Microwave-assisted Solid-state Reaction Research Articles

Brighten strontium aluminate long-persistence materials via optimizing defect energy level distribution

Afterglow brightness of inorganic persistent luminescent (PersL) materials upon ceasing light excitation represents an important parameter for various glow-in-the-dark applications. Although the emission wavelength of PersL materials is developed to cover over the whole spectral range from ultraviolet to near infrared light, and light emission is sufficiently long-lasting with a fractional number of rare-earth doped PersL materials commercially available, PersL materials with high initial afterglow brightness at room-temperature condition remain rarely reported. Employing trap-controlled temperature dependency of persistent luminescence mechanism, defect energy level distribution, and microwave-assisted solid-state reaction, here a highly bright green-emitting strontium aluminate phosphor is reported. Higher initial afterglow brightness (a photometric luminance of 99.8 cd/m2, enhanced 1.7 times than that of the commercial one) is achieved due to the massive aggregation of charge carriers at shallow-trap energy levels. The relation between initial afterglow brightness and trap energy level distribution is investigated. The glowing-in-the-dark composite panel composed of Sr4Al14O25:Eu2+, Dy3+ and Polydimethylsiloxane can light up the safety sign and the map of fire evacuation route. These findings may provide a major step forward to developing high-brightness PersL materials and are expected to further benefit a wide range of PersL material systems for practical glow-in-the-dark applications.

Highly thermally stable and tunable luminescence in microwave-assisted synthesized Na3Ca4(TeO3)(PO4)3:Dy3+,Eu3+ for ultra-high color rendering white light-emitting diodes

For the commercial application of the Eu3+-activated red phosphors in NUV (∼365 nm)-excited phosphor-converted white light-emitting diodes (pc-wLED), the serious obstacle is that they cannot be efficiently excited by ∼365 nm. To deal with the trouble, we employed the energy transfer between Dy3+ sensitizer excited by ∼365 nm and Eu3+ activator, and a color-tunable phosphor Na3Ca4(TeO3)(PO4)3 (NCTP):Dy3+,Eu3+ was prepared via a fast microwave-assisted solid-state reaction. Under the 363 nm excitation, the luminous color is adjusted to red owing to the Dy3+→Eu3+ energy transfer with high efficiency, which is controlled by the dipole–dipole interaction. Moreover, the introduction of Dy3+ sensitizers in NCTP:Eu3+ enhances the structural rigidity, resulting in high luminescence thermostability. The luminescent intensity at 423 K remains 90.7% of that at 298 K. Notably, the 365 nm chip-excited pc-wLED device assembled with NCTP:0.09Dy3+,0.4Eu3+, commercial blue BaMgAl10O17:Eu2+, and green (Ba,Sr)2SiO4:Eu2+ phosphors emits warm-white light (0.3657,0.3725) with the ultra-high Ra (94.9) and low CCT (4399 K). This work offers a feasible Dy3+→Eu3+ energy transfer path for the development of efficient Eu3+-activated red phosphor towards ultra-high color rendering pc-wLED.

Microwave-assisted synthesis and thermally stable red fluorescence of Ba3(ZnB5O10)PO4:Eu3+ solid solution

Red-emitting materials play a significant role in phosphor-converted white light-emitting diodes (WLEDs), since it can effectively improve the chromatic properties of the solid-state lighting source. In this work, we employ a microwave-assisted solid-state reaction to prepare a red-emitting Ba3(ZnB5O10)PO4:Eu3+ (BZBP:Eu3+) phosphor. Eu3+ activators are solidly dissolved into the BZBP host via occupying the Ba2+ positions. Excited by 395 ​nm, the title phosphor yields red emission with high color purity, which is dominated by the electric dipole transition of Eu3+. Base on the investigation of photoluminescence in response to the Eu3+ content, the content quenching mechanism is understood. Besides, the study on the luminescence temperature quenching reveals the good thermal stability and resistance to chromaticity shifting. The results indicate that the studied phosphor would be an alternative red-emitting material for WLEDs.

Fine Control of Multiferroic Features of Nanoscale BiFeO3 Powders Synthesized by Microwave-Assisted Solid-State Reaction

Fine Control of Multiferroic Features of Nanoscale BiFeO3 Powders Synthesized by Microwave-Assisted Solid-State Reaction

Consequence of microwave synthesis of Li3.6Si0.6V0.4O4 for electrode application using LiNO3, V2O3, and silica obtained from rice husk ash

Lithium silicon vanadium oxide (Li3.6Si0.6V0.4O4) was synthesized by microwave-assisted solid-state reaction with grinding times of 1, 2, 4, and 6 h and applied as electrode material using silica from rice husk ash and crushed V2O3 and LiNO3 at 600 watts. This research found that the influence of microwave heating affects the generation Li3.6Si0.6V0.4O4 and the microwave wattage can remove excess nitrate in the system. As a result of different wattages, different products are produced, with 600 watts providing good crystallinity. Fourier transform infrared (FTIR) and Raman spectroscopy were used to measure bond vibrations within the molecules to confirm the presence of (Si − O), (Li − O), (Si − O−Si), and (V–O), while X-ray diffraction was conducted to confirm the phase of Li3.6Si0.6V0.4O4 as an orthorhombic lattice. X-ray absorption near edge structure (XANES) identified oxidation states of vanadium in the product as V4+ and V5+ while scanning electron microscopy (SEM) images showed the morphology to be highly porous with compact crystallinity. The product has high specific capacitance with a grinding time of 6 h and heated at 600 W at 289–461 F.g−1 using a scanning rate of 5 mV.s−1.

Modulating trap distribution of persistent phosphors upon simple microwave-assisted solid-state reactions

Trap distribution of Li 2 ZnGeO 4 :Mn 2+ is modulated into shallow trap range upon a simple microwave-assisted solid-state approach. Trap re-shuffling is identified towards both lower energy level (shallow traps) and higher energy levels (deep traps) upon light stimulation. This work provides a fundamental advance in revealing re-trapping behavior and offers a guidance for the modulation of trap distribution using a facile approach. • Trap distribution of Li 2 ZnGeO 4 :Mn 2+ is modulated upon a facile MASS method. • Li 2 ZnGeO 4 :Mn 2+ made by MASS shows excellent low-temperature glow-in-the-dark property. • Trap re-shuffling is found towards both lower energy level (shallow traps) and higher energy levels (deep traps). The trap distribution due to defects in persistent luminescent materials plays a significant role in their scope of applications. However, it is a big challenge to manipulate or modulate this trap distribution. In this work, the trap distribution of green emitting persistent phosphor Li 2 ZnGeO 4 :Mn 2+ is modulated upon a facile microwave-assisted solid-state reaction. A series of systematic temperature dependent trapping, de-trapping and re-trapping measurements are designed to shed light on trap information. An appealing feature of the present synthesis approach is that the trap distribution is modulated towards shallow traps, which offers great promise in low-temperature glow-in-the-dark applications. More importantly, trap re-shuffling can be achieved towards two directions, both lower energy level (shallow traps) and higher energy levels (deep traps) upon light stimulation. These findings indicate there are optically active trapping defects with photo-stimulated re-trapping behavior in this persistent phosphor. This work not only provides a fundamental advance in revealing re-trapping behavior, but also offers a guidance for the modulation of trap distribution in persistent phosphors upon a facile approach.

Dielectric and mechanical properties of CaCu3Ti3.925(Nb0.5Al0.5)0.075O12 & Al reinforced epoxy-composites (0–3) for embedded capacitor applications

CaCu3Ti3.925(Nb0.5Al0.5)0.075O12 [CCTNAO] ceramics were synthesized by microwave assisted solid state reaction technique. CCTNAO ceramics possessed room temperature (RT) dielectric constant (εr) ∼ 24,173 with tanδ ∼0.149 at 1 kHz frequency. Commercially available epoxy-resin, hardener, Al-powder along with CCTNAO powder were used to prepare epoxy based 0–3 composites. Maximum εr ∼33.37 with tanδ ∼0.107 at RT were obtained for 40 vol% CCTNAO loading in epoxy. For x = 0.2 in (1-x)[0.8 Epoxy-0.2 CCTNAO]-x Al Epoxy composites, highest εr ∼77.6 with tanδ ∼ 0.15 at 1 kHz frequency were observed. Increase in εr with the increase of Al filler content in composites is attributed to interfacial polarization and cluster formations. Different theoretical models were discussed to explain the dielectric properties of synthesized composites. Experimentally measured values of εeff were in close agreement with EMT model (n = 0.13) and Yamada Model (η = 7). An empirical proposed power law εeff = εm(1+x)n, with n ∼ 10 had a considerable agreement with the experimental results. Vickers hardness test study was carried out to ascertain the mechanical properties of the synthesized composites.

Microwave-Assisted Synthesized Gadolinium Doped Barium Strontium Titanate Nanostructures: Structural and Optical Properties for DSSC Applications

Gadolinium (Gd) doped barium strontium titanate (BST) was prepared using the microwave-assisted solid-state reaction method for dye sensitized solar cell (DSSC) applications. The optical properties and the structural analysis of the prepared samples reveal the optical band gap and the morphology. The XRD pattern of the annealed samples confirms the polycrystalline nature with the cubic crystal structure. When the dopant is added, the bandgap increases slightly from 3.11 to 3.27 eV. The J-V characteristics of DSSCs prepared with pure and doped BST were investigated. The efficiency of the DSSCs remained constant and there is a slight increase in the Jsc for highly doped samples under 1-sun illumination. Gadolinium doped barium strontium titanate shows variation in the J-V characteristics and could be a potential candidate for the solar photovoltaic applications.

Structural and electrical properties of donor-doped NBT system synthesized by microwave-assisted solid-state reaction route

Structural and electrical properties of donor-doped NBT system synthesized by microwave-assisted solid-state reaction route

Cerium substituted BCZT-ceramics synthesized through microwave assisted solid state reaction method

Cerium substituted BCZT-ceramics synthesized through microwave assisted solid state reaction method

Microstructure and electrical properties of microwave sintered Nb-doped NBT ceramics

Nb5+-doped sodium bismuth titanate (NBT) ceramics ((Na0.5Bi0.5)1-x/2Ti1-xNbxO3 where x = 0, 0.005, 0.01 and 0.015) were obtained by microwave assisted solid state reaction route and microwave sintered at 1000 ?C. Microwave processing technique was chosen for the sintering as it is a powerfulmethod which enables sintering in a short time with fast heating rate avoiding grain growth. The influence of Nb5+-doping on microstructure and electrical properties of the NBT ceramics was studied. X-ray diffraction analyses revealed that solubility limit of niobium in NBT lattice is up to 1mol%, as with further increase in niobium concentration pyrochlore appeared. Microstructure of all the ceramics was investigated by field emission scanning electron microscopy and it was observed that the average grain size decreased with doping. Temperature dependent dielectric study was carried out for all the ceramics at different frequency. All ceramics show diffusive dielectric behaviour around Tm and introduction of Nb even increases compositional fluctuation compared to the parent NBT. Nb-doping shifts the Tm toward lower temperature. Leakage current study showed that for whole range of electric field ohmic type conduction mechanism is dominant for all the ceramics. Room temperature polarization-electric field (P-E) hysteresis loop confirms the ferroelectric behaviour of all the ceramics.

Microwave-sintering preparation, phase evolution and chemical stability of Na1-2xSrxZr2(PO4)3 ceramics for immobilizing simulated radionuclides

Sodium zirconium phosphate (NaZr2(PO4)3, NZP) family ceramics were considered as a potential host matrix for the immobilization of nuclear waste. In this study, the dense Sr-incorporated NZP ceramics with the formula of Na1-2xSrxZr2(PO4)3 (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4, and 0.5) were fabricated by microwave-assisted solid-state reaction method. The phase evolution, densification behavior and chemical stability of the as-prepared samples were systematically investigated by XRD, Rietveld refinement, Raman, SEM-EDS and PCT method. The results demonstrated that Na in the NZP lattice could be substituted by the simulated fission product Sr, and the phase composition gradually changed from NZP to Sr0.5Zr2(PO4)3 (SrZP) with the increase of Sr content. The samples presented high densification and uniform elements distribution after microwave sintering at 1100 °C for 2 h. Moreover, the as-prepared samples exhibited the superior chemical stability. The normalized elemental leaching rate of Sr, Na, P, and Zr were 10−3, 10−4, 10−3, and <10−7 g⋅m−2⋅d−1, respectively.

Evidence of magneto-electric coupling and electrical study of CFO modified BNT/BT composites

(1-x)(0.93Bi0.5Na0.5TiO3/0.07BaTiO3)-xCoFe2O4 ((1-x)BNT/BT-xCFO, where x = 0.1, 0.2, 0.3, 0.4 and 0.5) composite samples were synthesized by microwave assisted solid state reaction route and sintered at 1050 °C. X-ray diffraction study showed the presence of ferroelectric/ferromagnetic (FE/FM) phases without any peak of secondary phase. This was further confirmed by SEM study showing the presence of both FE/FM grains distinctly. Frequency dependent dielectric study showed maximum dielectric constant ("r) for the composite sample with x = 0.4. Polarization versus electric field (P-E) loop study revealed that maximum remnant polarization (2Pr = 1.75 μC/cm2) was found also for the 0.6BNT/BT-0.4CFO sample. Remnant magnetization (Mr) of the composite sample with x = 0.4 was found to be ∼7.81 emu/g. Magnetodielectric (MD) study of the 0.6BNT/BT-0.4CFO composite sample showed decrease in "r with the application of magnetic field and a MD effect of ∼2.4% (at 10 kHz) was found. Low leakage current value (∼10−4 A) was obtained in the 0.6BNT/BT- 0.4CFO composite sample. Change in piezoresponse force microscopy contrast after poling indicated on the changes in polarization of the ferroelectric domains. Reduction in Mr, observed in magnetic force microscopy contrast gave a clear evidence of presence of electric field induced magneto-electric (ME) coupling in the 0.6BNT/BT-0.4CFO composite sample.

Microstructural, dielectric and ferroelectric properties of Sr0.8Bi2.15Ta2O9 ceramics synthesized by microwave processing technique

ABSTRACTSr0.8Bi2.15Ta2O9 (SBT) ceramics were synthesized by microwave-assisted solid-state reaction route. SBT ceramics were sintered at three different temperatures namely 1050°C, 1100°C and 1150°C for 30 min, respectively. XRD study confirmed the retention of single phase of SBT ceramics sintered at 1050°C and 1100°C. Plates like with non-uniform distribution of grains were observed from the FESEM study. Dielectric constant and dielectric loss were found to decrease with the increase of sintering temperature. From room temperature P–E loop study, remnant polarization and coercive field were found to increase with the increase in sintering temperature. From the J–E plot study, leakage current was found to decrease with the increase in sintering temperature. Minimal degradation of polarization was obtained from fatigue characteristics. SBT ceramics sintered at 1100°C show better ferroelectric properties and make it suitable for memory applications.

Low-temperature synthesis of nanoscale BaTiO3 powders via microwave-assisted solid-state reaction

Microwave-assisted solid-state reactions (MSSR) are investigated for their ability to synthesize nanocrystalline BaTiO3 powders at low temperatures. Ba(OH)2·H2O and TiO2·xH2O are, respectively, initial precursors for Ba and Ti. In this study, these precursors were mixed according to their chemical stoichiometry and heated in a temperature range of 100–1000 °C by MSSR. Nanocrystalline BaTiO3 powders having an average size of 26 nm were produced by MSSR, even at 100 °C. The crystallization-related activation energy for the formation of BaTiO3 with the precursors by MSSR was ~ 9.6 kJ/mol, which is less than 1/10 of the value (120 kJ/mol) when the conventional solid-state reaction was applied. The nanostructural and physical features of the MSSR-based powders are compared with those prepared using the conventional solid-state reaction.

Structural, Dielectric, Ferroelectric and Magnetic Properties of (BNT-BT)-NCZF Composites Synthesized by a Microwave-Assisted Solid-State Reaction Route

(1 − x)[Bi0.5Na0.5TiO3-0.07BaTiO3]-xNi0.3Cu0.08Zn0.62Fe2O4 [(1 − x)BNT-BT-xNCZF] ceramics, where x = 0.1, 0.2, 0.3, 0.4, and 0.5, were synthesized a by microwave-assisted solid-state reaction route. X-ray diffraction of the sintered ceramics showed the presence of both the ferroelectric and ferromagnetic phases, which was confirmed by surface microscopy study. Dielectric study showed a strong frequency as well as temperature dependence. Polarization versus electric field (P–E) hysteresis loop study revealed that the composite samples with x = 0.4 composition showed the highest remnant polarization. M–H loop and theoretical assessment of magnetic susceptibility (χ) showed enhancement in magnetisation as well as an χ value with the incorporation of ferrite phase in the piezoelectric matrix.

Low-temperature rapid synthesis of sodium zirconium phosphate by microwave-assisted solid-state method

Sodium zirconium phosphate (NZP) was synthesized by microwave-assisted solid-state reaction method with addition of x wt.% excess Na2CO3 powders (where x = 0, 2.5, 5, 7.5, and 10). The effects of the synthesis temperature and the excess sodium content on the phase compositions of the resultant samples were systematically investigated. XRD and Raman results showed that pure NZP phase could be synthesized successfully at 1100 °C for 2 h when 5 wt.% of excess sodium was introduced. Comparing with the traditional solid-state reaction method, the microwave-assisted solid-state method with the addition of appropriate excess sodium was beneficial to the synthesis of pure NZP phase, which would provide a new idea of achieving the low-temperature rapid synthesis of compounds of NZP family.

Synthesis of BaFe1‐xNixCuxO3‐δ new ceramic composition as solid oxide fuel cell cathode by microwave‐assisted solid‐state reaction

AbstractIn this research, new ceramic BaFe0.8Ni0.1Cu0.1O3‐δ powder was synthesized by solid‐state reaction method in conventional and microwave furnaces. Then, characterization, structure, and morphology of the resulting powders were studied. For characterization of synthetic powders, X‐ray diffraction, powder density gas pycnometer method, particle size analysis, scanning electron microscopy, and energy‐dispersive spectroscopy were performed. The results showed that the BaFe0.8Ni0.1Cu0.1O3‐δ powder synthesized in microwave furnace at 1,000 °C without soaking time and in conventional furnace at the same temperature with 12‐hr soaking time. In addition, the X‐ray diffraction results demonstrated that the main peak is shifted to lower angles by substitution iron ions with nickel and copper ions. Furthermore, the crystal structures of powders were hexagonal and tetragonal, and their density were 5.88 and 5.43 g/cm3, respectively, in conventional and microwave furnaces. Finally, the morphology and particle size of the synthesized powders were the same in both furnaces.

A Phosphosilicate Compound, NaCa3PSiO8: Structure Solution and Luminescence Properties.

NaCa3PSiO8 was synthesized in a microwave-assisted solid-state reaction. The crystal structure of the synthesized compound was solved using a least-squares method, followed by simulated annealing. The compound was crystallized in the orthorhombic space group Pna21, belonging to Laue class mmm. The structure consisted of two layers of cation planes, each of which contained three cation channels. The cation channels in each of the layers ran antiparallel to that of the adjacent layer. All the major cations together constituted four distinct crystallographic sites. The Rietveld refinement of the powder X-ray diffraction data, followed by the maximum-entropy method analysis, confirmed the obtained structure solutions. The electronic band structure of the compound was analyzed through density function theory calculations. Luminescence properties of the compound, upon activating with Eu2+ ions, were analyzed through photoluminescence measurements and decay profile analysis. The compound was found to exhibit green luminescence centered at ∼502 nm, with a typical broadband emission due to the transition from the crystal-field split 4f65d to 4f7 levels.

Alternative route for LiFePO4 synthesis: Carbothermal reduction combined with microwave-assisted solid-state reaction

LiFePO4 was synthesized via a microwave-assisted solid-state reaction. The precursors LiOH·H2O, FePO4·4H2O, glucose, and graphite were first subjected to carbothermal reduction at 200°C during 3h and subsequently calcined under microwave irradiation at 800W for very short times varying from 1 to 5min. The products obtained at different microwave calcination times were systematically investigated through thermal (TGA-DTG and DSC), structural (XRD), morphological (SEM), and electrochemical (cyclic voltammetry) analyses. The best results were attained for the product obtained at the microwave calcination time of 3min: smallest particle size (majority in the range of 100–150nm), crystallographic pattern of LiFePO4 and some by-products, and voltammetric profile characteristic of LiFePO4. Thus, the here-presented synthesis methodology implies a significant reduction in processing time while yielding LiFePO4 nanoparticles with good electrochemical activity for the Li ion intercalation process.