Synchrotron-based x-ray absorption near-edge structure(XANES)spectroscopy is applied to investigate the variation of Ti valence in the discharge and charge processes of Li_(4)Ti_(5)O_(12).Through analysis of the XANES...Synchrotron-based x-ray absorption near-edge structure(XANES)spectroscopy is applied to investigate the variation of Ti valence in the discharge and charge processes of Li_(4)Ti_(5)O_(12).Through analysis of the XANES data,the average valence of Ti can be calculated,which allows quantitative determination of the ratios of Ti^(3+)/Ti^(4+) as a function of Li content in the electrodes.It is found that the ratios in the composites of Li_(4)Ti_(5)O_(12)/acetylene black(AB)-carbon are larger than those in Li_(4)Ti_(5)O_(12)/Ag/AB-carbon after the discharge to 1.1 V,indicating a larger amount of Li inserted into the former than that into the latter.This finding provides a good explanation for the fact that the Li_(4)Ti_(5)O_(12)/AB-carbon samples exhibit larger storage capacities than the Li_(4)Ti_(5)O_(12)/Ag/AB-carbon ones prepared in this work,concerning the larger Ti^(3+)/Ti^(4+) ratio and the larger amount of Li^(+) inserted in the electrode for satisfying the charge neutralization requirement.展开更多
The large coercive field of domain switching in poly(vinylidene fluoride-trifluoroethylene)thin films is in much part due to the contribution of nonpolar impurity phases rather than the manifestation of an intrinsic d...The large coercive field of domain switching in poly(vinylidene fluoride-trifluoroethylene)thin films is in much part due to the contribution of nonpolar impurity phases rather than the manifestation of an intrinsic domain switching mechanism of the ferroelectric layer.We coincidentally derive the equivalent electrical capacitance for the total non-ferroelectric capacitive layers from either domain switching current transient or voltage dependence of the switched polarization.Unexpectedly,the non-ferroelectric capacitance reduces by more than 71%with the enhancement of domain switching speed spanning over 5 orders of magnitude in company with the continuous reduction of the remanent polarization,which suggests the thickening of the above capacitive layers with enhanced domain switching speed.展开更多
大气元素沉降的地衣移植法监测常将地衣样品移植于乔木冠层下,但冠层有无与移植时长对地衣元素组成的影响研究不多。本研究将河北省偏远地区的中国树花(Ramalina sinensis)移植于污染区,基于元素含量增高倍数EC(exposed to control rat...大气元素沉降的地衣移植法监测常将地衣样品移植于乔木冠层下,但冠层有无与移植时长对地衣元素组成的影响研究不多。本研究将河北省偏远地区的中国树花(Ramalina sinensis)移植于污染区,基于元素含量增高倍数EC(exposed to control ratio)评估了55种元素的生物积累程度,检验了冠层(2水平:有冠层或无冠层)和移植时长(3水平:7、8或9个月)对地衣元素含量的影响。结果显示,中国树花的元素背景含量低于已有研究中地衣元素含量的背景值/基线值,有效反映了背景区较低的大气污染程度。中国树花适用于除Co和Hg(二者含量的背景噪声过高)之外的53种元素的大气沉降监测。移植后绝大多数元素含量显著高于背景区,其中交通相关元素Pb和Sb为“极重度积累”,与农业活动和植物生理活性有关的元素(As、K、P、S和Se)以及Ag和Ge为“无积累”或“轻度积累”,其他44种元素(Al、B、Ba、Be、Bi、Ca、Cd、Ce、Cr、Cs、Cu、Dy、Er、Eu、Fe、Gd、Ho、La、Li、Lu、Mg、Mn、Mo、Na、Nb、Nd、Ni、Pr、Rb、Tb、Sc、Si、Sm、Sn、Sr、Th、Ti、Tl、Tm、U、V、Y、Yb和Zn)为“中度积累”,表明移植区大气污染程度较高,交通排放贡献大。冠层和移植时长对中国树花元素含量的影响具有元素特异性:26种元素的含量或因冠层淋溶作用而在冠层下高于无冠层,Pb含量或因冠层截留作用而呈相反格局;移植时长超过7个月后,绝大多数元素(41种)含量不再增加,11种元素含量呈增高趋势,Ni含量呈下降趋势。表明利用地衣移植法进行大气元素沉降监测时,冠层有无需保持一致,且移植时间不可过长。展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 10979069,U1232111,the One-Hundred Talents Project of Chinese Academy of Sciences.
文摘Synchrotron-based x-ray absorption near-edge structure(XANES)spectroscopy is applied to investigate the variation of Ti valence in the discharge and charge processes of Li_(4)Ti_(5)O_(12).Through analysis of the XANES data,the average valence of Ti can be calculated,which allows quantitative determination of the ratios of Ti^(3+)/Ti^(4+) as a function of Li content in the electrodes.It is found that the ratios in the composites of Li_(4)Ti_(5)O_(12)/acetylene black(AB)-carbon are larger than those in Li_(4)Ti_(5)O_(12)/Ag/AB-carbon after the discharge to 1.1 V,indicating a larger amount of Li inserted into the former than that into the latter.This finding provides a good explanation for the fact that the Li_(4)Ti_(5)O_(12)/AB-carbon samples exhibit larger storage capacities than the Li_(4)Ti_(5)O_(12)/Ag/AB-carbon ones prepared in this work,concerning the larger Ti^(3+)/Ti^(4+) ratio and the larger amount of Li^(+) inserted in the electrode for satisfying the charge neutralization requirement.
基金Supported by Shanghai Key Program(1052nm07600)the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning.
文摘The large coercive field of domain switching in poly(vinylidene fluoride-trifluoroethylene)thin films is in much part due to the contribution of nonpolar impurity phases rather than the manifestation of an intrinsic domain switching mechanism of the ferroelectric layer.We coincidentally derive the equivalent electrical capacitance for the total non-ferroelectric capacitive layers from either domain switching current transient or voltage dependence of the switched polarization.Unexpectedly,the non-ferroelectric capacitance reduces by more than 71%with the enhancement of domain switching speed spanning over 5 orders of magnitude in company with the continuous reduction of the remanent polarization,which suggests the thickening of the above capacitive layers with enhanced domain switching speed.
文摘大气元素沉降的地衣移植法监测常将地衣样品移植于乔木冠层下,但冠层有无与移植时长对地衣元素组成的影响研究不多。本研究将河北省偏远地区的中国树花(Ramalina sinensis)移植于污染区,基于元素含量增高倍数EC(exposed to control ratio)评估了55种元素的生物积累程度,检验了冠层(2水平:有冠层或无冠层)和移植时长(3水平:7、8或9个月)对地衣元素含量的影响。结果显示,中国树花的元素背景含量低于已有研究中地衣元素含量的背景值/基线值,有效反映了背景区较低的大气污染程度。中国树花适用于除Co和Hg(二者含量的背景噪声过高)之外的53种元素的大气沉降监测。移植后绝大多数元素含量显著高于背景区,其中交通相关元素Pb和Sb为“极重度积累”,与农业活动和植物生理活性有关的元素(As、K、P、S和Se)以及Ag和Ge为“无积累”或“轻度积累”,其他44种元素(Al、B、Ba、Be、Bi、Ca、Cd、Ce、Cr、Cs、Cu、Dy、Er、Eu、Fe、Gd、Ho、La、Li、Lu、Mg、Mn、Mo、Na、Nb、Nd、Ni、Pr、Rb、Tb、Sc、Si、Sm、Sn、Sr、Th、Ti、Tl、Tm、U、V、Y、Yb和Zn)为“中度积累”,表明移植区大气污染程度较高,交通排放贡献大。冠层和移植时长对中国树花元素含量的影响具有元素特异性:26种元素的含量或因冠层淋溶作用而在冠层下高于无冠层,Pb含量或因冠层截留作用而呈相反格局;移植时长超过7个月后,绝大多数元素(41种)含量不再增加,11种元素含量呈增高趋势,Ni含量呈下降趋势。表明利用地衣移植法进行大气元素沉降监测时,冠层有无需保持一致,且移植时间不可过长。
