Influence of microwave energy on structural and photoluminescent behavior of CaTiO3 powders (original) (raw)
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Chemical Engineering Journal, 2008
Calcium titanate (CaTiO 3 ) powders were synthesized by the polymeric precursor method and processed in different furnaces. The structural evolution of CaTiO 3 powders heat treated in conventional furnace and adapted domestic microwave oven was analyzed by X-ray diffraction (XRD), micro-Raman scattering (MRS) spectroscopy and ultraviolet-visible (UV-vis) absorption spectroscopy. XRD, MRS and Rietveld refinement revealed that the CaTiO 3 powders heat treated in both furnaces are free of deleterious phases and crystallize in an orthorhombic structure. UV-vis measurements suggested the presence of intermediary energy levels into the optical band gap of structurally disordered CaTiO 3 powders. CaTiO 3 powders heat treated in microwave oven showed a rapid structural organization than powders heat treated in conventional furnace. The optical absorption values revealed a different behavior due to the changes in the structural order-disorder degree of the CaTiO 3 lattice. The differences verified in the heating process of CaTiO 3 powders processed in conventional furnace and adapted domestic microwave oven were discussed.
Ceramics International, 2016
Calcium titanate (CaTiO 3-CT) and samarium doped calcium titanate (CaTiO 3 :Sm 3 þ-CT:Sm) powders in different Sm 3 þ concentrations (0.5-5.0% molar ratio of Sm 3 þ) were obtained by the Hydrothermal Microwave Methodology at 140 1C for 16 min. These crystals were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. Field emission scanning electron microscopy images were employed to observe the shape and size of the crystals. The optical properties were investigated by ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) measurements. The XRD indicated structural organization at long range while MR revealed short range order for all undoped and Sm-doped samples. Morphological analysis revealed a new cubic morphology for CT:Sm, presenting an average size of 3.0 μm. Further, the ultraviolet-visible absorption spectra indicated the existence of intermediary energy levels within the band gap. The maximum intensity PL emission occurred due to 4 G 5/2-6 H 7/2 and 4 G 5/2-6 H 9/2 transitions of Sm 3 þ. CIE chromaticity coordinates of the samples were determined and support these materials are promising candidates for applications as phosphors in the visible orange range. This research concluded that the methodology employed here was responsible for the presence of unusual and interesting properties for these new luminescent materials.
Calcium titanate, CaTiO 3 , an important microwave dielectric material and one of major phases in synroc (synthetic rock), a titanate ceramic with potential application for fixation of high level nuclear waste was synthesized from calcium titanyl oxalate [CaTiO (C 2 O 4 ) 2 ⋅6H 2 O] (CTO) by employing microwave heating technique. CTO heated in microwave heating system in air at 500 o C for 1 h gave a perovskite, CaTiO 3 . The product obtained by heating of CTO in the same system at 700°C for the same duration was however, much more crystalline. CaTiO 3 obtained by the present method was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET surface area measurement.
CaTiO3:Eu3+ obtained by microwave assisted hydrothermal method: A photoluminescent approach
Optical Materials, 2010
Europium doped calcium titanate (CT:Eu 3+) powders containing 0.5%, 1.0% and 2.0% mol of Eu 3+ were synthesized by hydrothermal microwave method (HTMW) at 140°C for 10 min resulting in the samples CT:Eu 3+ (0.5%) CT:Eu 3+ (1.0%) and CT:Eu 3+ (2.0%). Eu 3+ ion was introduced into the perovskite lattice aiming to study the synthesis, photoluminescence emissions and morphological properties of these powders. X-ray diffraction patterns present a single phase indexed as Pbnm space group in a typical orthorhombic CaTiO 3 (CT) structure. FT-Raman spectra of CT indicated a great arrangement in a short range, while UVvis measurements did not show any substantial changes in the optical absorbance behavior of CT:Eu 3+ samples. The existence of two small absorbance bands at 394 and 466 nm suggests the presence of Eu 3+ in the CT lattice, confirmed by excitation and photoluminescence emission spectra. The emission line shape transitions from 5 D 0 to 7 F J (J = 0, 1-4) levels of the Eu 3+ was noticed at, respectively 579, 589, 613, 654 and 695 nm, and the most intense one at 613 nm is ascribed to the hypersensitive 5 D 0 ? 7 F 2 transition. Among the samples, the most intense photoluminescence results were observed for the CT:Eu 3+ (1.0%).
Facile Microwave-Assisted Synthesis of Lanthanide Doped CaTiO3Nanocrystals
Journal of the Brazilian Chemical Society, 2015
This article discusses a simple approach for the microwave-assisted synthesis of good quality nanosized calcium titanate crystals doped with trivalent Tm and Yb lanthanide ions. The prepared nanoparticles had a microcube-like structure and a crystallite size of ca. 47 nm. The structure of the nanocrystals was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their spectroscopic behavior was examined at a laser excitation wavelength of 350.7 nm. It was found that doping CaTiO 3 nanocrystals with Yb and Tm leads to about 250-fold brighter photoluminescence (PL) emissions in the blue and near-infrared regions than that emitted by pure CaTiO 3 nanocrystals. The PL emission was correlated with the structural disorder.
Zinc Calcium Titanate Ceramics (Zn x Ca 1-x TiO 3, X=0.6-0.9) samples were synthesized by using solid state reaction route with equal molar ratio using metal oxide powders of 99.9% purity. The samples were well grained and calcined at 900 o C for 10 hours and sintered at 950 o C for 6 hours. The characterization of the samples were carried out by using XRD for Structural characterization, SEM with EDAX for Micro structural and HIOKI 3532-50 LCR Hitester for Dielectric studies. The structure of the samples was estimated as rhombohedral by using XRD studies. From the SEM micrographs the average grain size was calculated and it was observed that it varied in the range of 0.25-5 μm for the given sample of Zn x Ca 1-x TiO 3 (X=0.6-0.9).
Acta Materialia, 2009
CaTiO 3 powders were synthesized using both a polymeric precursor method (CT ref ) and a microwave-assisted hydrothermal (CT HTMW ) method in order to compare the chemical and physical properties of the perovskite-based material as a function of the synthesis method. To this end, X-ray diffraction, Raman spectroscopy, inductively coupled plasma atomic emission spectroscopy and experimental Ti and Ca K-edge X-ray absorption near-edge structure spectroscopy, as well as measurements of photoluminescence (PL) emission, were used to characterize the typical bottom-up process of the CaTiO 3 perovskite phase at different times. Detailed Rietveld refinements show a random polycrystalline distortion in the powder structure, which can be associated with the tilting (a angle < O-Ti-O) between adjacent TiO 6 octahedra (intermediate range) for CT HTMW samples and an intrinsic TiO 6 distortion (short range) in relation to the polymeric precursor CT ref sample. These properties were further investigated by first-principles calculations based on the density functional theory at the B3LYP level. The relationship between this tilting on the PL profile is highlighted and discussed. Thus, a structural model derived from both experimental results and theoretical simulations reveals a close relationship between this tilting and the presence of intermediate energy states within the band gap which are mainly responsible for PL emissions.
Effect of Zr4+ on the structural and microwave dielectric properties of CaTiO3 ceramics
Ferroelectrics, 2021
Abstract The new ceramic composite of Ca(ZrxTi1-x)O3 had been prepared using the conventional mixed oxide solid state reaction method. The effects of Zr4+ ions substation over Ti4+ ions on the microwave dielectric properties of the CaTiO3 ceramics were investigated. The phase analysis showed that the specimens Ca(ZrxTi1-x)O3 presented single phase with orthorhombic structure in the range of x = 0.0–0.7 when sintered at 1300 °C for 3 h. The addition of Zr4+ facilitated the formation of large round-like grains with porous microstructure. The solid solution with x = 0.7 sintered at 1300 °C for 3 h showed a good combination of dielectric properties: and (at 2.5 GHz).
Influence of titanium precursor on photoluminescent emission of micro-cube-shaped CaTiO3
Journal of Luminescence, 2015
For this research, we studied the influence of titanium tetrachloride (TC) and titanium tetraisopropoxide (TTP) precursors on CaTiO 3 (CTO) synthesis by employing a microwave-assisted hydrothermal (MAH) method regarding their respective short-, medium-and long-range features to determine if the use of different titanium precursors enhances the structural evolution of the material. The growth mechanism for the formation of the micro-cube-shaped CTO is proposed to obtain nanoparticle aggregation of selfassembly nanoplates. The disorder coupled to the oxygen vacancies of [TiO 5 ]-[TiO 6 ] in complex clusters in the CTO 1 powder and twists in bonding between the [TiO 6 ]-[TiO 6 ] complex clusters in the CTO 2 powder were mainly responsible for photoluminescent (PL) emission.
2018
Calcium titanate (CaTiO3) is used as a thermally sensitive resistance element in one of the important materials of ferroelectric ceramics due to its negative temperature coefficient. It has other wide range of applications as components of capacitors, RAM, SYNROC (used for immobilization of nuclear waste). In the present work, we report the preparation of nano-sized calcium titanate (CaTiO3) by using solid state mechano-chemical solventless method, which fulfills the requirements of green chemistry. The starting materials used for this synthesis were CaCO3 and TiO2. They were mixed in equimolar ratio (1:1). The mechanical grinding of the reactant mixture was carried in high energy micronizer ball mill by varying the milling time for 0.5h, 1h, 2h, 4h and 5h resulting the peak intensity decrease for the mixture of CaCO3 and TiO2 accompanied by decrease in particle size. The as-synthesized products were characterized by X-ray diffraction (XRD) at different stages of milling. After mill...