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Structural and AC electrical properties study of solid metal urea complexes

Journal of Advanced Dielectrics 2018年第2期8卷 60-66页

作者： Ragab Mahani Saleh D.Mekky Badr A.El Sayed Gamal S.EL-Bahy Azza Ward Microwave Physics and Dielectrics Department National Research Centre 33 EL Bohouth St.(former EL Tahrir St.)Giza-Egypt-P.O.12622 Chemistry Department Faculty of ScienceAlazhar University Nasr CityCairoEgypt Spectroscopy Department National Research Centre 33 EL Bohouth St.(former EL Tahrir St.)Giza-Egypt-P.O.12622

The complexation of solid urea with(Co^(2+)),(Cu^(2+))or(Ni^(2+))ions has been studied by using dielectric spectroscopy technique over a wide frequency range at different temper ***'structure were investigated by XRD,FTIR and FT-Raman *** and Raman analy sis indicated that the urea coordinates with the metal atoms through the same oxygen-metal bond(O-M).Furthermore,XRD analysis showed that the samples have polycrystalline structure with single *** pemittivity of complexes was found at much higher values than that of the ligand(pure urea),showing structure ***,two relaxation peaks were observed in the dielectric loss spectra corresponding to the orientation po larization of urea molecule,and some parts of urea molecule may be NH2 *** relaxation peaks correspond to thermally activated because they were shifted to higher frequency with the temperature *** peak position for the low frequency relaxation peak was observed lht the same relaxation time(τ=7.6× 10^(-4) s),corresponding to the coordination mode through the same O-M *** of this work is the successful finding of the relationship between the crystalline phase,coordination mode and the dy namic molecular behavior of solid urea and its complexes using the dielectric spec-troscopy techn ique.

关键词： Urea complexes IR XRD permitivity

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Dielectric properties of BaMg_(1/3)Nb_(2/3)O_(3) doped Ba_(0.45)Sr_(0.55)TiO_(3) thin films for tunable microwave applications

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Journal of Advanced Dielectrics 2015年第4期5卷 21-29页

作者： Fikadu Alema Konstantin Pokhodnya Center for Nanoscale Science and Engineering North Dakota State University Fargo ND 58108USA Agnitron Technology Incorporated Eden Prairie MN 55344USA

Ba(Mg_(1/3)Nb_(2/3))O_(3)(BMN)doped and undoped B_(0.45)Sr_(0.55)TiO_(3)(BST)thin films were deposited via radio frequency magnetron sputtering on PUTiO_(2)/SiO_(2)/Al_(2)O_(3) *** surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy,resulting in an improved insulating properties of the BST *** tunability,loss,and leakage current(LC)of the undoped and BMN doped BST thin flms were *** BMN dopant has remarkably reduced the dielectric loss(~38%)with no significant effect on the tunability of the BST film,leading to an increase in figure of merit(FOM).This is attributed to the opposing behavior of large Mg2+whose detrimental effect on tunability is partially compensated by small Nb5+as the two substitute Ti4+in the *** coupling between Mg″_(Ti)and V_(o)charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti *** LC of the films was investigated in the temperature range of 300-450K.A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from Mg″_(Ti),V_(o)and Nb_(Ti) charged *** carrier transport properties of the films were analyzed in light of Schottky thermionic emission(SE)and Poole-Frenkel(PF)enmission *** result indicated that while the carrier transport mechanism in the undoped film is interface limited(SE),the conduction in the BMN doped film was dominated by bulk processes(PF).The change of the conduction mechanism from SE to PF as a result of BMN doping is atributed to the presence of uncoupled Nb_(Ti) stting as a positive trap center at the shallow donor level of the BST.

关键词： Barium strontium titanate sputtering frreletric thin film tunability leakage current permitivity loss figure of merit defect dipole

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