Manipulating mechanical properties of CaTiO3:Eu3+ flexible fiber membrane by fiber design

Flexible inorganic functional materials have received extensive attention in recent years due to their unique properties and potential application prospects. Among various flexible materials, ceramic fiber membranes have great application prospects due to their functional original structure. Unlike other materials, such as one-dimensional flexible ice, two-dimensional BaTiO₃, and three-dimensional α-Ag₂S, ceramic fiber membranes are high-performance materials with a functional unit structure. In the field of electrospinning, electrospinning technology can effectively control the microstructure of ceramic fibers, allowing for multileveled structure design, such as ordered electrospinning technology and disordered electrospinning technology, which can effectively control the functional primitive structure. However, the mechanical behavior of these structures is still poorly understood. In this groundbreaking study, we investigated the functional original structure of CaTiO₃:Eu³⁺ electrospinning fiber membranes from the bottom-up and explored the effect of grain diameter ratio on mechanical behavior and studied the effect of Eu³⁺ ions on the luminescent properties of CaTiO₃ functional fiber membranes. By controlling the electrospinning parameters and avoiding inherent mechanical property differences between the microcrystals, we realized the stress concentration design from the perspective of functional element structure. Our results show that the stress concentration design at the bottom of the multileveled structure significantly affects the overall mechanical behavior. This work proposes a new method to control the mechanical properties of inorganic functional ceramic fiber membranes through functional element structure design and provides the first bottom-ordered regulation method, offering a new dimension for future research in this field.     

Controllable synthesis of bifunctional material Ca2Ti2O6:Eu3+ and its comparative study on luminescence and photocatalytic properties with CaTiO3:Eu3+

Pure pyrochlore Ca₂Ti₂O₆, perovskite CaTiO₃, and their mixed crystalline phases with different proportions were controllably synthesized via a solvothermal method, followed by a subsequent calcination process. RIR (reference intensity ratio) data of Ca₂Ti₂O₆ were first obtained by X-ray diffraction (XRD), which can be used to quantitatively analyze the phase composition. When Eu³⁺ is doped into these calcium titanium oxides, they can be used as luminescent and photocatalytic materials. The structure, luminescence, and photocatalytic properties of pure pyrochlore Ca₂Ti₂O₆:Eu³⁺ and perovskite CaTiO₃:Eu³⁺ were comparatively studied in detail. The relative intensities of the excitation peaks and the emission peaks in Ca₂Ti₂O₆:Eu³⁺ and CaTiO₃:Eu³⁺ are different, which is attributed to the different symmetries of Eu³⁺ inhabiting the two kinds of lattices. In addition, although the luminescence intensity of CaTiO₃:3%Eu³⁺ is higher than that of Ca₂Ti₂O₆:3%Eu³⁺ under excitation at 394 nm, the luminescence intensity of Ca₂Ti₂O₆:3%Eu³⁺ is superior to that of CaTiO₃:3%Eu³⁺ under excitation at 464 nm and 533 nm. Photocatalytic experiments show that Ca₂Ti₂O₆:3%Eu³⁺ has better photocatalytic performance than CaTiO₃:3%Eu³⁺, which is mainly due to its smaller crystallite size, higher specific surface area and pyrochlore structure. In addition, biphase (Ca₂Ti₂O₆–CaTiO₃):3%Eu³⁺ has the best photocatalytic activity compared with the single phase Ca₂Ti₂O₆:3%Eu³⁺ and CaTiO₃:3%Eu³⁺, owing to the presence of heterojunctions that significantly reduced the band gap. It is anticipated that the discovery of this bifunctional Ca₂Ti₂O₆:Eu³⁺ would expand the application of rare earth-doped calcium titanium oxide materials.     

Synthesis and photocatalytic activity of Na+ co-doped CaTiO3:Eu3+ photocatalysts for methylene blue degradation

The Na⁺ co-doped CaTiO₃:Eu³⁺ powders were produced through the solution combustion method. The phase structure and optical properties of the synthesized samples were adequately characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra, ultraviolet–visible (UV–vis) diffuse reflection spectroscopy and scanning electron microscopy (SEM). The XRD patterns revealed that a low level of Eu³⁺ doping could not cause lattice distortion of CaTiO₃. Photoluminescence (PL) displayed the CaTiO₃:0.5% Eu³⁺ sample synthesized at 900 °C has the weakest PL emission and the low electrons and holes recombination rate. The morphology of the sample was small nanoscale spherical particles. The UV–vis diffuse reflection spectra proved that doping Na⁺ and Eu³⁺ enlarged the absorption region and reduced band energy of pure CaTiO₃. The photocatalytic properties of Na⁺ co-doped CaTiO₃:Eu³⁺ samples were investigated via degrading methylene blue (MB) under ultraviolet light irradiation. The CaTiO₃:0.5% Eu³⁺, 0.5% Na⁺ sample, by contrast, exhibited the greatest photocatalytic property and the degradation rate was as high as 96.62%, which makes it a promising multi-functional material (photocatalytic material and red phosphor) for decreasing organic pollution in water.     

Synthesis of CaTiO3 and CaTiO3/TiO2 nanoparticulate compounds through Ca2+/TiO2 colloidal sols: Structural and photocatalytic characterization

CaTiO₃ and CaTiO₃/TiO₂ nanocompounds have been synthesized through a colloidal sol-gel route using Ca²⁺/TiO₂ nanoparticulate sols. The peptization time was determined so that as higher is the Ca²⁺ concentration, shorter is the peptization time. The obtained cryogels from the respective sols were calcined at different temperatures (300–900 °C) and the structural and morphological changes were characterized mainly by X-ray diffraction and transmission electron microscopy. In all cases, the formation of the CaTiO₃ phase was observed after calcination at temperatures as low as 500 °C. Mesoporous cryogels with nanoparticles with sizes below 50 nm were obtained and their photocatalytic activity changes as a function of the calcination temperature and the applied wavelength were determined. Quantum yield values revealed that either CaTiO₃ or the CaTiO₃/TiO₂ (0.4 M ratio) compound can be chosen as the most efficient photocatalyst at higher calcination temperatures and longer wavelengths, while TiO₂ is more effective at low calcination temperatures and shorter wavelengths.     

Improvement of the luminescence properties of CaTiO3:Pr obtained by modified solid-state reaction

Using tetra-n-butyl titanate and nitrates as starting materials, the red persistent phosphor CaTiO₃:Pr has been successfully synthesized by modified solid-state reaction. In order to improve the luminescent properties of the phosphor, boric acid as flux regent and aluminum ion as charge compensator were added in, and the influences of partially replacing Ca²⁺ in CaTiO₃ with Zn²⁺ or Mg²⁺ on the long persistent properties were studied. The results of luminescence spectrometer (PL), X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that a certain quantity of boric acid, Al³⁺, Mg²⁺ or Zn²⁺ was effective in improving the photoluminescence intensity of CaTiO₃:Pr phosphor particles, and the optimum molar ratios of Al³⁺ and boric acid to Ca²⁺ were about 0.1% and 30%, respectively. The photoluminescence brightness and decay curves showed that the sample of Ca_0.8Zn_0.2TiO₃:Pr with 0.l% Al³⁺ and 30% H₃BO₃ obtained at the sintering temperature of 900 °C exhibited the optimal luminescent properties.     

Wavelength conversion using rare earth doped oxides in polyolefin based nanocomposite films

Nanocomposites are a new class of polymeric materials which include organic or inorganic nano‐phase materials. These nanocomposite films can show interesting properties which have many applications for wavelength conversion and energy saving. In this paper, we present polyolefin based nanocomposite films prepared using wavelength‐converting red ‘phosphors’ such as Y₂O₃: Eu³⁺ and LiAl₅O₈:Fe³⁺ and blue ‘phosphor’ CaMgSi₂O₆: Eu²⁺. The durability of the polymer chain is unaffected by incorporation of inorganic nanoparticles as there is no direct interaction between them. The addition of surfactant in the nanocomposite film helps to improve the dispersion ability of the nanoparticles and increase the flexibility of the polymer film. Wavelength‐converting ‘nanophosphors’ incorporated in a polymer matrix help to increase the tensile strength of the film. The films show excellent wavelength conversion ability of UV light into the visible and near IR range. These nanocomposite films have great application in energy saving devices. Copyright © 2012 Society of Chemical Industry     

Yb3+/Er3+ co-doped Gd2Te4O11 nanosheets with intrinsic polarity: One-step hydrothermal synthesis and upconverted optical temperature measuring ability

The digadolinium tellurite phosphors of Gd₂Te₄O₁₁(GTO):Yb³⁺/Er³⁺ have been successfully synthesized as upconversion luminescence (UCL) materials via one-step hydrothermal method. The crystal structure, morphology, and upconversion luminescence property were systematically characterize by XRD, SEM, and spectroscopy techniques. The Rietveld refinements of crystal structure were carried out on the XRD patterns and the feature of crystal structure was analyzed. Under the 980 nm NIR excitation, these materials showed very bright upconverted emissions. The concentrations of Yb³⁺ and Er³⁺ were optimized and the strongest upconverted emissions were achieved in the GTO:15%Yb³⁺/1%Er³⁺. The possible energy transfer mechanism of UCL was proposed based upon the analysis of power-dependent UCL and fluorescence kinetics. Furthermore, the fluorescence intensity ratio (FIR) derive from the two thermally coupled energy levels (²H_11/2 and ⁴S_3/2) of Er³⁺ was employed as indicator for temperature measurement. The maximum absolute sensitivity can be achieved to be 7.34 × 10^?3 K^?1 at 501 K. This material exhibited good reliability and repeatability in optical temperature measurement, which could be a novel promising candidate for noncontact temperature sensors.     

Phosphor SrZrO3:Sm3+ with fluorescence modulation and photochromic characteristics for erasable optical storage

At present, for inorganic photochromic materials, the single function limits their application level in the field of optical storage and anti-counterfeiting. Generally, the reversible modulation of photoluminescence is achieved through a photochromic process, thereby improving the ability of the photochromic material to store information. Here, we designed a Sm³⁺ doped perovskite oxide (SrZrO₃:Sm³⁺) inorganic photochromic material. Combined with its red photoluminescence and photochromic properties, it can realize dual information storage and recognition functions. The fluorescence regulation function is realized by the doping of Sm³⁺, which is conducive to the application in the direction of optical switch. The mechanism of photoluminescence and photochromism was studied. Finally, a flexible film with SrZrO₃:Sm³⁺ material was fabricated to demonstrate rewritable optical recording and storage and reading of dual optical information.     

Crystal symmetry and magnetism in Ti substituted Bi0.8Ba0.2FeO3 ceramic

The effect of Ti⁴⁺ substitution on the crystal structure and magnetic properties of the Bi_0.8Ba_0.2FeO₃ ceramic nanoparticles was investigated. Bi_0.8Ba_0.2Fe_1−xTi_xO₃ (x=0, 0.05, 0.10, 0.15 and 0.20) ceramics have been prepared by tartaric acid modified sol-gel method. Rietveld refinement of the XRD profile pattern of Bi_0.8Ba_0.2FeO₃ ceramic revealed the formation of pseudo-cubic (Pm3m) phase and confirms structural distortion on incorporation of Ti⁴⁺ ions, which consequently transform pseudo-cubic (Pm3m) structure to tetragonal (P4mm) structure. The saturation magnetization increases appreciably on Ti⁴⁺ ions substitution in Bi_0.8Ba_0.2FeO₃ and is found to be 0.57 emu/g for Bi_0.8Ba_0.2Fe_0.95Ti_0.05O₃ ceramic. The increase in the magnetization by the substitution of non-magnetic Ti⁴⁺ ions has been ascribed to crystal structure modification made by the Ti⁴⁺ ions. However, a sudden decrease in the magnetization has been observed for Bi_0.8Ba_0.2Fe_0.8Ti_0.2O₃ ceramic nanoparticles. The prominent Ti (3d) – O (2p) hybridization would stabilize the ferroelectric distortion and consequently reduce the magnetization. Scanning Electron Microscope (SEM) image of Bi_0.8Ba_0.2Fe_0.8Ti_0.2O₃ ceramic sample revealed the formation of dense microstructure with uniform grains size.     

Influence of manganese substitution into the A-site of perovskite type Ca1−xMnxTiO3 ceramic

Ca_1−xMn_xTiO₃ (x = 0–1.0) perovskite ceramics were prepared by conventional solid state reaction. XRD was used to confirm the microcrystalline nature of the Ca_1−xMn_xTiO₃ crystals. For the x = 0 composition, the XRD patterns were those of a single orthorhombic perovskite while for x = 0.2–0.8, the XRD spectra were those of two orthorhombic perovskite phases: CaTiO₃ and MnTiO₃. For x = 1, XRD pattern was that of the MnTiO₃ phase only. The morphology and particle size of the grains of the different composition were observed using SEM. The size of the particles increased from 0.2 μm to 2–3 μm as x increased from 0 to 0.6. The room temperature dielectric constant at the frequency of 110 kHz for the x = 0.2 and x = 1.0 ceramics were ∼3.41 × 10⁴ and ∼4.99 × 10³, respectively. The ESR linewidth of samples increased with increasing manganese content due to the formation of magnetic cluster. Our ESR studies indicate that the manganese ions are in the Mn⁴⁺ state.     

Ca-containing additives in PTC-BaTiO3 ceramics: effects on the microstructural evolution

Two series of Ca²⁺-modified BaTiO₃ ceramics have been prepared of the gross composition La_0.002Ba_0.998–xCa_xTi_1.01O_3.02 (0<x<0.24). In the first series, CaCO₃, BaCO₃, TiO₂ and La₂(C₂O₄)₃·9H₂O were used as starting materials. The calcination of mixtures with x⩽0.08 resulted in the formation of the corresponding titanate solid solution (Ba_1–xCa_x)TiO₃. With values of x higher than 0.08, CaTiO₃ was observed as an additional phase. In the second series, a La_0.002Ba_0.998TiO₃ starting powder was hydrothermally recrystallized in Ca(NO₃)₂ solution. High resolution imaging and analytical methods revealed that the BaTiO₃ grains are surrounded by small CaTiO₃ crystallites, which influence the evolution of the microstructure of the ceramic in the sintering process strongly by acting as seeds during the recrystallization of the matrix material. Thus, it was possible to optimize the microstructural and electrical characteristics of a ceramic of the second series by adding only 4 mol% Ca, while in case of the first series 16 mol% Ca are necessary.     

Replication Route Synthesis of Mesoporous Titanium–Cobalt Oxides and Their Photocatalytic Activity in the Degradation of Methyl Orange

Mesoporous Ti–Co oxides were synthesized via a replication route, using a 3-D wormlike mesoporous silica as template and tetra-tert-butyl orthotitanate (TBOT) and Co(NO₃)₂ as source materials. The prepared materials were characterized by X-ray diffraction (XRD), N₂-physisorption, TEM, EDS, and UV/Vis-DRS and found to possess a spherical morphology and a 3-D wormhole-like mesoporous structure, with the average pore size between 4.5 and 16.0 nm. The pore walls consisted mainly of a cobalt-incorporated anatase phase. The Co³⁺ ions were generated in the replicated mesoporous Co–Ti oxides, via the transfer of electrons from Co²⁺ to Ti⁴⁺ ions. The formation of cobalt-incorporated anatase phase and Co³⁺ ions were both favored by larger Co/Ti atomic ratios and by relatively low calcination temperatures. The specific surface area decreased and the mesopore sizes increased, with increasing Co/Ti atomic ratio or calcination temperature. The average crystal size of the anatase phase decreased with increasing Co/Ti atomic ratio but increased with increasing calcination temperature. The photocatalytic activity of the replicated mesoporous Co–Ti oxides in the degradation of methyl orange dye was investigated. It was observed that the photocatalytic activity increased with increasing Co/Ti atomic ratio and exhibited a maximum with increasing calcination temperature. With the exception of those prepared at too high calcination temperatures, the replicated mesoporous Co–Ti oxides were much more active than the pure titania. It is concluded that, in addition to a higher diffusion, the cobalt-containing anatase, as the active phase, and the Co³⁺ ions, as the active sites, are responsible for the high photocatalytic activity of the replicated mesoporous Co–Ti oxide.     

Strong Red Emissions in Pr3+‐Doped (K0.5Na0.5)NbO3–CaTiO3 Diphase Ceramics

The photoluminescence and temperature sensing properties based on down‐shifting emission of Pr³⁺‐doped (K_0.5Na_0.5)NbO₃–yCaTiO₃ (KNN: yCT) diphasic materials were systematically investigated. Under 447‐nm excitation, Pr³⁺‐doped KNN: yCT samples exhibited significantly enhanced red emission at 603 nm assigned to ¹D₂→³H₄ transitions of Pr³⁺ ions. The red emission intensities reached the optimum value with y = 0.05 near the polymorphic phase transition region. The origin of the enhanced red emission is mainly ascribed to the doping‐induced lattice symmetry change. The energy level transitions from the typical f–f transitions to the valence‐to‐conduction transitions were observed as CaTiO₃ concentration increases above a critical concentration of y = 0.05. Furthermore, the sample with y = 0.05 also possessed excellent temperature response properties in a wide temperature range 300–473 K and the maximum sensing sensitivity was 0.016 K^?1. The Pr³⁺‐doped (K_0.5Na_0.5)NbO₃–yCaTiO₃ red emission materials with admirable intrinsic piezoelectric properties may have important technological promise in novel multifunctional devices.     

A Sucrose‐Mediated Sol–Gel Technique for the Synthesis of MgO–Y2O3 Nanocomposites

A sucrose‐mediated aqueous sol–gel procedure was developed to synthesize MgO–Y₂O₃ nanocomposite ceramics for potential optical applications. The synthesis involves the generation of a precursor foam containing Mg²⁺ and Y³⁺ cations via the chemical and thermal degradation of sucrose molecules in aqueous solution. Subsequent calcination and crushing of the foam gave MgO–Y₂O₃ nanocomposites in the form of thin mesoporous flake‐like powder particles with uniform composition and surface areas of 27–85 m² g ^{? 1}, depending on calcination conditions. The flakes exhibited a homogeneous microstructure comprising intimately mixed nanoscale grains of the cubic MgO and Y₂O₃ phases. This microstructure was resistant to grain coarsening with average grain sizes of less than 100 nm for calcination temperatures of up to 1200°C. The results indicate that the sucrose‐mediated sol–gel process is a simple effective method for making nanoscale mixed oxides.     

Cathodoluminescence mapping and thermoluminescence of Pr3+ doped in a CaTiO3/CaGa2O4 composite phosphor

In order to probe the properties of the one pot prepared composite phosphor of CaTiO₃ and CaGa₂O₄, cathodoluminescence mapping, thermoluminescence and lifetime measurements were carried out. The structural study showed both irregular and rod shaped particles, which match with CaTiO₃ and CaGa₂O₄, respectively, according the x-ray maps. The cathodoluminescence spectrum showed emission peaks from ³P₀→³H₄ and ¹D₂→³H₄ transitions, with the earlier transition completely absent in CaTiO₃:Pr emission at room temperature. The diffuse reflectance spectrum showed a shifted band of the inter-valence charge transfer from 360 nm to 388 nm, which is not observable for CaTiO₃:Pr³⁺and CaGa₂O₄:Pr³⁺. Additionally, the phosphorescence decay curve was recorded and the presence of electron trapping centers was confirmed using thermoluminescence spectroscopy.     

Fabrication of CaAl12O19–CaTiO3 composites and their potential usage for TiAl alloy smelting

CaAl₁₂O₁₉–CaTiO₃ (CA₆–CT) materials are fabricated using a solid sintering method to investigate the effects of TiO₂ content on the phase composition, properties, and microstructure of the materials. With increasing TiO₂ content, the preferential replacement of Al³⁺ by Ti⁴⁺ in the CA₆ crystal increases the concentration of vacancy defects, thereby promoting ion diffusion and mass transfer, which improves the sintering reaction activity. However, as more TiO₂ is added, the CaTiO₃ phase formed increases the thermal conductivity and mean expansion coefficient of the material at high temperatures, which degrades its thermal shock stability. The CA₆–CT refractory showed good corrosion resistance to the Ti₆Al₄V melt. Except for a slight penetration of iron element, no obvious corrosion occurred at the reaction interface.     

Enhanced photoluminescence of SiO2 coated CaTiO3:Dy3+,Li+ nanophosphors for white light emitting diodes

Systematic analysis of SiO₂@CaTiO₃:Dy³⁺_{(3 mol %)}:Li⁺_{(0.25–1 mol %)} core shell nanoparticles (C–S NPs) were carried out. CaTiO₃:Dy³⁺ _{(3 mol %)}, Li⁺ _{(0.25–1 mol %)} NPs were prepared using low temperature solution combustion method. C–S structured samples were synthesized using SiO₂ in equal weight quantities. All samples were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) in order to study and compare its structural properties. Photoluminescence (PL) properties of uncoated and SiO₂ coated samples were studied in detail and optimum luminescence behaviour was investigated. Higher luminescence intensity is observed for codoped CaTiO₃:Dy³⁺_{(3 mol %)}:Li⁺_{(0.5 mol %)} sample. Further enhancement was observed in SiO₂@CaTiO₃:Dy³⁺:Li⁺ structured nanoparticles. Emission spectra of SiO₂@CaTiO₃:Dy³⁺_{(3 mol %)}:Li ⁺_{(0.25–1.0 mol %)} C–S nanophosphors exhibit white emission dominated by ⁴F_9/2 → ⁶H_13/2 (570 nm) transition of Dy³⁺ ions under. All the results suggested that the present material provides a platform for fabricating new functional materials which can be applied in the field of wLEDs and solid state display applications.     

The effects of Mg2+ and Ba2+ dopants on the microstructure and magnetic properties of doubly-doped LaFeO3 perovskite catalytic nanocrystals

Using citrate sol-gel method, we prepared La_0.85Mg_0.15-xBa_xFeO₃(x?=?0.02–0.12) samples. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) were used to investigate whether the microstructure, composition, and magnetic properties of LaFeO₃ were affected by the following parameters: calcination temperature, calcination time, and the doping concentration of Mg²⁺ ion and Ba²⁺ ions. The XRD spectra showed that a trace of impurity phase (MgFe₂O₄) is visible when the content of Mg²⁺ ions was higher; however, there was no change in the orthorhombic perovskite structure of LaFeO₃ even at higher doping concentrations. The space group was still Pnma. No other phase was generated in the sample subjected to low-temperature calcination. Furthermore, FT-IR spectra confirmed the presence of some functional groups in the sample. Then, SEM showed that the size distribution of the particles is uniform in the sample, and the grain boundary is also clear. Finally, VSM measurements proved that the significant changes were produced in the magnetic properties of samples when they were doubly doped with Mg²⁺ and Ba²⁺ ions. Moreover, calcination temperature has a great influence on the magnetic properties of the samples.     

Effects of CaTiO3 addition on the densification and microwave dielectric properties of BiSbO4 ceramics

In this study, the effects of CaTiO₃ addition on the sintering characteristics and microwave dielectric properties of BiSbO₄ were investigated. Pure BiSbO₄ achieved a sintered density of 8.46 g/cm³ at 1100 °C. The value of sintered density decreased with increasing CaTiO₃, and sintering at a temperature higher than 1100 °C led to a large weight loss (>2 wt%) caused by the volatile nature of the compound. Samples either sintered above 1100 °C or with a CaTiO₃ content exceeding 3 wt% showed poor densification. SEM micrographs revealed microstructures with bimodal grain size distribution. The size of the smaller grains ranged from 0.5 to 1.2 μm and that of the larger grains between 3 and 7 μm. The microwave dielectric properties of the (1−x) BiSbO_4−x CaTiO₃ ceramics are dependent both on the x value and on the sintering temperature. The 99.0 wt% BiSbO₄–1.0 wt% CaTiO₃ ceramic sintered at 1100 °C reported overall microwave dielectric properties that can be summarized as ε_r≈21.8, Q×f≈61,150 GHz, and τ_f≈−40.1 ppm/°C, all superior to those of the BiSbO₄ ceramics sintered with other additives.     

Room-temperature synthesis and luminescence properties of Eu3+/Tb3+-doped La(1,3,5-BTC)(H2O)6

The facile, rapid, and effective synthesis of coordination polymer La(1,3,5-BTC)(H₂O)₆ has been realized via direct precipitation at room temperature. It is found that the crystal structure is of monoclinic, space group Cc. The doped Eu³⁺ or Tb³⁺ ions samples have the same phase and exhibit red and green emissions under UV light excitation, respectively.