| In recent years,bismuth-based perovskite-like ferroelectric materials have attracted great interest in ferroelectrics and solid electrolyte fields.Their applications have become popular in the solid-state electronics.They are promising candidates for applications of integrated non-volatile memories and intermediate-low temperature solid oxide rule cells,due to their high Cutie temperature,low dielectric constant, high ionic conductivity,fatigue-flee and environment-friendly properties.However, the development of practical devices are still hindered by some problems,such as the anisotropy and structure stability for bismuth-based ferroelectric films,the deposition process and thermal stability for solid electrolyte films.In this work,Bi2VO5.5(BVO) and metal doped BVO materials were synthesized. The characteristics of BVO system films and Bi2ME0.1V0.9O5.5-δ(BIMEVOX.10) solid electrolyte materials were investigated.The main results are as follow:(1) High quality BVO thin films with c-preferred orientation were successfully fabricated on LaNiO3(LNO)/Si(100) and Pt/TiO2/SiO2/Si(100) substrates via chemical solution deposition(CSD).The CSD process was improved by using vanadium inorganic salt instead of the original vanadyl acetylacetonate.It has successfully solved the problem that the metal alkoxides are pricey and difficult to keep.It was intensively investigated the influence of annealing temperatures on the characteristics of BVO thin films.The films annealed at 700℃showed the highest c-preferred orientation and the best ferroelectric properties.The values of remnant polarization and leakage current were improved to 10.62μC/cm2 and 1.92x10-8 A/cm2.The dielectric properties were studied in 260-480 K temperatures.It was found that a poly-dispersive dielectric relaxation in the films originated from localized charge carrier like oxygen vacancy diffusion.The conductivity mechanism was mainly due to oxygen ion conductivity.(2) The C-V characteristics of BVO/p-Si(100) films with a MFIS (Metal-Ferroelectrics-Insulator-Semiconductor) structure were studied.Its memory window was about 0.5 V.The research provides a better process for the ferroelectric field effect memory applications of BVO films.The optical constants were obtained by ellipsometry spectra,which were beneficial to developing the applications of optical characteristics.(3) It was the first time to synthesize the Bi2VO5.5-Bi4Ti3O12 films with mixed bismuth-based perovskite-like structure.It showed good ferroelectric properties.The values of remnant polarization and leakage current were improved to 12.62μC/cm2 and 1.17×10-8 A/cm2.The results provide a new technological approach to optimize the ferroelectric properties for BVO films.(4) La-doping BVO films were studied extensively for the first time.The dielectric permittivity and dispersion increased by La doping,especailly with 0.025 mole ratio of La doping.The mechanism can be explained as follow:When La ions go into BVO structure,some of them possibly preferentially enter V sites.A readjustment of lattice structure toward a defective structure will happen,which is due to volume increase and distortion caused by the nonequivalent substitution and large radii difference.It results in defects such as oxygen vacancies,giving rise to a deterioration of dielectric properties and dispersion increase.(5) BIMEVOX.10(ME=Ti,Co,Fe,Ni,Mn) thin films were successfully prepared by CSD.The structure and electrical properties were studied and the electrical properties of BIMNVOX.10 films were selectively analyzed in 300-485 K temperatures.The results indicated that the dielectric relaxation in the films was a poly-dispersive dielectric dispersion which originated from oxygen ion conductivity. Furthermore,a weak room temperature ferromagnetism was observed in the BIMNVOX.10 thin films.(6) It was intensively investigated the preparation and characteristics of Bi2Cu0.1V0.9O5.35(BICUVOX.10) powders and thin films.BICUVOX.10 nano-powders were obtained through chemical solution methods,which synthesis temperature was lower about 300℃compared with that of conventional solid-state process.The relationships of dispersivity,synthesis methods and the PEG4000 surfactant additive capacity were studied.It was found that PEG4000 had a great effect on disagglomeration of nano powders and its additive content was associated with the synthesis process.In the reversing titration co-precipitation process,the average grain size of the sample was about 20 nm when with 5 wt%PEG4000.The results provide a way to get BIMEVOX nano-powders with good dispersivity. Furthermore,high quality BICUVOX.10 thin films were deposited on LNO/Si(100) substrates with a tendency of c-preferred orientation.The films showed good oxide ion conductivity and thermal stability in the intermediate-low temperatures from 300 to 620 K.The activity energy of oxide vacancy was about 0.3 eV and the oxygen conductivityσ600 K was 5×10-2 S·cm-1.(7) It was the first time to probe the magnetism of BVO and BIMEVOX.10 (ME=Mn,Fe,Co) powders.It was found room temperature ferromagnetism in these samples.The ferromagnetism became stronger when doped with transition metal ions, especially by Mn doping.The remnant magnetization,saturation magnetization,and coerced field of BVO and BIMNVOX.10 were 2.11 and 4.67 memu/g,3.33 and 11.02 memu/g,0.02 and 0.04 kOe,respectively.The Curie temperature of 279℃was observed for BIMNVOX.10 powders.Theoretically,the presence of oxygen vacancies was used to explain the room temperature ferromagnetism behaviors.The variety of magnetization was mainly caused by the redistribution of unpaired electron spin state,which resulted from the d-electron spinning of doped ions. |
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