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Öğe Altered isotope charge distribution of acetylcholine neurotransmitter and Myasthenia Gravis(Churchill Livingstone, 2016) Bayri, A.; Unal, S.; Altin, S.; Bulut, F.; Dayanc, B. E.Acetylcholine (ACh) is a central neurotransmitter that is used for signal transmission among neurons. For signal transmission in neurons, a neurotransmitter must bind to its receptor in order to produce an action potential. It is known that in Myasthenia Gravis (MG) cases, autoantibodies could block this binding. In the future, the treatment of MG could be achieved via modulation of molecular interaction between ACh and acetylcholine receptor (AChR). This study suggests that if an atom on a ligand (i.e. a neurotransmitter) is replaced with its isotope, it may cause charge redistribution such as that the binding between ligand and its receptor may be improved. Hence suggesting that with replacement of atoms with their isotopes in any biologically important ligand could alter its affinity towards its corresponding receptor, which would have a wide array of applications in medicine. (C) 2016 Elsevier Ltd. All rights reserved.Öğe Alternating Heisenberg s=1/2 spin chain(Natl Inst Optoelectronics, 2006) Isik, F.; Ekmekci, S.; Bayri, A.Spin ladder systems containing CuCl3 and CuBr3 show very interesting magnetic behaviour, which are alternate Heisenberg chains with ferromagnetic and antiferromagnetic interactions. Since these systems contain triangles of magnetic centers, we developed a model based on non-interacting triangular units, which may be used for interpretation of magnetic measurements of these systems in some extreme limits. We took the Heisenberg model type interactions for magnetic center and used different types of exchange coupling between the neighbours. The results obtained from our approximations may be used in order to interpret the experimental magnetic measurements in KCuCl3 and TiCuCl3 complexes and for the singlet-triplet transition temperature.Öğe Electrochemical effects and magnetic properties of B substituted LiCoO2: Improving Li-battery performance(Elsevier Science Sa, 2016) Oz, E.; Altin, S.; Demirel, S.; Bayri, A.; Altin, E.; Baglayan, O.; Avci, S.LiCo(1-x)BxO(2) (x = 0, 0.125, 0.25, 0.375, 0.5, 0.75 and 1) samples were synthesized via solid state reactions. They were characterized by SEM, X-ray powder diffraction, FTIR, Raman, electrical and magnetic measurements. XRD data show impurity phases for x >= 0.25 samples due to boron content. Based on FTIR studies, the peak position of CoO6 shifts with increasing B content. The Raman spectra of LiCoO2 shows the presence of three broad bands, indicating the possible formation of spinel structure. The effective magnetic moments of the samples were calculated using Curie-Weiss law with temperature independent term. The M-H curves of x = 0.375 and 0.5 samples show very weak hysteresis loops. Effects of boron substitution on battery performance are also investigated. x = 0.125 and x >= 0.25 samples give promising results due to their enhanced reversibility of cycling compared to pristine LiCoO2. Capacity retentions for 100 cycles for x = 0, 0.125 and 0.25 samples are 22%, 81% and 83%, respectively. (C) 2015 Elsevier B.V. All rights reserved.Öğe An energy competition of Co3+ and Co4+ ions during spin state transition in Ca3Co4O9 complex(Iop Publishing Ltd, 2016) Karaman, N.; Bayri, A.; Ekmekci, S.The magnetic behavior of Ca3Co4O9 complex shows a very interesting phase transition at high temperature. It is probably that this ordering is due to the spin states of Co3+ and Co4+ ions. It is quite obvious that spin states of Co ions generally change as a function of temperature. We have shown that there is a strong correlation between oxidation states and ligand field parameters during spin state transitions.Öğe Enhancement of battery performance of LiMn2O4: correlations between electrochemical and magnetic properties(Royal Soc Chemistry, 2016) Demirel, S.; Oz, E.; Altin, S.; Bayri, A.; Altin, E.; Avci, S.We report the results of a systematic investigation of structural, electrical transport, magnetic, and electrochemical properties of LiBxMn2-xO4 (where x = 0.0-1), synthesized via a one-step solid state reaction technique. We find that the parent compound (x = 0) has the non-stoichiometric Li1.05Mn2O4 phase and the B ions successfully incorporate the structure for x <= 0.5. The resistivity anomaly of the parent compound below 100 K is attributed to the antiferromagnetic correlations. The linear part of the chi(-1)-T data are used to calculate the effective magnetic moments and to determine the total number of Mn3+ and Mn4+ ions. Magnetization measurements show that Jahn-Teller active Mn3+ ions have high spin configuration. Average valance of Mn ions increases with increasing boron content. Electrochemical studies show improved capacity retention for x = 0.125 for 100 charge-discharge cycles. This improvement is attributed to subtle modifications in the structural and magnetic properties upon substitution.Öğe An enhancement ZT and spin state transition of Ca3Co4O9 with Pb doping(Elsevier Science Sa, 2015) Demirel, S.; Altin, E.; Oz, E.; Altin, S.; Bayri, A.We reported the structural, electrical, thermal and magnetic properties of Pb-doped Ca3Co4O9 in the range of 300-5 K. DTA analysis showed that the stability of the Ca3Co4O9 was increased with Pb doping. According to XRD analysis, it is found that Pb ions were successfully doped in the Ca3Co4O9 structure. The temperature of resistivity minima, T-min, increased by increasing the Pb doping level and it is seen that incommensurate spin density wave state becomes more stable with Pb doping. The enhancement of thermopower was explained that Pb doping in Ca sites caused a decrease of Co4+ fraction such that Co4+ ions transformed into Co3+ or Co2+. The room temperature ZT value of the polycrystalline sample reaches about 16 times larger value than that of the un-doped polycrystalline sample which is the promising candidate for high temperatures in the thin film applications. According to magnetic susceptibility measurement, the increase of effective magnetic moment by Pb concentration was explained by spin state transition of Co3+ from low spin to intermediate spin and high spin state together with some orbital angular momentum contribution which comes from T-5(2) term due to a decrease of the ligand field splitting energy. (C) 2014 Elsevier B. V. All rights reserved.Öğe Fabrication of Ca-Mn-Nb-O compounds and their structural, electrical, magnetic and thermoelectric properties(Iop Publishing Ltd, 2018) Oz, E.; Demirel, S.; Altin, S.; Altin, E.; Baglayan, O.; Bayri, A.; Avci, S.CaMn1-xNbxO3-delta (0 <= x <= 1) were synthesized by conventional solid state reaction method. The structural properties were determined by FTIR, Raman, XRD, XAS measurements. The FTIR and Raman modes change by increasing Nb content and the lattice volume increases by increasing Nb content. The solubility limit of Nb is determined as x <= 0.3 and impurity phases start to appear above this limit. The temperature dependence of the magnetization data shows an antiferromagnetic transition below 120 K for low Nb content. Increasing the Nb content causes a change in the magnetic phase from antiferromagnetic to paramagnetic. The oxygen deficiency in CaMnO3-delta may cause the formation of polaron effect which is destroyed by the Nb ions. The difference graph of XAS data for x = 0 and 0.5 show that the number of Mn3+ ions increases by increasing Nb content to maintain the charge neutrality.Öğe Fabrication of Cr doped Na0.67Fe0.5Mn0.5O2 compounds and investigation of their structural, electrical, magnetic and electrochemical properties(Springer, 2019) Altin, E.; Altundag, S.; Altin, S.; Bayri, A.The main purpose of the study is to investigate the battery properties behind the electrical and magnetic properties. The first part of the study is about the fabrication of Cr-doped Na0.67Fe0.5Mn0.5O2 and the structural properties of the powders, which were investigated by XRD, EXAFS, FTIR and Raman Spectroscopy. Temperature-dependent resistivity measurements showed that room temperature resistivity values increased with Cr-ion content and all samples show an exponential decrease with increasing temperature. The magnetic properties of the Cr-doped samples were investigated, and it was found that the Cr ions strongly affected the magnetic structure of the samples. The second part of the study is about battery performance using the samples as cathode materials. Hence, CR2032 coin cells were fabricated by using the Cr-doped samples and the CV measurements showed that a high level doping of Cr ions in the structure prevented Na diffusion in the cells. The obtained CV graphs were discussed from the viewpoint of lattice dynamics. The EIS and cycling properties showed that Cr-ions in Na0.67Fe0.5Mn0.5O2 decrease of the capacity fade of the cells.Öğe Growth mechanism and magnetic and electrochemical properties of Na0.44MnO2 nanorods as cathode material for Na-ion batteries(Elsevier Science Inc, 2015) Demirel, S.; Oz, E.; Altin, E.; Altin, S.; Bayri, A.; Kaya, P.; Turan, S.Nanorods of Na0.44MnO2 are a promising cathode material for Na-ion batteries due to their large surface area and single crystalline structure. We report the growth mechanism of Na(0.44)Mno(2) nanorods via solid state synthesis and their physical properties. The structure and the morphology of the Na0.44MnO2 nanorods are investigated by X-ray diffraction (XRD), scanning and tunneling electron microscopy (SEM and TEM), and energy-dispersive X-ray (EDX) techniques. The growth mechanism of the rods is investigated and the effects of vapor pressure and partial melting of Na-rich regions are discussed. The magnetic measurements show an antiferromagnetic phase transition at 25 K and the Pelf is determined as 3.41 and 3.24 mu(B) from the chi-T curve and theoretical calculation, respectively. The electronic configuration and spin state of Mn3+ and Mn4+ are discussed in detail. The electrochemical properties of the cell fabricated using the nanorods are investigated and the peaks in the voltammogram are attributed to the diffusion of Na ions from different sites. Na intercalation process is explained by one and two Margules and van Laar models. (C) 2015 Elsevier Inc. All rights reserved.Öğe High temperature spin state transitions in misfit-layered Ca3Co4O9(Elsevier Science Sa, 2014) Altin, S.; Aksan, M. A.; Bayri, A.This study reports high temperature magnetic properties of the unsubstituted one together with B and Sb-substituted Ca3Co4O9 system. The measured data indicated that there is an anomaly in the magnetic susceptibility, chi, between 680 and 920 K. It is believed that this anomaly is related to a critical threshold number of the high spin Co-ions such that when this threshold number is achieved, some exchange interactions between Co3+ and Co4+ take place which causes an abrupt increase in the chi-T curve. The anomaly was further investigated with B and Sb-substitutions. It is realized that both dopants promote more Co-ions in the rock salt unit cell to high spin state. (C) 2013 Elsevier B.V. All rights reserved.Öğe Improving of the battery performance of Dy-substituted LiCoO2 and investigating the mechanism of the cells(Springer, 2019) Altin, S.; Altundag, S.; Altin, E.; Bayri, A.In this study, we successfully fabricated LiCo1-xDyxO2 (where x = 0.0-0.5) samples and investigated the structural and electrochemical properties. The Dy-substituted LiCoO2 samples were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), Fourier-transform infrared (FTIR), and Raman measurements before and after cycling. The lattice volume and effective magnetic moment were increased by the substitution of the Dy ions in the structure. The capacity fading mechanism of Dy-substituted LiCoO2 via ex situ X-ray diffraction, XAS, Raman and FTIR spectroscopy were investigated. According to the electrochemical performance of the batteries, the x = 0.04 electrode had better cycling properties up to 400 cycles, which are better than that of the pure LiCoO2. We suggested that the critical number of Dy in LiCoO2 facilitates the Li-diffusion by increasing lattice volume. According to the battery performance temperature dependence analysis from 10 to 50 degrees C, the electrolyte just below degradation temperature shows better cycling since the ions are more mobile in this case.Öğe Investigation of Spin State Transition of [FeC17H31N7]2+ Compound by Using the Density Functional Method(Springer, 2017) Isik, F.; Sabaner, M. A.; Erboz, Duygu; Sahinbas, Taylan; Bayri, A.The symmetry of the [FeC17H31N7](2+) novel compound is close to octahedral which has spin crossover properties (SCO). In this study, geometrical optimization, IR vibration frequencies, and HOMO-LUMO energy differences at various temperatures of the compound were calculated by DFT. It is realised that the computed splitting energies and splitting free enthalpies together with the mole fraction of HS state are compatible with the experiment.Öğe An investigation of the improvement in energy storage performance of Na2/3Mn1/2Fe1/2O2by systematic Al-substitution(Springer, 2020) Altin, S.; Altundag, S.; Altin, E.; Harfouche, M.; Bayri, A.We successfully fabricated Na2/3Mn1/2Fe1/2-xAlxO2, wherex = 0, 0.01, horizontal ellipsis 0.10, by a modified solid-state reaction technique. The structural properties of the Al-substituted samples were investigated by x-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy and x-ray absorption fine structure (XAFS) measurements. It was found that there were no impurity phases in the XRD patterns of the samples and they fit the P63/mmc symmetry. The Al substitution in Na(2/3)Mn(1/2)Fe(1/2)O(2)causes a decrease in the a-lattice parameter, but the c-parameter starts to increase after a certain substitution value of Al. We suggest that a certain proportion of Al in the samples triggers the change of the spin configuration of the Fe ions, and it may cause an increase in the lattice parameters. The size of the grains was found to be less than 0.9 mu m, from SEM images for all samples. The valence states of the substituted samples as well as the local structure around Fe and Mn were investigated by means of XAFS measurements. The highest capacity for the first cycle was obtained as 134.3 mAh/g forx = 0.07, and the best capacity fade was found to be 0.23 forx = 0.08 substitution. So, the highest performance of the Al-substituted cells was found when 0.08 >= x >= 0.06. The environmental temperature effects on the battery cells were determined at 10 oC, room temperature and 50 oC, and it was found that the temperature plays a crucial role in the Na-ion batteries.Öğe LiNi0.8Co0.15Ti0.05O2: synthesis by solid state reaction and investigation of structural and electrochemical properties with enhanced battery performance(Springer, 2020) Bayri, A.; Gocer, E.; Altin, E.; Altundag, S.; Oz, E.; Harfouche, M.; Altin, S.Solid state synthesis is an essential technique for large-scale production of electrode active materials in battery industry. However, solid state synthesis of LiNi0.8Co0.15Al0.05O2(NCA), which is a well-known commercial cathode material for Li-ion batteries, provides electrochemically inactive compound. Here, we report the solid state synthesis of Li(x)Ni(0.8)Co(0.15)Ti(0.05)O(2)wherex = 1.03, 1.06, and 1.09, which is a modified version of conventional NCA. Our thorough studies consist of characterization of compounds by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and magnetization measurements. The results point out the significant effects of Li content on structural and magnetic properties of the samples. Battery performance tests show that Li(1.06)Ni(0.8)Co(0.15)Ti(0.05)O(2)exhibits better cycling properties than conventional NCA. X-ray absorption spectroscopy (XAS) technique is utilized to determine structural modifications upon cycling of this compound via ex-situ analysis. We conclude that substitution of Ti ions in Li(1.06)Ni(0.8)Co(0.15)Ti(0.05)O(2)improves the cycling capability of the cells by reducing the formation of NiO insulating layer which hinders the redox reactions. The capacity value ofx = 1.06 sample increases up to 150 mAh g(-1)at C/3 rate during cycling and the capacity fade is negative for the first 10 cycles. Possible mechanism for the negative capacity fade is also discussed.Öğe Magnetic and microstructural properties of LiCrO2.Cr2O3 system by doping of the boron ions(Springer, 2015) Demirel, S.; Oz, E.; Bayri, A.; Altin, S.In this study, we reported the structural, electrical and magnetic properties of B-doped LiCrO2.Cr2O3 system by boron doping. XRD pattern of the samples showed that the boron ions were substituted with Cr ions in both lattices and the volume of the cells were decreased by increasing boron content. The particle size and strain calculations were performed by using XRD pattern and it is found that the particle sizes were not changed much by boron doping but the strain were increased by increasing boron in the samples. The susceptibility of the undoped sample shows two different phase behavior with decreasing temperature and it is found that the magnetic properties of Cr2O3 were dominant at room temperature to 100 K and the peak at 62 K was due to the LiCrO2 phase. It should be noted that the boron doping were caused the decrease of the room temperature susceptibility and the antiferromagnetic interactions were destroyed by boron incorporation of the lattice.Öğe Sizeable amount of antiferromagnetic exchange interactions in newly reported dimeric cobalt (II) complex of the antiprine Schiff base of 3-formylsalicylic acid(Natl Inst Optoelectronics, 2008) Avcu, F. M.; Aytekin, O.; Karakaplan, M.; Bayri, A.This study reports the magnetic properties of newly reported cobalt(II) complex of the antiprine Schiff base of 3-formylsalicylic acid. Assuming the isotropic Heisenberg model is valid it is suggested that there is a sizeable amount of antiferromagnetic exchange interactions between metal centers in dimeric units. It is also suggested that the system become demagnetized below a certain temperature.Öğe Structural, magnetic, electrical and electrochemical properties of SrCo02.5, Sr9Co2Mn5O21 and SrMnO3 compounds(Elsevier Sci Ltd, 2017) Demirel, S.; Oz, E.; Altin, S.; Bayri, A.; Baglayan, O.; Altin, E.; Avci, S.SrCo1-xMnxO3-d (0 <= x <= 1) were synthesized by conventional solid state reaction method. We found that Mn substitution hinders the decomposition of carbonate at 900 degrees C and increases the synthesis temperature of SrCo1-xMnxO3-d to 1200 degrees C. Three different main phases emerge as the Mn content is increased; SrCoO2.5, Sr9Co2Mn5O21 and SrMnO3. Structural properties of the samples were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray diffraction (XRD) and scanning electron microscopy (SEM). Valance states of the transition metal (TM) ions were estimated based on lattice parameters and ionic radii of TM ions. High temperature resistivity measurements show hysteresis upon heating and cooling and is attributed to oxygen release without any endothermic/exothermic activity. The spin configurations of Co and Mn ions in SrCoO2.5, Sr9Co2Mn5O21. and SrMnO3 were estimated by Curie-Weiss fitting of X-T curves. Electrochemical measurements show two anodic/cathodic peaks indicating two main types of oxygen sites in the unit cell.Öğe Symmetry related magnetic interactions in (CuCl3) complexes(İnönü Üniversitesi, Fen Edebiyat Fakültesi, Fizik Bölümü, Malatya, Türkiye, 2001) Atalay, F.E; Bayri, A.; Ekmekci, S.Abstract: CuCl3 komplekslerinde ferromagnetik ve antiferromagnetik iki tür magnetik etkileşimin olduğu bildirilmiştir. Bu etkileşimler exchange sabitinin işareti ile birbirlerinden tamamen ayrılırlar .Bu kompleksin moleküler orbitallerini bulmak için, molekülün lokal simetrisini kullandık. Bu orbitalleri kullanarak her iki yöndeki exchange sabitini hesapladık.Öğe Synthesis of Na2Ti3O7 nanorods by a V-assisted route and investigation of their battery performance(Royal Soc Chemistry, 2020) Altin, S.; Demirel, S.; Oz, E.; Altin, E.; Hetherington, C.; Bayri, A.; Avci, S.We report the V-assisted synthesis of Na2Ti3O7 nanorods via a conventional solid state reaction technique. Energy dispersive X-ray spectroscopy (EDS) mapping showed that V-ions are not incorporated into the main structure of the nanorods but rather V behaves as a flux agent during the growth of the nanorods. The cyclic voltammetry (CV) analysis of the samples shows changes in the redox peaks as a function of V content. Our detailed ex situ X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) analyses after 1000 cycles show that the degradation mechanism is the formation of various titanium oxide impurity phases which inhibits the Na-ion diffusion.Öğe Synthesis of ultra-thin nanobristles of Na-Mn-O compounds and their magnetic and structural properties(Elsevier Sci Ltd, 2016) Oz, E.; Demirel, S.; Altin, S.; Bayri, A.; Avci, S.Boron substituted Na0.44MnO2 nanorods were synthesized via conventional solid state reaction technique. Optimum synthesis temperature of the nanorods is determined as 750 degrees C. As the temperature increases, the nanorods start merging each other. As the boron content increases, amount of nanorods decrease due to the emergence of impurity phases. 12.5% boron substitution (x=0.25 in NaMn2-xBxO4 nominal composition) into Mn site striggers the formation of ultra-thin nanobristles on the surface of the nanorods. These nanobristles disappear completely in x=0.75 sample. We attribute the formation of these nanobristles to the increase in the internal energy upon increase in the unit cell volume. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
