Dielectric Loss Mechanisms For Resonator Ceramics At Mobile Communication Base Station

Microwave dielectric ceramics as a new kind of functional ceramics,plays an irreplaceable role in promoting the development of wireless communication technology.Microwave dielectric resonators that possess high quality factor?Q?and good temperature stability have become the key materials of the next generation 5G base station equipment.Now large-scale applications of base station equipment require that microwave dielectric ceramic materials not only have better performance,but also have simple process,low cost and energy consumption,so the research of phase composition,defective formation mechanism and internal structure in the forming process has great significance in improving the microwave dielectric performance of ceramic materials.Ba(Co_0.7Zn_0.3)_1/3Nb_2/3O₃ ceramics as medium dielectric constant resonator materials with composite perovskite structure have been used widely for many years,because they have near zero temperature coefficient of resonant frequency??_f?and high Q value.The influence of heat treatment atmosphere on ceramic internal ion composition,grain and grain boundary phase structure was investigated in this paper.The conductive mechanism of PN extrinsic semi-conduction under different oxygen partial pressure was established.The sinterability of Ba(Co_0.7Zn_0.3)_1/3Nb_2/3O₃ ceramics has been studied,and the results show that the ceramic body sintered at 1500oC/40h will achieve the highest Q×f value?72000 GHz?.When the sintering temperature is too low or the holding time is too short,the sample cannot achieve the biggest densification.The increase in the sintering temperature or the holding time is not also helpful for the improvement of performance.After annealing at 1350oC/5h under three atmospheres?O₂,air,and N₂?,the samples with surface layer have Q×f value of about 20000 GHz.After removing the surface layer,all the Q×f values are improved?75000 GHz in O₂,81000 GHz in air,and 70000 GHz in N₂?.This paper then study the influence of annealing atmosphere on ceramic electric performance,and the impedance value of unpolished samples is as follows:N₂>air>O₂ in the same temperature.After removing the surface layer,the impedance value tends to be the same.In N₂,the time constant of grain and grain boundary has the largest difference based on the impedance semicircle,and the difference is smallest in O₂.On the analysis of the-Z''-M''-f spectrum,the M''-f and-Z''-f Debye peak of grain corresponds to different frequencies in N₂,and the two Debye peaks cover at the same frequency range,showing better electric uniformity in air and O₂.XPS analysis found that the high oxygen partial pressure would lead to the oxidization of Co²⁺to Co³⁺in the heat treatment process,and generate holes with positive charge,form p-type semi-conductor in the sample.Low oxygen partial pressure would lead to the reduction of Nb⁵⁺to Nb⁴⁺,and generate electrons with negative charge,form n-type semi-conductor in the sample.The ions valence change and elements volatilization occur in surface of sample,and has a concentration gradient,however the inner core will not be affected.After polishing the samples and removing certain thickness,the inner layer has no valence change,and no oxygen vacancy.