Papers by Smagul Karazhanov
Phase stability, electronic structure and optical properties of BiInO3under strain
Journal of Physics D: Applied Physics, 2014
ABSTRACT We use density functional calculations to elucidate the effects of compressive and tensi... more ABSTRACT We use density functional calculations to elucidate the effects of compressive and tensile strain on the structural, ferroelectric, electronic, and optical properties of BiInO3. Compared to tensile strain, compressive strain results in larger changes to the related physical properties of BiInO3. At a compressive strain about 6.3%, BiInO3 undergoes a first-order phase transition from ferroelectric state to paraelectric state. In the case of tensile strain, BiInO3 can retain its ferroelectricity, and while in its ferroelectric state, become unstable. The ferroelectric polarization and band gap of BiInO3 can be tuned by strain. The optical dielectric function under strain was also investigated. Based on the calculated energy band structures, the transitions peaks of dielectric function are discussed in detail. The change of energy band structures also indicated that the first-order phase transition in BiInO3 occurs under compressive strain. Our results suggest that BiInO3 should be one of the most promising candidates for replacing the widely used ferroelectric and piezoelectric material PbTiO3, and solve the environmental issues associated with the toxicity of lead.
Electronic and Photocatalytic Properties of Gadolinium Oxyhydride
Solar Energy Materials and Solar Cells, Oct 1, 2019
In this work, we investigate the chemical composition of a reactively sputtered photochromic YHxO... more In this work, we investigate the chemical composition of a reactively sputtered photochromic YHxOy thin film by non-destructive ion beam-based techniques, i.e., Rutherford Backscattering Spectrometry, Particle-Induced X-Ray Emission, Time-of-Flight/Energy coincidence Elastic Recoil Detection Analysis and Elastic Backscattering Spectrometry. To enhance the accuracy of the analysis, the set of spectra was evaluated in an iterative self-consistent approach. This procedure resulted in high-resolution depth profiles of the chemical composition and revealed a thin oxygen-rich-layer on the surface, which apparently does not act as a self-passivation layer. In the film, the concentration of Y remains practically constant, whereas O replaces H during the oxidation process. In-situ light illumination was performed during the compositional analysis in a high vacuum setup. The results from these measurements demonstrate that, for these samples, the induced reversible photochromism is not linked to any detectable change in the bulk composition of the film and can thus take place even in a vacuum environment.
Materials Today: Proceedings, 2020
Hole-conducting poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a material... more Hole-conducting poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a material receiving increasing interest for use in photovoltaic devices. In this work, we present the results of study of the degradation of the optical and electrical properties of pure PEDOT:PSS and PEDOT:PSS doped with Si-nanoparticles. The PEDOT:PSS has been deposited on top of Si wafers by spin coating. We found that incorporation of Si nanoparticles into PEDOT:PSS enhances the surface passivation of the surface of the Si wafer by increasing the carrier lifetime measured by the photoluminesence quasi-steady state photoconductance (PL QSS-PC) method from about 320 ms to 420 ms at a minority carrier injection level of 2*10 15 cm À3 . Analysis showed that incorporation of the Si nanoparticles does not change the kinetics of degradation of lifetime considerably.
Philosophical Magazine, May 1, 2009
In this work band structure of hydrides has been studied by the density functional calculations. ... more In this work band structure of hydrides has been studied by the density functional calculations. From analysis of band structures it is found that similar to semiconductors some hydrides possess open fundamental band gap and those hydrides can be classified based on the following three characteristic features. The first one is based on value of the fundamental band gap and therefore the hydrides have been classified as narrow band gap and wide band gap materials. The second one is based on relative location in k space of the bottommost conduction band and topmost valence band compared to each other. Therefore the hydrides can be classified also as direct band gap and indirect band gap materials. The third one is based on the origin of the topmost valence and depends on the dominant contribution of s-, p-, and d-electrons to the topmost VB. According to this criterion the hydrides can be classified as type-s, -p, -d or hybridised materials. The classifications can be useful for applications of hydrides for the construction and processing of electronic devices in frame of the recently invented "hydride electronics".
Photochromic properties of yttrium oxyhydride thin films: Surface versus bulk effect
Materialia, Jun 1, 2020
Abstract Photochromic yttrium oxyhydride (YHO) films of different thicknesses but similar chemica... more Abstract Photochromic yttrium oxyhydride (YHO) films of different thicknesses but similar chemical composition were grown by reactive magnetron sputtering. Photochromic response of the films defined as the relative change in transmittance upon illumination increases almost linearly with thickness for films below 600 nm and saturates (≈ 50%) for thicker ones. These results suggest that the photochromic effect on YHO films has a bulk nature and might be limited by material transport on the microscale.
Similarity of optical properties of hydrides and semiconductors for antireflection coatings
Philosophical Magazine, Jul 21, 2010
ABSTRACT The electronic structure and optical properties of the complex hydrides Ca2FeH6, Ca2RuH6... more ABSTRACT The electronic structure and optical properties of the complex hydrides Ca2FeH6, Ca2RuH6, Mg2FeH6, Mg2RuH6, Sr2FeH6, Sr2RuH6 and Sr2OsH6 were studied using first-principles calculations. Optical spectra of the hydrides were compared with those of SiNx, In2O3 and ZnO determined from theoretical calculations and measured experimentally. Based on an analysis of band structure, it is found that the electrical conductivity of the hydrides is expected to be poor. However, optical properties of the hydrides in the energy range 0–3 eV are found to be almost the same as those of SiNx, In2O3, ZnO and TiO2. Hydrides are suggested to be used as antireflection layers and for passivation of surface and bulk defects. This finding could be useful for electronic device technology including solar cells.
Materials Today: Proceedings, 2020
The version presented here may differ from the published version. If citing, you are advised to c... more The version presented here may differ from the published version. If citing, you are advised to consult the published version for pagination, volume/issue and date of publication
Journal of Applied Physics, Sep 1, 2009
We present a study of the electronic structure and optical properties of Si 3 N 4 and Si 2 N 3 H ... more We present a study of the electronic structure and optical properties of Si 3 N 4 and Si 2 N 3 H in crystalline and amorphous phases by first-principles calculations. We find that besides structural disorder those matrix atoms with dangling and floating bonds contribute to energy levels close to the Fermi level. From a comparative analysis of calculated optical spectra we conclude that the difference in optical properties between crystalline and amorphous silicon nitrides-either hydrogenated or unhydrogenated-is only small. It is present mainly in the energy range close to the fundamental band gap. At larger energies the difference is negligible. It is found that the structural disorder in silicon nitrides investigated does not affect essentially the electronic structure and optical properties of these materials. It is concluded that such amorphous silicon nitrides can be used instead of their crystalline counterparts for various applications in which optical properties of such materials are important.
Microstructure profiling and photoluminescence characteristics of V(1-x)2 Ni3xO5-δ compound systems
Materials Letters, May 1, 2020
Abstract V2-xNi3xO5-δ (V-Ni-O) based multi-cation materials have been prepared by high-temperatur... more Abstract V2-xNi3xO5-δ (V-Ni-O) based multi-cation materials have been prepared by high-temperature solid-state reaction for x between 0.03 and 0.06. The as synthesized V-Ni-O complex ceramic materials were subjected to microstructure profiling and photoluminescence studies. Structural analysis by x-ray diffraction pattern shows preferential growth direction analogous to that of V2O5. Scanning electron microscopy and energy dispersive x-ray spectroscopy shows dense lattice and the presence of Ni cations. Photoluminescence spectra of the samples exhibited both near band edge and deep level emissions. The optical band gap is found restructured in the compound due to the presence of Ni. The observed band edge emissions are broad with significant Gaussian asymmetry and are deconvoluted for individual components. The luminescent peaks between 2.28 eV and 2.31 eV have been observed for varying mole fractions.
The dependence of structural, electrical and optical properties on the composition of photochromic yttrium oxyhydride thin films
Materialia, Jun 1, 2019
Abstract Thin films of yttrium oxyhydride (YHO) exhibit reversible light-induced resistivity and ... more Abstract Thin films of yttrium oxyhydride (YHO) exhibit reversible light-induced resistivity and transmission changes at room temperature and ambient pressure. Establishing how the physical properties of YHO films are influenced by their chemical composition is an important challenge that can open the way toward practical applications. In this work, we have prepared YHO thin films with lateral gradient of oxygen and hydrogen concentrations by reactive magnetron sputtering deposition. This enables us to efficiently investigate the effect of changes in the composition of the films on their structural, electrical and optical properties. The as-deposited YHO film appeared to be black opaque and non-photochromic in the oxygen-poor part of the film, and it changed to yellow transparent and photochromic in the oxygen-rich part of the film. We report a gradual increase in the lattice constant with increasing oxygen content of the film, as revealed by grazing incidence X-ray diffraction measurements. Electrical resistivity measurements unveiled that persistent photoconductivity was strongly enhanced as the oxygen content decreased in the photochromic yellow transparent film. Analysis of the kinetics of the photochromic reaction indicated that the bleaching speed increased with increasing oxygen content in the photodarkened film. Unusual large persistent photochromism was discovered in the same yellow YHO film with lowest oxygen content which lasted for almost 10 days. Moreover, it was shown that the optical constants can be tuned by varying the oxygen content in the photochromic film as well.
Journal of Alloys and Compounds, Sep 1, 2011
Metal hydrides have earlier been suggested for utilization in solar cells. With this as a motivat... more Metal hydrides have earlier been suggested for utilization in solar cells. With this as a motivation we have prepared thin films of yttrium hydride by reactive magnetron sputter deposition. The resulting films are metallic for low partial pressure of hydrogen during the deposition, and black or yellow-transparent for higher partial pressure of hydrogen. Both metallic and semiconducting transparent YH x films have been prepared directly in-situ without the need of capping layers and post-deposition hydrogenation. Optically the films are similar to what is found for YH x films prepared by other techniques, but the crystal structure of the transparent films differ from the well-known YH 3-η phase, as they have an fcc lattice instead of hcp.
The Possibility of the Exploration of Influence of External Factors on the Solar Panels in Laboratory Conditions
Applied Solar Energy, Apr 1, 2023
Applied sciences, Oct 25, 2022
For decades, partially oxidized hydrides were commonly considered as undesirably contaminated pha... more For decades, partially oxidized hydrides were commonly considered as undesirably contaminated phases and were avoided by scientists. Nevertheless, more recently, it was realized that in some hydrides and oxides, partial substitution of dissimilar H -and O 2-anions allows one to obtain unique optical and electrical properties that might have appealing applications in commercial products. It was determined that specific properties of so called oxyhydride materials strongly depend on the used synthesis methods; therefore, there is a great interest in exploring various variants of oxyhydride formation. In the current study, TiH x O y films were deposited by a reactive magnetron sputtering process in Ar-O 2 -H 2 gas mixtures. Color, transparency and crystal phase composition of the films coherently reacted to the Ar:O 2 :H 2 gas ratio. Namely, the rise in partial hydrogen pressure promoted the formation of anatase phase TiO 2 structure and darkening of the films. Interestingly, this had only minimal impact on the band gap values, but had a relatively strong negative effect on the photocatalytic activity of the films. The unaccustomed results stressed the difference between the partially reduced TiO 2 with a significant amount of oxygen vacancies and synthesized TiH x O y films where some O 2-ions are implicitly substituted by H -ions.
Low Temperature Deposition of Chemically Converted Graphene Films on Large Area Silicon For Solar Cell Applications
World Conference on Photovoltaic Energy Conversion, Oct 10, 2011
Because of the many useful electronic, optical, and mechanical properties, graphene has emerged a... more Because of the many useful electronic, optical, and mechanical properties, graphene has emerged as a promising candidate for applications in a range of technologies. This expectation depends on the feasibility of largescale production of graphene layers that can cover surface areas of different substrates of a size relevant for solar cells and other applications. This presently remains to be one of the main challenges. The method of forming chemically converted graphene has the potential to overcome this problem. Another important issue is that the deposition steps for the films need to take place at temperatures low enough not to harm solar cell structures. In the present paper we report deposition of chemically converted graphene film on large area Si at room temperature. The chemical structure of the graphene films have been characterized by Raman spectroscopy and surface morphology by scanning electron microscopy. From UV/vis absorbance spectroscopy it is shown that ~10 nm chemically converted graphene layers transmit >93% of sunlight. Photovoltaic properties of the Si based solar cell structures obtained using the chemically converted graphene method have also been investigated.
Performance of crystalline Si solar cells and module on temperature and illumination intensity
Materials Today: Proceedings, 2022
Materials research express, Jan 24, 2017
It is well known that optical properties of Mg-Ni-H films can be tuned by hydrogen uptake from Mg... more It is well known that optical properties of Mg-Ni-H films can be tuned by hydrogen uptake from Mg-Ni-H and upload into Mg-Ni systems. In this work we show that modulation of optical properties of Mg-Ni-H can take place as a result of thermal processing in air as well. When reactively sputter deposited semiconducting Mg-Ni-H films are annealed at temperatures of 200-300 ºC in air, gradual band gap change from 1.6 eV to 2.04 eV occurs followed by change in optical appearance, from brown, to orange and, subsequently, to yellow. We investigate this phenomenon using optical and structural characterization tools, and link the changes to an atomic rearrangement and a structure reordering of the [NiH 4 ] 4-complex. The films are X-ray amorphous up to 280 ºC, where above this temperature an increase in crystallite size and establishing of long-range order lead to a formation of the cubic crystalline phase of Mg 2 NiH 4 . Also, the results suggest that even though annealing was conducted in air, no oxidation or other changes in chemical composition of the bulk of the film occurred. Therefore, the band gap of this semiconductor can be tuned permanently by heat treatment, in the range from 1.6 to 2 eV.
Clay and Clay-based minerals have fascinated attention because of their unique properties and a v... more Clay and Clay-based minerals have fascinated attention because of their unique properties and a vast range of applications in innumerable industrial fields. In order to assess the potential applications, six different processed local kaolin-based raw minerals were collected from the Aral Sea region of Uzbekistan, and the total mineralogical properties have been investigated. The result reveals that some significant differences occurred based on the elemental percentage of silica and alumina in all the mineral samples. The presence of corundum, quartz, and kaolinite structural phases of the mineral was determined by XRD studies. At the same time, the FTIR and Raman studies expose the primary peaks which are associated with the functional groups of Al-OH, Al-O, and Si-O in higher-frequency stretching and lower-frequency bending modes. The elemental and chemical compositional (XRF and XPS) analysis demonstrates the presence of major elements (Al, Si, Na, Fe, Ti) in the raw mineral and ...
Functional MAterials for EneRgy, Environment And BiOmedical ApplicatioNs (FARAON-2021)
Materials Today: Proceedings, Sep 1, 2022
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Papers by Smagul Karazhanov