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Effects of A-site nonstoichiometry on oxide ion conduction in 0.94Bi_(0.5)Na_(0.5)TiO_(3)-0.06BaTiO_(3) ceramics

Journal of Advanced Dielectrics 2016年第2期6卷 70-78页

作者： Sasiporn prasertpalichat Whitney Schmidt david p.cann Materials Science School of Mechanical Industrial and Manufacturing Engineering Oregon State UniversityCorvallisOR 97331USA

Lead free 0.94(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping(through Bi-excess)and acceptor-doping(through Na-excess).Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry.A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess *** spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction *** with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by3-4 orders of magnitude and an associated activation energy of 1.57 eV which was close to half of the optical *** contrast,an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess *** addition,the Na-excess compositions exhibited low resistivities(ρ-10^(3)Ω-cm)with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in(Bi_(0.5)Na_(0.5))TiO_(3).Long term annealing studies were also conducted at 800℃to identify changes in crystal structure and electrical *** results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)ceramics are very sensitive to Bi/Na stoichiometry.

关键词： A-site nonstoichiometry oxide ion conduction lead free BNT-BT ceramics impedance spectroscopy ceramics.

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Synthesis and electrical properties of BaBiO_(3)and high resistivity BaTiO_(3)-BaBiO_(3)ceramics

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Journal of Advanced Dielectrics 2016年第4期6卷 53-60页

作者： Nitish Kumar Stephen L.Golledge david p.cann Materials Science School of Mechanical Industrialand Manufacturing Engineering Oregon State UniversityCorvallisOregon 97331USA School of Materials Science and Engineering The University of New South Wales New South Wales 2052 Australia CAMCOR Surface Analytical Facility University of Oregon Eugene Oregon 97403USA

Ceramics of the composition BaBiO_(3)(BB)were sintered in oxygen to obtain a single phase with monoclinic I2/m symmetry as suggested by high-resolution X-ray diffraction.X-ray photoelectron spectroscopy confirmed the presence of bismuth in two valence states—3þand 5þ.Optical spectroscopy showed presence of a direct bandgap at-2.2 eV and a possible indirect bandgap at-0.9 *** combined with determination of the activation energy for conduction of 0.25 eV,as obtained from ac impedance spectroscopy,suggested that a polaron-mediated conduction mechanism was prevalent in *** BB ceramics were crushed,mixed with BaTiO_(3)(BT),and sintered to obtain BT–BB solid *** the ceramics had tetragonal symmetry and exhibited a normal ferroelectric-like dielectric *** ac impedance and optical spectroscopy,it was shown that resistivity values of BT–BB were orders of magnitude higher than BT or BB alone,indicating a change in the fundamental defect equilibrium conditions.A shift in the site occupancy of Bi to the A-site is proposed to be the mechanism for the increased electrical resistivity.

关键词： BaBiO_(3) BaTiO_(3) conduction mechanism transport properties synchrotron X-ray photoelectron spectroscopy impedance spectroscopy defects.

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Dual-shell silicate and alumina coating for long lasting and high capacity lithium ion batteries

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Journal of Energy Chemistry 2022年第5期31卷 314-323页

作者： Marcos Lucero Tucker M.Holstun Yudong Yao Ryan Faase Maoyu Wang Alpha T.N’Diaye david p.cann Joe Baio Junjing Deng Zhenxing Feng School of Chemical Biologicaland Environmental EngineeringOregon State UniversityCorvallisOR 97331United States Advanced photon Source Argonne National LaboratoryArgonneIllinois 60439United States Advanced Light Source Lawrence Berkeley National LaboratoryBerkeleyCalifornia 94720United States Materials Science School of MechanicalIndustrialand Manufacturing EngineeringOregon State UniversityCorvallisOR 97331United States

Here we demonstrate a theory-driven, novel dual-shell coating system of Li_(2)SrSiO_(4) and Al_(2)O_(3), achieved via a facile and scalable sol-gel technique on LiCoO_(2) electrode particles. The optimal thickness of each coating can lead to increased specific capacity(~185 m Ah/g at 0.5 C-rate) at a cut-off potential of 4.5 V, and greater cycling stability at very high C rates(up to 10 C) in half-cells with lithium metal. The mechanism of this superior performance was investigated using a combination of X-ray and electron characterization methods. It shows that the results of this investigation can inform future studies to identify still better dual-shell coating schemes, achieved by such industrially feasible techniques, for application on similar, nickel-rich cathode materials.

关键词： Lithium cobalt oxide Surface coating Sol-gel Silicate Alumina X-ray absorption spectroscopy

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DIELECTRIC AND pIEZOELECTRIC pROpERTIES OF(K,Na)NbO_(3)-BASED pIEZOELECTRIC CERAMICS

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Journal of Advanced Dielectrics 2011年第3期1卷 345-349页

作者： ERIC A.pATTERSON david p.cann Materials Science School of Mechanical Industrialand Manufacturing Engineering Oregon State UniversityCorvallisOR 97331USA

Solid solutions based on Li,Ta and Sb-doped(K_(0.5)Na_(0.5))NbO_(3)(KNN)lead-free perovskite systems were created using standard solid-state methods.X-ray diffraction was used to conrm that all compositions were single phase and to verify the phase transition from tetragonal to cubic at T_(C)=302℃.The three compositions examined,originally developed by Saito and Li,were shown to be strongly ferroelectric with sharp peaks in permittivity present at the Curie *** optimum composition had loss tangent values below 5%up to 100 kHz at room *** hysteresis measurements showed high values for both maximum polarization(25 and 21μC/cm^(2))and remenant polarizations(20 and 16μC/cm^(2))for undoped and 0.2 wt%CuO-doped *** strain values of greater than 0.23%were observed.

关键词： Lead-free systems piezoelectricity dielectric perovskite ferroelectrics

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