Structural and Transport Properties of La0.85Te0.15MnO3 Manganite and its Composite with Al2O3

The manganite systems investigated during the present work are pure La0.85Te0.15MnO3 (LTMO) and its composite with 12% concentration of Al2O3 nano powder (LTMO + Al2O3). The materials were prepared by the modified auto combustion technique. The samples were characterized by X-ray diffraction. The powder X-ray diffraction pattern of pure LTMO at room temperature shows that sample is in single phase with no detectable secondary phases and the sample have a rhombohedral structure in hexagonal with the space group R3c. The XRD pattern of LTMO + 12% Al2O3 indicates the clear presence of Al2O3 nano phase in the composite. In the present study, the FTIR Spectroscopy of both samples was carried out. It is clear from the Vibrational assignment for the value of corresponding peak position of FTIR spectra that no extra unwanted impurity is present in samples. A quantitative analysis of the energy dispersive spectroscopy (EDS) data indicates that the observed concentration of elements are very close to the calculated values from its chemical formula. R-T measurements reveals that the addition of secondary phase in manganite strongly influenced on electronic and magnetoresistance behaviour. We summarise some of the salient features of the results.

Understanding the Seebeck coefficient of LaNiO3 compound in the temperature range 300-620 K

Transition metal oxides have been attracted much attention in thermoelectric community from the last few decades. In the present work, we have synthesized LaNiO3 by a simple solution combustion process. To analyze the crystal structure and structural parameters we have used Rietveld refinement method wherein FullProf software is employed. The room temperature x-ray diffraction indicates the rhombohedral structure with space group R 3 c (No. 167). The refined values of lattice parameters are a = b = c = 5.4071 Å. Temperature dependent Seebeck coefficient (S) of this compound has been investigated by using experimental and computational tools. The measurement of S is conducted in the temperature range 300-620 K. The measured values of S in the entire temperature range have negative sign that indicates n-type character of the compound. The value of S is found to be ∼ -8 µV/K at 300 K and at 620 K this value is ∼ -12 µV/K. The electronic structure calculation is carried out using DFT+U method due to having strong correlation in LaNiO3. The calculation predicts the metallic ground state of the compound. Temperature dependent S is calculated using BoltzTraP package and compared with experiment. The best matching between experimental and calculated values of S is observed when self-interaction correction is employed as double counting correction in spin-polarized DFT + U (= 1 eV) calculation. Based on the computational results maximum power factors are also calculated for p-type and n-type doping of this compound.

Recycling Rusty Iron with Natural Zeolite Heulandite to Create a Unique Nanocatalyst for Green Hydrogen Production

Corrosion-induced iron rust causes severe danger, pollution, and economic problems. In this work, nanopowders of Fe2O3 and Fe2O3/zeolite are synthesized for the first time using rusted iron waste and natural zeolite heulandite by chemical precipitation. The chemical composition, nanomorphologies, structural parameters, and optical behaviors are investigated using different techniques. The Fe2O3/zeolite nanocomposite showed smaller sizes and greater light absorption capability in visible light than Fe2O3 nanopowder. The XRD pattern shows crystalline hematite (α-Fe2O3) with a rhombohedral structure. The crystallite sizes for the plane (104) of the Fe2O3 and Fe2O3/zeolite are 64.84 and 56.53 nm, respectively. The Fe2O3 and Fe2O3/zeolite have indirect bandgap values of 1.87 and 1.91 eV and direct bandgap values of 2.04 and 2.07 eV, respectively. Fe2O3 and Fe2O3/zeolite nanophotocatalysts are used for solar photoelectrochemical (PEC) hydrogen production. The Fe2O3/zeolite exhibits a PEC catalytic hydrogen production rate of 154.45 mmol/g.h @ 1 V in 0.9 M KOH solution, which is the highest value yet for Fe2O3-based photocatalysts. The photocurrent density of Fe2O3/zeolite is almost two times that of Fe2O3 catalyst, and the IPCE (incident photon-to-current conversion efficiency) reached ~27.34%@307 nm and 1 V. The electrochemical surface area (ECSA) values for Fe2O3 and Fe2O3/zeolite photocatalysts were 7.414 and 21.236 m2/g, respectively. The rate of hydrogen production for Fe2O3/zeolite was 154.44 mmol h−1/g. This nanophotocatalyst has a very low PEC corrosion rate of 7.6 pm/year; it can retain ~97% of its initial performance. Therefore, the present research can be applied industrially as a cost-effective technique to address two issues at once by producing solar hydrogen fuel and recycling the rusted iron wires.

Optical, Structural, Morphological Properties of Chromium (III) Oxide Nanostructure Synthesized Using Spray Pyrolysis Technique

Nanostructure of chromium oxide (Cr2O3-NPs) with rhombohedral structure were successfully prepared by spray pyrolysis technique using Aqueous solution of Chromium (III) chloride CrCl3 as solution. The films were deposited on glass substrates heated to 450°C using X-ray diffraction (XRD) shows the nature of polycrystalline samples. The calculated lattice constant value for the grown Cr2O3 nanostructures is a = b = 4.959 Å & c = 13.594 Å and the average crystallize size (46.3-55.6) nm calculated from diffraction peaks, Spectral analysis revealed FTIR peak characteristic vibrations of Cr-O Extended and Two sharp peaks present at 630 and 578 cm-1 attributed to Cr-O “stretching modes”, are clear evidence of the presence of crystalline Cr2O3. The energy band gap (3.4 eV) for the chromium oxide nanostructures was measured using the UV-VIS-NIR Optical Spectrophotometer. It was found that by scanning electron microscopy (SEM) and image results, there is a large amount of nanostructure with an average crystal size of 46.3-55.6 nm, which indicates that our synthesis process is a successful method for preparing Cr2O3 nanoparticles.

Electroplating Deposition of Bismuth Absorbers for X-ray Superconducting Transition Edge Sensors

An absorber with a high absorbing efficiency is crucial for X-ray transition edge sensors (TESs) to realize high quantum efficiency and the best energy resolution. Semimetal Bismuth (Bi) has shown greater superiority than gold (Au) as the absorber due to the low specific heat capacity, which is two orders of magnitude smaller. The electroplating process of Bi films is investigated. The Bi grains show a polycrystalline rhombohedral structure, and the X-ray diffraction (XRD) patterns show a typical crystal orientation of (012). The average grain size becomes larger as the electroplating current density and the thickness increase, and the orientation of Bi grains changes as the temperature increases. The residual resistance ratio (RRR) (R300 K/R4.2 K) is 1.37 for the Bi film (862 nm) deposited with 9 mA/cm2 at 40 °C for 2 min. The absorptivity of the 5 μm thick Bi films is 40.3% and 30.7% for 10 keV and 15.6 keV X-ray radiation respectively, which shows that Bi films are a good candidate as the absorber of X-ray TESs.

Preparation and Characterization of Nanosized Substituted Perovskite Compounds with Orthorhombic Structure

In this work, five substituted perovskite such as (Gd0.9Sr0.1) Mn0.8Co0.2O3, Tb0.8Sr0.2FeO3, Gd0.6Sr0.4RuO3, SrCe0.95Y0.05O3, and Mn0.6Co0.4SnO3 were synthesized by tartrate and hydroxide precursor method. The resulting samples were characterized by inductively coupled plasma spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy, thermal analysis, X-ray powder diffraction, transmission electron microscope (TEM), selected field of electron diffraction (SAED), d.c. electrical conductivity, Hall effect, dielectric measurements, and low-temperature magnetization measurements. The X-ray diffraction pattern for all compounds was indicated the formation of single-phase perovskite with orthorhombic structure except Tb0.8Sr0.2FeO3 and Mn0.6Co0.4SnO3 perovskite. These compounds showed a cubic and rhombohedral structure, respectively. The lattice parameter and the unit cell volume slightly decreased as ionic radii decrease in agreement with the lanthanide contraction. The average size of cation ˂ RA ˃, mismatch factor (σ2), and tolerance factor (t) gives the combined effects of disorder and inhomogeneity in these compounds. The average particle size determined from TEM was in the range of 22 to 77 nm for all compounds. The temperature dependence of electrical conductivity for all compounds showed a definite break in 500 K to 610 K. except the Gd0.6Sr0.4RuO3 compound, which corresponds to semiconducting behavior. While the Gd0.6Sr0.4RuO3 sample shows a metallic-like semiconductor. The thermoelectric power and Hall effect measurements for all compounds were n-type semiconductivity except the SrCe0.95Y0.05O3 compound. It showed p-type semiconductivity. The frequency dependence of the dielectric constant and dielectric loss in these substituted perovskites were discussed using the Maxwell-Wagner model. Magnetic studies showed that the thermo-magnetic irreversibility for all compounds.

Coexistence of structural and magnetic phases in van der Waals magnet CrI3

CrI3 has raised as an important system to the emergent field of two-dimensional van der Waals magnetic materials. However, it is still unclear why CrI3 which has a ferromagnetic rhombohedral structure in bulk, changed to anti-ferromagnetic monoclinic at thin layers. Here we show that this behaviour is due to the coexistence of both monoclinic and rhombohedral crystal phases followed by three magnetic transitions at TC1 = 61 K, TC2 = 50 K and TC3 = 25 K. Each transition corresponds to a certain fraction of the magnetically ordered volume as well as monoclinic and rhombohedral proportion. The different phases are continuously accessed as a function of the temperature over a broad range of magnitudes. Our findings suggest that the challenge of understanding the magnetic properties of thin layers CrI3 is in general a coexisting structural-phase problem mediated by the volume-wise competition between magnetic phases already present in bulk.

Solvent-Mediated Structural Evolution Mechanism from Cs4PbBr6 to CsPbBr3 Crystals

The study of the solvent-mediated structural evolution mechanism of the Cs4PbBr6 powders prepared using the solvothermal method is presented. The Cs4PbBr6 powders with a rhombohedral structure and an intense green emission (i.e., mainly due to the presence of complex defect states in the forbidden gap), which is stable in its solid-state form, but a distinct behavior is observed in different dispersions, easily detectable when irradiated with ultraviolet (UV) light. Depending on the polarity of the solvent, a change in the emission color from green to red is observed, easily detectable when irradiated with ultraviolet (UV) light. Our findings suggest that the solvent polarity affects the surface decomposition process, leading to a different change in composition, structure and crystal shape. This peculiar behavior plays a pivotal role in the control of the properties of Cs4PbBr6, and this study, therefore, offers a fundamental understanding needed for Cs4PbBr6 potential future applications.

Thermomagnetic Correlation in La0.85-xBixNa0.15MnO3 Soft Ferromagnet due to Nonmagnetic Bi3+ Substitution

We report the structural, magnetic, and magnetocaloric properties of Bismuth (Bi)-substituted manganite La0.85-xBixNa0.15MnO3 (x=0, 0.1, 0.2, 0.25, and 0.3). X-ray diffraction data implicates the rhombohedral structure with $$ R\overline{3}c $$ R 3 ¯ c space group. Bi2O3 has helped in ensuring phase pure, densified compounds even at low sintering temperature and hence avoiding the evaporation of volatile sodium. The increase in grain size and decrease in magnetic transition temperature (TC) are due to the Bi chemical activity and electronic structure. The samples have shown indirect magnetic transformation from soft ferromagnet to canted ferromagnet/antiferromagnet with Bi. Griffiths phase-like behavior in the inverse magnetic susceptibility was observed for x=0.1; with further increase in Bi, the samples are found to develop the antiferromagnetic competing phase. The phenomenological model was used to model the thermomagnetic behavior of all the samples. The sample with x=0.1 shows an increase in magnetic entropy change upon Bi substitution and the maximum of magnetic entropy change is seen at 275K emphasizing its potential in room temperature magnetic refrigeration.