction. The structures were refined by the Rietveld method using powder X-ray diffraction data. The synthesis of Li₅La₃Sb₂O₁₂ resulted in the well known garnet-related structure plus 5 wt.% of La₂LiSbO₆ in the bulk. In contrast to that, Li₆SrLa₂Sb₂O₁₂ could be synthesised in single garnet-related type phase. Lithium ion conductivities of Li₅La₃Sb₂O₁₂ and Li₆SrLa₂Sb₂O₁₂ were studied by the ac impedance method. The grain-boundary contribution to the total (bulk + grain-boundary) resistance is very small and about 5 and 3% for Li₅La₃Sb₂O₁₂ and Li₆SrLa₂Sb₂O₁₂, respectively, at 24 °C and decreases further with increase in temperature. Among the investigated compounds, Li₅La₃Sb₂O₁₂ exhibits the highest total (bulk + grain-boundary) and bulk ionic conductivity of 7.8 × 10⁻⁶ and 8.2 × 10⁻⁶ S cm⁻¹, respectively, at 24 °C. The structural data indicate that the coupled substitution Li + Sr ⇒ La leads to a closure of the bottle neck like O-O distances of the shared edges of neighbouring Li octahedra and therefore reduces the mobility of Li ions in Li₆SrLa₂Sb₂O₁₂. Scanning electron microscope (SEM) images of the Li₆SrLa₂Sb₂O₁₂ compound revealed well crystallised large homogeneous grains (∼4.8 μm) and the grains were in good contact with the neighbouring grain, which leads to a smaller grain-boundary contribution to the total resistance.     

Photocatalysis and characterization of the gel-derived TiO2 and P-TiO2 transparent thin films

The gel-derived TiO₂ and P-TiO₂ transparent films coated on fused-SiO₂ substrates were prepared using a spin-coating technique. Effects of phosphorus dopants and calcination temperature on crystal structure, crystallite size, microstructure, light transmittance and photocatalytic activity of the films were investigated. By introducing P atoms to Ti-O framework, the growth of anatase crystallites was hindered and the crystal structure of anatase-TiO₂ could withstand temperature up to 900 °C. The photocatalytic activities of the prepared films were characterized using the characteristic time constant (τ) for the photocatalytic reaction. The titania film with a smaller τ value possesses a higher photocatalytic ability. After exposing to 365-nm UV light for 12 h, the P-TiO₂ films calcined between 600 °C and 900 °C can photocatalytically decomposed ≥ 84 mol% of the methylene blue in water with corresponding τ ≤ 7.1 h, which were better than the pure TiO₂ films prepared at the same calcination temperature.     

Microwave dielectric properties of LaMgAl11O19

The suitable choice of a substrate material is one of the aims to be fulfilled in high speed microwave technology. LaMgAl₁₁O₁₉ oxide ceramic material, which belongs to the magnetoplumbite family, has been reported earlier as a potential candidate for such applications. This material has been prepared by conventional solid-state ceramic route. The structure has been studied by X-ray diffraction and characterized at microwave frequencies. The effect of dopant and glass addition on the microwave dielectric properties of this material has also been investigated. LaMgAl₁₁O₁₉ has relatively low dielectric constant (ε_r=14), low dielectric loss or high quality factor (Q_u×f>28,000 GHz at 7 GHz) and small temperature variation of resonant frequency (τ_f=−12 ppm/°C) at room temperature (300 K). These properties make LaMgAl₁₁O₁₉ as a good substrate material and as a dielectric resonator to be used in microwave devices operating at relatively high frequencies.     

Processing, dielectric properties and impedance characteristics of Na0.5Bi0.5Cu3Ti4O12 ceramics

Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of NBCTO ceramics sintered at various temperatures with different soaking time were investigated. Pure NBCTO phase could be obtained with increasing the temperature and prolonging the soaking time. High dielectric permittivity (13,495) and low dielectric loss (0.031) could be obtained when the ceramics were sintered at 1000 °C for 7.5 h. The ceramics sintered at 1000 °C for 7.5 h also showed good temperature stability (−4.00 to −0.69%) over a large temperature range from −50 to 150 °C. Complex impedances results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance (R_g) was 12.10 Ω cm and the grain boundary resistance (R_gb) was 2.009 × 10⁵ Ω cm when the ceramics were sintered at 1000 °C for 7.5 h.     

Resistive switching characteristics of multilayered (HfO2/Al2O3)n n = 19 thin film

A transparent resistive random access memory used as Indium Tin Oxide (ITO) electrode, ITO/HfO₂/Al₂O₃/…/HfO₂/Al₂O₃/ITO capacitor structure is fabricated on glass substrate by atomic layer deposition. The unipolar resistive switching characteristics can be performed by applying the positive- or negative-bias through top electrode, however, the differences of switching and stability in the two different operations can be observed. The diversities of electrical property are attributed to different oxide/ITO interface materials, which influence the current flow of the injected electrons.     

High-pressure substitutions for Cd In Cd2Nb2O7 and Cd2Ta2O7

Substitutions into cadmium niobate of the type Cd_2?xA_xNb₂O₇ (x≤0.5) have been carried out at 58 kbars and 1100°C. The substituting A cations were Mg, Mn, Fe, Co, Ni, Cu, and Zn which are all smaller than Cd. Rhombohedral or triclinic distortions derived from cubic Cd₂Nb₂O₇ were achieved at values of x as low as 0.05. All the substituted phases appear to be centric at room temperature. Analogous substitutions into Cd₂Ta₂O₇ were also made.     

Nouveaux verres fluores dans les systems AF2 - MF2 - MF3New fluoride glasses in the AF2-MF2-MF3

Glass formation has been investigated in ternary systems AF₂ - BF₂ - MF₃ with A = Pb, Ba ; B = Mn, Zn, Cd, Sn, Ba ; M = Fe, Ca, In. Twelve new fluoride glasses systems are shown. The most stable glasses are obtained in the PbF₂ - BaF₂ - InF₃ system with characteristic temperatures : Tg = 250°C, Tc = 318°C and Tf = 588°C for 30 PbF₂ - 20 BaF₂ - 50 InF₃, the refractive index is n_D = 1.5492 and the glasses are transparent up to 8.2 μm.The study of PbF₂ - MF₂ - FeF₃ glassy systems with M = Mg, Ca, Sr, Ba confirms the network former behavior of octaedrally coordinated 3d transition metal ions.     

Effect of pre-strain on martensitic transformation of Ni43Mn43Co7Sn7 high- temperature shape memory alloy

In the present work, the effect of pre-strain on martensitic transformation of Ni₄₃Mn₄₃Co₇Sn₇ (at.%) alloy was investigated. The results show that Ni₄₃Mn₄₃Co₇Sn₇ alloy undergoes a martensitic transformation at 288 °C upon cooling. The thermal cycling does not affect the transformation behavior of the alloy, indicating the good thermal stability. The reverse transformation of the deformed martensite is pre-strain dependent. When the pre-strain is higher than 7.5%, the reverse transformation occurs in two-stage manner upon first heating due to the nonuniform martensite deformation. In contrast, during the first martensitic and second reverse transformation, the pre-strain shows little effect on the transformation temperatures.     

Comparative study of photoinduced wettability conversion between [PW12O40]/brookite and [SiW12O40]/brookite hybrid films

Two tungsten-based Keggin-type heteropolyacids (PW₁₂: ([PW₁₂O₄₀]³⁻) and SiW₁₂: ([SiW₁₂O₄₀]⁴⁻)) were hybridized with brookite-type TiO₂. Then photocatalytic decomposition activity, photoinduced hydrophilicity, and sustainability of the hydrophilicity in the dark were evaluated using gaseous 2-propanol (IPA) decomposition and sessile drop method. The obtained films were transparent in the visible wavelength range. Both hybrid films exhibited higher photocatalytic decomposition activity and had higher photoinduced hydrophilicizing rates than pure brookite films under UV illumination. The PW₁₂/TiO₂ film exhibited better photocatalytic performance than the SiW₁₂/TiO₂ film did. Atmosphere dependence, XPS analysis, and electrochemical experiments indicated the cause of these two films' different levels of sustainability of hydrophilicity to be differences in their electron storage capability. Results show that the electron scavenger capability and reoxidation efficiency of the heteropolyacid are key factors affecting the overall performance of wettability conversion of this hybrid film system before and after UV illumination.     

Preparation and characterization of Y3Al5O12 (YAG) nano-powder by co-precipitation method

YAG precursor was synthesized by a co-precipitation method from a mixed solution of aluminum and yttrium nitrates with aqueous ammonia as the precipitator. The structure, phase evolution and morphology of YAG precursor and the sintered powders were studied by means of IR, TG/DTA, XRD, TEM methods. It was found the precursor with approximate composition of Al(OH)₃·0.3[Y₂(OH)₅·(NO₃)₂·2H₂O] directly transformed to pure-YAG phase at 800 °C and no intermediate phases were detected. YAG nanocrystalline powders from sintering the precursor at different temperatures were less-aggregated and the diameters of the grains were about 40-100 nm. BET surface area of the particles decreased with increase of calcination temperature and the powder sintered at 800 °C can be used for fabrication of transparent YAG ceramics.