Ofeliya Kostadinova - Academia.edu (original) (raw)
Papers by Ofeliya Kostadinova
Chalcogenide glasses (ChGs) are produced by alloying together a “chalcogen” element” (S, Se or Te... more Chalcogenide glasses (ChGs) are produced by alloying together a “chalcogen” element” (S, Se or Te) with other elements, generally from group V (Sb, As) or group IV (Ge, Si) to form covalently bonded solids. A variety of stable non-crystalline materials can be prepared in bulk, fiber, and thin film forms using melt-quenching, vacuum deposition, and other less common techniques. Being amorphous semiconductors, ChGs exhibit a variety of photo-induced phenomena when irradiated with proper light and therefore find a wide range of technological applications (optical data storage, telecommunications, IR optics, etc). As research in this field is strongly driven by the needs of high-tech industry, physical properties related to the applications are more systematically investigated than the atomic structure, which is ultimately related to the macroscopic properties. A shortcoming of not having yet established microstructure-properties relations in ChGs is the lack of a strategic design of ne...
Automation is applied in continuously extending fields of application in the modern communities. ... more Automation is applied in continuously extending fields of application in the modern communities. In this respect, sensors are indispensable elements of systems for automatic regulation. Besides, the use of multitudes of sensor elements enables statistical data acquisition from large time and long distance monitoring. Consequently, the requirements for application of multitudes of sensor elements impose a need for elaboration of advanced sensor element production. In this context anodized aluminum oxide (AAO) layers enable the elaboration of relatively simple, large scale technology for reliable and durable sensor elements. The present review is devoted to a summary of the basic concepts related to the elaboration of reliable and durable sensor elements on the basis of anodized aluminum. Furthermore, various examples are provided regarding the recent research activities in this field.
Lithium sodium sulphate (LNS) has been synthesised by two methods: mechanical ball milling and me... more Lithium sodium sulphate (LNS) has been synthesised by two methods: mechanical ball milling and melt quenching. The obtained materials have been studied by means of X-ray diffraction, scanning electron microscopy (SEM), Infrared spectroscopy and differential scanning calorimetry. The influence of the synthesis method on the structure and behaviour of the materials will be discussed.
NATO Science for Peace and Security Series A: Chemistry and Biology, 2014
The aim of the present work is the synthesis and characterization of novel oxide materials in vie... more The aim of the present work is the synthesis and characterization of novel oxide materials in view of their potential use as active material in lithium ion batteries. Bulk materials from (TiO2)x(V2O5)y(P2O5)100-x-y system, where x = 5, 10, 15 and y = 60, 70, were prepared by means of the melt quenching method. The materials were characterized by physical chemical and electrochemical methods, i.e. X-ray diffraction, infrared spectroscopy and cyclic voltammetry measurements. The electrochemical properties were investigated against metallic lithium as active materials in a half-cell system.
Journal of Non-Crystalline Solids, 2009
The structure of Sb x Se 100Àx bulk glasses is investigated with the aid of Raman scattering over... more The structure of Sb x Se 100Àx bulk glasses is investigated with the aid of Raman scattering over a wide composition range. The Raman spectra of the glasses exhibit unusual features when compared with other structurally similar binary glasses, owing to the phase separation of the present glasses in a certain composition range. The evolution of the Raman spectra and the depolarization ratio of the polarized and depolarized Raman intensities are consistent with the phase separation effect. The present findings are discussed alongside with calorimetric data from the literature that have been used up to now to extract structural information in an indirect way. The capability of Raman scattering as a tool for investigating phase separation in homogeneous media is demonstrated.
Journal of Non-Crystalline Solids, 2009
We report a structural investigation of bulk Ge-rich Ge-S-AgI chalcohalide glasses. A vibrational... more We report a structural investigation of bulk Ge-rich Ge-S-AgI chalcohalide glasses. A vibrational spectroscopic study of the quaternary system (AgI) x (GeS 1.5) 100Àx (0 6 x AgI 6 20) has been undertaken using infrared spectroscopy and Fourier transform Raman scattering. It was found that the GeS 1.5 Raman spectrum is compatible with a glass structure composed of corner-and edge-sharing mixed GeS n Ge 4Àn (n = 0-4) tetrahedra where units with n = 2-4 dominate, whilst the fraction of corner-sharing units are significantly lower than the corresponding fraction in the stoichiometric GeS 2 glass. The addition of AgI has revealed a subtle but systematic effect in the structure of the Ge-rich glass matrix, manifested by mild decrease of the ES units and the concomitant increase of complex GeS n I 4Àn or GeS n Ge m I 4-nÀm tetrahedra whose vibrational modes form a continuum at low frequencies. Although, AgI seems to cause subtle structural changes due to the formation of Ge-I bonds, it is also evident that AgI does not act as a real modifier that would depolymerize appreciably the Ge-S network structure.
![Research paper thumbnail of Structure of As[sub x]Te[sub 100−x] (20≤x≤60) glasses investigated with x-ray absorption fine structure, x-ray and neutron diffraction, and reverse Monte Carlo simulation](https://attachments.academia-assets.com/87895874/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2008
A systematic and detailed investigation of the structure of As x Te 100−x glasses ͑20ഛ x ഛ 60͒ ha... more A systematic and detailed investigation of the structure of As x Te 100−x glasses ͑20ഛ x ഛ 60͒ has been undertaken using a combination of structure-probing techniques including high energy x-ray diffraction, neutron diffraction, and x-ray absorption fine structure measurements at the As and Te K edges. The experimental datasets were modeled simultaneously with the reverse Monte Carlo simulation technique. The results revealed that homonuclear bonding for both As and Te atoms is important over the whole glass concentration region studied. At the stoichiometric composition ͑As 40 Te 60 ͒ the average As-As and Te-Te coordination numbers are as high as 1.7Ϯ 0.2 and 1.3Ϯ 0.1, respectively. The number of As-As and Te-Te bonds, as well as the average number of bonds/atom, evolves monotonically with composition. Arsenic atoms are threefold coordinated for all compositions investigated. It has also been shown that, in contrast to the results of previous studies, Te is predominantly twofold coordinated for x ഛ 50. Our results suggest that ͑i͒ chemical ordering does not play a decisive role in the formation of short-range order and ͑ii͒ similar to some other amorphous tellurides ͑e.g., Ge 2 Sb 2 Te 5 , GeSb 2 Te 4 , and As 25 Si 40 Te 35 ͒ binary As x Te 100−x ͑x ഛ 50͒ alloys obey the "8 − N" rule. A detailed comparison has been advanced between the structural details obtained from the present study and several physicochemical properties of As-Te. The comparison revealed striking similarities between the concentration dependence of structural and physicochemical properties.
... 1.5. The structural investigation has been implemented with the aid of FTIR and FT-Raman tech... more ... 1.5. The structural investigation has been implemented with the aid of FTIR and FT-Raman techniques. Elucidation ... additive. However structural studies on theseglasses are practically absent in the literature. 2. Experimental. ...
Journal of Solid State Chemistry, 2011
We report an investigation of the structure and vibrational modes of (AgI) x (AsSe) 100 À x , bul... more We report an investigation of the structure and vibrational modes of (AgI) x (AsSe) 100 À x , bulk glasses using Raman spectroscopy and first principles calculations. The short-and medium-range structural order of the glasses was elucidated by analyzing the reduced Raman spectra, recorded at off-resonance conditions. Three distinct local environments were revealed for the AsSe glass including stoichiometriclike and As-rich network sub-structures, and cage-like molecules (As 4 Se n , n ¼ 3, 4) decoupled from the network. To facilitate the interpretation of the Raman spectra ab initio calculations are employed to study the geometric and vibrational properties of As 4 Se n molecular units that are parts of the glass structure. The incorporation of AgI causes appreciable structural changes into the glass structure. AgI is responsible for the population reduction of molecular units and for the degradation of the As-rich network-like sub-structure via the introduction of As-I terminal bonds. Ab initio calculations of mixed chalcohalide pyramids AsSe m I 3 À m provided useful information augmenting the interpretation of the Raman spectra.
Journal of Materials Research and Technology, 2021
Abstract Novel proton conducting materials with composition 85SiO2-9P2O5-6TiO2, modified by addit... more Abstract Novel proton conducting materials with composition 85SiO2-9P2O5-6TiO2, modified by addition of liquid xH3PO4 in different amounts xH3PO4 = 0; 17; 35; 52 mmol, were synthesized via sol-gel route. XRD patterns show amorphous nature for “pure” (xH3PO4= 0 mmol) sample and crystalline for all H3PO4-doped samples. FTIR and SEM analysis revealed that this modification led to appreciable structural changes on molecular level and morphology, which, heavily impacts the water intake ability, impedance behavior as well as the dielectric parameters. The detailed impedance examination showed distinct response of changing parameters such as relative humidity and temperature, while the dielectric parameters derived from the impedance spectra, provide in-depth understanding of proton conduction dynamic. Based on these observations different models were proposed gathering proton transfer in humid and dry atmospheres. The enhanced proton conduction is a basic requirement for successful usage of the material for hydrogen gas detection.
Egyptian Journal of Chemistry
I NFLUENCE of the preparation method and different precursors are important for the absorber phot... more I NFLUENCE of the preparation method and different precursors are important for the absorber photovoltaic layer parameters of SnS. Synthesis of SnS compounds was carried out via two preparation methods; solid state reaction and hydrothermal; using different sulfur precursors. The morphology of particles and phase identification were studied using Field Emission Scanning Electron Microscope (FESEM) and X-ray diffraction (XRD) techniques. The XRD diffraction pattern of SnS revealed the existence of two crystal structure phases: the major is orthorhombic and the minor phase is tetragonal. The optical properties were determined using UV-Vis spectrophotometer showing absorbance peaks around 485 nm. The lowest bandgap of 1.74 eV is for SnS sample prepared from L-cystine. Electrochemical impedance spectroscopy (EIS) revealed that SnS cell prepared from L-cystine gave the lowest resistance of 171Ω. The photoelectrochemical measurements of this cell showed the highest power conversion efficiency per unit area of 2.5%.
NATO Science for Peace and Security Series B: Physics and Biophysics, 2011
Chapter 23 Structure of AgI-AsSe Glasses by Raman Scattering and Ab Initio Calculations Ofeliya K... more Chapter 23 Structure of AgI-AsSe Glasses by Raman Scattering and Ab Initio Calculations Ofeliya Kostadinova, T. Petkova, A. Chrissanthopoulos, Plamen Petkov, and SN Yannopoulos Abstract We report a structure investigation of (AsSe) 100Àx (AgI) x bulk glasses using Raman ...
Chapter 23 Structure of AgI-AsSe Glasses by Raman Scattering and Ab Initio Calculations Ofeliya K... more Chapter 23 Structure of AgI-AsSe Glasses by Raman Scattering and Ab Initio Calculations Ofeliya Kostadinova, T. Petkova, A. Chrissanthopoulos, Plamen Petkov, and SN Yannopoulos Abstract We report a structure investigation of (AsSe) 100Àx (AgI) x bulk glasses using Raman ...
NATO Science for Peace and Security Series A: Chemistry and Biology, 2014
Journal of Non-Crystalline Solids, 2009
We report a structural investigation of bulk Ge-rich Ge-S-AgI chalcohalide glasses. A vibrational... more We report a structural investigation of bulk Ge-rich Ge-S-AgI chalcohalide glasses. A vibrational spectroscopic study of the quaternary system (AgI) x (GeS 1.5 ) 100Àx (0 6 x AgI 6 20) has been undertaken using infrared spectroscopy and Fourier transform Raman scattering. It was found that the GeS 1.5 Raman spectrum is compatible with a glass structure composed of corner-and edge-sharing mixed GeS n Ge 4Àn (n = 0-4) tetrahedra where units with n = 2-4 dominate, whilst the fraction of corner-sharing units are significantly lower than the corresponding fraction in the stoichiometric GeS 2 glass. The addition of AgI has revealed a subtle but systematic effect in the structure of the Ge-rich glass matrix, manifested by mild decrease of the ES units and the concomitant increase of complex GeS n I 4Àn or GeS n Ge m I 4-nÀm tetrahedra whose vibrational modes form a continuum at low frequencies. Although, AgI seems to cause subtle structural changes due to the formation of Ge-I bonds, it is also evident that AgI does not act as a real modifier that would depolymerize appreciably the Ge-S network structure.
Chalcogenide glasses (ChGs) are produced by alloying together a “chalcogen” element” (S, Se or Te... more Chalcogenide glasses (ChGs) are produced by alloying together a “chalcogen” element” (S, Se or Te) with other elements, generally from group V (Sb, As) or group IV (Ge, Si) to form covalently bonded solids. A variety of stable non-crystalline materials can be prepared in bulk, fiber, and thin film forms using melt-quenching, vacuum deposition, and other less common techniques. Being amorphous semiconductors, ChGs exhibit a variety of photo-induced phenomena when irradiated with proper light and therefore find a wide range of technological applications (optical data storage, telecommunications, IR optics, etc). As research in this field is strongly driven by the needs of high-tech industry, physical properties related to the applications are more systematically investigated than the atomic structure, which is ultimately related to the macroscopic properties. A shortcoming of not having yet established microstructure-properties relations in ChGs is the lack of a strategic design of ne...
Automation is applied in continuously extending fields of application in the modern communities. ... more Automation is applied in continuously extending fields of application in the modern communities. In this respect, sensors are indispensable elements of systems for automatic regulation. Besides, the use of multitudes of sensor elements enables statistical data acquisition from large time and long distance monitoring. Consequently, the requirements for application of multitudes of sensor elements impose a need for elaboration of advanced sensor element production. In this context anodized aluminum oxide (AAO) layers enable the elaboration of relatively simple, large scale technology for reliable and durable sensor elements. The present review is devoted to a summary of the basic concepts related to the elaboration of reliable and durable sensor elements on the basis of anodized aluminum. Furthermore, various examples are provided regarding the recent research activities in this field.
Lithium sodium sulphate (LNS) has been synthesised by two methods: mechanical ball milling and me... more Lithium sodium sulphate (LNS) has been synthesised by two methods: mechanical ball milling and melt quenching. The obtained materials have been studied by means of X-ray diffraction, scanning electron microscopy (SEM), Infrared spectroscopy and differential scanning calorimetry. The influence of the synthesis method on the structure and behaviour of the materials will be discussed.
NATO Science for Peace and Security Series A: Chemistry and Biology, 2014
The aim of the present work is the synthesis and characterization of novel oxide materials in vie... more The aim of the present work is the synthesis and characterization of novel oxide materials in view of their potential use as active material in lithium ion batteries. Bulk materials from (TiO2)x(V2O5)y(P2O5)100-x-y system, where x = 5, 10, 15 and y = 60, 70, were prepared by means of the melt quenching method. The materials were characterized by physical chemical and electrochemical methods, i.e. X-ray diffraction, infrared spectroscopy and cyclic voltammetry measurements. The electrochemical properties were investigated against metallic lithium as active materials in a half-cell system.
Journal of Non-Crystalline Solids, 2009
The structure of Sb x Se 100Àx bulk glasses is investigated with the aid of Raman scattering over... more The structure of Sb x Se 100Àx bulk glasses is investigated with the aid of Raman scattering over a wide composition range. The Raman spectra of the glasses exhibit unusual features when compared with other structurally similar binary glasses, owing to the phase separation of the present glasses in a certain composition range. The evolution of the Raman spectra and the depolarization ratio of the polarized and depolarized Raman intensities are consistent with the phase separation effect. The present findings are discussed alongside with calorimetric data from the literature that have been used up to now to extract structural information in an indirect way. The capability of Raman scattering as a tool for investigating phase separation in homogeneous media is demonstrated.
Journal of Non-Crystalline Solids, 2009
We report a structural investigation of bulk Ge-rich Ge-S-AgI chalcohalide glasses. A vibrational... more We report a structural investigation of bulk Ge-rich Ge-S-AgI chalcohalide glasses. A vibrational spectroscopic study of the quaternary system (AgI) x (GeS 1.5) 100Àx (0 6 x AgI 6 20) has been undertaken using infrared spectroscopy and Fourier transform Raman scattering. It was found that the GeS 1.5 Raman spectrum is compatible with a glass structure composed of corner-and edge-sharing mixed GeS n Ge 4Àn (n = 0-4) tetrahedra where units with n = 2-4 dominate, whilst the fraction of corner-sharing units are significantly lower than the corresponding fraction in the stoichiometric GeS 2 glass. The addition of AgI has revealed a subtle but systematic effect in the structure of the Ge-rich glass matrix, manifested by mild decrease of the ES units and the concomitant increase of complex GeS n I 4Àn or GeS n Ge m I 4-nÀm tetrahedra whose vibrational modes form a continuum at low frequencies. Although, AgI seems to cause subtle structural changes due to the formation of Ge-I bonds, it is also evident that AgI does not act as a real modifier that would depolymerize appreciably the Ge-S network structure.
The Journal of Chemical Physics, 2008
A systematic and detailed investigation of the structure of As x Te 100−x glasses ͑20ഛ x ഛ 60͒ ha... more A systematic and detailed investigation of the structure of As x Te 100−x glasses ͑20ഛ x ഛ 60͒ has been undertaken using a combination of structure-probing techniques including high energy x-ray diffraction, neutron diffraction, and x-ray absorption fine structure measurements at the As and Te K edges. The experimental datasets were modeled simultaneously with the reverse Monte Carlo simulation technique. The results revealed that homonuclear bonding for both As and Te atoms is important over the whole glass concentration region studied. At the stoichiometric composition ͑As 40 Te 60 ͒ the average As-As and Te-Te coordination numbers are as high as 1.7Ϯ 0.2 and 1.3Ϯ 0.1, respectively. The number of As-As and Te-Te bonds, as well as the average number of bonds/atom, evolves monotonically with composition. Arsenic atoms are threefold coordinated for all compositions investigated. It has also been shown that, in contrast to the results of previous studies, Te is predominantly twofold coordinated for x ഛ 50. Our results suggest that ͑i͒ chemical ordering does not play a decisive role in the formation of short-range order and ͑ii͒ similar to some other amorphous tellurides ͑e.g., Ge 2 Sb 2 Te 5 , GeSb 2 Te 4 , and As 25 Si 40 Te 35 ͒ binary As x Te 100−x ͑x ഛ 50͒ alloys obey the "8 − N" rule. A detailed comparison has been advanced between the structural details obtained from the present study and several physicochemical properties of As-Te. The comparison revealed striking similarities between the concentration dependence of structural and physicochemical properties.
... 1.5. The structural investigation has been implemented with the aid of FTIR and FT-Raman tech... more ... 1.5. The structural investigation has been implemented with the aid of FTIR and FT-Raman techniques. Elucidation ... additive. However structural studies on theseglasses are practically absent in the literature. 2. Experimental. ...
Journal of Solid State Chemistry, 2011
We report an investigation of the structure and vibrational modes of (AgI) x (AsSe) 100 À x , bul... more We report an investigation of the structure and vibrational modes of (AgI) x (AsSe) 100 À x , bulk glasses using Raman spectroscopy and first principles calculations. The short-and medium-range structural order of the glasses was elucidated by analyzing the reduced Raman spectra, recorded at off-resonance conditions. Three distinct local environments were revealed for the AsSe glass including stoichiometriclike and As-rich network sub-structures, and cage-like molecules (As 4 Se n , n ¼ 3, 4) decoupled from the network. To facilitate the interpretation of the Raman spectra ab initio calculations are employed to study the geometric and vibrational properties of As 4 Se n molecular units that are parts of the glass structure. The incorporation of AgI causes appreciable structural changes into the glass structure. AgI is responsible for the population reduction of molecular units and for the degradation of the As-rich network-like sub-structure via the introduction of As-I terminal bonds. Ab initio calculations of mixed chalcohalide pyramids AsSe m I 3 À m provided useful information augmenting the interpretation of the Raman spectra.
Journal of Materials Research and Technology, 2021
Abstract Novel proton conducting materials with composition 85SiO2-9P2O5-6TiO2, modified by addit... more Abstract Novel proton conducting materials with composition 85SiO2-9P2O5-6TiO2, modified by addition of liquid xH3PO4 in different amounts xH3PO4 = 0; 17; 35; 52 mmol, were synthesized via sol-gel route. XRD patterns show amorphous nature for “pure” (xH3PO4= 0 mmol) sample and crystalline for all H3PO4-doped samples. FTIR and SEM analysis revealed that this modification led to appreciable structural changes on molecular level and morphology, which, heavily impacts the water intake ability, impedance behavior as well as the dielectric parameters. The detailed impedance examination showed distinct response of changing parameters such as relative humidity and temperature, while the dielectric parameters derived from the impedance spectra, provide in-depth understanding of proton conduction dynamic. Based on these observations different models were proposed gathering proton transfer in humid and dry atmospheres. The enhanced proton conduction is a basic requirement for successful usage of the material for hydrogen gas detection.
Egyptian Journal of Chemistry
I NFLUENCE of the preparation method and different precursors are important for the absorber phot... more I NFLUENCE of the preparation method and different precursors are important for the absorber photovoltaic layer parameters of SnS. Synthesis of SnS compounds was carried out via two preparation methods; solid state reaction and hydrothermal; using different sulfur precursors. The morphology of particles and phase identification were studied using Field Emission Scanning Electron Microscope (FESEM) and X-ray diffraction (XRD) techniques. The XRD diffraction pattern of SnS revealed the existence of two crystal structure phases: the major is orthorhombic and the minor phase is tetragonal. The optical properties were determined using UV-Vis spectrophotometer showing absorbance peaks around 485 nm. The lowest bandgap of 1.74 eV is for SnS sample prepared from L-cystine. Electrochemical impedance spectroscopy (EIS) revealed that SnS cell prepared from L-cystine gave the lowest resistance of 171Ω. The photoelectrochemical measurements of this cell showed the highest power conversion efficiency per unit area of 2.5%.
NATO Science for Peace and Security Series B: Physics and Biophysics, 2011
Chapter 23 Structure of AgI-AsSe Glasses by Raman Scattering and Ab Initio Calculations Ofeliya K... more Chapter 23 Structure of AgI-AsSe Glasses by Raman Scattering and Ab Initio Calculations Ofeliya Kostadinova, T. Petkova, A. Chrissanthopoulos, Plamen Petkov, and SN Yannopoulos Abstract We report a structure investigation of (AsSe) 100Àx (AgI) x bulk glasses using Raman ...
Chapter 23 Structure of AgI-AsSe Glasses by Raman Scattering and Ab Initio Calculations Ofeliya K... more Chapter 23 Structure of AgI-AsSe Glasses by Raman Scattering and Ab Initio Calculations Ofeliya Kostadinova, T. Petkova, A. Chrissanthopoulos, Plamen Petkov, and SN Yannopoulos Abstract We report a structure investigation of (AsSe) 100Àx (AgI) x bulk glasses using Raman ...
NATO Science for Peace and Security Series A: Chemistry and Biology, 2014
Journal of Non-Crystalline Solids, 2009
We report a structural investigation of bulk Ge-rich Ge-S-AgI chalcohalide glasses. A vibrational... more We report a structural investigation of bulk Ge-rich Ge-S-AgI chalcohalide glasses. A vibrational spectroscopic study of the quaternary system (AgI) x (GeS 1.5 ) 100Àx (0 6 x AgI 6 20) has been undertaken using infrared spectroscopy and Fourier transform Raman scattering. It was found that the GeS 1.5 Raman spectrum is compatible with a glass structure composed of corner-and edge-sharing mixed GeS n Ge 4Àn (n = 0-4) tetrahedra where units with n = 2-4 dominate, whilst the fraction of corner-sharing units are significantly lower than the corresponding fraction in the stoichiometric GeS 2 glass. The addition of AgI has revealed a subtle but systematic effect in the structure of the Ge-rich glass matrix, manifested by mild decrease of the ES units and the concomitant increase of complex GeS n I 4Àn or GeS n Ge m I 4-nÀm tetrahedra whose vibrational modes form a continuum at low frequencies. Although, AgI seems to cause subtle structural changes due to the formation of Ge-I bonds, it is also evident that AgI does not act as a real modifier that would depolymerize appreciably the Ge-S network structure.