The Ferroelectric Properties Of Metal Oxide Co-doping On Barium Titanate Ceramics

With the development of the electronic technique, miniaturization,integration and intelligent for all kinds of electronic device become ahotspot research. For barium titanate based ceramics widely used incapacitor, the way to upgrade its capacity is the distance decreasing ordielectric constant increasing. At present, thickness stretches the deviceto the limits and preparation the materials with high dielectricproperties is imperative. Doping as the common effective modificationhas drawn wide attention, especially isovalent doping which cancompensate electrovalence and improve the dopant solubility.The doping BaTiO₃ceramics with different concentration of metaloxide were prepared by a conventional solid-state method. The phasecomposition, microstructure, dielectric properties and ferroelectricproperties have been characterized by X-ray diffraction dielectricmeasurements and ferroelectric measurements as a function of chemicalcomposition and temperature. In order to obtain the BaTiO₃-basedceramics with high dielectric constant and low dielectric loss, wediscuss the doping modification mechanism and set up the theoreticalmodel.（1） For Cr₂Ti₃O₉doping BaTiO₃ceramics, the peculiar double-hysteresis-like loops were found to have striking similarities totetragonal ferroelectrics, besides following random local strainsmechanism driven by the displacement of oxygen octahedral in shrunkcrystal cells. The introduction of Cr₂Ti₃O₉induces the phase transitionand the shrinkage of some local crystal cells in the lattice. Thedouble-hysteresis-like loops can transform into a normal one because ofthe increasing of long-range polar order by heat activation.（2） For Cr₂Ti₃O₉and Bi₂O₃co-doping BaTiO₃ceramics, the peak value of the dielectric constant first increased and then decreased withincreasing of the Bi/Cr ratio. As acceptors were completelycompensated by the donors, the dielectric constant reached to7311, andthe dielectric loss was0.02when the Bi₂O₃and Cr₂Ti₃O₉content was1.0mol%.（3） A perovskite structure was revealed for all samples but theformation of a secondary phase, BaCrO3was crystallized when theamount of Bi₂O₃and Cr₂Ti₃O₉simultaneously reached to1.0mol%.Moreover, the dielectric constant exhibited a broadened and diffuseferroelectric paraelectric phase transition. The nonferroelectric phaseBaCrO3and excessive electron caused a distribution of BaTiO₃composition, giving rise to the strong broadening effects on thediffuseness of the transition.（4） As Bi₂O₃and Cr₂O₃co-doping BaTiO₃ceramics, the Curietemperature was shifted to a lower temperature with increasing of Bi₂O₃and Cr₂O₃. The dielectric constant exhibited a diffuse ferroelectricparaelectric phase transition and the value of Princreased. Its Prvalueincreased because of the origin of diffuse phase transition behavior.（5）(Ba_0.94Bi_0.06)(Ti_0.94Cr_0.06)O₃ceramics exhibited a diffuse phasetransition characterized by a strong temperature and frequencydispersion of permittivity. The quantitative characterization based onempirical parameters （△Tm, γ,△Trelax, and△Tdif） confirmed its relaxornature. The P-E loops obtained at the temperature quite above Tmsupported the diffuse phase transition behavior of the samples. Thefrequency dispersion of permittivity can be well matched withArrhenius equation not Vogel-Fulcher equation, the Eawas calculatedas0.0155eV. The origin of relax ferroelectric behavior is caused by thepolar nanoclusters, which were arose due to the heterovalentsubstitutions of Bi³⁺and Cr³⁺at Ba²⁺and Ti4+sites. This relaxorbehavior was referred to superparaelectric mold not glassy state mold.