Reitveld Refinement Research Articles

Gd-doped ceria with extraordinary oxygen-ion conductivity for low temperature solid oxide fuel cells

Doped ceria has been extensively explored as an efficient electrolyte material for intermediate to low temperature solid oxide fuel cell. Among other ceria electrolytes, gadolinia doped ceria (GDC) is one of the most extensively studied electrolyte materials for low temperature SOFC applications. Here, co-precipitation method is employed to synthesize GDC nanoparticles with stoichiometric ratio of GdxCe1−xO2−δ (with 0 ≤\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le$$\\end{document} x ≤\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le$$\\end{document} 0.20). In this process, the molecular water of the precursors has been utilized during the co-precipitation to avoid possible agglomeration caused by hydrogen bonding. The cubic phase formation was examined using X-ray diffraction (XRD) and Raman profile ascribing absence of other phases. XRD along with Reitveld refinement confirm the presence of cubic phase of ceria and Raman profile confirms the oxygen vacancies due to the non-stoichiometry created in CeO2 lattice. The granularity of the sample was observed using field emission scanning electron microscopy (FESEM) with elemental mapping by EDS. It is observed from FESEM that the grains are compact in nature and the density observed was around 98% of the theoretical density. The electrochemical behavior was investigated using electrochemical impedance spectroscopy (EIS), which was taken between the temperature ranges of 350–700 °C. It is observed from the EIS study that ceria doped with 15 mol % Gd3+ (Gd0.15Ce0.85O2−δ) is having highest grain boundary ionic conductivity of about 0.104 S cm−1 at 700 °C with an activation energy of 0.81 eV. This work demonstrates the correlation between oxygen vacancy generation and the enhancement of ionic conductivity with Gd3+ doping in ceria.

Investigations of structural, photoluminescence, colorimetric, lifetime, and luminous efficiency of Tb3+ and Sm3+ co-doped calcium tungstate for WLEDs

Structure, photoluminescence, colorimetric, and thermoluminescence analysis of Ca1-x-yTb2x/3Sm2y/3WO4; x = 0.01; y = 0.01–0.05 ceramics are reported in this manuscript. The materials are made by the use of the solid-state method. Reitveld refinements of the obtained X-ray diffraction patterns are done by using the Fullprof Suite software. The obtained results denoted that the synthesized materials have a tetragonal structure and I41/a space group. Energy bandgaps are found in the UV–visible absorbance spectra. Photoluminescence investigations of the phosphors are done. The critical quenching concentrations of the phosphor are found to be x = 0.01; and y = 0.04. Moreover, the critical distance of energy shift with the adjacently presented ions is computed. Dexter’s theory is employed to elucidate that the dipole-dipole electronic interactions are the imperative reasons for the transfer of energy in the phosphor. The white color of emission is achieved for x = 0.01, y = 0.04 Tb, and Sm doped CaWO4 material. Moreover, great values in color purity, correlated color temperature, color rendering index as well as luminous efficiency of radiation are obtained from the CIE Chromaticity coordinates. Quantum yield efficiency of x = 0.01, y = 0.04 Tb & Sm codoped CaWO4 is measured. Photoluminescence decay analysis of all the samples is done to study the long-after glow properties and also the average lifetime values are evaluated. This is an indication of the suitable usage of the prepared materials in the white light-emitting diodes. Concentration as well as dose-dependent Thermoluminescence spectroscopy is investigated thoroughly. Kinetic parameters are calculated by deconvoluting the spectra of x = 0.01; y = 0.01 Tb & Sm codoped CaWO4 irradiated with 15 min of UV excitation dose. These results are denoted by high trap depth, second-order kinetics, and low UV dosimetry of the phosphor.

Effect of annealing temperature on structural, optical and magnetic properties of green synthesized ZFO nanoparticles for electrochemical energy storage applications

The aim of this work is to explore the effect of annealing temperature on structural, optical, magnetic properties and electrochemical properties of green synthesized ZnFe2O4 (ZFO) nanoparticles (NPs) for energy storage applications. ZFO NPs annealed at 400 °C sample showed an enormous improvement in electrochemical energy as compared to as-synthesized and other NPs annealed at different temperatures because of its higher surface area and mesoporous distribution of pore sizes. Reitveld refinement analysis of HR-XRD spectra revealed the formation of cubic spinel phase with Fd-3 m (227) space group and crystallite size significantly increased when annealing increased from 400 °C to 1000 °C because of Oswald ripening effect. The HR-TEM showed a clear irregular cubical structure of ZFO NPs with an average size of 61.20 nm for 1000 °C annealed sample. Fourier transform infra-red spectra of ZFO NPs shows metal-oxide peaks of ZnO and FeO at wavenumbers 525 cm−1 and 353 cm−1 respectively. The optical bandgap of ZFO NPs decreases with increasing temperature due to increase in the crystallite size. In addition, it is observed that, ZFO NPs showed superparamagnetic nature at room temperature and ferromagnetic nature at low temperature. The ZFO NPs annealed at 400 °C exhibit the highest specific capacitance of 435.45 F/g at 1 A/g current density. Thus, annealing temperature significantly effects the properties of green synthesized ZFO NPs. We believe the cost effective green synthesized spinel structure of ZFO NPs has great potential for electrochemical energy storage applications.

Spectroscopic and energy transfer analysis in Dy3+/Eu3+ activated/co-activated LiNaSO4 phosphors: Structural and optical properties

Sulphate based phosphors shows great impact in the field of luminescence in recent times. In the present investigation, Dy3+, Eu3+ activated/co-activated LiNaSO4 phosphor prepared by simple combustion method using urea as a fuel. Phase identification and crystal structure of prepared phosphor is investigated by XRD and Reitveld refinement. Vibrational features of proposed phosphors were confirmed by Fourier Transform Infrared Spectroscopy (FTIR). Morphological study of the proposed phosphor with elemental analysis of the sample is investigated by SEM analysis. Photoluminescence study of the proposed phosphor shows three simultaneous emission peaks in the visible range gives white light emission. These all results confirm that the proposed phosphor is potential candidate for WLEDs and solid state lighting applications.

Synthesis and Study of Optical Properties of Dy3+ Doped Yellow Emitting Fluoroapatite for White -LED Applications

In this article, we report that Ca8BiNa(PO4)6F2 fluorapatites, which were synthesised using a modified Pechini method and were first time doped with Dy3+ ions, are a promising material for yellow emitting phosphor for various optical applications. This fluorapatite has the ability to position activator Dy3+ ions in any of two cationic sites, namely M1 and M2, with distinct symmetries Cs and C3, respectively. After the sample was characterised, it was determined by XRD and Reitveld refinement analysis that it had crystallised into a hexagonal shape and belonged to the space group P63/m, matching the JCPDS file number 96-900-1879 According to the results of the PL analysis carried out by the Hitachi F-7100 spectrofluorophotometer, two emission peaks were obtained: one at 481 nm, which falls under the blue region, and the other at 575 nm, which falls under the bright yellow region. These two emission peaks correspond to the 4F9/2 to 6H15/2 and 4F9/2 to 6H13/2 transitions, respectively (Figure 5b). We suggest that the Ca8BiNa(PO4)6F2: Dy3+ can be employed as an excellent luminescent material with ultraviolet radiation as an excitation source for a variety of optical applications based on its optical properties. White light for WLED applications can be produced by a special phase doping of Dy3+ species in the host material with yellow and blue emission.

Thermo-physical properties and microstructural characteristics of U-xZr (x = 40.5, 52 & 75 wt%) alloys

Zr rich U-xZr (x = 40.5, 52 & 75 wt%) alloys were prepared by arc melting technique that improved the homogeneity and microstructural attributes of the alloys. The solidus-liquidus temperatures, phase transformation and crystallographic growth of these alloys were studied with spot technique, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and field emission scanning electron microscopic (FESEM) techniques. The solidus-liquidus temperatures were determined as 1895, 1948, 2015 K and 1951, 1996, 2046 K for 40.5, 52 and 75 wt% Zr alloys, respectively. In addition, the peritectoid transformation for 40.5 wt% Zr alloys was obtained at 868 K and the eutectoid transformation for 75 wt% Zr alloy was obtained at 864 K. Lattice parameters of the alloys were estimated through Reitveld refinement of the XRD patterns, and the variations of lattice parameters as a function of Zr content were compared with the existing literature data. It was observed that U-Zr alloys with 40.5 and 52 wt% Zr consisted of hexagonal δ-UZr2 phase only, however, alloy with 75 wt% Zr showed the presence of both δ-UZr2 and α-Zr phases. The compositional analysis by Davies and Gray method revealed that the maximum uncertainties in determining the composition for U and gravimetry for Zr were less than 0.5 wt% and 1 wt%, respectively.

Structure, microstructure and magneto-elastic property study on Co40Ni29Al31 ferromagnetic shapememory alloy ribbon

Ferromagnetic shapememory Alloys having huge magnetic field and stress-induced strain are suitable materials for sensors and actuators. Ni2MnGa being the prototype of these materials and because of its brittleness alternative systems CoNiAl/Ga were recently developed. CoNiAl being a ductile material because of its two-phase microstructure and the large range of transformation temperatures. In this line, a ribbon with nominal composition Co40Ni29Al31 was prepared using melt-spun technique. The structure and microstructure of the sample was determined using XRD and SEM. The transformation temperatures were determined using four probe method using a cryocooler within the temperature range of 4 K to 350 K. The elastic and magneto-elastic properties were studied using a Vibrating reed method within the temperature 80 K to 300 K. A constant magnetic field of 300 Oe is applied with a coil wound on the cryostat of the vibrating reed setup. As was expected the sample has two phases of microstructure, from the XRD data, a high amount of β phase with a few amount of γ phase was found and it was also replicated in SEM photographs. The phase fractions were found by fitting the XRD data with Reitveld refinement. The transformation temperatures of the sample were obtained from the four probe resistivity measurements, and they are TMs = 133 K, TMf = 83 K, TAs = 130 K and TAf = 179 K. From the sound velocity and internal friction study without and with the magnetic field interesting results were found. The martensitic and inter martensitic transformations were suppressed with the application of magnetic field. It was clearly seen in the sound velocity change plots as a function of temperature and the same was replicated in the internal friction plots. Such studies through light on the magneto-elastic coupling-related issues and are quite useful for the application of these materials for the Micro Electro Mechanical Systems at different operating conditions.

Experimental observation of spin-phonon coupling in Cr2O3 and Fe2O3 solid solution and bandgap engineering

In this work, we present experimental evidence of spin-phonon coupling at room temperature in the solid solutions of Cr2O3 and Fe2O3. The bulk ceramics of Cr2-xFexO3 were fabricated by sol–gel method. The corundum crystal structure with R-3c space group confirmed by Reitveld refinement. Spin-flop transitions observed in the 100–400 K temperature ranges from M−H studies were observed in the lower doping range. The magnetic transition observed from the temperature dependent magnetic studies showed the transition is consistent with the previous reports. The spin-phonon coupling in the ceramics is observed from the two phonon modes in the materials originating from Eg and A1g modes in the Raman spectroscopy. Eg mode shifts towards lower frequency, while A1g mode shifts towards high frequency. UV–vis spectral studies revealed the narrowing of bandgap originating from the Cr-O-Fe hybridisation. Impedance spectroscopy analysis shows that relaxation peaks shift from 90 K to 240 K towards high temperatures. The activation energy value is 0.32 – 0.21 eV, indicating the polaron hopping conductivity in the bulk ceramics.

Energy transfer properties of CaYAlO4:Bi3+, Mn4+ phosphor for indoor crop cultivation LED lighting

This paper reports a series of Bi3+/Mn4+ doped CaYAlO4 (CYAO:Bi3+, Mn4+) phosphors prepared via sol-gel method. The phase purity and accurate crystal structure information of these phosphors were confirmed by the measurement of XRD, TEM and Reitveld refinement. Under excitation of 346 nm, CYAO:Bi3+, Mn4+ phosphors show two broad emission bands centered at 407 nm and 709 nm, respectively. The results of PL spectra and decay lifetime measurement prove that the energy transfer from Bi3+ to Mn4+ in CYAO host can be realized. The emitting intensity of CYAO:0.01Bi3+, 0.005Mn4+ phosphor can be enhanced by 184% than Bi3+-free sample and its energy-transfer efficiency and internal quantum efficiency (IQE) reach up to 85% and 54% respectively. With the introduction of Bi3+, the activation energy of CYAO:0.01Bi3+, 0.005Mn4+ can be improved from 0.31eV to 0.44eV as compared with CYAO:0.005Mn4+ phosphor, indicating that its thermal stability performance has a great enhancement. Furthermore, the CIE value and the luminous efficiency the fabricated pc-LED device are (0.7211, 0.2788) and 0.6 l m/W. Meanwhile, its emission spectrum matches well with the absorption spectrum of PFR, which implies that this phosphor can be a potential candidate for application in indoor crop cultivation.

Experimental and theoretical investigations on fullerene (C60) induced compact CH3NH3PbI3 perovskite thin films

In the present work, pure and Fullerene (C60)-doped methyl ammonium lead halide (CH3NH3PbI3) perovskite thin films were prepared on glass substrates by spin coating method at different concentrations of fullerene (C60).The structural, morphological, and optical characteristics of as-prepared thin films were analysed using experimental and computational methods. The X-ray diffraction studies and their Reitveld refinement analysis of the samples confirms that all deposited perovskite thin films have tetragonal structure and are highly oriented along the (110) plane. The morphology of the perovskite films was investigated by field emission scanning electron microscope (FE-SEM). The elemental composition of perovskite thin films was confirmed by Energy Dispersive X-rays Analysis (EDAX). The addition of fullerene (C60) resulted in the increase of grain size sand a more compact surface development of the perovskite thin films with fewer flaws as compared with perovskite thin films without (C60) was evaluated. Also, geometrical, electronic and optical properties were studied by using the first principles DFT computational method. Optical properties have been studied experimentally and verified computationally. All the perovskite thin film samples exhibit direct band-gap which is suitable for solar cells applications.

Investigation of structural, photoluminescence, and thermoluminescence properties of Praseodymium doped CaWO4 phosphor

The structural, optical, photoluminescence and thermoluminescence behaviors of Praseodymium doped CaWO4 (Ca1−xPr2x/3WO4; x = 0.01, 0.02, 0.03, 0.04, 0.05) phosphors prepared via conventional solid-state reaction route were reported in this paper. X-ray diffraction study revealed the fact that all the synthesized samples crystallize in a tetragonal structure with I41/a (88) space group and the structural parameters were obtained from the Reitveld refinement. The unit cell volume was found to rise with the increase in Pr concentration. The bandgaps of the prepared samples were obtained from the UV-Visible absorbance spectra by using the Wood-Tauc method. Bandgap and unit cell volume of the prepared samples were directly proportional to each other. Photoluminescence behaviors were investigated from the excitation and the emission spectra. The PL spectra highlight that the quenching occurs at x = 0.02 and the critical distance for energy transfer of the phosphor was found to be 20 Å. Dexter theory was applied to determine the mechanism of quenching and confirmed that the concentration quenching was caused by the dipole-dipole interaction. CIE Chromaticity denoted that the phosphors emit red color. Color purity and CCT of the material were calculated. Thermoluminescence behaviors were studied with different durations of UV dose for the composition x = 0.02 and the kinetic parameters were calculated. Variations of TL emission intensity with temperature confirmed the second-order kinetics of the phosphor with a critical quenching concentration at x = 0.02.

Effect of shock wave on optical properties of Propyl p-hydroxybenzoate single crystal: A self-defocusing third order nonlinear optical material

This work focuses on the effect of shock wave on optical properties of propyl p-hydroxybenzoate single crystal. An optically transparent single crystal was grown by adopting slow evaporation solution growth technique (SEST). Its structure was confirmed by powder X-ray diffraction using Reitveld refinement. The Hirshfeld surface morphology and the intermolecular interaction of titled compound was scrutinized using crystal explorer. Three shock waves generated at constant air compressor pressure of 0.78 Mpa with calculated Mach number 1.7 were allowed to interact with the grown crystal. The UV–vis spectroscopy analysis on shock wave treated sample shows an increase in transmittance for 1st and 2nd shock and a reduction of transmittance for the 3rd shock wave. The defects induced after each shockwave – sample interaction was investigated by photoluminescence spectroscopy and surface morphology studies in detail. The third order nonlinear properties like self – defocusing and reverse saturation absorption of grown crystal were studied using a femto-second Ti-sapphire laser source. The nonlinear absorption coefficient, refractive index were calculated to be 4.04 ˟ 10−10 cm/W and −8.47 ˟ 10−15 cm2/W using open and closed aperture Z-scan measurement respectively.

Influence of particle size on magnetic and electromagnetic properties of hexaferrite synthesised by sol-gel auto combustion route

Magnetoplumbite barium hexaferrite (BaFe11.8Co0.2O19) is synthesised through sol-gel auto-combustion method under two pH conditions of precursor solutions (acidic i.e. pH < 1 and neutral i.e. pH = 7). The XRD analysis followed by Reitveld refinement indicates the formation of phase pure samples in both cases but the barium hexaferrite obtained from acidic precursor solution has smaller crystallite sizes. The Transmission Electron Microscopy (TEM) analysis followed by High Resolution Transmission Electron Microscopy (HRTEM) confirms a lower particle size of ∼20 nm for barium hexaferrite synthesised from acidic pH precursor solution. The shift in Raman peak (520-540 cm−1) by 20 cm−1, represents the whole structural block and further confirms the differences in the distribution of particle sizes due to the method of synthesis. The magnetic studies display a lower coercive field for the samples with smaller particle sizes. This is due to the crystalline size-induced microstrain that controls the magneto-crystalline anisotropy, shape anisotropy and stress anisotropy. The electromagnetic characterisation confirms broader absorption in the range of 8–18 GHz (X-band) with RL ≤ −7 db for the entire range for the samples with smaller particle sizes.

Energy transfer mechanism in K2Ba(PO4)F:Dy3+, Eu3+ co-activated phosphor: Spectral tuning phosphor for photovoltaic efficiency enhancement

Fluoride based phosphor makes a special impact in the field of luminescent spectroscopy as well as in photovoltaic applications from several decades. In the proposed work Dy3+, Eu3+ co-activated K2Ba(PO4)F phosphors have been synthesized via low temperature simple combustion method using urea as a fuel. Phase confirmation and crystal structure determination of proposed sample were confirmed by Reitveld refinement analysis. Crystal structure of the proposed phosphor is in the tetragonal phase with space group I4/mcm. The particle size of the proposed phosphors was in the range of sub-micrometers confirmed by SEM analysis. Photoluminescence study of the proposed sample confirms the spectral tuning from blue to red. I-V characteristics of the optimum phosphor coated on solar cell shows the efficiency enhancement of the cell by 16.02% by blank cell. All these results shows that the Dy3+, Eu3+ co-activated K2Ba(PO4)F phosphors are proving their worth as they are might be the potential candidate for WLEDs and photovoltaic applications.

Structural Characterization and Physical Properties of Double Perovskite La2FeReO6+δ Powders.

The structural, optical, dielectric, and magnetic properties of double perovskite La2FeReO6+δ (LFRO) powders synthesized by solid-state reaction method under CO reduced atmosphere are reported on in this paper. Reitveld refinements on the XRD data revealed that the LFRO powders crystallized in an orthogonal structure (Pbnm space group) with column-like morphology. The molar ratios of La, Fe, and Re elements were close to 2:1:1. XPS spectra verified the mixed chemical states of Fe and Re ions, and two oxygen species in the LFRO powders. The LFRO ceramics exhibited a relaxor-like dielectric behavior, and the associated activation energy was 0.05 eV. Possible origins of the dielectric relaxation behavior are discussed based on the hopping of electrons among the hetero-valence ions at B-site, oxygen ion hopping through the vacant oxygen sites, and the jumping of electrons trapped in the shallower level created by oxygen vacancy. The LFRO powders display room temperature ferromagnetism with Curie temperature of 746 K. A Griffiths-like phase was observed in the LFRO powders with a Griffiths temperature of 758 K. The direct optical band gap of the LFRO powders was 2.30 eV, deduced from their absorption spectra, as confirmed by their green photoluminescence spectra with a strong peak around 556 nm.

Thermal expansion study on LnMgAl11O19 (Ln=La, Gd) by high temperature X-ray diffraction

Thermal expansion performance is essential for lanthanide magnesium hexaaluminate (LnMgAl11O19, Ln=La, Gd) top-coating as the thermal barrier coatings materials. In the present work, LnMgAl11O19 (Ln= La and Gd) with magnetoplumbite structure was synthesized by the chemical co-precipitation method. The lattice thermal expansion behavior of both the samples was investigated using a high-temperature X-ray diffraction test combined with Reitveld refinement. The results showed that the thermal expansion of the a-axis was smaller than that of the c-axis, which was related to the anisotropic elongation of Ln-O bonds in the [LaO12] clusters. Meanwhile, the lattice expansion coefficient of the LaMgAl11O19 was higher than that of GdMgAl11O19. This was confirmed by the result of the macroscopic thermal expansion which was measured using a high-temperature dilatometry. The underlying mechanism was discussed, which was due to the weaker bond energy of La–O than that of Gd–O.

Non-Arrhenius Ionic Conductivity Transitions in Sodium Antiperovskite Ionic Conductors

Anti-perovskites materials have recently attracted great interest as a family of solid state electrolytes with high ionic conduction.[1] Typical solid-state ionic conductors have temperature-dependent ionic conductivity following Arrhenius behavior over a substantial range of temperature, corresponding to a constant activation energy Ea. In the Na3OCl antiperovskite (Fig. 1), there are regimes of Arrhenius behavior separated by broad transitions, all while the structure remains cubic, Figure 2. Such non-Arrhenius ionic conductivity of Na3OCl has been observed in previous literature. [2][3] However, there is no clear explanation for this non-Arrhenius transition. Differential scanning calorimetry shows thermal transitions in the vicinity of these conductivity transitions, Figure 3, suggesting order/disorder phase transitions. Reitveld refinement on temperature dependent synchrotron XRD of Na3OCl suggests changes in octahedral tilt systems, which is CmCm in the low temperature region, Pnma in the medium temperature region, and P4/mbm in the high temperature geion, Figure 4. In this work, we use multiple temperature-resolved characterization methods including synchrotron XRD, transport measurements, and calorimetry, and modeling by AIMD and DFT, to understand this behavior and to gain insight into tuning antiperovskites for high ionic conductivity.This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Figure 1

Structural and optical properties along with magnetization reversal and bipolar switching in CeCr1−xFexO3 (x = 0 and 0.05) nanoparticles

Nano-crystalline, CeCr1−xFexO3 (x = 0 and 0.05) compounds synthesized by a facile nitrate-solution combustion method are crystallized in orthorhombic, Pnma structure. Reitveld refinement of diffraction patterns reveal an expansion of lattice parameter and lattice volume after the substitution of Fe. Structural analysis evidences an increase in distortion in orthorhombic structure due to bending of Cr-O6 octahedra which is a sheer consequence of the lattice expansion. The optical band gap decreases from 2.9 to 2.6 eV due to the increase in particle size and decrease in strain after Fe substitution estimated from Williamson-Hall analysis. Besides the decrease in Neel temperature from 260 to 253 K after Fe incorporation, temperature-dependent magnetization exhibits some peculiar features such as compensation temperature, Tcomp, and spin reorientation temperature, TSR. While TSR enhances from 15 to 30 K, we observe two Tcomp at 13 and 110 K for x = 0.05 in contrast to only one Tcomp at 61 K for the pristine phase. Moreover, we for the first time demonstrate a stable switching behavior of magnetization by varying the external field in the same direction. The increase in Tcomp and TSR along with a decrease in band gap from 2.9 eV to 2.6 eV makes this material suitable for bipolar magnetic switching and photocatalytic applications.

Simultaneous enhancement in thermopower and electrical conductivity of SnTe-Te nano heterostructures

SnTe nanomaterials are investigated as the potential “Lead” free thermoelectric material owing to their low thermal conductivity induced enhanced figure of merit in comparison with their bulk counterpart. In this work, SnTe and its SnTe-Te heterostructures were synthesized for the first time by changing the protocol of heating time using microwave-assisted solvothermal processes. The confocal and scanning electron microscope images demonstrate the nano-flower-like morphology of SnTe-Te heterostructures. Multi-phase Reitveld refinement structural analysis exhibits a significant increase in tellurium occupancies, whereas elemental mapping confirms the presence of SnTe-Te heterostructure. Interestingly, room temperature thermoelectric power of SnTe-Te heterostructures (~60 μV/K) is increased by ~55% when compared to SnTe nanostructures (~45 μV / K). Simultaneous enhancement of both electrical conductivity and Seebeck coefficient are attributed to the increment of carrier mobility and effective mass respectively which is due to the novel strategy of SnTe-Te heterostructures formation that is promising for large scale p-type thermoelectric applications.

Structural, dielectric, magnetic and optical properties of double perovskite oxide Sm2NiMnO6 nanoparticles synthesized by a sol−gel process

Here we report on the structural, dielectric, magnetic and optical properties of double perovskite Sm2NiMnO6 (SNMO) nanoparticles synthesized by a sol−gel method. Structural Reitveld refinements on x-ray powder diffraction data revealed that the SNMO nanoparticles crystallized in a monoclinic crystal structure with P21/n space group. SEM and (HR)TEM images revealed the phase purity and single-crystalline nature of the SNMO nanoparticles. XPS spectra confirmed the presence of Sm3+, Ni2+ and Mn4+ ions in the SNMO nanoparticles and oxygen in the forms of lattice oxygen and the hydroxyls species. SNMO ceramics exhibited relaxor-type dielectric behavior, well fitted by modified Curie−Weiss law. Such dielectric behavior originated from the interactions of random dipoles arisen from the B-site cations disorder accompanied with the variations in local electric fields and local strain fields due to the different radii of B-site cations, and/or the virtual electrons hopping between the Ni2+ and Mn4+ cations. Magnetic data demonstrate the variations of the magnetic transitions at low temperatures and the spin glass-like behavior below 11 K, which is attributed to the spin fluctuations induced by the competing interactions between the ferromagnetic (FM) and antiferromagnetic phases. Large positive Curie−Weiss temperature (θ p) indicates the dominant FM super-exchange interactions in the SNMO samples. The SNMO nanoparticles have a direct optical band gap of 1.42 eV, close to 1.34 eV in a single junction solar cell. That enables the SNMO nanoparticles to be useful for solar cell absorbers.