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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.
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.
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.
Fabrication and electrochemical properties of LiCo1-xRuxO2 cathode materials for Li-ion battery
(Elsevier Science Sa, 2016) Oz, E.; Demirel, S.; Altin, S.
LiCo1-xRuxO2 (where x - 0.0-0.5) are prepared by conventional solid-state reaction technique. The effect of Ru substitutions on the structural properties and electrochemical performance of LiCoO2 cathode materials is investigated in detail. The XRD analysis shows that increasing Ru content in LiCoO2 above x = 0.1 causes formation of different phases such as Li1.4RuO3, Li2Ru0.5Co0.5O3 and RuO2 which are used in the Li-ion batteries as an electrode materials. It is found in the XRD analysis that the Ru doping causes a decrease in the crystallite size which is important for improving the battery performance. The CV analysis shows that the Ru doping till x = 0.1 can produce an improvement in the performance of the cell and the capacity retention after 50 cycle is much better than that of the cell that fabricated using the pure LiCoO2. (C) 2016 Elsevier B.V. All rights reserved.
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.
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.
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.
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.
Ring-expanded iridium and rhodium N-heterocyclic carbene complexes: a comparative DFT study of heterocycle ring size and metal center diversity
(Taylor & Francis Ltd, 2017) Karaca, E. O.; Akkoc, M.; Oz, E.; Altin, S.; Dorcet, V.; Roisnel, T.; Gurbuz, N.
A new series of ring-expanded six-and seven-membered N-heterocyclic carbene precursors (re-NHCs) and their transition metal complexes were synthesized. The basic properties of the synthesized materials were investigated by density functional theory (DFT). The six- and seven-membered re-NHCs were synthesized in good yield via reaction of the corresponding alkyldibromides or alkyldiiodides with N,N'-bis-(2-phenylbenzene)formamidine in the presence of K2CO3 under aerobic conditions. Complexes, represented by the formula [ML1,2(COD)Cl] (where M = Ir or Rh and L is a ring-expanded N-heterocyclic carbene ligand), were synthesized in the presence of the corresponding free carbene and iridium or rhodium metal precursors in tetrahydrofuran. All new re-NHC complexes were characterized by different analytical techniques, including NMR spectroscopy, X-ray diffraction, UV spectroscopy and elemental analysis. According to molecular electrostatic potential calculations, the electrophilic properties of the complexes were aligned, from highest to lowest, as Ir-6-DiPh, Rh-6-DiPh and Ir-7-DiPh. The HOMO, LUMO and energy gaps of the complexes were calculated by DFT. On the basis of the DFT analysis, it can be predicted that Rh-6-DiPh is the most stable complex and Ir-7-DiPh is more reactive than Ir-6-DiPh. [GRAPHICS] .
Structural and magnetic properties of Ni2-xCoxMnSb (x: 0.00, 0.25, 0.50 and 1.00) Heusler alloys: The relationship between Curie temperature and lattice parameter
(Elsevier Sci Ltd, 2019) Ak, F.; Oz, E.; Saatci, B.
Ni2-xCoxMnSb Heusler alloys were fabricated by arc melting process. The endothermic/exothermic reactions with increasing temperature were determined by DTA analysis and it was found that the chancing Co concentration in the system causes the change in the reaction temperatures. The temperature dependence of the magnetization from base temperature to 600 K, a crucial value for the Curie temperature, and lattice parameters of the samples were determined. It was suggested that increasing Co in the samples causes the change of the grain formation and the increasing Co concentration in the system also causes the change of the Curie temperature values with decreased the lattice parameters.
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.
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.
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.
Thermal and mechanical properties of La-Al-Sb alloys
(Springer, 2014) Altin, E.; Oz, E.; Demirel, S.; Erdem, M.
We fabricated La-Al-Sb alloy by arc melter system and the fabrication conditions were described in detail. Microstructural analyses were performed and it was found that LaSb, Al11La3 Al4La, AlLa3 and Sb phases formed for different heat treatment conditions. The resistivity results showed the metallic and semiconducting type behavior depending on heat treatment temperatures. The thermal-conductivity measurement was performed in the range of 2-300 K and the data were analyzed by the sum of lattice and carrier components. The linear temperature dependence of thermo power indicates metallic type characteristic of the samples. The micro-hardness values of the phases in the samples were analyzed and it was found that there are two different hardness regions in the samples.
Thermoelectric and mechanical properties of Mg-Al-Sb alloys
(Springer, 2015) Altin, E.; Oz, E.; Erdem, M.; Demirel, S.; Aydogdu, Y.; Altin, S.
We fabricated Mg-Al-Sb alloy by arc melting system. Microstructural analyses were performed and it was found that only Mg3Sb2 and AlSb phases formed for different heat treatment conditions. The phase transition at 580 degrees C according to DTA analysis was determined as partial melting and it was supported by phase analyses studies in the literature. The resistivity results showed the metallic and the semiconducting type behavior depending on the heat treatment temperatures. The thermal conductivity measurement was performed in the range of 2-300 K and the data were analyzed by the sum of lattice and carrier components. The thermopower data showed negative and positive values which indicate the sign of total carriers. The linear temperature dependence of thermopower indicates metallic type characteristic of the samples. Mechanical properties of the sample showed two type hardness values dependent on heat treatment temperature.
Vortex pinning and magnetic peak effect in Eu(Eu,Ba)2.125Cu3Ox
(Springer, 2014) Altin, E.; Gokhfeld, D. M.; Demirel, S.; Oz, E.; Kurt, F.; Altin, S.; Yakinci, M. E.
Eu-Ba-Cu-O composition was synthesized by solid state reaction technique. To determine optimum growth temperature, heat treatment was examined on the material at 880-1,100 A degrees C. Microstructural evolution, phase formation and elemental distribution depending on heat treatments were examined by using X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope analysis. Optimum fabrication conditions were determined as 1,020 A degrees C for 24 h under oxygen atmosphere and detailed characterization of corresponding compound was performed. The magnetization hysteresis loops are expounded to be the product of superconducting Eu-123 grains and magnetic Eu2+ ions. The peak effect on the magnetization curves was described by the extended critical state model. Scaling of the pinning force was found such that the peak position is proportional to the irreversibility field H (irr) and the maximum pinning force is proportional to H (irr) (2) .

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