Papers by Keyword: Strontium Titanate

Abstract: Lanthanum (La) and Nickel (Ni)-codoped Strontium Titanate (SrTiO₃) with the formula of Sr_1-xLa_xTi_1-yNi_yO₃ has been synthesized using the coprecipitation method. This research aimed to determine the effect of nickel and lanthanum co-doping on the photocatalytic activity of SrTiO₃. Here, the Ni concentration (y) was constant at 4%, while La concentrations (x) were varied at 1% and 2%. The synthesized samples were tested via X-ray diffraction (XRD) instrument to determine the crystal structure. It exhibited that the crystallite size reduced along with increased lanthanum concentration. The photocatalytic activity of Sr_1-xLa_xTi_1-yNi_yO₃ was observed under UV and Visible light irradiation against methylene blue (MB) pollutant dyes, and the absorption was measured via a UV-Vis spectrophotometer. It revealed that all samples succeeded in degrading MB solution under the two light sources with exposure times of 1, 2, 3, and 4 hours. Further, it was found that photocatalytic activity with UV lamp irradiation resulted in a better degradation percentage than visible light irradiation. The highest degradation about 60% was achieved by Sr_0.99La_0.01Ti_0.96Ni_0.04O₃ under UV light exposure for 4 hours.

Abstract: This research investigated the Fe doping effects on the Strontium Titanate (SrTiO₃) structure to improve its photocatalytic activity. The so-called Fe-doped STO photocatalysts with a stoichiometry formula of SrTi_1-xFe_xO₃ (x = 0, 0.01, and 0.05) were successfully fabricated using the coprecipitation method. The XRD characterization confirmed the formation of STO, SrTi_0.99Fe_0.01O₃, and SrTi_0.95Fe_0.05O₃ photocatalysts and the shrinkage crystallite size due to increasing Fe content. The FTIR characterization supported the XRD results, where all samples revealed Sr-Ti-O bonds with no observed Fe-O bonds indicating the successful fabrication and doping. The photocatalytic activity was examined by the degradation of Methylene Blue (MB) dye under UV light for 1, 2, 3, 4, and 5 irradiation times, and the absorbance was determined using a Spectrophotometer instrument. All samples have successfully degraded MB dye where the %degradation linearly increased with longer irradiation times. The results further exhibited that the SrTi_0.95Fe_0.05O₃ sample had the highest %degradation at 75.3% while SrTi_0.99Fe_0.01O₃ samples achieved the highest kinetic rate at 0.2557 min^-1. All Fe-doped samples revealed better photocatalytic activity than the undoped STO, proving that Fe doping could improve the photocatalytic activity of SrTiO₃.

Abstract: SStrontium titanate (STO) is well recognized as promising perovskite photocatalytic material. The catalytic characteristics of STO can be improved by modification with Mn metal. In this study, SrTi_0.80Mn_0.20O₃ has been successfully fabricated using coprecipitation technique with varied sintering temperatures of 700°C, 800°C, 900°C, and 1000°C. This study aimed to investigate the effect of sintering temperature on the photocatalytic activity of SrTi_0.80Mn_0.20O₃. The photocatalyst activity of SrTi_0.80Mn_0.20O₃ could be observed by the degradation of Methylene blue (MB) dye. Based on the X-Ray Diffraction (XRD) and Fourier Transform Infra-Red (FTIR) data, the SrTi_0.80Mn_0.20O₃ has been made. The data also showed that the impurities phases have been reduced and eliminated by the higher sintering temperatures. Nevertheless, all varied samples of the SrTi_0.80Mn_0.20O₃ have successfully exhibited their photocatalyst activity by degrading the MB dye under UV light irradiation with irradiation times of 0, 1, 2, 3, 4, 5, and 6 hours. According to the UV-Vis absorption data, the irradiation time could considerably decline the absorption peaks of MB dye in SrTi_0.80Mn_0.20O₃. Besides, the higher sintering temperature did not influence the absorption peaks position but slightly changed their intensity (at the same irradiation time). Furthermore, the higher sintering temperature and longer irradiation time tended to produce higher DR% of up to 66.63%.

Abstract: Strontium titanate SrTiO₃ thin films have been fabricated by radio frequency magnetron sputtering on P-type Si at substrate temperature of 200°C. Two different postdeposition annealing methods were applied on the sputtered films. Specifically, conventional thermal annealing at 300°C for 60 min and photoactivation treatment under deep ultraviolet-ozone for 30 min. The dielectric properties of the SrTiO₃ thin films were investigated by fabricating Au/STO/p-Si MOS capacitors. A dielectric constant (κ) with a value of 13 was obtained for as-deposited film, which has a thickness of 107 nm. While post-annealed samples showed elevated values of κ, precisely, 15.33 and 19.32 for films exposed to deep ultraviolet-ozone photoactivation and films annealed at 300°C, respectively. All devices showed a leakage current in the order of 10^-8 A/cm² at 1V. Based on XPS analysis, photo-activated films revealed the lowest percentage of oxygen vacancies, which designates the capability of this technique to enhancing films quality at a lower temperature.

Abstract: A novel graphene-bridged SrTiO₃ (STO) thin film loaded on the glass was fabricated using a facile sol-gel method followed by the dip-coating and spin-coating method. As-prepared STO film and GO/STO film were tested by XRD, SEM to identify the composition and surface morphology. The as-prepared thin film catalyst was employed to degrade methylene blue (MB) in water under near ultraviolet ray irradiation. Compared to pure STO, GO/STO prepared by dip-coating method displayed good photocatalytic degradation efficiency with 58% removal of MB (60 mL, 5mg/L) in 6.0 h, the GO/STO prepared by spin-coating method displayed more superior degradation efficiency with 94% removal of MB (60 mL,5mg/L) in 6.0 h. The influences of MB volume and the different methods were also investigated in details. The enhanced photocatalytic activities could be attributed to the suppression of charge recombination, high specific surface area and great adsorption capability of GO/STO. This work provides a promising approach to construct novel film GO/STO with high stability and photodegradation efficiency that can be applied in efficient treatment pollutants in wastewater.

Abstract: Present investigation provides experimental studies on cylindrical dielectric resonator antennas (CDRAs) fabricated from SrTi_1-xZr_xO₃ ceramic with different substitution of Zr in place of Ti for (0 ≤ x ≤1). Ceramic powder were prepared using conventional solid state reaction method. X-ray Diffraction exposes physical properties Zr-doped SrTiO₃ which exhibit phase transition from cubic, tetragonal to orthorhombic phase. The electrical properties such as dielectric constant (ε_r) and dielectric loss (tan δ) were studied in variation of temperatures and frequencies. At room temperature the dielectric constant decreased from 240 to 21 with increase of Zr content however the amazing result was obtained for multiband antenna by Zr content. The dielectric loss obtain shows very low loss value roughly below 0.07 for all samples. The variations of return loss, resonance frequency and bandwidth of CDRAs at their respective resonant frequencies are studied experimentally.

Abstract: It has been accepted that compositions and microstructures significantly affected dielectric properties of materials. In general, chemical compositions were influenced by additive contents, while consolidation techniques controlled microstructure of the materials to have appropriate grain sizes. This study, therefore, aimed at examining effects of aluminium contents and consolidation techniques on chemical compositions and microstructures of the strontium titanate. Experimental results revealed that at higher aluminium contents, only small quantities of TiO 2 secondary phase were present, while grain sizes generally decreased. The results also indicated that the cold isostatic pressing technique led to high sintered density. The greatest dielectric constant (281.5 at 1 MHz) obtained in this study was achieved in strontium titanate sample with 30 at% of Al addition, pressed by cold isostatic pressing. Enhancement of dielectric constant of the sample was attributed to low secondary phase, fine grain sizes and high sintered density.

Abstract: Alternative synthesis routes to obtain ceramics with advanced electronics applications have been investigated to improve the properties of these materials. Calcination and sintering by microwave irradiation is a very promising production method, which performs a rapid solid-state reaction and consolidation of particles due to the high heating rates (about 1000°C/min) aided by the microwave irradiation effect. To produce strontium titanate powder (SrTiO₃ - STO), TiO₂ and SrCO₃ raw precursors were mixture in a ball mill for 3.5 h and after, this mixture was dried at 70°C for 24h. The resulting mixture was divided in two portions to produce STO powders following two procedures: (i) in the conventional method (STO-cC), the mixture was calcined at 1000°C with a heating rate of 10oC/min for 2h, and (ii) in the microwave method (uC) other part of mixture was calcined at 1000°C with a heating rate of 1000°C/min for 15 min, 30 min and 60 min. The powders obtained by both methods were characterized by X-ray diffraction (XRD) to evaluate the crystalline phase presents in the powders. The STO crystalline phase was identified in both samples, but it was also noted the presence of SrCO₃ spurious phase in the STO-cC and STO-uC (15 and 30min). On the other hand, STO-uC powder calcined for 60 minutes did not showed this spurious phase. Dilatometric analysis was performed on STO-cC and STO-uC (60min) discs shaped powders by uniaxial load pressing (180 MPa) in order to determine the sintering temperature. Green bodies were sintered at 1380oC in conventional oven for 2h (cS) and in microwave oven at three different soaking times: 15, 30 and 60 minutes (uS). The microstructures of the cS and uS ceramics were analyzed by scanning electron microscopy (SEM). Significant difference between densification of the STO-cC-cS (88%) and STO-uC-uS (99%) ceramics were obtained to ceramics sintered by 60 minutes. The values of grain size of ceramics obtained by uC/uS indicates that microwave irradiation is an effective technique to avoid grain growth.

Abstract: Thermoelectric ceramics are those capable of converting thermal into electricity energy by the Seebeck effect. The non-conventional synthesis of ceramic powders and the doping of these powders with rare earth elements are factors that can improve the efficiency in energy conversion. The objective of this work was to synthesize and analyze pure and doped SrTiO₃ powders by solid state reaction (SSR) and ultrasonic synthesis (USS). The precursors of SSR were: strontium carbonate (SrCO₃), titanium oxide (TiO₂) and lanthanum and neodymium oxide (La₂O₃ and Nd₂O₃). They were mixed in a ball mill for 3.5h in stoichiometric ratio to obtain SrTiO₃ (STO), Sr_0.96La_0.04TiO₃ (STO-04La), Sr_0.96Nd_0.04TiO₃ (STO-04Nd) and Sr_0.96La_0.02Nd_0.02TiO₃ (STO-02La02Nd). The powder mixtures were calcined at 1000°C in a conventional oven for 2h. The USS powders were produced by solubilization of Ti (C₄H₉O)₄ and SrCO₃ in an HNO₃ aqueous solution. The solution was precipitated with NH₄OH and, then, this powder was dried at 70°C for 24h, in air. The dried powder was added to a solution of KOH and subjected to ultrasound irradiation. The same procedure was followed for the synthesis of USS doped powders, STO-04La, STO-04Nd, and STO-02La02Nd powders using as dopant lanthanum and neodymium oxides. The powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and crystallite sizes were calculated by the Scherrer equation to evaluate the differences on structural and microstructural properties.

Abstract: Powder samples of (Ca,Sr)TiO₃:Er were prepared by a solid-state reaction method. Photoluminescence due to f-f transitions of Er³⁺ was not induced by band-gap excitation of (Ca,Sr)TiO₃ but by f-f transitions of Er³⁺. An electroluminescent device in which thin films of Ca_0.6Sr_0.4TiO₃:Er and SnO₂:Sb are stacked alternately was prepared by sol-gel and spin-coating methods. Very weak electroluminescence due to f-f transition of Er³⁺ was observed in the device.