Modifications on the Structural, Optical, and Magnetic Properties of Ce‐Doped Ni‐Cu‐Co Spinel Nanoferrites Synthesized by Sol–Gel via Auto‐Combustion Method

<sec>Two-dimensional materials have shown excellent optical, mechanical, thermal or magnetic properties, and have promising applications in the high performance electronic, optical, spintronic devices and energy transfer, energy storage, etc. Monolayer transition metal silicide CrSi<sub>2</sub> has shown ferromagnetism and metal properties in previous studies, and it is expected to become a new two-dimensional material. The Ti, V, Co, Ni doped two-dimensional CrSi<sub>2</sub> are studied with different doping concentrations by using the first-principal pseudopotential plane wave method based on density functional theory, and electronic structure, magnetic and optical properties are calculated and analyzed. The results show that the density of states in the two-dimensional CrSi<sub>2</sub> system is asymmetric, and the crystal cells have obvious ferromagnetism with a magnetic moment of 3.55 <i>μ</i>B. Two-dimensional CrSi<sub>2</sub> has strong absorptivity and reflectivity in the far infrared and ultraviolet range, showing excellent optical properties.</sec><sec>The electronic structures and magnetic properties of Ti, V, Co or Ni doped CrSi<sub>2</sub> with different concentrations are calculated and analyzed, and the results show that the magnetic moment of the two-dimensional CrSi<sub>2</sub> varies after doping different elements at a doping concentration of 3.70 at%. After doping Ti, the magnetic moment of the system changes to 0 <i>μ</i>B at a doping concentration of 3.70 at%, showing that it is an indirect semiconductor. After doping V, the magnetic moment becomes smaller at a doping concentration of 3.70 at%, and the system has two degrees of freedom: electron charge and spin, showing the properties of diluted magnetic semiconductors. After doping Ni, the band gap <i>E</i><sub>g</sub>=0.09 eV appears in the spin-up band of the system at a doping concentration of 3.70 at%, while the spin-down band is metallic, and the system shows semi-metallic properties. The magnetic moment changes to 3.71 <i>μ</i>B after doping Ti at a doping concentration of 7.41 at%. After doping Co and Ni, the magnetic moment of the system becomes smaller at the doping concentration of 7.41 at%, and the spin-down 3<i>d</i> orbital electrons of ferromagnetic elements take the dominant position. After doping Ni, the magnetic moment becomes 0.37 <i>μ</i>B at the doping concentration of 7.41 at%. After doping Ti, the magnetic moment becomes 2.79 <i>μ</i>B at a doping concentration of 33.3 at at%, after doping V, the magnetic moment becomes 2.27 <i>μ</i>B, and the degree of spin becomes weaker at a doping concentration of 11.1 at%. After doping Co, the magnetic moment becomes 1.81 <i>μ</i>B at the doping concentration of 11.1 at%. The magnetic moment becomes 1.5 <i>μ</i>B after doping Ni at the doping concentration of 11.1 at%, which proves that the spin-up <i>d</i> orbital has less electronic contribution to the magnetic moment. The energy band range of each system is enlarged, and the interaction between atoms is enlarged, and the energy level splitting energy is enlarged at the doping concentration of 11.1 at%, which indicates that the effective mass of the system becomes smaller, the mobility of carriers turns stronger, and the metallization of materials grows stronger.</sec><sec>The optical properties of Ti, V, Co or Ni doped CrSi<sub>2</sub> with different concentrations are calculated and analyzed, and the results show that the two-dimensional CrSi<sub>2</sub> after being doped has good optical properties. For most of systems, their optical properties are improved and blue-shifted at the doping concentrations of 3.70 at% and 7.41 at%, but the absorption peak is red-shifted at the doping concentration of 11.1 at%. By studying the properties of doped two-dimensional CrSi<sub>2</sub>, it is found that the two-dimensional CrSi<sub>2</sub> has excellent electronic structure and optical properties, and the electronic structure, magnetic and optical properties of the two-dimensional CrSi<sub>2</sub> can be effectively changed by doping. Two-dimensional CrSi<sub>2</sub> is expected to be a promising material for preparing new high reliability and high stability spintronic devices, and the present research provides an effective theoretical basis for developing the two-dimensional CrSi<sub>2</sub> based devices.</sec>

Effect of cerium incorporation on the structural and optical properties of CdS film

Transparent conducting oxide (TCO) materials with high transmittance and good electrical conductivity have been attracted much attention due to the development of electronic display and devices such as organic light emitting diodes (OLEDs), and dye-sensitized solar cells (DSSCs). Aluminum doped zinc oxide thin films (AZO) have been well known for their use as TCO materials due to its stability, cost-effectiveness, good optical transmittance and electrical properties. Especially, AZO thin film, which have low resistivity of 2-4 x 10(-4) omega x cm which is similar to that of ITO films with wide band gap semiconductors. The AZO thin films were deposited on glass substrates by sol-gel spin-coating process. As a starting material, zinc acetate dihydrate (Zn(CH3COO)2 x 2H2O) and aluminum chloride hexahydrate (AlCl3 6H2O) were used. 2-methoxyethanol and monoethanolamine (MEA) were used as solvent and stabilizer, respectively. After deposited, the films were preheated at 300 degrees C on a hotplate and post-heated at 650 degrees C for 1.5 hrs in the furnace. We have studied the structural and optical properties as a function of Al concentration (0-2.5 mol.%).

Manganese substituted nickel–cobalt ferrite nanoparticles having the basic composition Ni0.2MnxCo0.8−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) were synthesized using sol–gel auto combustion method. The effect of Mn substitution on structural and magnetic properties of nickel–cobalt ferrite has been studied. All the prepared samples show that the single-phase cubic spinel structure by X-ray diffraction. The average microcrystalline size of the prepared samples is about 50 nm calculated by Scherrer equation. With the increase of Mn content, the lattice constant decreases first and then increases for the prepared samples. Fourier transform infrared measurements also confirm the formation of the cubic spinel structure of ferrite. The absorption peak of the Fe–O bond at tetrahedral position shifted to the low frequency with the increase of manganese ion content. By transmission electron microscope observation of the preparation of samples with spherical cube crystallite particles. Energy dispersive X-ray confirmed that the synthesis with pure phase and structure of ferrite, and successfully realized the Mn2+ doping. Vibration sample magnetometer measurement confirm that the Ni0.2MnxCo0.8−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) nanoparticles have ferromagnetic behavior. It is observed that the saturation magnetization (Ms), remanent magnetization (Mr), rectangular ratio (Mr/Ms) and magnetic moment are decreasing with the increase of manganese ion content. The prepared ferrites have high coercivity, and the decrease of coercivity of samples is due to excessive Mn substitution. At the same time, the magnetization is expected to decrease because of the conversion of equivalent amounts of Fe3+ (5 µB) to Fe2+ (4 µB).

Effect of Ni toward the optical and transport properties of the spinel solid solution NixCu1−xFe2O4 nanoparticles

In the present research article, structural, optical, and magnetic properties along with Curie temperature of lithium substituted magnesium ferrite nanoparticles, Mg0.5+xLi1−2xFe2O4 (0 ≤ x ≤ 0.35) have been reported. The nanomaterial was prepared successfully using chemical-based citrate precursor sol–gel method and annealed at 550 °C. The X-ray diffraction analysis of the prepared nanomaterials confirms the formation of cubic spinel structure. The W–H plots were used to calculate crystal structure and lattice strain. The crystallite size was found to be 24 nm, 78 nm, and 50 nm, respectively, for three composition. The lattice strain was found to decrease and lattice constant was found to increase as the molar concentration of Li ion increases. The EDS measurements confirmed the presence of Mg, Fe, and oxygen. Functional group was measured using FTIR in the range of wave number 1000–400 cm−1 which confirms spinel structure. SEM are used for grain size determination with surface morphology analysis and found agglomerated nanocrystalline of different sizes. The optical properties were measured using UV/Vis/NIR and photoluminescence (PL) spectrometer. The energy bandgap was found 2.5 eV, 1.98 eV, and 2.41 eV, respectively, for the three prepared nanomaterials. While enhancement in photoluminescence spectra measured using PL spectrometer observed with decrease in lithium concentration. The magnetic properties were measured using vibrating sample magnetometer. The magnetic parameters like saturation magnetization, coercivity, and anisotropic constants were found to be increasing with the decrease in lithium ion concentration (Ms 11.63 emu/g–16.24 emu/g, Hc 110.81Oe–156.67Oe and (1342.41 to 2650.33). This non-stoichiometric structure was observed to affect the Curie temperature from 479 °C to 454 °C which often provides the possibility of this nanomaterial for broad range of applications in memory devices, isolators, circulator, etc.

Gamma-ray irradiation-induced effects on Er3+-doped Li2O-Bi2O3-B2O3-TeO2 glass: Structural, optical, luminescence, and radiation shielding properties

The structural, electronic, optical and thermal properties of chalcopyrite LiAlTe2 are studied using the full potential linearized augmented plane wave (FP-LAPW) method framed within density functional theory (DFT). The Wu-Cohen generalized gradient approximation (WC-GGA) was used as exchange-correlation potential to calculate the structural properties. Furthermore, the Tran and Blaha modified Becke-Johnson (mBJ) functional was also employed to compute the electronic and optical properties in order to get best values. The structural parameters at equilibrium are in good agreement with previous experimental and theoretical calculations. The band structures and density of states are calculated and it is found that LiAlTe2 compound is a direct band gap (-) semiconductor. In addition, the optical properties such as dielectric function, refractive index, reflectivity and absorption coefficient are calculated for photon energies up to 25 eV. This study on the optical properties has also been enriched by the introduction of the analysis of birefringence and anisotropy for this material. The calculated values of all parameters are compared with the available theoretical data where a reasonable agreement has been obtained. The study of the material properties at high temperatures and pressures is very important to understand the behavior of a material in severe conditions, so the temperature and pressure dependencies of unit cell volume, bulk modulus, Debye temperature and specific heat capacities are obtained at different temperatures (0-1000 K) and pressures (0-8 GPa) using the quasi-harmonic Debye model. To our knowledge this is the first theoretical prediction of the thermal properties for LiAlTe2 compound and still awaits experimental confirmations. We have included the spin-orbit interaction (SOI) in our calculations which is known to have significant influence on the electronic and optical properties when heavy elements are present. A weak effect is observed for the studied compound. Keywords: DFT, Wien2k, Chalcopyrite, band gap, dielectric function, thermal properties.

CONSPECTUS: After the discovery of graphene and the development of powerful exfoliation techniques, experimental preparation of two-dimensional (2D) crystals can be expected for any layered material that is known to chemistry. Besides graphene and hexagonal boron nitride (h-BN), transition metal chalcogenides (TMC) are among the most studied ultrathin materials. In particular, single-layer MoS2, a direct band gap semiconductor with ∼1.9 eV energy gap, is popular in physics and nanoelectronics, because it nicely complements semimetallic graphene and insulating h-BN monolayer as a construction component for flexible 2D electronics and because it was already successfully applied in the laboratory as basis material for transistors and other electronic and optoelectronic devices. Two-dimensional crystals are subject to significant quantum confinement: compared with their parent layered 3D material, they show different structural, electronic, and optical properties, such as spontaneous rippling as free-standing monolayer, significant changes of the electronic band structure, giant spin-orbit splitting, and enhanced photoluminescence. Most of those properties are intrinsic for the monolayer and already absent for two-layer stacks of the same 2D crystal. For example, single-layer MoS2 is a direct band gap semiconductor with spin-orbit splitting of 150 meV in the valence band, while the bilayer of the same material is an indirect band gap semiconductor without observable spin-orbit splitting. All these properties have been observed experimentally and are in excellent agreement with calculations based on density-functional theory. This Account reports theoretical studies of a subgroup of transition metal dichalcogenides with the composition MX2, with M = Mo, or W and X = Se or S, also referred to as "MoWSeS materials". Results on the electronic structure, quantum confinement, spin-orbit coupling, spontaneous monolayer rippling, and change of electronic properties in the presence of an external electric field are reported. While all materials of the MoWSeS family share the same qualitative properties, their individual values can differ strongly, for example, the spin-orbit splitting in WSe2 reaches the value of 428 meV, nearly three times that of MoS2. Further, we discuss the effect of strain on the electronic properties (straintronics). While MoWSeS single layers are very robust against external electric fields, bilayers show a linear reduction of the band gap, even reaching a semiconductor-metal phase transition, and an increase of the spin-orbit splitting from zero to the monolayer value at rather small fields. Strain is yet another possibility to control the band gap in a linear way, and MoWSeS monolayers become metallic at strain values of ∼10%. The density-functional based tight-binding model is a useful tool to investigate the electronic and structural properties, including electron conductance, of large MoS2 structures, which show spontaneous rippling in finite-temperature molecular dynamics simulations. Structural defects in MoS2 result in anisotropy of the electric conductivity. Finally, DFT predictions on the properties of noble metal dichalcogenides are presented. Most strikingly, 1T PdS2 is an indirect band gap semiconductor in its monolayer form but becomes metallic as a bilayer.

This is a novel way of synthesis with a unique combination of the chemical sol–gel and combustion process. The process is simple, inexpensive and less time consuming as compared to other wet chemical methods which resulting a nano-sized, homogeneous, highly reactive powder. The results revealed that the nitrate–citrate gel exhibits self-propagating combustion behaviour. The structural and electrical properties of the compounds were studied. X-ray diffraction measurements confirm the formation of single phase cubic spinel structure. We note a nonlinear relationship between the structure and composition due to Ni, which demonstrates that structural properties are strongly tied to the Ni substitution.

Magnetic nanoparticles are found to exhibit exciting and substantially distinct magnetic properties due to high surface-to-volume ratio and several crystal structures in comparison to those discovered in their bulk counterparts. The properties of nanoparticles also largely depend on the route of their synthesis. In the present work, we report the synthesis of superparamagnetic nanoparticles of Mn0.5Zn0.5LaxFe2−xO4 (x = 0, 0.025, 0.050, 0.075, 0.1) ferrites by co-precipitation method. Structural, morphological and elemental study has been performed using x-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), FESEM and EDS. Different structural parameters (crystallite size, interplanar spacing and lattice constant) have been calculated from XRD. Formation of cubical spinel structure has been confirmed from XRD and FTIR. Cation distribution for all the samples has been proposed and used for calculation of various theoretical parameters. Magnetic properties have been investigated using vibrating sample magnetometer at room temperature and show transition between paramagnetic and superparamagnetic behavior. Maximum saturation magnetization and magnetic moment have been obtained at x = 0.050. The results are attributed to the solubility of La in Mn–Zn ferrite and the size of nanoparticles. The samples have also been analyzed for dielectric, electric and optical properties. For x ≤ 0.050, a blue shift in absorbance and photoluminescence measurements has been observed due to quantum confinement.

The widespread utilization of perovskite-based photovoltaics requires probing both the structural and optical properties under extreme operating conditions to gain a holistic understanding of the material behavior under stressors. Here, we investigate the temperature-dependent behavior of mixed A-site cation lead triiodide perovskite thin films (85% methylammonium and 15% formamidinium) in the range from 300 to 20 K. Through a combination of optical and structural techniques, we find that the tetragonal-to-orthorhombic phase transition occurs at ∼110 K for this perovskite composition, as indicated by the change in the diffraction pattern. With decreasing temperature, the quantum yield increases with a concurrent elongation of the carrier lifetimes, indicating suppression of nonradiative recombination pathways. Interestingly, in contrast to single A-site cation perovskites, an additional optical transition appears in the absorption spectrum when the phase transition is approached, which is also reflected in the emission spectrum. We propose that the splitting of the optical absorption and emission is due to local segregation of the mixed cation perovskite during the phase transition.

Perovskite single crystals have emerged as potential candidates in the field of optoelectronic devices because of their low trap state densities, long diffusion lengths, and high charge carrier mobilities. However, the presence of lead (Pb) in perovskite causes serious concerns due to lead’s high-perceived toxicity and poor environmental stability. Therefore, development of lead-free perovskites as a potential alternative material and an environment-friendly candidate has received critical attention. Here, we report the synthesis of all-inorganic millimeter-sized lead-free bismuth-based halide perovskite Cs3Bi2X9 (X = Cl, Br, I) single crystals and their structural disorderness, optical, and spin relaxation properties in detail. Higher Urbach energy in Cs3Bi2X9 single crystals reveals a high degree of local structural disorderness and a short range of crystallinity. We show that structural disorder affects not only the optical properties but also the magnetic and spin relaxation properties. We observe that increased structural disorder leads to enhanced smearing of local energy bands and high spin–orbit coupling. The spin relaxation time is determined in the picoseconds time scale, which corresponds to fast charge carrier dynamics. Our work provides a design strategy and in-depth understanding to develop environment-friendly lead-free and stable perovskite-based optoelectronics and spintronic devices.

Dispersion-correction density functional theory (DFT+D) and spin-orbit coupling (SOC) method into the structural, electronic, optical and mechanical properties of CH3NH3PbI3

This first principles study explores the structural, electronic, optical, and thermoelectric properties of the CsTmCl3 halide perovskite using density functional theory. The structural and thermoelectric properties are calculated without considering the spin‐orbit coupling (SOC), while both the electronic and optical properties are calculated with and without the SOC effect. A comparison of the results obtained with and without SOC reveals that inclusion of the SOC effect reduces the band gap from 1.18 to 0.99 eV due to shifting of the Tm‐d states toward the Fermi level. However, direct nature of the band gap remains the same in both the cases. The effect of SOC on the optical properties is, however, only visible in shifting of the third characteristic peak to lower energies. Strong optical absorption in the visible and ultraviolet regions shows effectiveness of CsTmCl3 in the optical devices working in these regions. Moreover, the calculated transport properties reveal CsTmCl3 as a useful thermoelectric material at room temperature.