Performance Adjustment And Loss Mechanism Investigation Of Rutile-like Dielectric Ceramics

With the application of 5G technology becoming increasingly mature,the research on the next-generation wireless communication technology was gradually launched,and the corresponding spectrum resources are expanded to the terahertz frequency band.As the communication frequency continually rised,the attenuation of the electromagnetic wave by air and water vapor was more obvious in the transmission process,which shortened the distance of signal transmission,expanding the amount of the base station installations.The problem of energy consumption in wireless communication system needed to be solved.Among them,the total energy consumption of the system could be effectively reduced by reducing the power consumption of passive devices,which was the key to realize the development of high-frequency wireless communication systems.Low-loss dielectric ceramics were the basis for the development of the new generation of low-power passive devices.Research on the dielectric response and loss mechanism of dielectric ceramics in microwave and terahertz regimes could provide a guide for the development of new low-loss dielectric ceramic systems and devices.According to the application requirements of high frequency and low loss of passive devices in microwave and terahertz regimes,the rutile-like system based on transition metal ions was selected in this dissertation.By means of electron paramagnetic resonance spectrum,terahertz time domain spectrum and Raman scattering spectrum,the fourth period transition metal ions(including Mn²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺)in the crystal structure were systematically studied,so as to explore the dielectric loss mechanism of the system in microwave and terahertz regimes.On this basis,combined with the calculation of complex chemical bond theory,the ion doping mechanism of rutile like system in microwave and terahertz regimes was improved.In order to optimize the dielectric properties of rutile like system in microwave frequency band,the composite method was used to control the components of the dielectric layer.The main works of the dissertation were as follow:1.The influence mechanism of the order degree of cations on the dielectric loss of rutile like system was studied.(1)The tin-manganese-tantalite structural Mn O-Sn O₂-Ta₂O₅(MST)system with cation-ordered space occupation were prepared.The crystal structure and phase composition of the system were analyzed and determined,and the order degree of cations was adjusted by annealing process,so that the Qf value of the system was increased by nearly 60%.The correlation between the order degree and microwave dielectric loss was established by calculating the change of the order degree of cations in the system.(2)On this basis,combined with the first principle calculation,the energy band structure of the ground state of the system was studied,concluding that the electronic structure of transition metal ions was the key factor which affecting the microwave dielectric loss of the system.2.Combined with the first-principles calculation results above,the Cu Zr Nb₂O₈system with wolframite structure and the ANb₂O₆ system with columbite structure(A=Zn,Co,Mn,Ni)were selected to launch the research on the correlation mechanism between transition metal ions and microwave dielectric loss:(1)Based on group theory analysis,the behavior of transition metal ion Cu²⁺in crystal structure was systematically explored,and the inhibition of coordination environment on its Jahn teller effect was clarified.The correlation mechanism between the electronic structure of Cu²⁺and the microwave dielectric properties of the system was established,and the microwave magnetic loss in rutile like system was predicted.(2)Based on the terahertz time domain spectral analysis,the dielectric response characteristics of ABB type niobium iron structure ANb₂O₆(a=Zn,Co,Mn,Ni)system in terahertz frequency band were explored.Combining with the coordination chemistry theory,the mechanism of microwave magnetic loss in rutile like system was further demonstrated and clarified,which could provide a guide for the design of low loss rutile like system.3.Based on the understanding of the microwave dielectric loss mechanism of the rutile-like system,the ion doping mechanism is further improved.The ZnTiNb₂O₈system of rutile like manganese tantalite structure with disordered cation occupation is selected for modification in this dissertation,in which the following two parts is mainly included:(1)Based on the crystal field theory,the occupation characteristics of Ge⁴⁺ions in the doping process were determined,and then the influence of the crystal structure changed and the second phase on the microwave dielectric loss of the system was analyzed.The Qf value of the original system could be increased by nearly 30%with minute quantities of Ge⁴⁺ions.(2)The charge compensation was based on the combination of(Al Nb)⁴⁺and Nb⁵⁺without d-layer electronic structure.Based on the complex chemical bond calculation,the change of chemical bond properties caused by doping was evaluated,the dielectric loss mechanism of the system in microwave and terahertz regimes was explored,and the ion doping modification mechanism of rutile like system in terahertz frequency band was preliminarily established.In the end,the Qf value of the original system was increased by more than 30%,the dielectric loss was less than 0.005 at 0.5 THz,and the absorption coefficient was less than 10 cm^-1,which was expected to meet the application requirements of low-loss next-generation passive devices.4.Based on the optimization of Qf value in ZnTiNb₂O₈ system,the rutileTiO₂was used to control its microwave dielectric properties.(1)Based on the analysis of X-ray diffraction pattern and scanning electron microscope line scanning mode,to explore the best composite formula,Zn Ti_0.97Ge_0.03Nb₂O₈ ceramics with low sintering temperature were used as the matrix,the composite system of Zn Ti_0.97Ge_0.03Nb₂O₈-Ti O₂ was prepared by random distribution and laminated distribution,respectively.(2)Based on the parallel distribution model,the influence mechanism of microwave dielectric propertiess under the mode of laminated composite was explored by adjusting the components of the dielectric layer.(3)Finally,thebestmicrowavedielectricpropertiesof Zn Ti_0.97Ge_0.03Nb₂O₈-Ti O₂-Zn Ti_0.97Ge_0.03Nb₂O₈ system were:?_r=42.1,Qf=51,477 GHz,?_f=+1.9×10^-6/?.On the basis of optimizing the temperature stability,the Qf value of the random distribution system could be increased by nearly 50%and the dielectric constant by nearly 10%compared with the theoretical value,which was expected to meet the application requirements of high-performance microwave dielectric resonators and provided support for the design of new generation microwave passive devices.