Calcium titanate doped with praseodymium was prepared through solid state reaction and it exhibited intense red emission at 612 nm. Phosphors were characterized for photoluminescence, thermo-luminescence and afterglow...Calcium titanate doped with praseodymium was prepared through solid state reaction and it exhibited intense red emission at 612 nm. Phosphors were characterized for photoluminescence, thermo-luminescence and afterglow emissions. Study of effects of rare earths on photoluminescence as well as afterglow intensity was reported. Presence of gadolinium enhanced luminescence. Presence of some monovalent ions enhanced both afterglow and photoluminescence emission. Thermo-luminescence glow curves were analyzed and ...展开更多
Uranium-europium mixed oxides(U_(1-y)Euy)O_(2-x)(y=0.2-0.8)were prepared by the citrate gel combustion technique and characterized by X-ray diffraction(XRD).Single phase fluorite structure was observed in those solid ...Uranium-europium mixed oxides(U_(1-y)Euy)O_(2-x)(y=0.2-0.8)were prepared by the citrate gel combustion technique and characterized by X-ray diffraction(XRD).Single phase fluorite structure was observed in those solid solutions with y≤0.6.The solid solutions with y>0.6 were found to be biphasic,with the second phase being cubic Eu2O3.Heat capacity and enthalpy increment measurements were carried out by using differential scanning calorimeter(DSC)and drop calorimeter in the temperature range 298-800 K and 800-1800 K,respectively.The,pm C values at 298 K for(U_(1-y)Euy)O_(2-x)(y=0.2,0.4,0.6)are 64.8,64.6,and 63.5 J·K^(-1)·mol^(-1),respectively.An anomalous increase was observed in the heat capacity in all of the solid solutions with the onset temperature around 950 K.This could be attributed to the contribution from Frenkel pair oxygen defects.From the excess heat capacity data,the enthalpy for the formation of these defects was computed and found to be in the range of 2.10±0.02 eV.展开更多
This paper reviews the recent progress in the understanding of the dynamics of Pb(B_(1/2)B0_(1/2))O_(3)-type relaxor ferroelectrics using of broadband micro-Brillouin scattering spectroscopy,which covers a large frequ...This paper reviews the recent progress in the understanding of the dynamics of Pb(B_(1/2)B0_(1/2))O_(3)-type relaxor ferroelectrics using of broadband micro-Brillouin scattering spectroscopy,which covers a large frequency range from 1 to 1000 GHz by a tandem multi-pass FabryPerot interferometer.In contrast to Pb(B_(1/3)B0_(2/3))O_(3)-type relaxors,there is no frustration on the B-site of perovskite structure and the degree of order of B-site cations depends on heat treatment.Remarkable softening of sound velocity and an intense central peak are observed above the Curie temperature TC owing to the polarization°uctuations in polar nanoregions(PNRs).Unlike the Pb(B_(1/3)B0_(2/3))O_(3)relaxors,Pb(B_(1/2)B'_(1/2))O_(3)does not undergoes a typical diffuse phase transition without lead vacancies on A-site which enhances randomfields.For the(1-x)Pb(B_(1/2)B'_(1/2))O_(3-x)PbTiO_(3)solid solutions,the long range polar order increases as the PbTiO_(3)content increases.Nevertheless,a central peak owing to dynamic PNRs still remains even for the composition near the MPB,and a critical slowing down is clearly observed in the vicinity of TC.展开更多
文摘Calcium titanate doped with praseodymium was prepared through solid state reaction and it exhibited intense red emission at 612 nm. Phosphors were characterized for photoluminescence, thermo-luminescence and afterglow emissions. Study of effects of rare earths on photoluminescence as well as afterglow intensity was reported. Presence of gadolinium enhanced luminescence. Presence of some monovalent ions enhanced both afterglow and photoluminescence emission. Thermo-luminescence glow curves were analyzed and ...
文摘Uranium-europium mixed oxides(U_(1-y)Euy)O_(2-x)(y=0.2-0.8)were prepared by the citrate gel combustion technique and characterized by X-ray diffraction(XRD).Single phase fluorite structure was observed in those solid solutions with y≤0.6.The solid solutions with y>0.6 were found to be biphasic,with the second phase being cubic Eu2O3.Heat capacity and enthalpy increment measurements were carried out by using differential scanning calorimeter(DSC)and drop calorimeter in the temperature range 298-800 K and 800-1800 K,respectively.The,pm C values at 298 K for(U_(1-y)Euy)O_(2-x)(y=0.2,0.4,0.6)are 64.8,64.6,and 63.5 J·K^(-1)·mol^(-1),respectively.An anomalous increase was observed in the heat capacity in all of the solid solutions with the onset temperature around 950 K.This could be attributed to the contribution from Frenkel pair oxygen defects.From the excess heat capacity data,the enthalpy for the formation of these defects was computed and found to be in the range of 2.10±0.02 eV.
文摘This paper reviews the recent progress in the understanding of the dynamics of Pb(B_(1/2)B0_(1/2))O_(3)-type relaxor ferroelectrics using of broadband micro-Brillouin scattering spectroscopy,which covers a large frequency range from 1 to 1000 GHz by a tandem multi-pass FabryPerot interferometer.In contrast to Pb(B_(1/3)B0_(2/3))O_(3)-type relaxors,there is no frustration on the B-site of perovskite structure and the degree of order of B-site cations depends on heat treatment.Remarkable softening of sound velocity and an intense central peak are observed above the Curie temperature TC owing to the polarization°uctuations in polar nanoregions(PNRs).Unlike the Pb(B_(1/3)B0_(2/3))O_(3)relaxors,Pb(B_(1/2)B'_(1/2))O_(3)does not undergoes a typical diffuse phase transition without lead vacancies on A-site which enhances randomfields.For the(1-x)Pb(B_(1/2)B'_(1/2))O_(3-x)PbTiO_(3)solid solutions,the long range polar order increases as the PbTiO_(3)content increases.Nevertheless,a central peak owing to dynamic PNRs still remains even for the composition near the MPB,and a critical slowing down is clearly observed in the vicinity of TC.
