Auto-igniting Combustion Technique Research Articles

Structure and properties of Ln6MoO12 (Ln = Nd, Sm, Gd, Dy) optoelectronic nanoceramics

Auto-igniting combustion technique is used for preparing Ln6MoO12 (Ln = Nd, Sm, Gd, Dy) nanoceramics. Crystallographic phase is ascertained by comparing the XRD patterns of prepared samples with ICDD data. X-ray diffraction line broadening is used to decide the average crystal size. Vibrational tools like Raman and FTIR spectroscopy are used to evaluate the metal oxide stretching frequencies. TEM analysis is used to investigate the particulate properties and SEM analysis is used to study the surface morphology of the sintered material. The ultraviolet–visible absorption spectra and photoluminescence spectra of the samples are noted and examined. The examination of ultraviolet absorption spectra discloses intense broad absorption in the UV-to-visible region with peaking at near UV region. Electrical properties of Nd6MoO12 are investigated using Impedance spectroscopy. The contributions of bulk and grain boundary to the overall electric response of the material are inferred by studying the electrical properties as a function of frequency (50 – 5 MHz) at various temperatures (400 – 850 °C).

Single step auto-igniting combustion technique grown CeO2 and Ni-doped CeO2 nanostructures for multifunctional applications

In the present study, pristine and Ce1-xNixO2(x = 0.1) nanoparticles are grown by low cost modified combustion process. The surface morphology and phase pureness of the pristine and Ce1-xNixO2(x = 0.1) nanostructures is achieved by Scanning Electron Microscopy (SEM) and powder X-Ray Diffraction (XRD) techniques. The closed and open mode Z-scan studies reveal that these synthesized nanostructures possess excellent reverse saturation absorption behaviour, which can be utilized for optical limiting applications in defence and healthcare systems. By analyzing the photocatalytic properties against Eosin Yellow dye, the degradation efficiency of synthesized samples is found to be 91% and 93% respectively. Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopic (EIS) are the techniques which help to study the electrochemical properties of the synthesized materials for electrode materials of supercapacitor. From GCD, the specific capacitance of pristine and Ce1-xNixO2(x = 0.1) is 305 and 446 F g-1 respectively. Even after 2000 GCD cycles, the cyclic stability and coulombic efficiency of Ce1-xNixO2(x = 0.1) remains at 96.1% and 97.5%, while for pure CeO2 it is 88.3% and 91% respectively.

Structural and temperature dependent dielectric properties of nanocrystalline PbTiO3 synthesized through auto-igniting combustion technique

Nanocrystalline PbTiO3 has been synthesized through an auto-ignited combustion method. The structure of the powder was examined using X-ray diffraction, thermogravimetric analysis, differential thermal analysis and Fourier Transform Raman spectroscopy. Rietveld-refinements were performed in order to determine the structural parameters of the material. The crystalline size of the particle was calculated using Scherrer formula and examined using transmission electron microscopy. The nanopowder could be sintered to 95% of the theoretical density at 1100 °C for a short duration of time 2 h. The microstructure of the sintered surface was examined using scanning electron microscopy. The variation of dielectric properties of the specimen was studied at different frequencies and temperatures. A maximum of dielectric constant 30901 obtained at 50 Hz when the temperature is 500 °C (near transition temperature, Tc). The excellent dielectric properties of the PbTiO3 ceramics at different conditions assure the sample is useful to many electronic devices.

Synthesis and characterization of AZrTi2O7 (A = mg, ca, Sr and Ba) functional nanoceramics

Nanocrystalline AZrTi2O7 (A = Mg, Ca, Sr and Ba) system has been synthesized by an auto-ignited combustion technique. The structure of the system is analyzed by powder X-ray diffraction and vibrational spectroscopic tools. The cation deficient zirconolite (CaZrTi2O7) is found to be a monoclinic structure with the space group C2/c. A narrow size distribution of the nanoparticles is observed by transmission electron microscopy with a peak at 11 nm. The optical band gap of the ceramics obtained by using Tauc’s plot is in between 3.10 eV and 3.30 eV. The photoluminescence emission spectra of the samples are investigated and the probable transitions producing the emissions are identified. The microstructure of the sintered pellets are examined by scanning electron microscopy and the elemental compositions are confirmed by energy-dispersive spectrometry. Impedance spectroscopic analysis of the sample showed that ions are the main source of conduction. Ionic conduction and grain boundary conduction stimulate high conductivity to the material. Electrical property measurements in the temperature range 500–850 °C indicate that CaZrTi2O7 is stable and can be utilized over a wide range of temperatures and frequencies. These materials are found suitable for optical and solid oxide fuel cell applications.

Structural and Spectroscopic Studies of Nanostructured Alumina Doped LaFeO3 a Photo catalyst Ceramics Synthesized Through an Auto Igniting Combustion Synthesis

LaFeO3 with an orthorhombic phase of the ABO3 type perovskite structure has become a currently attractive research topic because it is proposed for various applications in several advanced technologies such as catalysts, various kinds of chemical and gas sensors and electrode materials in solid oxide fuel cells. In the present work La1-xAlxFeO3 (x = 0.01) nanopowder was prepared through an auto ignited combustion technique. In order to study the phase stability, the structural, vibrational and optical properties, the as prepared material was heat treated at 600°C. The phase purity of the powder was examined using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies. XRD studies show that the powder possesses an orthorhombic structure with lattice constants a=5.55, b=7.85 and c=5.55. The transmission electron microscopic study confirmed the ultrafine nanocrystallite nature of the powder. The thermal stability of the nanopowder studied using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) shows that the nanopowder has ∼7% weight loss in the temperature range 100-600°C. The UV-Visible diffuse reflectance spectroscopy study carried out on the alumina doped LaFeO3 ceramics indicate that the sample has narrow optical band gap of ∼2.08 eV. These results show the strong visible-light absorption characteristics of the sample and it perfectly satisfies the band gap requirements of an ideal visible light active photo catalyst.

Microwave assisted sintering of Nanostructured Infrared-Transparent Nd0.1Y1.9O3 ceramics Synthesized by a Modified Combustion Technique

Synthesis of nano particles of Nd0.1Y1.9O3 ceramics (∼15nm) by a single step auto-igniting combustion technique, followed by microwave sintering to optimum density, and their remarkable infrared transmission characteristics are presented in this paper. The XRD pattern of the as prepared sample clearly indicates that the Nd3+ ions are effectively replacing Y3+ ions in the yttria cubic structure and it matches very well with the JCPDS file no-89-5591. The size of the crystallites was calculated using Scherrer formula and they found to be in the size range of 10-19 nm and the average size of the crystallites was 15 nm. The HRTEM analysis confirms the nano nature and the well-defined lattice structure of the sample. The UV-Visible and FTIR spectroscopy were effectively used to characterise the powder and to obtain the transmittance properties of the sintered samples. Microwave heating was successfully employed to sinter the sample pellets. A soaking duration of 20 minutes at 1500°C yielded well sintered (98.8% ) translucent pellet with reduced average grain size of 500nm and it showed a transmittance of 77% in the UV-Visible region and 78% in the mid infrared region. Microwave assisted sintering of the combustion synthesized powder is therefore a promising fabrication technique, especially for infrared transparent ceramics, which considerably reduces the sintering temperature, soaking duration, the grain size and enhances the transmittance properties. These results clearly indicate that by prudently tuning the concentration of the additives, the IR transmittance properties can be improved and they can be used very effectively for the fabrication of infrared transparent windows and domes.

Effect microwave sintering in enhancing the infrared transmittance properties of combustion synthesized nanostructured Y2O3 ceramics comprising La3+ ion in the matrix

Synthesis of nano particles of La3+ ion subsituted Y2O3 ceramics (∼16nm) by a single step auto-igniting combustion technique, followed by microwave sintering to optimum density, and their remarkable infrared transmission characteristics are presented in this paper. The XRD pattern of the as prepared sample clearly indicates that the La3+ ions are effectively replacing Y3+ ions in the yttria cubic structure and it matches very well with the JCPDS file no-89-5591. As the percentage of La3+ increases a slight increase in lattice parameter was observed. The size of the crystallites were calculated using Scherrer formula and they found to be in the size range of 10-20 nm and the average size of the crystallites was 16 nm. The phase purity and nano nature of the crystallites were confirmed using HRTEM. The UV-Visible and FTIR spectroscopy were effectively used to characterise the powder and to obtain the transmittance properties of the sintered samples. The pellets with green density 52% of the theoretical density were sintered using a microwave furnace. The pellets achieved 99% of the theoretical density at 1520°C for a soaking duration of 20 minutes. The pellets were translucent and the SEM analysis revealed that they were well sintered with reduced average grain size of ∼430nm. The pellet showed an enhanced transmittance of 77% in the UV-Visible region and 72% in the mid infrared region. The transmittance properties shown by the pellets are superior to those in the case of pure Y2O3 and is due to the superior powder quality and the fast uniform densification via microwave sintering. Microwave assisted sintering of the combustion synthesized powder is therefore a promising fabrication technique, especially for infrared transparent ceramics, which considerably reduces the sintering temperature, soaking duration, the grain size and enhances the transmittance properties.

Electrical and optical properties of pure and zirconium added dysprosium titanates

Nanoparticles of Dy2Ti2O7 and Dy2Ti1.5Zr0.5O7 (abbreviated as DTO and DTZO, respectively) have been prepared through an auto-igniting combustion technique. The structure of the system is analyzed by powder X-ray diffraction and vibrational spectroscopic tools. The samples are crystallized with cubic pyrochlore structure with the space group $$Fd\bar {3}m$$. The particle size obtained from XRD and TEM analysis shows that the samples are nanocrystalline. The Fourier-transform infrared and Raman spectra of the samples are investigated in detail. The ultraviolet–visible absorption spectra of the samples are also recorded and their optical bandgap energy values are calculated. The photoluminescence spectra of the samples are recorded and the transitions causing emissions are identified. The surface morphology of the sintered pellets were studied by scanning electron microscopy which indicates minimum porosity, and the elemental composition was confirmed by energy-dispersive spectrometry. Impedance spectroscopic studies of the samples are carried out at different temperatures. The conductivity of the samples increased with temperature, and the highest conductivity of 1.93 × 10−1 S/m at 850 °C is obtained for DTO. The materials are suitable candidates for optoelectronic applications and the fabrication of electrolytes in solid oxide fuel cells at moderate temperatures.

Optical and dielectric investigations of nano crystalline scheelite A0.5B0.5MoO4 (A=B=Ba, Sr and Ca)

The synthesis of nanocrystalline A0.5B0.5MoO4 by an auto-igniting combustion technique is reported. The structural characterization done by X-ray diffraction, Fourier transform Raman spectroscopy and infrared spectroscopy reveals that the as-prepared powder itself is phase pure with tetragonal structure. The particle size determined from Transmission electron microscopy are in the range 23–25 nm. The optical band gap determined show that the compounds are wide bandgap semiconductors. The photoluminescence spectrum of A0.5B0.5MoO4 shows green emission, associated with the perfect order and crystallinity of the sample. All the samples are sintered at a temperature less than 875°C. The dielectric constant and loss factor of the samples are measured at radiofrequency range and its variation with temperature is also studied. The effect of change in composition of A2+ site of scheelite AMO4 compounds comparative are also presented. The experimental results show that nano A0.5B0.5MoO4 is an excellent luminescent material and also a promising ‘Low temperature Co-fired Ceramic. Also it is inferred that we can fine tune both optical and dielectric properties to desired values according to our requirements by adjusting the cationic stoichiometric ratio in [AO8] octahedron.

Structural and optical characterization of Y2Ti2O7 and Y2Ti1.5Hf0.5O7 nanomaterials

Single step auto ignited combustion technique has been used to prepare nanosized Y2Ti2O7 (YTO) and Y2Ti1.5Hf0.5O7 (YTHO). The structure of the samples analyzed by X-ray diffraction method is found to be cubic with space group (Z = 8). This is further confirmed using vibrational spectroscopic analysis. The average crystalline sizes of both the samples are calculated using Scherrer formula and using High Resolution Transmission Electron Microscopy. Energy dispersive spectroscopic analysis confirmed the presence of elements in the stoichiometric ratio. Optical studies of the as prepared samples are carried out by UV–Vis and Photoluminescence spectroscopy. The optical band gap determined using Kubelka–Munk formalism and Tauc’s plot are found to be 3.8 and 3.1 eV for YTO and YTHO, respectively. Photocatalytic activity is analyzed by the degradation of methylene blue (MB) under UV light. The percentage degradation of YTO and YTHO are 40 and 19.5% respectively. The rate of degradation is also analyzed for both the samples.

Electrical and Optical Properties of Nanocrystalline A8ZnNb6O24 (A = Ba, Sr, Ca, Mg) Ceramics

Nanoparticles of A8ZnNb6O24 (A = Ba, Sr, Ca, and Mg, abbreviated as BZN, SZN, CZN, and MZN) have been synthesized by an auto-igniting combustion technique and their structural and optical properties characterized. The phase purity, crystal structure, and particle size of the prepared nanopowders were examined by x-ray diffraction (XRD) analysis and transmission electron microscopy. The XRD results revealed that all the samples crystallized with hexagonal perovskite structure in space group P63cm. The Fourier-transform infrared and Raman (FT–Raman) spectra of the samples were investigated in detail. The ultraviolet–visible (UV–Vis) absorption spectra of the samples were also recorded and their optical bandgap energy values calculated. The nanopowders synthesized by the combustion technique were sintered to 95% of theoretical density at temperature of 1250°C for 2 h. The surface morphology of the sintered pellets was studied by scanning electron microscopy. The photoluminescence spectra of the samples showed intense emission in the blue–green region. Complex impedance analysis was used to determine the grain and grain boundary effects on the dielectric behavior of the ceramics.

Optical and dielectric characterisation of Ceria nanocrystals synthesized by an auto-igniting combustion technique

Nanocrystalline Ceria (CeO2) was synthesized through auto-ignited combustion technique. The X-ray diffraction studies of CeO2 nanoparticles have shown that the as-prepared powder was single phase, crystalline and has a face centred cubic structure. The phase purity of the powder was further examined using Fourier Transform Infrared and Raman spectroscopic techniques. The transmission electron microscopic studies have shown that the particle size of the as prepared powder was in the range of 30–40 nm. The band gap of nanoparticles as calculated from the absorption spectrum was found to be 3.51 eV. The photoluminescent spectrum of the samples exhibited a number of emission peaks which forms a broad band emission between 400 and 500 nm originating from 2T2g(5d)–2F7/2, 2F5/2(4f) transition of Ce3+ ion due to spin–orbit coupling under the influence of O h crystal field. The nanopowders were sintered to about 95 % of the theoretical density at 1450 °C for 2 h. The microstructure of the sintered surface was examined using scanning electron microscopy. The dielectric constant (er) and loss tangent (tanδ) at 5 MHz are found to be about 25.1 and 0.0118 respectively. The complex impedance plots show semicircular arcs resolving at high temperature which confirms the existence of the non-Debye type of relaxation in the sintered CeO2 samples.

Single step combustion synthesis of nanocrystalline scheelite Ba0.5Sr0.5MoO4 for optical and LTCC applications: Its structural, optical and dielectric properties

The synthesis of nanocrystalline Ba0.5Sr0.5MoO4 by an auto-igniting combustion technique is reported. The structural characterization done by X-ray diffraction, Fourier transform Raman spectroscopy and infrared spectroscopy reveals that the as-prepared powder itself is phase pure with tetragonal structure. The particle size determined from Transmission electron microscopy is 21 nm. The ultraviolet-visible absorption spectrum of the sample shows maximum absorption in the UV region and the optical band gap determined is 4.71 eV. The photoluminescence spectrum of Ba0.5Sr0.5MoO4 shows green emission, associated with the perfect order and crystallinity of the sample. The sample is sintered at a relatively low temperature of 815 °C. Scanning electron microscopy showed that the sample achieved 95 % of its theoretical density. The dielectric constant and loss factor of the sample measured at 5 MHz is found to be 10.58 and 1.66.×10−3 at room temperature. The effect of change in composition of A2+ site of scheelite AMO4 compounds comparative are also presented. The experimental results show that nano Ba0.5Sr0.5MoO4 is an excellent luminescent material and also a promising ‘Low temperature Co-fired Ceramic’. Also it is inferred that we can fine tune both optical and dielectric properties to desired values according to our requirements by adjusting the cationic stoichiometric ratio in [AO8] octahedron.

Enhanced infrared transmittance properties in ultrafine MgAl2O4 nanoparticles synthesised by a single step combustion method, followed by hybrid microwave sintering

Infrared transparent ceramics found to have potential applications as infrared windows and domes in strategic defence and space missions. Synthesis of ultrafine nanostructured MgAl2O4 ceramics by a modified single step auto-igniting combustion technique, followed by sintering of the sample by resistive and resistive-microwave hybrid heating to high density and their excellent infrared transmission characteristics are presented in this paper. Structural characterisations of MgAl2O4 nanoparticles reveal that the as prepared powder is phase pure, with average crystallite size ∼15nm and possess a cubic structure. Optical band gap calculated using the Kubelka–Munk method is 5.75eV. The thermal stability of the nanopowder at elevated temperatures has been studied using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). Hybrid heating yield a substantial reduction in sintering temperature and soaking time relative to the conventional resistive heating, and the samples achieved >99% density by microwave-resistive hybrid heating. Scanning electron micrograph (SEM) showed that the pellets are well sintered. The pellet sintered by hybrid heating showed a better transmittance of ∼79% in the UV–Visible region and ∼82% in the mid IR region compared to pellet sintered by resistive heating which has ∼68% in the UV–Visible region and ∼66% in the mid IR region. The results confirm the effective use of nanocrystalline powders from modified combustion synthesis as starting material for the development of high quality IR transparent windows and domes. In addition the microwave hybrid sintering technique employed in the present study also contributes to the results of better transmittance characteristics in highly densified MgAl2O4 ceramic pellets.

Infrared transmittance of hybrid microwave sintered yttria

Synthesis of nano particles of yttria (Y2O3) ceramics (~15nm) by a single step auto-igniting combustion technique, followed by sintering of the sample by three variants of sintering methods viz. resistive, microwave and microwave hybrid heating to optimum density and their remarkable infrared transmission characteristics are presented in this paper. In microwave hybrid sintering there was a considerable reduction in the sintering temperature and the soaking time compared to the resistive and microwave sintering. The pellets sintered by microwave hybrid heating at 1450°C for 20min achieved a density 99.2% of the theoretical density with reduced average grain size of 220nm and the pellet showed enhanced transmittance of ~80% in the visible and ~80% in the mid infrared region. The results clearly indicate that the yttria ultra fine nanophase powder synthesised by the single step combustion method and sintered via microwave hybrid heating shows better transmittance properties and can be used very effectively for the fabrication of infrared transparent windows and domes.

Optical properties of nanocrystalline HfO2 synthesized by an auto-igniting combustion synthesis

The optical properties of nanocrystalline HfO2 synthesized using a single-step auto-igniting combustion technique is reported. Nanocrystalline hafnium oxide having particle size of the order 10–15 nm were obtained in the present method. The nanopowder was characterized using X-ray diffraction, Fourier transform infrared and Fourier transform Raman spectroscopic studies. All these studies confirm that the phase formation is complete in the combustion synthesis and monoclinic phase [P21/c(14)] of HfO2 is obtained without the presence of any impurities or additional phases. The powder morphology of the as-prepared sample was studied using transmission electron microscopy and the results were in good agreement with that of the X-ray diffraction studies. The optical constants such as refractive index, extinction coefficient, optical conductivity and the band gap were estimated from UV–vis spectroscopic techniques. The band gap of nanocrystalline HfO2 was found to be 5.1 eV and the sample shows a broad PL emission at 628 nm. It is concluded that the transitions between intermediate energy levels in the band gap are responsible for the interesting photoluminescent properties of nanocrystalline HfO2.

Study on the optical band gap and photoluminescence of PbMoO4 nano powder synthesized by an auto igniting combustion technique

Nano crystalline PbMoO4 was synthesized through an auto-ignited combustion technique. The X-ray diffraction studies of PbMoO4 nanoparticles reveals that the as-prepared powder itself is single phase and possess tetragonal structure. The average particle size of the as-prepared powder calculated using scherrer formula is 28nm. Fourier transform Infrared spectrum shows that the as prepared powder itself is phase pure with no formation of secondary phase .The optical band gap determined from UV-Visible absorption spectra is 3.20eV.Photoluminescence spectra of the samples shows blue emission.

Structural, Optical and Vibrational Characterization of Infrared - transparent Nanostructured MgAl2O4 Synthesized by a Modified Combustion Technique

In this paper we report the synthesis of MgAl2O4 (Spinel) by a modified auto-igniting combustion technique for the first time. The as prepared powder is phase pure and the average grain size is around 16nm with well defined lattice planes. The vibrational spectroscopic studies confirm the structure of the sample. The spinel ceramic pellet sintered to 98.5% of the theoretical density shows a transmittance of 71% in the visible region and 65% in the mid-infrared region, which can be further improved by polishing and consequently found applications as infrared transparent windows and domes.

Preparation, Characterization, and Ionic Transport Properties of Nanoscale Ln2Zr2O7 (Ln = Ce, Pr, Nd, Sm, Gd, Dy, Er, and Yb) Energy Materials

Nanoparticles of lanthanide (Ln)-based zirconates have been prepared through the autoignited combustion technique. The structure of the system was analyzed by powder x-ray diffraction and vibrational spectroscopic tools. The compounds with Ln = Ce, Pr, Nd, Sm, and Gd have pyrochlore cubic structure, whereas those with Ln = Dy, Er, and Yb possess anion-deficient disordered cubic fluorite structure. The optical properties of the powder were analyzed using ultraviolet–visible spectroscopy. Pellets of the compounds were sintered in the range from 1325°C to 1530°C for 2 h. The surface morphology of sintered Nd2Zr2O7 was analyzed by scanning electron microscopy. Impedance spectroscopic studies of the samples were carried out at different temperatures. The conductivity increased to the order of 10−2 S/m at 750°C, and the highest conductivity of 13.21 × 10−2 S/m was obtained for Er2Zr2O7. All samples of this system are suitable candidates for fabrication of electrolytes for use in solid oxide fuel cells, particularly at moderate temperatures.

Structural, Optical, and Compactness Characteristics of NanocrystallineCaNb2O6Synthesized through an Autoigniting Combustion Method

Nanoparticles of calcium metaniobate compound are prepared by an autoigniting combustion technique and its structural, optical, and dielectric properties are investigated. The X-ray diffraction, Fourier-transform Raman, and infrared studies reveal that calcium metaniobate possesses phase pure orthorhombic columbite structure with space group of Pbcn. The average particle size of the as-prepared nanoparticles obtained from both the Scherrer formula and transmission electron microscopy is ~37 nm. The optical band gap calculated from Tauc's Plot is 3.25 eV. Photoluminescence studies reveal that Calcium metaniobate can be used as an idealphotoluminarmaterial. The powders are pelletised and sintered at an optimized temperature of1350∘Cin a short duration of two hours, yielding a high density. The morphology of the sintered pellet is further examined using scanning electron microscopy. The dielectric constant and loss factor values measured at 5 MHz for a well-sintered Calcium metaniobate pellet are found to be 27.6 and5.3×10−4respectively, at room temperature.