Fabrication, Structure And Electrical Property Of Ca_0.5Re_0.5MnO₃/BaTiO₃Perovskites

The ceramic conductive composite powder with specific morphology wasfabricated to enhance the combination property of conductive adhesive and to achievethe application in the realm of electronic packaging. In this thesis, the fabricationtechnique of the Ca_0.5Re_0.5MnO₃/BaTiO₃composite powders with core-shell structurewas investigated preliminarily based on the preparation of Ca_0.5Re_0.5MnO₃perovskitepowders by Sol-gel auto-combustion method and the synthesis of BaTiO₃byhydro-thermal route.The electrical properties, strucucture, and morphology of Ca_0.5Re_0.5MnO₃powderswere investigated. With the progress of rare earth element, the resistivity ofCa_0.5Re_0.5MnO₃（Re=La，Pr，Sm，Gd, and Er） powders at room temperature wasdemonstrated the apparente W type fluctuation. However, with the increase incalcination temperature, the resistivity was manifested the V type tendency evidently.The lowest resistivity point of5.78Ω m was obtained by calcining the Ca_0.5Pr_0.5MnO₃precursor at1100centigrade. However, the saddle point of bivariate functionalrelationship was the resistivity of Ca_0.5Sm_0.5MnO₃powder calcined by900centigrade,which is the maximum point of element type function and the minimum point ofcalcination temperature function. The resistivity analysis with variable temperatures ofCa_0.5Re_0.5MnO₃powders indicates that the feature of ρ-T response and conductivemechanism were mostly affected by the element type. The Ca_0.5La_0.5MnO₃andCa_0.5Er_0.5MnO₃powder were in accordance with the Thermal Active model, and theCa_0.5Sm_0.5MnO₃powder were in accordance with the Small Polaron Hopping model inthe high temperature. The saddle point of resistivity function of Ca_0.5Sm_0.5MnO₃powdergained the maximum activation energy for conduction. The XRD and SEM analysesillustrate that there was the corresponding relation between the function of element typeand calcination temperature to resistivity and the function of cell parameters toresisitivity. Additionally, the element type influenced the geometrical shape, particlesize, and aggregation state of the modified powders distinctly. However, the enhancedcalcination temperature promoted the growth of crystallite and the evolution ofspherical morphology.The first principle studies based on the density functional theory and plane wavepseudo-potential method illuminate that the single point energy of CaMnO₃was -11874.743eV and the width of band gap was0.6eV. The doping method of replacingthe two distant Ca atoms with La, L1type Ca_0.5La_0.5MnO₃, impacted the crystalstructure markedly. The the single point energy of L1type Ca_0.5La_0.5MnO₃increased to-11599.656eV, however, the width of band gap decreased to0.4eV. But the dopingmethod of replacing the two undistant Ca atoms with La, L2type Ca_0.5La_0.5MnO₃,influenced the crystal structure slightly. The single point energy of L2typeCa_0.5La_0.5MnO₃decreased to-11599.815eV, and the width of band gap decreased to0.37eV. The simulation analysis indicats the L2type Ca_0.5La_0.5MnO₃was more agreedwith experimental facts. More over, the charge density calculation shows that the bondsbetween La³⁺and other ion in the doping system were transformed distinctly to thecovalent bonds. And the density of states analysis indicats that the band structure nearfermi level was formed by3d electron of Mn, and the decrease in band gap width wascaused by the generation of additional level at the bottom of conduction band.The BaTiO₃nanofiber was facbricated by preserve the morphology of onedimensional titanate and process under the hydrothermal condition with lowconcentration of mineralizer. Promoting the concentration of mineralizer led to thetransition of BaTiO₃crystal structure from cubic to tetragonal phase, and the evolutionof nanofiber to spherical morphology. Increasing the hydrothermal temperature andconcentration of mineralizer resulted in the transition of BaTiO₃crystal structure fromcubic to tetragonal phase, and promoted the growth of grain, when using TiO₂powderas Ti source precursor. When utilizing tetrabutyl titanate as Ti source precursor, theenhancement of mineralizer concentration affected the crystal structure slightly,however, promoted the minimize of grain size and the evolution of BaTiO₃particles touniformly dispersed spherical morphology. Integrating the hydrothermal synthesis withthe solvent evaporation induced self-assembly, the Ca_0.5Re_0.5MnO₃/BaTiO₃compositepowder with core-shell structure was fabricated preliminarily. After coating, themorphology stated the same, and the particle size has been increased.