Solid-state Microwave Synthesis Research Articles

The role of precursor decomposition in the formation of samarium doped ceria nanoparticles via solid-state microwave synthesis

The impact on the final morphology of ceria (CeO2) nanoparticles made from different precursors (commercial: cerium acetate/nitrate) and in house: cerium tri(methylsilyl)amide (Ce-TMSA)) via a microwave solid state reaction has been determined. In all instances, powder X-ray diffraction indicated that the cubic fluorite CeO2 phase (PDF# 04–004-9150, with the space group Fm-3 m) had formed. Scanning electron microscopy (SEM) images revealed spherical nanoparticles were produced from the Ce-TMSA precursor. The commercial acetate and nitrate precursors produced particles with irregular morphology. The roles of the precursor decomposition and binding energy in the synthesis of the nanocrystals with various morphologies, as well as a possible growth mechanism, were evaluated based on experimental and computational data. The formation of spherical shaped nanoparticles was determined to be due to the preferential single-step decomposition of the Ce-TMSA as well as the low activation energy to overcome decomposition. Due to the complicated decomposition of the commercial precursors and high activation energy the resulting particles adopted an irregular morphology. Highly uniform samarium doped ceria (SmxCe1-xO2-δ) nanospheres were also synthesized from Ce-TMSA and samarium tri(methylsilyl)amide (Sm-TMSA). The effects of reaction time and temperature, on the final morphology were observed through SEM. The rapid single-step decomposition of TMSA-based precursors as observed through thermogravimetric analysis (TGA) and confirmed through the calculation of potential energy surfaces and binding energies from density functional theory (DFT) calculations, indicated that nanoparticle formation follows LaMer’s classical nucleation theory.

Preparation of tetragonal barium titanate nanopowders by microwave solid-state synthesis

Tetragonal-phase BaTiO3 powders of particle size 370 nm were synthesized by microwave sintering at 850 °C. The raw materials were BaCO3, TiO2, and alanine. SiC microspheres were used as microwave conductors. The effects of the holding time, sintering aids, and SiC addition on the preparation of BaTiO3 were investigated. The results indicate that the addition of SiC as a microwave acceptor leads to formation of microwave micro-regions. This enables uniform heating of the raw materials and decreases the calcination temperature needed to obtain BaTiO3. Alanine coordinates with Ba, and this loosens the metal–CO3 bond and promotes separation of CO2, decreases the BaCO3 decomposition temperature, and provides a higher nucleation site density. It gives an idea about the microwave solid-state synthesis of BaTiO3 powder.

MnO2 Nanoparticle Improved Cyclic Stability of Carbon Fiber Cloth Supported NiO Battery-Type Supercapacitor Materials by Microwave Solid-State Method

MnO2 nanoparticles were rapidly grown on a carbon fiber cloth (CFC) substrate via microwave solid-state synthesis and used as an electrode material to improve the cycling stability of NiO battery-type supercapacitors. The morphology and electrochemical properties of NiO@CFC and NiO/MnO2@CFC composites were characterised, and the electrochemical properties of the electrode materials prepared under different feeding qualities and microwave conditions were compared. NiO/MnO2@CFC showed a high specific capacitance of 188.3 mAh/g at a current density of 1 A/g and excellent cycling stability (capacity retention of 88.4% after 2000 cycles); these results indicate that the MnO2 nanoparticles improve the cycling stability of CFC-supported NiO supercapacitors (37.8% capacitance loss after 1000 cycles). An asymmetric NiO/MnO2@CFC supercapacitor revealed a competitive energy density of 20.87 Wh/kg at a power density of 850 W/kg. The successful design and synthesis of these composites via the microwave-assisted solid-state method provides a novel strategy for preparing electrode materials for high-performance energy storage devices.

Structural, characterization and electrical properties of AgPbmSbTem+2 compounds synthesized through a solid-state microwave technique

AgPbmSbTe2+m compounds are prepared through solid-state microwave synthesis method with different elements ratio of m (0.0 ≤ m ≤ 10). The X-ray diffraction method confirmed that all of the synthesized samples are polycrystalline with a rock salt NaCl-type crystalline structure. The lattice constant of the prepared AgPbmSbTe2+m increases from 6.089 Å to 6.467 Å with the increase in the mole fraction (m) from 0.0 to 10, respectively. Scanning electron microscopy images showed that increasing the mole fraction allows the continuous growth of multigrains, and volume of these grains increased with m value. The electrical conductivity (σ) measurements of AgPbmSbTe2+m prepared with a different m ratio exhibited a degenerate semiconductor behavior for all samples, and the sample prepared with m = 0 showed a higher σ of 482.96 S/cm at 300 K compared by the others. All of the samples had a negative Seebeck coefficient (S), indicating that the AgPbmSbTe2+m compounds are of n-type conductivity. Moreover, the maximum value of S is −419.69 μV/K at 338 K that obtained for the sample prepared with m = 8 while the minimum value of S was ˗6.8 μV/K recorded when the composition ratio of 4.

Low temperature microwave solid-state synthesis of CaCO3: Eu3+, K+ phosphors

An Eu3+ singly doped material and a K+–Eu3+ co-doped calcium carbonate phosphor were synthesized successfully by microwave assisted sintering at low temperature. The sintering condition was set at 270°C for 3h in air. The structure and micro-morphology of samples were characterized and analyzed by X-ray powder diffraction (XRD) and scanning electronic microscope (SEM). Results showed that Eu3+ and K+ ions were uniformly introduced into the host lattice of CaCO3, taking place of Ca2+ ions. The photoluminescence (PL) properties were characterized by PL, PL excitation spectroscopy. The maximum photoluminescence intensity was obtained when the molar concentration of Eu3+ was 0.08. Under the excitation of 394nm, the transitions of 5D0→7FJ (J=0–5) for Eu3+ were observed, and the luminescent intensities of Eu3+–K+ co-doped CaCO3 phosphors could be greatly increased.

Microwave solid state synthesis and luminescence properties of green-emitting Gd2O2S:Tb3+ phosphor

Gd2−xO2S:xTb3+ phosphors were prepared by the microwave solid state method, and its phase formation and morphologies were studied by the X-ray powder diffraction (XRD) and scanning electron microscope (SEM) techniques. The photoluminescence (PL) properties, cathodoluminescence (CL) properties and PL thermal stability of the samples were investigated, which indicated that better luminescence properties can be obtained via the microwave method compared to the conventional high temperature solid-state method. The composition-optimized Gd1.85O2S:15%Tb3+ exhibited strong green emission peaking at 546nm upon excitation at 254nm with the CIE coordinates of (0.238, 0.382). Different electric voltage and current dependent CL spectra investigations of Gd1.85O2S:15%Tb3+ phosphor shows similar green spectral profile as PL emission and it also demonstrates the good luminescence stability suggesting its potential application as green emission component in cathode ray tube (CRT).

Plasma-enhanced microwave solid-state synthesis of cadmium sulfide: reaction mechanism and optical properties.

CdS synthesis by plasma-enhanced microwave physical vapor transport (PMPVT) has been developed in this work. The photoluminescence (PL), absorbance, Raman spectra and the mechanism of CdS crystal growth have been investigated. Furthermore, plasma-enhanced microwave chemical vapour transport (PMCVT) synthesis of CdS with additional chemical transport agents has been explored. In addition, other II-VI chalcogenides were also synthesized by PMPVT.

Rapid Microwave Synthesis and Structural Phase Diagram of LnxY1−xMnO3

YMnO3 is one of the primary examples of a multiferroic ceramic. We present a novel solid-state microwave sintering method for making high-purity ceramic samples of YMnO3 and related compounds in a few hours. This leads to determination of the structural phase diagram for the formation of single-phase, hexagonal samples when doping lanthanides into YMnO3. It is found that the solidstate microwave synthesis allows manufacture of high-quality samples in hours rather than days. The resulting phase diagram accords well with results from the literature, and from calculations based on the Goldschmidt tolerance factor for the stability of perovskite structures, suggesting that the transformation from hexagonal to perovskite with doping is driven essentially by ion sizes. Some results concerning the microwave synthesis of BaLnInO4 compounds, where Ln is a lanthanide, are noted. Microwave sintering of BaNdInO4 yields single-phase samples where conventional sintering does not.

Structural and electrical transport properties of Se-substituted p-type Bi2Se3xTe3(1−x) (x=0.0–1.0) alloys prepared by solid-state microwave synthesis

In this study, thermoelectric materials based on p-type Bi2Te3 and dispersed with x compositions of selenium (Se) (x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) in Bi2Se3xTe3(1−x) ingots were synthesized using a standard solid-state microwave method. The crystalline structures of the polycrystalline powders were examined by X-ray diffraction (XRD), which showed the formation of a rhombohedral structure. The surface morphology for the samples showed that the Se alloying is an effective approach for crystalline refinement, which has been characterized by scanning electron microscopy (SEM). The electrical transport properties of the samples were measured from room temperature up to 500K. The results indicate that the selenium substitution effectively adjusts the carrier concentration allowing an optimum value of 1.25×1020cm−3. Ascribing to the increased Seebeck coefficient for the sample with x=0.2 (176.3μV/K), the maximum power factor is 2.85mW/mK2 at 403K.

Complexes with a tridentate aroylhydrazone ligand: Microwave solid-state synthesis, crystalline architectures through supramolecular interactions and electrochemical properties

A series of complexes, [CuLCl]·1·5H2O (1); [ML2]·X (X=0, M=Cd, 2a; X=DMF, M=Hg, 2b; X=DMF, M=Ni, 2c); [Cu2(OOCCH3)2L2]·2CH3OH (3) have been synthesized by microwave solid-state method with a tridentate aroylhydrazone ligand HL (HL=N3-salicyloylpyridine-2-carboxamidrazone). All these compounds were characterized by element analysis, IR, X-ray diffraction and electrochemistry. Crystal analysis revealed that the coordination molecules extended to 3D supramolecular networks through plentiful H-bondings and weak molecular interactions between the ligand moieties and solvent molecules. Meanwhile, these compounds displayed diverse metal or ligand localized electrochemical properties.

Thermal sensors based on p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 thin films grown using thermal evaporation method

We utilize p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 ingots in a standard solid-state microwave synthesis route to fabricate thermally evaporated thin films. The nanostructure and composition of the films were studied through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX). The Seebeck coefficient and electrical conductivity were measured at a temperature range of 298–523K. The micro-thermoelectric devices were composed of 20 pairs and 10 pairs of p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 thin films on glass substrates, respectively. The dimensions of the thin films thermoelectric generators which comprised of 10-pair were 12mm×10mm, whereas, 20-pair were 23mm×20mm, respectively of legs connected through aluminum electrodes. The serial 20-pair p–n thermocouples generated a maximum output open-circuit voltage of 275.3mV and a maximum output power of 54.37nW at a temperature difference of ΔT=162K; the values are 109.4mV and 16.68nW at ΔT=162K for the 10-pair thermocouples, respectively.

Thermoelectric generation device based on p-type Bi0.4Sb1.6Te3 and n-type Bi2Se0.6Te2.4 bulk materials prepared by solid state microwave synthesis

This study reports on the fabrication of a chalcogen-based thermoelectric power generation (TEG) device using p-type Bi0.4Sb1.6Te3 and n-type Bi2Se0.6Te2.4 bulk thermoelectric materials. The microstructure of the samples was characterized by scanning electron microscope (SEM). The phase composition of the powders was characterized by X-ray diffraction (XRD), revealing a rhombohedral structure. The thermoelectric (TE) properties such as the Seebeck coefficient (S) and the electrical conductivity (σ) of the resulting alloys were studied in the temperature range of 300–523K. The power factor (Pfactor) for a Bi0.4Sb1.6Te3 as p-type sample was found to be 4.96mW/mK2 at 373K, whereas 2.22mW/mK2 was obtained at 383K for a Bi2Se0.6Te2.4 as n-type sample. Electrical power generation characteristics such as high open circuit voltage (Voc) and maximum output power (Pmax) were monitored by changing the temperature conditions required to generate maximum power. The significance of the resistances including the internal resistance (Rin) and contact resistance (RC) between legs and electrodes, are discussed. The maximum output power obtained with the 9 p–n couples device was 39.4mW under the thermal condition of TH=523K hot side temperature and ΔT=184K temperature difference.

Effect of Selenium on Structure and Electrical Property for Bi<sub>0.4</sub>Sb<sub>1.6</sub>Se<sub>3x</sub>Te<sub>3(1-x) </sub>Novel Hexagonal Rods

Novel hexagonal rods of Bi0.4Sb1.6Se3xTe3(1-x) (0.0≤x≤1.0) were synthesized successfully through solid-state microwave synthesis. These hexagonal rods were explored using field emission scanning electron microscopy images. The X-ray diffraction results indicate that the powders (0.0≤x≤0.8) can be indexed as the rhombohedral phase, whereas the sample with x=1.0 has an orthorhombic phase structure. The electrical conductivity gradually decreases as Se increased, resulting in an increase in the Seebeck coefficient. Ascribing to the increased Seebeck coefficient for the sample with x=0.8, the maximum power factor is 7.47 mW/mK2 at 373 K.

Thermoelectric Generators Using p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 Thin Films Prepared by the Thermal Evaporation Method

In this study, p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 ingots were used in a standard solid-state microwave synthesis route for fabricating thermally evaporated thin films. The nanostructure and composition of the films were studied through x-ray diffraction, field-emission scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Measurements of the Seebeck coefficient and electrical conductivity were performed at 298 K to 523 K. The microthermoelectric devices were composed of 20 pairs and 10 pairs of p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 thin films on glass substrates, respectively. The 20-pair p–n thermocouples in series generated a maximum output open-circuit voltage of 275.3 mV and a maximum output power of 54.37 nW at a temperature difference ΔT = 162 K, and 109.4 mV and 16.68 nW at ΔT = 162 K for 10 pairs, respectively.

Structural and Thermoelectric Properties of Bi<sub>0.4</sub>Sb<sub>1.6</sub>Se<sub>3x</sub>Te<sub>3(1-X)</sub> Quaternary Compound

Novel hexagonal rods of Bi0.4Sb1.6Se3xTe3(1-x) (0.0x1.0) were synthesized successfully through solid-state microwave synthesis. These hexagonal rods were explored using field emission scanning electron microscopy images. The X-ray diffraction results indicate that the powders (0.0x0.8) can be indexed as the rhombohedral phase, whereas the sample with x=1.0 has an orthorhombic phase structure. The electrical conductivity gradually decreases as Se increased, resulting in an increase in the Seebeck coefficient. Ascribing to the increased Seebeck coefficient for the sample with x=0.8, the maximum power factor is 7.47 mW/mK2 at 373 K.

Chalcogen-based thermoelectric power generation device using p-type Bi0.4Sb1.6Se2.4Te0.6 and n-type Bi2Se0.6Te2.4 prepared by solid-state microwave synthesis

This study reports on the fabrication of a chalcogen-based thermoelectric power generation (TEG) device using p-type Bi0.4Sb1.6Se2.4Te0.6 and n-type Bi2Se0.6Te2.4 legs. Electrical power generation characteristics were monitored by changing both the temperature conditions and the number of p–n couples required to generate maximum power. The significance of the resistances including the internal resistance and contact resistance between legs and electrodes, are discussed. The maximum output power obtained with the 18 p–n couples device was 273.2mW under the thermal condition of TH=523K hot-side temperature and ΔT=184K temperature difference.

Synthesis and electrochemical performance of Sn-doped Li3V2(PO4)3/C cathode material for lithium ion battery by microwave solid-state technique

Li3V2−xSnx(PO4)3/C cathode materials with uniform and fine particle sizes were successfully and fast synthesized by a microwave solid-state synthesis method. X-ray diffraction patterns demonstrated that the appropriate addition of Sn did not destroy the lattice structure of Li3V2(PO4)3/C, but decreased the unit cell volume. X-ray photoelectron spectroscopy analysis demonstrated that the main chemical state of V in the Li3V1.95Sn0.05(PO4)3/C composite is +3 valence, while the chemical state of Sn in the Li3V1.95Sn0.05(PO4)3/C is +4 valence. Scanning electron microscope analysis illustrated that the addition of Sn slightly affected the morphology of samples. As the cathode materials for Li-ion batteries, Li3V2−xSnx(PO4)3/C (x⩽0.10) exhibited higher discharge capacity and better cycle stability than the pure one. At a discharge rate of 0.5C in the potential range of 2.5–4.5V at room temperature, the initial discharge capacity of Li3V1.95Sn0.05(PO4)3/C was 136mAh/g. The low charge-transfer resistances and large lithium ion diffusion coefficients confirmed that Sn-doped Li3V2(PO4)3/C samples possessed better electronic conductivity and lithium ion mobility. These improved electrochemical performances can be attributed to the appropriate amount of Sn doping in Li3V2(PO4)3/C system by enhancing structural stability and electrical conductivity. The present study also demonstrates that the microwave processing is a fast, simple and useful method for the fabrication of Li3V2(PO4)3/C crystals.

Novel hexagonal rods and characterization of Bi0.4Sb1.6Se3xTe3(1 − x) using solid-state microwave synthesis

Novel hexagonal rods of Bi0.4Sb1.6Se3xTe3(1−x) (0.0≤x≤1.0) were synthesized successfully through solid-state microwave synthesis. These hexagonal rods were explored using field emission scanning electron microscopy and transmission electron microscopy images. The X-ray diffraction results indicate that the powders (0.0≤x≤0.8) can be indexed as the rhombohedral phase, whereas the sample with x=1.0 has an orthorhombic phase structure. The hole concentration gradually decreases as Se increased, resulting in a decrease in electrical conductivity and an increase in the Seebeck coefficient. Ascribing to the increased Seebeck coefficient for the sample with x=0.8, the maximum power factor is 7.47mW/mK2 at 373K.

Composition-dependent structural and electrical properties of PbSe1−xTex thin films

Polycrystalline PbSe1−xTex ingots were prepared by solid-state microwave synthesis. Thin films of PbSe1−xTex were then deposited onto clean glass substrates using vacuum evaporation technique. Their nanostructure morphologies and stoichiometric ratio were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectra (EDX). X-ray diffraction (XRD) patterns indicated that the lattice constants of PbSe1−xTex powders and thin films increased with the increasing amount of Te. From the electrical property measurements, the thin films were characterized by n-type behavior.

Significant Influences of Selenium on the Electrical Properties of Bi<sub>2</sub>Te<sub>3</sub> Compounds Synthesized Using Solid-State Microwave Irradiation

The thermoelectric materials based on p-type Bi2Se3xTe3 (1-x) bulk products and dispersed with x compositions of Se (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were fabricated using standard solid-state microwave synthesis procedures. The products were characterized by X-ray diffraction (XRD). The XRD characterizations revealed that these products are pure Bi2Te3 and Bi2Se3 with uniform structures. The electrical properties of the Bi2Te3, Bi2Se3 and Bi2Se3xTe3 (1-x) samples were measured in the temperature range of 303–523 K. The highest value of the Seebeck coefficient was 176.3 μV/ K for the Bi2Se0.6Te2.4 sample, but only 149.5 and 87.4 μV/K for the Bi2Te3 and Bi2Se3 samples, respectively.