This paper reports the F-centers and photostimulated luminescence of Eu^(2+)-activated Sr_3Ca_2(PO_4)_3X crystals.The influence of various halide ions on the F-centers and their energy level is discussed.The mechanism...This paper reports the F-centers and photostimulated luminescence of Eu^(2+)-activated Sr_3Ca_2(PO_4)_3X crystals.The influence of various halide ions on the F-centers and their energy level is discussed.The mechanism for the photostimulated luminescence and valence change of Eu ion in that process have been investigated.展开更多
Results of experimental investigation of relaxation aging processes in Pb(Zr,Ti)O_(3)-based solid solutions after termination of external actions are presented.Heating,DC electric field,uniaxial pressure and some of t...Results of experimental investigation of relaxation aging processes in Pb(Zr,Ti)O_(3)-based solid solutions after termination of external actions are presented.Heating,DC electric field,uniaxial pressure and some of their combinations were taken as external actions.In the main part of the present paper,we use heating as external action.The said processes are long-time one and are described by the logarithmic function of time.Reversible and nonreversible relaxation processes take place depending on the action intensity.The relaxation rate depends on the action intensity also,and the said dependence has nonlinear and nonmonotonic form if external action leads to domain disordering.The oxygen vacancies-based model for description of the long-time relaxation processes is suggested.The model takes into account oxygen vacancies on the sample's surface ends,their conversion into Fþ-and F0-centers under external effects(due to the liberation of the pyroelectric charge)and subsequent relaxation of these centers into the simple oxygen vacancies after the actions termination.The initial sample's state is electroneutrality one.F-center formation leads to the violation of the original sample's electroneutrality,and generates DC electric field into the sample.Relaxation of F-centers is accompanied by decreasing of electric field,induced by them,and dielectric constant relaxation as consequent effect.展开更多
The paper presents results of experimental study of the dielectric constant relaxation during aging process in Pb(Zr,Ti)O_(3) based solid solutions(PZT)after action of external DC electric field.The said process is a ...The paper presents results of experimental study of the dielectric constant relaxation during aging process in Pb(Zr,Ti)O_(3) based solid solutions(PZT)after action of external DC electric field.The said process is a long-term one and is described by the logarithmic function of time.Reversible and nonreversible relaxation process takes place depending on the field intensity.The relaxation rate depends on the field strength also,and the said dependence has nonlinear and nonmonotonic form,if external field leads to domain disordering.The oxygen vacancies-based model for description of the long-term relaxation processes is suggested.The model takes into account the oxygen vacancies on the sample's surface ends,their conversion into Fþ-and F^(0)-centers under external effects and subsequent relaxation of these centers into the simple oxygen vacancies after the action termination.F-centers formation leads to the violation of the original sample's electroneutrality,and generate intrinsic DC electric field into the sample.Relaxation of F-centers is accompanied by the reduction of the electric field,induced by them,and relaxation of the dielectric constant,as consequent effect.展开更多
The oxidative coupling of methane(OCM)isone of the most promising routes for the direct con-version of methane to ethylene[1].Ding et al[2]re-ported that a high surface concentration of alkaline earth metal cations fa...The oxidative coupling of methane(OCM)isone of the most promising routes for the direct con-version of methane to ethylene[1].Ding et al[2]re-ported that a high surface concentration of alkaline earth metal cations facilitated the formation of C_(2) hy-drocarbons during the OCM.Surface basicity is nec-essary for the OCM,and oxygen adsorbed on basic sites is also indispensable.The adsorbed electron defi-cient oxygen species on the catalyst surface plays a crucial role in methane conversion and the selectivity for Cz hydrocarbons.Our previous study[3]showed that increasing the Sr/Ti molar ratio in the per-ovskite-type SrTiO_(3) catalyst resulted in the surface enrichment of Sr,a larger amount of adsorbed oxygen species and higher selectivity for C_(2) hydrocarbons in the OCM.Recently,nanocatalysts have attracted much attention because of their remarkable catalytic performance[4.5].展开更多
基金The project supported by the National Natural Science Foundation of China
文摘This paper reports the F-centers and photostimulated luminescence of Eu^(2+)-activated Sr_3Ca_2(PO_4)_3X crystals.The influence of various halide ions on the F-centers and their energy level is discussed.The mechanism for the photostimulated luminescence and valence change of Eu ion in that process have been investigated.
文摘Results of experimental investigation of relaxation aging processes in Pb(Zr,Ti)O_(3)-based solid solutions after termination of external actions are presented.Heating,DC electric field,uniaxial pressure and some of their combinations were taken as external actions.In the main part of the present paper,we use heating as external action.The said processes are long-time one and are described by the logarithmic function of time.Reversible and nonreversible relaxation processes take place depending on the action intensity.The relaxation rate depends on the action intensity also,and the said dependence has nonlinear and nonmonotonic form if external action leads to domain disordering.The oxygen vacancies-based model for description of the long-time relaxation processes is suggested.The model takes into account oxygen vacancies on the sample's surface ends,their conversion into Fþ-and F0-centers under external effects(due to the liberation of the pyroelectric charge)and subsequent relaxation of these centers into the simple oxygen vacancies after the actions termination.The initial sample's state is electroneutrality one.F-center formation leads to the violation of the original sample's electroneutrality,and generates DC electric field into the sample.Relaxation of F-centers is accompanied by decreasing of electric field,induced by them,and dielectric constant relaxation as consequent effect.
文摘The paper presents results of experimental study of the dielectric constant relaxation during aging process in Pb(Zr,Ti)O_(3) based solid solutions(PZT)after action of external DC electric field.The said process is a long-term one and is described by the logarithmic function of time.Reversible and nonreversible relaxation process takes place depending on the field intensity.The relaxation rate depends on the field strength also,and the said dependence has nonlinear and nonmonotonic form,if external field leads to domain disordering.The oxygen vacancies-based model for description of the long-term relaxation processes is suggested.The model takes into account the oxygen vacancies on the sample's surface ends,their conversion into Fþ-and F^(0)-centers under external effects and subsequent relaxation of these centers into the simple oxygen vacancies after the action termination.F-centers formation leads to the violation of the original sample's electroneutrality,and generate intrinsic DC electric field into the sample.Relaxation of F-centers is accompanied by the reduction of the electric field,induced by them,and relaxation of the dielectric constant,as consequent effect.
基金Supported by the National Key Project for Basic Research of China(973 Project)(G1999022400).
文摘The oxidative coupling of methane(OCM)isone of the most promising routes for the direct con-version of methane to ethylene[1].Ding et al[2]re-ported that a high surface concentration of alkaline earth metal cations facilitated the formation of C_(2) hy-drocarbons during the OCM.Surface basicity is nec-essary for the OCM,and oxygen adsorbed on basic sites is also indispensable.The adsorbed electron defi-cient oxygen species on the catalyst surface plays a crucial role in methane conversion and the selectivity for Cz hydrocarbons.Our previous study[3]showed that increasing the Sr/Ti molar ratio in the per-ovskite-type SrTiO_(3) catalyst resulted in the surface enrichment of Sr,a larger amount of adsorbed oxygen species and higher selectivity for C_(2) hydrocarbons in the OCM.Recently,nanocatalysts have attracted much attention because of their remarkable catalytic performance[4.5].
