Photostimulated Luminescence and F-centers of Sr_3Ca_2(PO_4)_3X:Eu^(2+)(X=F,Cl,Br)

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.

F-centers mechanism of long-term relaxation in lead zirconate-titanate based piezoelectric ceramics.2.After-field relaxation

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.

Additional Y^(3+) or Al^(3+) Dopants on the Ferromagnetism of Co Doped Ceria Diluted Magnetic Oxide

Al2O3 and Y2O3 have been respectively chosen for additional dopants to investigate the influence on the ferromagnetism of Co doped CeO2 bulk. Results indicate that ferromagnetism （FM） of Co doped CeO2 decrease with additional Al^3＋. Accordingly, certain amount of Y^3＋ can readily be incorporated into the lattice of CeO2 with the decrease of its grain size as well as some pores formation, leading to an enhancement of FM with a positive correlation between magnetization and Y^3＋ doping content. This experimental result is helpful both in understanding FM origination in diluted magnetic oxide （DMO） as well as to improve the moments of DMO applicable in spintronic devices.

F-center mechanism of long-term relaxation in lead zirconate-titanate-based piezoelectric ceramics.1.After-heating relaxation

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.