Variation Of Band Gap Research Articles

Structural, dielectric and electronic properties of Ba1-xSrxZr0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.24, 0.27, 0.3) ceramics: Combined experimental and ab-initio study

Ba1-xSrxZr0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.24, 0.27 and 0.3) materials were synthesized using conventional solid state reaction route. Structural properties were investigated using X-ray diffraction analysis. All the samples reveal single phase structure. The dielectric properties of all the samples were investigated at different temperatures of 100 K to 300 K, and at different frequencies of 1 kHz to 500 kHz. The diffusivity rises with increase in Sr divalent cation concentration. It is seemed that with increase in Sr2+ concentration the transition temperature reduces for all compositions. This may because of the introduction of Sr2+ by replacing Ba2+ since Sr+2 has smaller ionic radius than Ba+2. Moreover, the dielectric constant maxima for Ba1-xSrxTi0.7Zr0.3O3 increases up to x = 0.24 and then further increment in Sr content up to x = 0.3, the maxima of dielectric constant shows decrease. Moreover, charge conduction mechanism and optical response of Ba1-xSrxZe0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.3) has been calculated theoretically by using CASTEP. Herein, the calculated density of states (DOS) and three dimensional integrated charge density reveal that concentration of Sr in Ba1-xSrxZe0.3Ti0.7O3 (x = 0.1, 0.2, 0.3) causes variation in energy band gap. As regards optical response of Ba1-xSrxTi0.7Zr0.3O3, with x = 0.3 the high frequency absorption decreases to minimal value in accordance to experimental findings.

Doped CeO2/water nanofluids analyzed the performance of thermal conductivity and heat transfer: An experimental and theoretical investigations

A combined experimental and theoretical study on thermal conductivity, heat transfer specific heat, and electronic properties has been done for doped CeO2/water nanofluid. First, the sol-gel method was implemented for the synthesis of doped CeO2 nanoparticles and then a mixture of nanoparticles with different concentrations of nanofluid. X-ray diffraction and SEM analysis confirm the structural phase purity and homogeneous mixing of nanofluids. Experimental thermal conductivity and specific heat of pure and 4f-doped CeO2 were estimated and found very close to our theoretical calculations. Experimental investigations have been carried out for the measurement of heat transfer using pure and doped CeO2/water nanofluid as the coolant. The experiments were aimed at determining the heat transfer and other thermal properties with different concentrations and with various fluid with Reynolds number 2500 and 3500. The heat transfer coefficient of nanofluids increases not only with an increase in the volume flow rate of the hot water but also increases with increase in the atomic number of dopant elements in CeO2. Electronic states show variation in band gap with doping which may also play an important role in the improvement of solar collectors. It is clear from experimental and theoretical findings that the thermal and electronic properties depend on number of valance electrons. Hence doping of 4f-element in CeO2 plays a vital role to increase the thermal conductivity and tuning of electronic properties leads to many applications in thermal sensors and solar cell-based industries.

Structural, Optical, Magnetic and Dielectric Properties of Ce-Doped MgFe2O4 Prepared by Microwave Hydrothermal Method

The microwave hydrothermal method has been used to synthesize MgFe2-x Ce x O4 (x = 0.0 – 0.10) nanoparticles, which have been characterized using X-ray diffraction (XRD), fourier transform Infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectrometer, vibrating sample magnetometer (VSM) and dielectric properties. XRD investigation confirms the cubic spinel structure, and the Debye–Scherrer formula was used to determine the crystallite size, showing values of 19 – 108 nm. FTIR confirms the presence of all functional groups and FE-SEM displays particle-like morphology. The UV-visible analysis was used to explain the variation of the optical bandgap as Ce3+ doping increased. VSM analysis of MgFe2-x Ce x O4 showed ferromagnetic behaviour. The samples exhibit low magnetization values ranging from 8.83 emu g−1 to 18.91 emu g−1. The values of the dielectric constant (ε′) and the dielectric loss (tanδ) decreased with frequency due to the influence of space-charge polarization and showed a dispersive behaviour at higher frequencies.

Role of nanoscale compositional inhomogeneities in limiting the open circuit voltage in Cu(In,Ga)S2 solar cells

As Si-based solar cell technologies approach their theoretical efficiency limits, alternative photovoltaic systems, such as tandem solar cells, are gathering increased attention due to their potential to reach higher efficiencies by better use of the solar spectrum. Cu(In,Ga)S2 (CIGS) is a promising material for the top cell due to its large, tunable bandgap energy (Eg), stability, and already established high efficiencies. However, the deficit in open circuit voltage is still large; therefore, an improved understanding of the efficiency losses is required. Scanning electron microscopy cathodoluminescence was used to study the role of the polycrystalline nature for radiative recombination in CIGS samples of varying Cu-content. Considerable differences between neighboring grains were observed in the emission energy and the emission intensity, with significant drops in emission energy at the grain boundaries. Lateral homogeneity in the near band edge (NBE) energy was found to reduce for samples with Cu-poor compositions, with its standard deviation halving (σNBE ∼ 20 meV) compared to the more stoichiometric films (σNBE ∼ 50 meV), which corresponds to an open circuit voltage loss contribution that is nearly an order of magnitude lower. Such inhomogeneities can be attributed mainly to local variations of the Ga concentration. Hence, the differences between the samples could be explained by the different deposition times at elevated temperature allowing for different extents of homogeneity. Thus, Cu-poor films are not only favorable because of lower concentrations of deep defects but also because of reduced bandgap variations.

Structural phase transition driven dielectric and optical properties with reduction in band gap in Sr2+ modified BaTiO3 ceramics

Ferroelectric materials with crystal symmetry transition from single phase to multiphase coexistence exhibit anomalous photosensitive properties. The optical properties (optical band gap and photosensitive) found on non-centrosymmetric and centrosymmetric systems achieved research interest because of their interesting behavior. In this regard, the lead-free polycrystalline Ba1−x Sr x TiO3 (BSTO, 0 ) has been synthesized to explore its crystal structure, dielectric, light absorption, and photocurrent sensing properties for various applications. Both experimental and theoretical studies on BSTO (0 ceramics confirm the crystal symmetry transition with the reduction of band gap as compared to pristine BaTiO3. This crystal symmetry transition plays an important role in varying the various physical properties as it involves the transition from the polar phase to the non-polar phase. The optical band gap has been estimated experimentally by the Tauc plot method and found that there is a small variation of energy band gap from 3.615 eV to 3.212 eV with Sr substitution. The highest dielectric constant was found to be 5327 at lower frequency on Ba0.76Sr0.24TiO3 after that for further increase in Sr concentration the dielectric constant decreases because of the introduction of the non-polar phase. A strong correlation between crystal structure and physical properties (dielectric, optical, etc.) has been observed. The photocurrent of the samples is significant which reveals that the sample is influenced by the photons. In a nutshell, the present study deepens the understanding of the correlation between crystal structure and various physical properties of BSTO and, hence provides an idea of required design parameters to construct a ferroelectric system for better photosensitive nature suitable for device applications.

Adsorption Analysis at Critical Temperature of PM2.5 Contaminants

Increasing levels of PM2.5 (Particulate Matter having a diameter less than 2.5 µm) offer the highest risk, leading to a multitude of serious health complications, and hence the high-performance monitoring of these tiny pollutants may help to safeguard people's health. The sensitivity of PM2.5 pollutants to bulk gold as an application of sensors is investigated using the industry standard virtual nanolab. Within the framework of linear combination of atomic orbital (LCAO) computation, the density functional theory (DFT) is implemented using the Kohn–Sham formulation to analyze the electronic properties of bulk gold Au (111) substrate for specific PM2.5 pollutants (sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon dioxide (CO2), nitric oxide (NO), and carbon monoxide (CO)) sensing. The results demonstrate that different gases are adsorbed differently on Au (111), depending on their critical temperature (TC ). Consequently, NO is observed to be highly sensitive to Au (111) substrate due to its large band gap variation of −31% to −57%, considerable adsorption energy of −1.05 eV, and an improved charge transfer of 0.02 eV.

Comparative analysis of photovoltaic thermoelectric systems using different photovoltaic cells

The photovoltaic-thermoelectric (PV-TE) system has emerged as a focal point in research endeavors aimed at harnessing the full spectrum of solar energy and enhancing the efficacy of solar power generation. Owing to the variations in bandgap and inherent material properties across diverse photovoltaic cells, the capacity to utilize the solar spectrum of PV-TE systems can be significantly affected when using different photovoltaic cells. Historically, investigations into the influence of photovoltaic cells on PV-TE systems have been predominantly rooted in theoretical simulations. These examinations have primarily concentrated on the holistic system efficiency under varying temperature conditions. In this study, we integrated three distinct types of photovoltaic cells into PV-TE systems. Both simulation and experimental methodologies were employed to evaluate the impact of these photovoltaic cell types on the PV-TE systems' performance. Additionally, we compared the back temperatures of standard PV systems with those of PV-TE systems. The average photovoltaic conversion efficiencies of PV-TE systems equipped with CIGS, CdTe, and a-Si photovoltaic cells were 21.9%, 19.7%, and 12.7%, respectively. Meanwhile, the average efficiencies of TEG were 0.256%, 0.102%, and 0.083% respectively, with average backplate temperatures of 39.3 °C, 44.0 °C, and 40.5 °C. The temperature disparities between the back of standard photovoltaic systems and PV-TEG-PCM systems stood at 4.70 °C, 2.32 °C, and 3.43 °C, respectively. Notably, CIGS photovoltaic cells, which harness a specific range of the solar spectrum more effectively, showcased superior performance. Furthermore, a broader usable solar spectrum band for a PV cell doesn't always translate to enhanced performance. These findings offer valuable insights for optimizing the power generation capabilities of photovoltaic-thermoelectric systems leveraging full-spectrum solar energy.

Modeling Size and Shape Dependence of Electro-Optical Properties of Semiconductor Nanosolids

Based on cohesive energy, the size and shape effect on Bandgap, Dielectric constant and Phonon frequency of low-dimension semiconductor nanomaterials are predicted with structural miniaturization down to the nanoscale. It is projected that nanomaterial’s optical and electrical properties no longer remain constant but become tunable. The model reports that the bandgap increases while the dielectric constant and phonon frequency drop on decreasing size to the nanoscale. The bandgap variation, dielectric constant and phonon frequency are reported for spherical, thin film, nanowire, regular tetrahedral and regular octahedral shapes of semiconductor nanosolids. The shape effect becomes prominent as the form changes from spherical to regular tetrahedral shape up to the size limit of 20 nm. A good agreement between our model predictions and the available experimental and simulation data justifies the theory’s validity.

Effect of precursors on ZnO nanoparticles to enhance the level-III ridge details of LFPs and anti-counterfeiting applications

Comparative analysis for the combustion-based synthesis of zinc oxide nanoparticles (NPs) utilizing various precursors of zinc was reported. l-ascorbic acid extraction was used as a fuel for the combustion process. The sizes, morphologies, structural details and purity of samples were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffractometry (XRD). XRD pattern matches with the standard JCPDS card of ZnO with good crystallite size. The average crystallite size of the NPs was confirmed the nano-regime. Variations in morphological structures and the energy band gap variation with the change in precursors was reported. Using a powder-dusting technique, on separate surfaces, level-III features of the fingerprints produced by these NPs without any background noise. The suggested powder composition was easy to make and effective for producing latent finger prints on a variety of dry and wet surfaces. In the area of counterfeit prevention, the fluorescent ink has several potential applications. Invisible security ink was developed for anti-counterfeiting applications based on the UV fluorescence feature of ZnO NPs. The fluorescent invisible security ink for screen printing was evaluated and proved to be stable on a variety of microporous papers. The new strategy adopted here lowers the cost of ink by using rare earth free ZnO NPs.

Optical characteristics of Mg-based (Mg/Co & Mg/Mn) TF for hydrogen storage applications

This study has proposed and analyzed the role of hydrogen gas on optical characteristics of Mg-based Mg/Co and Mg/Mn bilayer structures. Thermal evaporation at a pressure of 10-5 torr was used to prepare these Thin Films (TF), which were then effectively deposited onto glass substrates. To obtain homogenous structure, prepared TF were vacuum annealed at 573 K. Hydrogen gas was injected into the chamber at various pressures (10, 20 & 30 psi) to observe how hydrogenation influenced TF. Using a Hitachi-330 spectrophotometer, the UV–Vis transmission spectra were recorded in visible range of wavelength (300–800 nm). TF' optical transmission was reduced, and it was revealed that the energy band gap increased as hydrogen pressure increased. It implies that hydrogen absorption in TF can be used to tailor the energy band gap. An optical micrograph of a hydrogenated TF that has been annealed reveals a dark black state. The variation in energy band gap due to hydrogen and increasing value of the film resistance are evidence for the phase shifts caused on by hydrogenation from metal to semiconductor.

Facile synthesis and enhanced acetone sensing properties of ZnO/TiO2 nanocomposite at room temperature

This paper reports a clear outline of the synthesis and gas-sensing characteristics of pure ZnO, TiO2 nanoparticles (NPs) and ZnO/TiO2 (ZT) nanocomposite (NC) for acetone detection at room temperature for diabetes screening. Thesamples were synthesized using an uncomplicated low-cost co-precipitation method. The ZT nanocomposites have shown a combined phase structure of ZnO (wurtzite) and TiO2 (anatase) from X-ray diffraction. The absorbance of the samples was analyzed by UV–Vis Spectrophotometer and a variation in the optical bandgap is studied.A high-performance ZT NC gas sensor is successfully realized for excellent selectivity, and quick response-recovery towards acetone detection. The sensing mechanism is ascribed to the composition, morphology, and enhanced oxygen adsorptionsites revealing better performances than the pure ZnO and TiO2 NPs. The ZT NC of composition ZnO (0.60 at.%):TiO2 (0.40 at.%) is observed to enhance the acetonegas detection signal for the lowest sub micro level ppb concentration of 100 ppb (parts per billion) in comparison to the pure ZnO and TiO2 nanoparticles. A superior response time (τres) of 13 s and recovery time (τrec) of 11 s are observed for ZT-1 sample with a high sensitivity response of 179 % is studied and therefore the nanocomposite material can be successfully utilized for acetone biomarker in diabetes.

Quantum control of substitutional effects on the S-involved optoelectronic properties of BeSxSe1-X ternary alloys

The research on the quantum control of substitutional effects in BeSxSe1-x ternary alloys opens up exciting opportunities in semiconductor device engineering, photovoltaic, optoelectronic integration, and quantum information processing. By understanding and manipulating the optoelectronic properties of these alloys, researchers can pave the way for advanced technologies with enhanced performance, efficiency, and functionality in various fields. We are investigating how S alloying affects the structural, electronic and optical properties of tin chalcogenide materials. We are assessing the energy band structure and optical properties of BeSxSe1-x (x = 0%, 25%, and 50%) materials using density functional theory (DFT) within a full potential linearized augmented plane wave method (FP-LAPW) framework. The theoretically expected band energy gaps of BeSxSe1-x compounds indicate that S alloying improves their electrical and optical performances, based on the assumptions used in our calculations. The majority of the bonds in the BeSxSe1-x materials (x = 0%, 25%, and 50%) are covalent. All ternary alloys and binary compounds with (x = 0%, 25%, and 50%) exhibit direct (R-Γ) band gap semiconductor behavior, with a band gap energy (Eg). Each alloy system shows a nonlinear increase in the band gap (Eg) with increasing x. As BeSxSe1-x compound belongs to strongly correlated systems, therefore modified Becke–Johnson potential is used to calculate formation enthalpy (ΔHf), and optical properties of the compounds. The intense peaks in the imaginary part of the dielectric function εi(ω) in each spectrum are contributed by chalcogen Se, Be, and S optical excitations. Similar to the trend of band gap variation (Eg) with x, the zero-frequency limit of each imaginary dielectric function as well as the extinction coefficient, refractive index, and real dielectric function, exhibit a corresponding trend of change.

A new insight into transition metal doped graphene nanoribbon for hydrogen sulfide gas adsorption: First principle investigation

Detection of toxic gases is critical for the protection of human health and preserving nature's creation. This study uses armchair graphene nanoribbon (AGNR) and modified derivatives of AGNR to examine the hydrogen sulfide (H2S) gas adsorption using density functional theory (DFT). The modified derivatives considered are Cu and Pt doped AGNR. The feasibility and effectiveness of the modified AGNR optimized structures for H2S adsorption have been investigated along with geometrical variation, binding distance and binding energies. Furthermore, the electronic characteristics such as band gap (Eg) and density of states (DOS) have been computed. After adsorption of H2S, the semiconducting nature of AGNR has been changed by observing variation in band gap as a parameter of H2S binding distance from the AGNR surface. After Cu and Pt atom doping, the adsorption energy for H2S gas enhanced to -3.30 and -4.19 eV respectively, which is more than 7 times as compared to pristine AGNR surface. The substantial increase in the adsorption characteristics after Pt doping shows that Pt has a significant effect on improving AGNR's sensing capabilities for the adsorption of H2S gas. Thus, Pt-doped AGNR is a promising material for H2S gas adsorption and detection.

Optical and thermal characterization of pure CuO and Zn/CuO using laser-induced breakdown spectroscopy (LIBS), x-ray fluorescence (XRF), and ultraviolet–visible (UV–Vis) spectroscopy techniques

We present elemental analysis and thermal characterization of pure and two different concentrations of zinc-doped copper oxide (CuO) samples using different analytical techniques. The quantitative as well as qualitative investigations, were performed by incorporating calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technique. The plasma was generated on the samples surface by focusing a first harmonic of Nd: YAG laser of 1064 nm wavelength and the time-integrated emission spectra was achieved through a set of five spectrometers equipped with a charge-coupled-device. The acquired optical emission spectra from laser-generated plasma show different concentrations of zinc and copper in different samples which are consistent with their percentage composition measured during the sample synthesis. Using LIBS emission analytical lines, the Boltzmann technique was utilized for estimating the excitation temperature, while the number density was evaluated using the well-known Stark broadening line profile method. Besides, the CF-LIBS elemental analysis was validated by the x-ray fluorescence technique. For the optical study, ultraviolet–visible spectroscopical analysis was performed to find the bandgap of pure and zinc-doped copper oxide samples and consequently, variation in bandgap was studied with the growth of zinc doping. In addition, the thermal properties of the samples were analyzed using the beam deflection spectroscopy technique. The results shows that thermal diffusivity () and thermal conductivity (), increased with an increase in zinc concentration.

Effect of bandgap variation on photovoltaic properties of lead sulfide quantum dot solar cell

The tunable bandgap of quantum dot (QD)-based solar cells is their greatest advantage, providing control over light absorption region. However, the investigation of the effect of bandgap variation on QD-based photovoltaic properties is insufficient, in contrast to well-defined material properties. In this study, we analyze the electrical properties of solar cells fabricated with bandgap-tuned lead sulfide (PbS) QDs to examine the effect of bandgap variation on photovoltaic properties. We find that reducing the thickness of the QD active layer is necessary to achieve high power conversion efficiency mainly because the doping concentration of the QD film increases as the QD bandgap decreases. We suggest that QD photovoltaic device structures should be designed with consideration of their electrical characteristics in relation to the bandgap.

Study of energy gaps and their temperature-dependent modulation in LaCrO3: A theoretical and experimental approach

In the present study, the origin of three energy gaps of lanthanum chromium oxide, one arises due to the charge-transfer gap between O-2p and Cr-3d and two arises from the d–d transitions, is analyzed in detail using the diffuse reflectance spectroscopy technique. The spin allowed transitions, such as 4T1(P)→4A2, 4T1(F)→4A2, and 4T2→4A2, and the spin and parity forbidden 2E →4A2 transitions are depicted using a Tanabe–Sugano (T–S) diagram and an absorption spectrum. The high crystal field strength of 3.27 obtained from the T–S diagram provides high directional emission and makes the system suitable for near infrared lasing applications. Moreover, the investigations into the variation of a charge-transfer gap with temperature will provide insights into the modification of numerous optical properties toward development of optoelectronic devices. Using this temperature-dependent diffuse reflectance spectroscopy studies, we have obtained the important optical parameters, such as Urbach energy (Eu) and Urbach focus. Furthermore, first-principles calculations are carried out in order to validate the experimental findings on LaCrO3. The experimental results are in consonance with the charge-transfer gap obtained from the theoretical calculations. Furthermore, the bandgap variation with temperature is fitted using Varshni's relation, and the Debye temperature is calculated.

Correlating the Nonlinear Roughening and Optical Properties of Anatase Thin Films—A Fractal Geometric Approach

AbstractThe anatase phase of TiO2 is highly suitable for photocatalytic application consequently, prerequisite an unpretentious scale‐independent understanding of its roughening‐facilitated surface topography dynamics. Herein, the nonlinear roughening in anatase thin films and its correlation with the nonlinear trend of optical properties in the framework of fractal geometry are investigated. The self‐affine nature of analyzed surfaces is confirmed from the autocorrelation function. The dynamic scaling exponents indicate the existence of Kardar–Parisi–Zhang scaling in surface growth. In addition, the trend of generalized Hurst exponent and mass exponent indicates insignificant multifractal characteristics in the analyzed surfaces. Moreover, fractal analysis explains and aids to description of roughening trend from stereometric and Minkowski functionals analysis. Furthermore, the significance of fractal dimension for probing the surface roughening is validated from the principal component analysis. Consequently, variation in optical bandgap and linear refractive index are investigated in regards to the fractal dimension and root mean‐squared surface slope and regression equations are proposed for tuning of bandgap.

Interface engineered nanostructured phase formation at Se/In sites by Ag ion irradiation and its structural, optical and morphological behavior

Thermally evaporated Se/In bilayer films were irradiated by 120 MeV Ag ion at different fluences. Energy-dispersive X-ray fluorescence (EDXRF) spectra of the films showed the 1:2 ratio concentration of In and Se. After six months of preserving the films under ambient condition, four phases: In2Se3, In4Se3, In and Se developed in the films as revealed by Grazing incidence X-ray diffraction (GIXRD) study. The In4Se3 and In were completely insensitive to the irradiation while the other two phases (In2Se3 and Se) were completely amorphized at high ion fluences. The Poission fitting of the fluence dependence area under X-ray diffraction (XRD) peaks showed the radius of amorphized latent tracks along the path of 120 MeV Ag ions in In2Se3 and Se as 8.4 nm and 9.5 nm respectively. The lattice fringe images of High-resolution transmission electron microscopy (HRTEM) showed the presence of the four phases as observed by GIXRD study. The UV-visible study revealed the band gap reduction at the low fluence region from pristine to 3 × 1011ions cm−2 and increased at high fluence from 1 × 1012 ions cm-2 to 1 × 1013 ions cm-2. This variation of band gap may be due to the formation of localized states and annealing effect due to ion irradiation. Field emission scanning electron microscopy (FESEM) images showed the nano needle shaped structure formation at 1 × 1012 ions cm−2 which increased with ion fluences. The appearance of needle shaped structures may be due to the In2Se3 phase. The I-V study showed the excellent current response in mA range which enables the films for various electrical applications. The surface wettability study showed the hydrophobicity nature of the films which enables it for application in different coating materials.

Valence band spectroscopic study of Co-doped TiO2 nanoparticles using synchrotron based advanced spectroscopic techniques

In this work, we investigate the effects of Co-doping and high-temperature annealing from 400° C to 800 °C on the structural, optical, and electronic characteristics of titanium dioxide (TiO2) nanoparticles (NPs). Sol-gel route was adopted to prepare Ti0.95Co0.05O2 (TCO) NPs. The microstructural characterization using transmission electron microscopy suggests that the grain sizes of TCO NPs enhance with annealing temperatures. The selected area electron diffraction patterns of TCO annealed at 400° C, 600° C, and 800° C show the rings which correspond to anatase, mixed, and rutile phases respectively. Energy dispersive X-ray mapping in scanning transmission electron microscopy mode exhibits the distribution of NPs and their elemental compositions. UV–Visible absorption spectra show a prominent shift to the visible region with slight variation in bandgaps. The electron energy loss spectroscopy confirms the divalent and tetravalent nature of Co and Ti ions respectively. The photo-electron spectroscopic measurements mainly valence band and resonant photoelectron spectroscopies were used to investigate the electronic environment of Co ions in the TiO2 matrix. Valence band spectroscopic results of TiO2 NPs demonstrate the role of O-2p-derived states, but for TCO samples, Co-derived states are also seen. The resonant photo-electron spectra indicate that Co 3d ions are strongly hybridized with Ti3+ defective states.

Band gap predictions of double perovskite oxides using machine learning

The compositional and structural variety inherent to oxide perovskites spawn wide-ranging applications. In perovskites, the band gap Eg, a key material parameter for these applications, can be optimally controlled by varying the composition. Here, we implement a hierarchical screening process in which two cross-validated and predictive machine learning models for band gap classification and regression, trained using exhaustive datasets that span 68 elements of the periodic table, are applied sequentially. The classification model separates wide band gap materials, with Eg ≥ 0.5 eV, from materials which have zero or relatively small band gaps, namely Eg < 0.5 eV, and the second regression model quantitatively predicts the gap value of the wide band gap compounds. The study down-selects 13,589 cubic oxide perovskite compositions that are predicted to be experimentally formable, thermodynamically stable, and have a wide band gap. Of these, a subset of 310 compounds, which are predicted to be stable and formable with a confidence greater than 90%, are identified for further investigation. Our models are methodically analyzed via performance metrics and inter-dependence of model features to gain physical insight into the band gap prediction problem. Design maps to identify the variation of band gap with substitution of different elements are also presented.