Preparation Of Giant Dielectric Ceramics And The Effect Of Cu Segregation On Dielectric Properties In XO-CuO-TiO₂ Ternary System(XO=CdO,TaO_2.5)

The investigations about dielectric ceramic have attracted extensive attention,because the rapid development of electronic information industry requires more and more high dielectric ceramic,the core component of micro capacitor.However,the research on the polarization mechanism of ceramics has not been well understood,which greatly hinders the improvement of ceramic properties and the preparation of new ceramic materials.In this paper,the effect of Cu segregation on grain conductivity of CdCu₃Ti₄O₁₂-based ceramics was systematically studied by combining the determination of phase diagram and measurement of dielectric properties.Furthermore,the grain boundary composition dependent dielectric properties were discussed.The main conclusions were as follows:1.Establishment of subsolidus phase diagram for Cd_1-xCu_3+x+2yTi_4-yO₁₂?-7?x?0.07,-1.333?y?2.91?and effect of Cu segregation on dielectric properties for CdCu₃Ti₄O₁₂.A series of Cd_1-xCu_3+x+2y+x+2y Ti_4-yO₁₂?-7?x?0.07,-1.333?y?2.91?ceramics were synthesized by solid-state reaction method.Basing on the phase identification,subsolidus phase diagram of Cd_1-x-x Cu_3+x+2yTi_4-yO₁₂?-7?x?0.07,-1.333?y?2.91?was determined.The co-existence of hexagonal and orthorhombic CdTiO₃phases was observed in the line between CdTiO₃ and CuO.Furthermore,three typical ceramics with Cu-equal(CdCu₃Ti₄O₁₂),Cu-rich(Cd_0.930Cu_3.070Ti₄O₁₂),and Cu-pool(Cd_1.137Cu_2.863Ti₄O₁₂),showing high dielectric constant,were chosen as target samples to investigate the effect of Cu valence and cation segregation on dielectric behaviors.Cu³⁺ions,rather than Cu⁺ones as reported previously,formed in the grain to act as the hopping charge carriers as demonstrated by X-ray photoelectron spectroscopy?XPS?and High-energy X-ray absorption Near Edge Structure?XANES?.2.Subsolidus phase diagram of Ti_1-xCu_2x-2.5yx-2.5y Ta_yO₂?0.05?x?1,0?y?0.667?ternarysystemandpolarizationbehaviorofsinglesolidsolution Ti_1-x(Cu_0.333Ta_0.667)_xO₂?0<x?0.465?ceramics.Ti_1-xCu_2x-2.5yTa_yO₂?0.05?x?1,0?y?0.667?ceramics were prepared and the subsolidus phase diagram was established.The investigations of phase diagram and the analysis about microstructure,cation valence states and dielectric behaviors of rutile Ti_1-x(Cu_0.333Ta_0.667)_xO₂ compositions with various doping levels?x=0%,5%,18%,33%and 45%?demonstrated the existence of multiple polarization mechanisms in this ternary dielectric system,i.e.free carrier nearest-neighbor-hopping polarization and internal barrier and surface barrier layer capacitor effect,contribute to the overall dielectric behaviors.3.Interface composition dependent polarization behavior and dielectric property of Ti_1-x(Cu_0.333Ta_0.667)_xO₂?x=5%,20%and 45%?ceramics prepared under different sintering conditions.Ti_1-x(Cu_0.333Ta_0.667)_xO₂ ceramics?x=5%,20%and 45%?at different sintering temperature and Ti_0.8(Cu_0.333Ta_0.667)_0.2O₂ samples at different sintering time were carefully synthesized.And all ceramics were pure rutile type phase except that a little impure had been detected of the Ti_0.55(Cu_0.333Ta_0.667)_0.45O₂ceramic at 1300 ^oC and 10 h.The microstructures,valence states,element distribution of the interface and dielectric properties of these samples were systematically investigated.For the low doping level ceramic?x=5%?,the conduction mechanism of nonlocalized carriers at grain boundary belonged to the Mott variable-rang-hopping and that of high doping levels?x=20%and 45%?obeyed the Arrhenius type nearest-neighbour-hopping.With the improve of sintering temperature and time,the growth of grain size would enhance the surface barrier layer capacitor effect?SBLC?of?Cu+Ta?co-doped rutile ceramic and further cause the high dielectric constant.Simultaneously,the precipitation of Cu-rich or Ta-rich phase caused by the segregation of Cu at grain boundary would promote the growth of grain,and the change of interface compositions also caused the grain boundary effect?IBLC?.For Ti_0.8(Cu_0.333Ta_0.667)_0.2O₂ ceramic in high sintering temperature?1300 ^oC?,the giant permittivity??'=65314?should be attribute to the combined action of SBLC and IBLC polarization mechanism.Therefore,microscopic interface properties could be controlled by macroscopic sintering conditions?temperature and time?,which would induce the corresponding polarization mechanism,further cause different dielectric properties for Rutile-based ceramic.4.Dielectric properties of XCu₃Ti₄O₁₂(X=Na_1/2Nd_1/2,Na_1/2Sm_1/2,Na_1/2Gd_1/2and Na_2/3Ce_1/3)ceramics.A series of XCu₃Ti₄O₁₂(X=Na_1/2Nd_1/2,Na_1/2Sm_1/2,Na_1/2Gd_1/2 and Na_2/3Ce_1/3)ceramics were prepared.All the samples were single body-centered cubic perovskite-related structure.The co-doping of double cations in XCu₃Ti₄O₁₂ samples had greatly influenced on the conductivity of ceramic grain.The grain conductivity of Na_1/2Nd_1/2Cu₃Ti₄O₁₂ ceramic was much higher than that of Na_2/3Ce_1/3Cu₃Ti₄O₁₂ ceramics.The Na_1/2Nd_1/2Cu₃Ti₄O₁₂ ceramic after sintering at1000 ^oC had a high dielectric constant??10⁴?and low dielectric loss??0.01?in a wide frequency range?10-10⁵ Hz?.