| CaCu3Ti4O12(CCTO) ceramic samples are fabricated by solid state reaction. Influence ofNd2O3, Y2O3and Nb2O5doping on the performance of CCTO ceramics is studied.Investigations are also carried out on the influence of Y2O3and Nb2O5doping on theperformance of non-stoichiometric CCTO ceramics with Cu deficient based on the previousresearch results of our research group.In Chapter Two, the simulation of the Double Barrier Layer Capacitance (DBLC) model,which is adopted in this thesis to describe the electrical behaviours of the samples, is carriedout. Based on the simulation data, the frequency spectrums and the Cole–Cole diagrams of theimpedance related functions are constructed. The rules and characteristics of each figure areanalyzed, in order to provide a reference for the later analysis of the experimental data. In theexperiment part, the phase compositions of the five series of samples are analysed by X-raydiffraction (XRD), the morphology of the samples is observed by scanning electron microscopy(SEM), and their conduction mechanism is analyzed, combining the J–E curves, the dielectricspectrums(ε′–f), the loss tangent spectrums(tanδ–f), and the impedance related spectroscopies.Influence of different concentrations of Nd2O3that doped to the crystal structure’s A-siteon the performance of CCTO ceramics is studied, with the nominal chemical formula(Ca1xNdx)Cu3Ti4O12+0.5x, where x=0.00,0.04,0.08,0.12,0.16,0.20. It is found that thesemiconducting degree of the CCTO grains decreases with the doping of Nd2O3, indicating theacceptor nature of the Nd ions inside the n-type semiconducting CCTO grains. The electricalbehaviours of the Nd2O3-doped samples can be described by the Internal Barrier LayerCapacitance (IBLC) model, and the doping of Nd2O3results in a decrease in the grain boundarypermittivity Cgband an increase in the grain boundary resistivity Rgb, according to the analysison the impedance related spectroscopies.In Chapter Four, effect of different concentrations of Y2O3that doped to the crystalstructure’sA-site on the performance of CCTO ceramics is studied, with the nominal chemicalformula (Ca1yYy)Cu3uTi4O12+0.5y u, where u=0.00,0.10and y=0.00,0.02,0.04,0.06,0.08,0.10. It is found that at the grain boundaries of the u=0.00series samples, an increase in theCu-rich phase is resulted from the doping of Y2O3. The semiconducting degree of the samplesshows a U-pattern change with the increase of doping concentration, exhibiting a feature similarto the typical donor doping semiconducting characteristic of barium titanate. The doping ofY2O3elevates the apparent dielectric constant while as well increasing the loss. The DBLCmodel, in which the SBLC (Surface Barrier Layer Capacitance) and IBLC work together, is adopted as the equivalent circuit for the samples. According to the analysis on the IS, theequivalent circuit elements Csl, Cgb, Rgband Rgof the two series distinguished by u all show aU-pattern change with the increase of doping concentration. In addition, the Csl, Cgband Rgbofthe u=0.00series are greater than that of the u=0.10series due to the existence of the Cu-richphase at the grain boundaries.Influence of different concentrations of Nb2O5doping to the B-site on the performance ofCCTO ceramics is also studied, with the nominal chemical formula CaCu3u(Ti4zNbz)O12+0.5x u,where u=0.00,0.10and z=0.00,0.02,0.04,0.06,0.08,0.10. It is found that the variation inthe electrical performance is similar to that of Y2O3. In addition, the doping of Nb2O5can inhibitthe grain growth, and an improvement in low-frequency dielectric performance can be achievedwith the doping concentration of Nb2O5being10%.When Cu is deficient, with the chemical formula CaCu2.9Ti4O12, making the stoichiometryof the CCTO ceramic materials deviated, CCTO ceramics with refined grains can be obtained,and the Cu-rich phase at the grain boundaries can reduced. |
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