Gd^3+-doped lead molybdato–tungstates with the chemical formula of Pb1–3xxGd2x(MoO4)1–3x(WO4)3x(where x=0.0455,0.0839,0.1430,corresponding to 9.53,18.32,33.37 mol%of Gd^3+,respectively,as well asdenotes cationic va...Gd^3+-doped lead molybdato–tungstates with the chemical formula of Pb1–3xxGd2x(MoO4)1–3x(WO4)3x(where x=0.0455,0.0839,0.1430,corresponding to 9.53,18.32,33.37 mol%of Gd^3+,respectively,as well asdenotes cationic vacancies)were successfully synthesized via combustion route.The XRD and SEM results confirmed the formation of single-phase,tetragonal scheelite-type materials(space group I41/a)with the uniform,spherical and oval grains ranging from 5 to 20mm.Individual grains are strongly agglomerated into big clusters with the size even above 50mm.The magnetic measurements as well as the Brillouin fitting procedure showed paramagnetic state with characteristic superparamagnetic-like behaviour and the short-range ferromagnetic interactions.The electrical and broadband dielectric spectroscopy studies revealed insulating properties with the residual electrical n-type conduction of 2×10^–9 S/m and low energy loss(tand»0.01)below 300 K.Dielectric analysis showed that no dipole relaxation processes in the Gd^3+-doped materials were observed.A fit of dielectric loss spectra of Gd^3+-doped samples by sum of the conductivity and the Havriliak–Negami,Cole–Cole,and Cole–Davidson functions confirmed this effect.展开更多
Single crystal of Eu3þ-doped cadmium molybdate(Cd0.9268M0.0244Eu0.0488MoO_(4),where M denotes cationic vacancies)has been successfully grown by the Czochralski method in air and under 1 MPa.X-ray diffraction anal...Single crystal of Eu3þ-doped cadmium molybdate(Cd0.9268M0.0244Eu0.0488MoO_(4),where M denotes cationic vacancies)has been successfully grown by the Czochralski method in air and under 1 MPa.X-ray diffraction analysis indicates that as-grown single crystal exhibits tetragonal scheelite-type structure(a=b=5.16188(14)Å;c=11.2080(5)Å;space group I41/a).Eu^(3+) þions do not show long-range order and they are randomly distributed in CdMoO_(4) framework substituting Cd^(2+ )þones.UVevis diffuse reflectance measurements revealed very close optical band gap(Eg)values,i.e.-1.74 eV along[100]and[001]crystallographic directions that are twice smaller than Eg of microcrystalline pure CdMoO_(4) as well as powder Eu3þ-doped single crystal.Magnetic and electrical studies of Eu3þ-doped cadmium molybdate single crystal showed a paramagnetic and n-type semiconducting behaviour with the metal-insulator transition above 350 K along both crystallographic directions.Dielectric results analysis using the Cole-Cole fit function revealed that the dipole relaxation process has different time scale depending on the crystallographic direction and exhibits Arrhenius temperature dependence for both studied directions.This fact is accompanied by the colossal dielectric permittivity withεr>8,103.The above results are considered in the framework of narrow europium multiplets of energy comparable to thermal energy.展开更多
基金This work was partly supported by Ministry of Science and Higher Education(Poland)and funded from Science Resources:No.1S-0300–500-1-05-06 and UPB-DZS 518-10-020-3101-01/18One of us(M.Maciejkowicz)would like to thank for the financial support from National Science Center of Poland for the grant PRELUDIUM 14 No.UMO-2017/27/N/ST8/00741.
文摘Gd^3+-doped lead molybdato–tungstates with the chemical formula of Pb1–3xxGd2x(MoO4)1–3x(WO4)3x(where x=0.0455,0.0839,0.1430,corresponding to 9.53,18.32,33.37 mol%of Gd^3+,respectively,as well asdenotes cationic vacancies)were successfully synthesized via combustion route.The XRD and SEM results confirmed the formation of single-phase,tetragonal scheelite-type materials(space group I41/a)with the uniform,spherical and oval grains ranging from 5 to 20mm.Individual grains are strongly agglomerated into big clusters with the size even above 50mm.The magnetic measurements as well as the Brillouin fitting procedure showed paramagnetic state with characteristic superparamagnetic-like behaviour and the short-range ferromagnetic interactions.The electrical and broadband dielectric spectroscopy studies revealed insulating properties with the residual electrical n-type conduction of 2×10^–9 S/m and low energy loss(tand»0.01)below 300 K.Dielectric analysis showed that no dipole relaxation processes in the Gd^3+-doped materials were observed.A fit of dielectric loss spectra of Gd^3+-doped samples by sum of the conductivity and the Havriliak–Negami,Cole–Cole,and Cole–Davidson functions confirmed this effect.
基金the Institute of Physics(University of Silesia)for providing practical and technical assistance.
文摘Single crystal of Eu3þ-doped cadmium molybdate(Cd0.9268M0.0244Eu0.0488MoO_(4),where M denotes cationic vacancies)has been successfully grown by the Czochralski method in air and under 1 MPa.X-ray diffraction analysis indicates that as-grown single crystal exhibits tetragonal scheelite-type structure(a=b=5.16188(14)Å;c=11.2080(5)Å;space group I41/a).Eu^(3+) þions do not show long-range order and they are randomly distributed in CdMoO_(4) framework substituting Cd^(2+ )þones.UVevis diffuse reflectance measurements revealed very close optical band gap(Eg)values,i.e.-1.74 eV along[100]and[001]crystallographic directions that are twice smaller than Eg of microcrystalline pure CdMoO_(4) as well as powder Eu3þ-doped single crystal.Magnetic and electrical studies of Eu3þ-doped cadmium molybdate single crystal showed a paramagnetic and n-type semiconducting behaviour with the metal-insulator transition above 350 K along both crystallographic directions.Dielectric results analysis using the Cole-Cole fit function revealed that the dipole relaxation process has different time scale depending on the crystallographic direction and exhibits Arrhenius temperature dependence for both studied directions.This fact is accompanied by the colossal dielectric permittivity withεr>8,103.The above results are considered in the framework of narrow europium multiplets of energy comparable to thermal energy.
