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Homogeneous interface-type resistance switching in Au/La_(0.67)Ca_(0.33)MnO_3/SrTiO_3/F:SnO_2 heterojunction memories

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Chinese Physics B 2012年第4期21卷 467-472页

作者：张婷丁玲红张伟风 Key Laboratory of Photovoltaic Materials of Henan Province School of Physics and ElectronicsHe'nan UniversityKaifeng 475004China

La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer. The current-voltage characteristics of the heterojunetions exhibit an asymmetric and resistance switching behaviour. A homogeneous interface-type conduction mechanism is also reported using impedance spectroscopy. The spatial homogeneity of the charge carrier distribution leads to field- induced potential-barrier change at the Au-La0.67Ca0.33MnO3 interface and a concomitant resistance switching effect. The ratio of the high resistance state to the low resistance state is found to be as high as 1.3 x 10^4% by simulating the AC electric field. This colossal resistance switching effect will greatly improve the signal-to-noise ratio in nonvolatile memory applications.

关键词： La0.67Ca0.33MnO3 thin films resistance switching impedance spectroscopy metal-oxide interface

Improvement in corrosion resistance of magnesium coating with cerium treatment

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Rare Metals 2009年第3期28卷 277-283页

作者： Samia Ben Hassen Latifa Bousselmi Patrice Berot El Mustafa Rezrazi Ezzeddine Triki Unité de Recherche Corrosion & Protection des Métalliques ENITBP 37Tunis-BelvédèreTunisia Institut UTINAM CNRS UMR 6213Université de Franche-Comté16 route de Gray 25030 Besanon CedexFrance Laboratoire Traitement et Recyclage des Eaux CERTEBorj CedriaTunisia

Corrosion protection afforded by a magnesium coating treated in cerium salt solution on steel substrate was investigated using open circuit potential, polarization curves, and electrochemical impedance spectroscopy （EIS） in 0.005 M sodium chloride solution （NaCl）. The morphology of the surface was characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and X-ray diffraction （XRD）. The cerium treated coating was obtained by immersion in CeCl3 solution. The results showed that the corrosion resistance of the treated magnesium coating was improved. The corrosion potential of the treated coating was found to be nobler than that of the untreated magnesium coating and the corrosion current decreased significantly. impedance results showed that the cerium treatment increased corrosion protection. The improvement of anti-corrosion properties was attributed to the formation of cerium oxides and hydroxides that gave rise to a physical barrier effect.

关键词： magnesium coating cerium corrosion protection impedance spectroscopy

Dielectric relaxation and conduction mechanism in Aurivillius ceramic Bi_(5)Ti_(3)FeO_(15)

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International Journal of Minerals,Metallurgy and Materials 2021年第6期28卷 1063-1071页

作者： Rasmita Jena K.Chandrakanta P.Pal Md.F.Abdullah S.D.Kaushik A.K.Singh Department of Physics and Astronomy National Institute of Technology RourkelaRourkela-769008OdishaIndia UGC-DAE Consortium for Scientific Research Mumbai Centre BARCMumbai-400085India

For this study,we synthesized Aurivillius Bi_(5)Ti_(3)FeO_(15) ceramic using the generic solid-state reaction route and then performed roomtemperature X-ray diffraction to confirm that the compound had a single phase with no *** surface morphology of the prepared sample was observed to contain microstructural grains approximately 0.2–2μm in *** dielectric properties of the sample were determined as a function of frequency in a range of approximately 100 Hz to 1 MHz at various temperatures(303 K≤T≤773 K).Nyquist plots of the impedance data were found to exhibit a semi-circular arc in the high-temperature region,which is explained by the equivalent electrical circuit(R_(1)C_(1))(R_(2)QC_(2)),where R_(1) and R_(2) represent the resistances associated with the grains and grain boundaries,respectively,C_(1) and C_(2) are the respective capacitances,and Q is the constant phase element(CPE),which accounts for non-Debye type of *** results indicate that both the resistance and capacitance of the grain boundaries are more prominent than those of the *** alternating current(ac)conductivity data were analyzed based on the Jonscher universal power law,which indicated that the conduction process is dominated by the hopping *** calculated activation energies of the relaxation and conduction processes were very similar(0.32 to 0.53 eV),from which we conclude that the same type of charge carriers are involved in both processes.

关键词： Nyquist plot impedance spectroscopy activation energy ac conductivity hopping

Ionic Conductivity in Gelatin-Based Hybrid Solid Electrolytes:The Non-trivial Role of Nanoclay

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Journal of Materials Science & Technology 2014年第11期30卷 1096-1102页

作者： Ali Ghadami Nader Taheri Qazvini Nasser Nikfarjam Polymer Division School of ChemistryCollege of ScienceUniversity of Tehran Biomaterials Research Center (BRC) University of Tehran

In this study, the ionic conductivity behavior in hybrid gelatin-based transparent electrolytes including various types of nanoclays with different size, shape and surface properties was characterized. The effects of nanoclay type and nanoclay concentration as well as different experimental conditions, e.g., pH, temperature and crosslinking were also investigated. In general, the impedance spectroscopy results suggested a non- trivial role for nanoclay. Regardless of the nanoclay type, the ionic conductivity slightly increased first and then decreased by increasing the nanoclay concentration. Furthermore, among sodium montmorillonite （Na＋MMT）, lithium montmorillonite （Li＋MMT）, laponite and hydrotalcite, the hybrid electrolytes prepared by Li＋MMT showed higher ionic conductivity. The results also showed that the chemical crosslinking along with sample preparation at optimum pH, where the gelatin chains might be efficiently adsorbed on exfoliated, negatively charged clay nanosheets, plays an important role. In comparison with the ionic conductivity of the neat sample at room temperature （～10-7 S cm-1）, a ten-fold increase was observed for the crosslinked sample containing 2 wt% of Li^＋MMT prepared at optimum pH 3.5. The conductivity behavior as a function of temperature revealed the obedience with the VogeI-Fulcher-Tammann （VFT） model for all samples, suggesting the important role of segmental motions in the ionic conductivity. Finally, a qualitative explanation was presented for the mechanism of the ionic conduction in gelatin-nanoclay hybrid electrolytes.

关键词： Gelatin Solid-state electrolytes Ionic conductivity Montmorillonitc Laponite impedance spectroscopy

Mo^(6+)Modified(K_(0.5)Na_(0.5))NbO_3 Lead Free Ceramics:Structural,Electrical and Optical Properties

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Journal of Materials Science & Technology 2014年第5期30卷 459-465页

作者： Jyoti Rani Piyush Kumar Patel Nidhi Adhlakha Hemant Singh K.L.Yadav Satya Prakash Smart Materials Research Laboratory Department of PhysicsIndian Institute of Technology Roorkee Metallurgical and Materials Engineering Department Indian Institute of Technology Roorkee

Lead free polycrystalline ceramics （K0.5Na0.5）Nb（1-x）MoxO3 （x = 0, 0.02, 0.04, 0.06 and 0.08） have been synthesized via solid state reaction method. The formation of single phase perovskite structure up to 6 mol% of Mo^6＋ has been confirmed by X-ray diffraction pattern. impedance spectroscopy reveals that bulk resistance decreases with increasing temperature, which indicates negative temperature coefficient of resistance （NTCR） behaviour of the compounds. The diffuse reflectance spectroscopy results indicate a red shift of the band gap energy of K0.5Na0.5NbO3 （KNN, from 4.28 to 3.61 eV） with increasing Mo^6＋ concentration due to structural modification. The photoluminescence spectra of doped samples are composed of two emission bands at room temperature. One emission band is near band edge ultraviolet （UV） emission （354 nm） and other is visible emission band （-397 nm） which may explore the possibility of these ceramics to be used in optical device applications.

关键词： Ceramics Characterization Dielectric constant impedance spectroscopy Optical band gap

impedance Studies of La_2Mo_(2-x)Sn_xO(9-δ) Oxide Ion Conductors

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Acta Metallurgica Sinica(English Letters) 2013年第4期26卷 425-434页

作者： Lakhi Nath Borah A.Pandey Department of Physics North Eastern Regional Institute of Science and Technology

A series of compounds La2Mo2-xSnxO9-6 （x=0-0.3） have been synthesized by solid-state reaction technique. Materials have been characterized by XRD, SEM, DSC and impedance study. In the temperature regime 520℃-590 ℃, the specimens with x〈0.05 have the conductivity higher than La2Mo2O9. Conductivity of Sn-doped compound decreases consistently with increasing Sn-doping, compared to the undoped compound both below and above phase transition, barring the specimens with x〈 0.05, where conductivity values remains almost same as that of undoped specimen in high temperature region. In the intermediate temperature regime （520℃-590℃）, the conductivity of doped compounds increases for x〈0.05 as compared to parent compound. Also, there is no indication of phase stabilization with Sn-doping in this compound even with the highest doping level, x=0.3. Electric modulus analysis suggests that thermally activated oxygen ion hopping mechanism is responsible for the conduction in Sn-doped compound.

关键词： Ionic conduction La2M0209 Oxide ion conductor impedance spectroscopy Electric modulus

Influence of Fabrication Parameters on the Phase Formation and Dielectric Properties of CaCu_3Ti_4O_(12 )Ceramics

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Journal of Materials Science & Technology 2012年第10期28卷 920-926页

作者： Qian Zheng Huiqing Fan State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytech-nical UniversityXi'an 710072China

The giant dielectric permittivity materials CaCu3Ti4012 （CCTO） were synthesized by conventional solid-state reaction techniques. X-ray diffraction and Raman scattering for the powder indicate that the powder calcined at 950 ℃ for 12 h has been completely transformed into the purer CCTO phase. Furthermore, the morphology and size of the grains of the ceramics sintered at 1090 ℃ in the dwell time range from 0 to 26 h were observed by scanning electron microscopy （SEM）. Dielectric properties of the polycrystalline CCTO ceramics were characterized in a broad frequency range （100 Hz-1 MHz） and at a temperature ranged from 300 to 500 K. The longer sintering time may lead to more defect structures and the enhanced conductivity, also leads to substantial improvements in permittivity. Grain size and density differences were not large enough to account for the enhancement in dielectric permittivity. Based on the observations, it is believed that the primary factor affecting dielectric behavior is the development of internal defects. The CCTO ceramics sintered at 1090 ℃ for 15 h exhibit lower dielectric loss （-0.05） near room temperature, and the dielectric relaxation behavior above 1 kHz was observed to follow the Arrhenius law. The activation energy （Ea） of 0.65 eV indicates that the doubly ionized oxygen vacancies in the grain boundaries are responsible for the dielectric relaxation of the CCTO ceramics.

关键词： Microstructure Dielectric properties impedance spectroscopy Relaxation

Structural and electrical transport properties of a rare earth double perovskite oxide:Ba_2ErNbO_6

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Journal of Rare Earths 2014年第4期32卷 334-342页

作者： Rajesh Mukherjee Binita Ghosh Sujoy Saha Chandrahas Bharti T.P.Sinha Department of Physics Ramananda College Department of Physics Bose Institute Sensor and Actuator Division CSIR-Central Glass and Ceramic Research Institute

The double perovskite oxide barium erbium niobate, Ba2ErNbO6 （BEN） was synthesized by solid state reaction technique. Rietveld refinement of the X-ray diffraction pattern of the sample showed cubic （Fm3m） phase at room temperature. Fourier trans-form infrared spectrum showed two primary phonon modes of the sample at around 387 and 600 cm-1. Raman spectrum of the sam-ple taken at 488 nm excitation wavelength showed four primary strong peaks at 106, 382, 747 and 814 cm-1. Lorentzian lines with 10 bands were used to fit the Raman spectrum. A group theoretical study was performed to assign all the Raman modes. impedance spectroscopy was applied to investigate the ac electrical conductivity of BEN in a temperature range from 303 to 673 K and in a fre-quency range from 100 Hz-1 MHz. The dielectric relaxation mechanism was discussed in the frame work of permittivity, conduc-tivity, modulus and impedance formalisms. The complex plane plot of the impedance data was modeled by an equivalent circuit con-sisting of two serially connected R-CPE units, （one for the grain and the other for the grain boundary）, each containing a resistor （R） and a constant phase element （CPE）. The R-CPE units were used to incorporate the non-ideal character of the polarization phenome-non instead of an ideal capacitive behaviour. The relaxation time corresponding to dielectric loss was found to obey the Arrhenius law with activation energy of 0.85 eV. The frequency dependent conductivity spectra followed the Jonscher power law. The Cole-Cole model was used to investigate the dielectric relaxation mechanism in the sample.

关键词： perovskites Rietveld refinement Raman spectroscopy impedance spectroscopy rare earths

Effects of structure and electronic properties of D-π-A organic dyes on photovoltaic performance of dye-sensitized solar cells

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Journal of Energy Chemistry 2021年第3期30卷 208-216页

作者： Min-Woo Lee Jae-Yup Kim Hyung-Geun Lee Hyun Gil Cha Duck-Hyung Lee Min Jae Ko Bio-Based Chemistry Research Center Advanced Convergent Chemistry DivisionKorea Research Institute of Chemical Technology(KRICT)Ulsan 44429Republic of Korea Department of Chemical Engineering Dankook UniversityYongin 16890Republic of Korea Department of Chemistry Sogang UniversitySeoul 04107Republic of Korea Department of Chemical Engineering Hanyang UniversitySeoul 04763Republic of Korea Institute of Nano Science and Technology Hanyang UniversitySeoul 04763Republic of Korea

Herein,we examine the performance of dye-sensitized solar cells containing five D-π-A organic dyes designed by systematic modification of π-bridge size and geometric *** dye has a simple push-pull structure with a triarylamino group as an electron donor,bithiophene-4,4-dimethyl-4 H-cyclopenta 1,2-b:5,4-b’]dithiophene(M11),4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophenethiophene(M12),thiophene-4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene(M13),4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene-benzene(M14),and 4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene(M15)units asπ-bridges,and cyanoacrylic acid as an electron acceptor/*** extension of theπ-bridge linkage favors wide-range absorption but,because of the concomitant molecular volume increase,hinders the efficient adsorption of dyes on the TiO_(2) film ***,higher loadings are achieved for smaller dye molecules,resulting in(i)a shift of the TiO_(2) conduction band edge to more negative values,(ii)a greater photocurrent,and(iii)suppressed charge recombination between the photoanode and the redox couple in the ***,under one-sun equivalent illumination(AM 1.5 G,100 mW/cm^(2)),the highest photovoltage,photocurrent,and conversion efficiency(η=7.19%)are observed for M15,which has the smallest molecular volume among M series dyes.

关键词： Dye-sensitized solar cells Donor-acceptor dyes Electron-rich unit Wide-range absorption impedance spectroscopy