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Ba(Sn_0.02Ti_0.98)O₃ thin films (BTS) were prepared by sol-gel route and deposited by spin-coating on commercial Pt/Ti/SiO₂/Si substrates. By modifying the annealing conditions from 750°C for 1 h to 950°C for 15 min, the grain size increased from 60 nm to 110 nm due to the increased driving force. The dielectric permittivity ε′ and tunability n_r are correlated with the grain size: these parameters increase with the grain size. At room temperature for the BST film annealed at 950°C, a record value of 76% of tunability is obtained at 10 kHz. This very high value of tunability makes BaSnTiO₃ a very good candidate for tunable devices.

Zinc sulfide (ZnS) nanoparticles are successfully deposited on the surface of natural halloysite nanotubes (HNTs) to produce ZnS/HNTs nanocomposites. The samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) analysis. The results indicate that ZnS nanoparticles are uniformly attached on the surface of HNTs with narrow particle size distribution center at ~10 nm, and are prevented from aggregation by HNTs and expose more active sites. ZnS/HNTs show excellent photocatalytic activity for the degradation of eosin B under UV light, better than pure ZnS and HNTs, indicating its potential application in the field of environmental protection. The mechanism for photocatalytic activity enhancement is also investigated.

Polyanionic cathode materials for lithium-ion batteries start to be considered as potential alternative for layered oxide materials. Among them, Li₂CoSiO₄, characterized by outstanding capacity and working voltage, seems to be an interesting substitute for LiFePO₄ and related systems. In this work, structural and electrical investigations of Li₂CoSiO₄ obtained by sol–gel synthesis were presented. Thermal decomposition of gel precursor was studied using EGA (FTIR)-TGA method. Chemical composition of the obtained material was confirmed using X-ray diffraction and energy-dispersive X-ray spectroscopy. The morphology of β-Li₂CoSiO₄ was studied using transmission electron microscopy. High temperature electrical conductivity of Li₂CoSiO₄ was measured for the first time. Activation energies of the electrical conductivity of two Li₂CoSiO₄ polymorphs (β and γ) were determined. The room temperature electrical conductivity of those materials was estimated as well.

Photovoltaic (PV) effect of polycrystalline Bi_0.975La_0.025Fe_0.975Ni_0.025O₃ (BLFNO) film grown on Pt(111)/Ti/SiO₂/Si(001) substrate using sol–gel method has been investigated. The BLFNO film possesses good ferroelectric property and large twice-remanent polarization. It is found that PV response exhibited a strong dependence on the potential of top indium tin oxide (ITO) and bottom Pt electrode. The open circuit voltage is -0.67 V when the potential of ITO electrode is higher than that of Pt electrode and 0.45 V when the potential of ITO electrode is lower than that of Pt electrode. This can be interpreted by the variation of barrier heights at both ITO/BLFNO and BLFNO/Pt interfaces.

Ba(Sn_0.02Ti_0.98)O₃ thin films (BTS) were prepared by sol–gel route and deposited by spin-coating on commercial Pt/Ti/SiO₂/Si substrates. By modifying the annealing conditions from 750°C at 1 h to 950°C at 15 min, the relative tunability n_r at 100°C in the paraelectric state increased from 45 to 70% while the DC dielectric permittivity ε′(0) increased as well. The evolutions of ε′(E) and n_r(E) are explained from Devonshire thermodynamic formalism. The very high value of tunability of 70% is explained by the grain size increase of our BTS thin films and the decrease of the dead layer effect when the annealing conditions are optimized.

In this work, La_0.5Sr_0.5CoO₃ (LSCO) perovskite oxide with perfect crystallinity was successfully synthesized via a sol–gel method and then used as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The DSSCs with LSCO CEs exhibited excellent electrocatalytic activity for the triiodide reduction and yielded a power conversion efficiency of 7.17%, which is greater than that of the Pt electrode (7.06%). Compared with the hydrothermal method and solvothermal method, sol–gel method is more suitable for large scale preparation. This work should open up a new class of CE materials for low-cost and high-efficiency DSSCs.

A ceramic solid-state electrolyte of lithium aluminum titanium phosphate with the composition of Li${}_{1.3}$Al${}_{0.3}$Ti${}_{1.7}$(PO${}_4{)}_3$ (LATP) was synthesized by a sol–gel method using a pre-dissolved Ti-source. The annealed LATP powders were subsequently processed in a binder-free dry forming method and sintered under air for the pellet preparation. Phase purity, density, microstructure as well as ionic conductivity of the specimen were characterized. The highest density (2.77$\mathrm{\text{g}}\cdot {\mathrm{\text{cm}}}^{-3})$ with an ionic conductivity of $1.88\times 10^{-4}\mathrm{\text{S}}\cdot {\mathrm{\text{cm}}}^{-1}$ (at 30${}^{\circ }$C) was reached at a sintering temperature of 1100${}^{\circ }$C. Conductivity of LATP ceramic electrolyte is believed to be significantly affected by both, the AlPO₄ secondary phase content and the ceramic electrolyte microstructure. It has been found that with increasing sintering temperature, the secondary-phase content of AlPO₄ increased. For sintering temperatures above 1000${}^{\circ }$C, the secondary phase has only a minor impact, and the ionic conductivity is predominantly determined by the microstructure of the pellet, i.e. the correlation between density, porosity and particle size. In that respect, it has been demonstrated, that the conductivity increases with increasing particle size in this temperature range and density.

Cobalt (Co) and sulfur (S) co-doped titanium dioxide (TiO₂) catalysts were synthesized via sol–gel method. The structure of TiO₂was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). The valence states of elements were studied by X-ray photoelectron spectroscopy (XPS), and the optical-absorption properties of the catalysts were tested using the ultraviolet–visible (UV–Vis) spectrophotometer. The results showed that the grain sizes of Co and S co-doped TiO₂ decreased with the increase of Co and S doping concentration within a certain range, and then the catalysts had obvious red shift on the absorption of visible light. Sample (2%Co–5%S–TiO₂) showed excellent light absorption characteristics and the photo-response threshold increased significantly to about 760nm. Also, the further degradation test under visible light shows the 2%Co–5%S-TiO₂ sample exhibit apparently improved degradation efficiency for Rhodamine B compared to the undoped one.

This paper describes a method for producing $\alpha$-Al₂O₃ at low temperatures by a combination of a hydrothermal process and a seeding technique. White aluminum hydroxide precipitate was prepared by a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution. Peptization of the precipitate by acetic acid at room temperature transformed it into a transparent alumina sol. The alumina sol was treated with a hydrothermal process. $\alpha$-Al₂O₃ particles serving as seeds were added to the hydrothermally treated alumina sol. The sol containing the $\alpha$-Al₂O₃ particles was transformed into an $\alpha$-Al₂O₃-seeded alumina gel by drying at room temperature. The non-seeded alumina gel was amorphous or showed fine crystallites and began to crystallize into $\alpha$-Al₂O₃ at 900${}^{\circ }$C. The $\alpha$-Al₂O₃-seeding promoted the crystallization of the alumina gel to $\alpha$-Al₂O₃. A remarkable $\alpha$-Al₂O₃ crystallinity was achieved with an increase in $\alpha$-Al₂O₃ particle content by weight in the final seeded alumina gel. For an $\alpha$-Al₂O₃ particle content of 5%, the seeded alumina gel was partially crystallized to $\alpha$-Al₂O₃ by annealing at temperatures as low as 600${}^{\circ }$C.

Sol–gel synthesis is a well-known method to synthesize metal oxides such as ZnO in a facile way. Different crystal morphologies of Al-doped ZnO were obtained by tuning the pH for the synthesis. Additionally, the influence of the morphology on the sensing properties of ZnO-based resistive gas sensors was investigated by producing sensor films which were exposed to low NO₂ concentrations. The results show a high and fast sensor response with a high aspect ratio of the crystal. Furthermore, a possible crystal forming mechanism was postulated. Thus, it can be assumed that the type of Zn${}^{2+}$ influences the crystal form. Ethanol amine can cause a capping of certain crystal planes and enhance the growth along one axis.

In this work, our effort was to improve the thermoelectric properties of Ca₃Co₄O₉ thermoelectric material. Ca₃Co${}_{4-x}$Y_xO₉ polycrystalline thermoelectric ceramics have been fabricated by sol–gel method plus spontaneous combustion and cold isostatic pressing process. The structure, surface topography and thermoelectric properties of Ca₃Co${}_{4-x}$Y_xO₉ polycrystalline thermoelectric were investigated by X-ray diffraction (XRD), SEM and ZEM3, respectively. The results showed that $Y$ doping affected the microstructure and thermoelectric performance remarkable. With the increasing of $Y$ doping, the electrical conductivity had a maximum value, and thermal conductivity has a minimum value. Seebeck coefficient gradually increased with $Y$ doping content increasing always. The figure of merit was 0.07 at 673K for the Ca₃Co${}_{3.7}$Y${}_{0.3}$O₉ sample. The results showed that the thermoelectric performance of Ca₃Co₄O₉ could be improved 39% with the substitution of $Y$ than the un-doped.

We report on the growth and characterization of undoped indium nitride (InN) thin films grown on a silicon substrate. The InN thin films were grown on aluminium nitride (AlN) template with gallium nitride (GaN) nucleation layer using a relatively simple and low-cost sol–gel spin coating method. The crystalline structure and optical properties of the deposited films were investigated. X-ray diffraction and Raman results revealed that InN thin films with wurtzite structure were successfully grown. For InN thin film grown on a substrate with the GaN nucleation layer, its strain and dislocation density are lower than that of the substrate with the AlN nucleation layer. From the ultra-violet-visible diffuse reflectance spectrum analysis, the energy bandgap of the InN thin films with the GaN layer was 1.70 eV. The potential application of the sol–gel spin-coated InN thin films was also explored. Metal–semiconductor–metal (MSM) infrared (IR) photodetectors were fabricated by depositing the platinum contacts using two interdigitated electrodes metal mask on the samples. The finding shows that the device demonstrates good sensitivity and repeatability towards IR excitation at a wavelength of 808 nm. The photodetector characteristics at dark and photocurrent conditions such as Schottky barrier height (SBH) and ideality factor are determined. Upon exposure to the IR source at 3V applied bias, InN/AlN/Si device configuration displays rapid rise time of 0.85 s and decay time of 0.78 s, while InN/GaN/AlNSi demonstrates slow rise time of 7.45 s and decay time of 13.75 s.

The control of polymorphism transition of Eu${}^{2+}$ ion-doped $\gamma$-, $\delta$-, $𝜃$- and $\alpha$-metastable alumina derived from boehmite is demonstrated by the sol–gel method through controlling the doping amount and firing temperature and the resultant luminescent properties are investigated. Nanosized boehmite ($\gamma$-AlOOH) particulates in boehmite sol effectively prevent the formation of impurity phases of EuAlO₂ and Eu₂O₃. The polymorphic structures of the induction-fired xerogel samples in weak reductive atmosphere can be held to the room temperature upon cooling down naturally. The luminescence properties of Eu${}^{2+}$ ions verify the polymorphic transitions from $\gamma$-, $\delta$-, $𝜃$- to $\alpha$-Al₂O₃ that are featured with their broad emission peaks positions at 410, 450, 480 and 500 nm, respectively. It is believed that boehmite sol–gel by taking the nanosized $\gamma$-AlOOH particulates as seeds assisted the dispersion of precursor constituents and is effective to adjust the onset of polymorphic transition temperatures and luminescence properties.