ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(...ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(2)-Nb_(2)O_(5)(CTN)ternary composite oxide additives with different composition ratios on sintering behavior and properties of ZnAl_(2)O_(4) microwave dielectric ceramics was investigated.When the molar fraction ranges of Cu,Ti and Nb elements in 5%CTN additives are 0.625-0.875,0-0.250 and 0.125-0.625,respectively,sintering temperature of ZnAl_(2)O_(4) ceramics can be reduced from above 1400℃to below 1000℃.The sintering additives CN(Cu:Nb=1:1,molar ratio)and CTN(Cu:Ti:Nb=4:1:3,molar ratio)can reduce sintering temperature of ZnAl_(2)O_(4) ceramics to 975 and 1000℃,respectively,while maintaining good dielectric properties(dielectric constantε_(r)=11.36,quality factor Q׃=8245 GHz andε_(r)=9.52,Q׃=22249 GHz)and flexural strengths(200 and 161 MPa),which are expected to be applied in preparation of low temperature co-fired ceramic(LTCC)materials with copper electrodes.Low-temperature sintering of the ZnAl_(2)O_(4)+CTN system is characterized as activated sintering.Nanometer-level amorphous interfacial films containing Cu,Ti,and Nb elements are observed at the grain boundaries,which may provide fast diffusion pathways for mass transportation during the sintering process.Valence changes of Ti and Cu ions,along with changes of oxygen vacancies,are confirmed,which provides a potential mechanism for reduced sintering temperature of ZnAl_(2)O_(4) ceramics.In addition,a series of reactions occurring at the grain boundaries can activate these boundaries and further promote the sintering densification process.These results suggest a promising way to design a novel LTCC material with excellent properties based on the low temperature sintering of ceramics with the sintering aid of CuO-TiO_(2)-Nb_(2)O_(5) composite oxide.展开更多
Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2...Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2)O_(3) ceramics have been fabricated at very high sintering temperatures,but their optical quality and sintering process still need further improvement.In this work,5%Yb:Sc_(2)O_(3)(in mass)nano-powders were obtained by co-precipitation,and then transparent ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing(HIP)post-treatment.The cubic Yb:Sc_(2)O_(3) nano-powders with good dispersity and an average crystallite of 29 nm were obtained.Influence of pre-sintering temperatures(1500-1700℃)on densification process,microstructure changes,and optical transmittance of Yb:Sc_(2)O_(3) ceramics was detected.Experimental data revealed that all samples have a uniform microstructure,while the average grain sizes increase with the increase of the sintering temperatures.Impressively,the optimum in-line transmittance of Yb:Sc_(2)O_(3) ceramics,pre-sintered at 1550℃after HIP post-treatment,reaches 78.1%(theoretical value of 80%)at 1100 nm.Spectroscopic properties of the Yb:Sc_(2)O_(3) ceramics reveal that the minimum population inversion parameterβ2 and the luminescence decay time of 5%Yb:Sc_(2)O_(3) ceramics are 0.041 and 0.49 ms,respectively,which demonstrate that the optical quality of the Yb:Sc_(2)O_(3) has been improved.Meanwhile,their best vacuum sintering temperature can be controlled down to a lower temperature(1550℃).In conclusion,Yb:Sc_(2)O_(3) nano-powders are successfully synthesized by co-precipitation method,and good optical quality transparent ceramics are fabricated by vacuum pre-sintering at 1550℃and HIP post-treatment.展开更多
基金National Natural Science Foundation of China (U24A2052)Shanghai Eastern Talent Plan。
文摘ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(2)-Nb_(2)O_(5)(CTN)ternary composite oxide additives with different composition ratios on sintering behavior and properties of ZnAl_(2)O_(4) microwave dielectric ceramics was investigated.When the molar fraction ranges of Cu,Ti and Nb elements in 5%CTN additives are 0.625-0.875,0-0.250 and 0.125-0.625,respectively,sintering temperature of ZnAl_(2)O_(4) ceramics can be reduced from above 1400℃to below 1000℃.The sintering additives CN(Cu:Nb=1:1,molar ratio)and CTN(Cu:Ti:Nb=4:1:3,molar ratio)can reduce sintering temperature of ZnAl_(2)O_(4) ceramics to 975 and 1000℃,respectively,while maintaining good dielectric properties(dielectric constantε_(r)=11.36,quality factor Q׃=8245 GHz andε_(r)=9.52,Q׃=22249 GHz)and flexural strengths(200 and 161 MPa),which are expected to be applied in preparation of low temperature co-fired ceramic(LTCC)materials with copper electrodes.Low-temperature sintering of the ZnAl_(2)O_(4)+CTN system is characterized as activated sintering.Nanometer-level amorphous interfacial films containing Cu,Ti,and Nb elements are observed at the grain boundaries,which may provide fast diffusion pathways for mass transportation during the sintering process.Valence changes of Ti and Cu ions,along with changes of oxygen vacancies,are confirmed,which provides a potential mechanism for reduced sintering temperature of ZnAl_(2)O_(4) ceramics.In addition,a series of reactions occurring at the grain boundaries can activate these boundaries and further promote the sintering densification process.These results suggest a promising way to design a novel LTCC material with excellent properties based on the low temperature sintering of ceramics with the sintering aid of CuO-TiO_(2)-Nb_(2)O_(5) composite oxide.
基金National Key R&D Program of China(2023YFE3812005)International Partnership Program of Chinese Academy of Sciences(121631KYSB20200039)+1 种基金National Center for Research and Development(WPC2/1/SCAPOL/2021)Chinese Academy of Sciences President’s International Fellowship Initiative(2024VEA0005,2024VEA0014)。
文摘Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2)O_(3) ceramics have been fabricated at very high sintering temperatures,but their optical quality and sintering process still need further improvement.In this work,5%Yb:Sc_(2)O_(3)(in mass)nano-powders were obtained by co-precipitation,and then transparent ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing(HIP)post-treatment.The cubic Yb:Sc_(2)O_(3) nano-powders with good dispersity and an average crystallite of 29 nm were obtained.Influence of pre-sintering temperatures(1500-1700℃)on densification process,microstructure changes,and optical transmittance of Yb:Sc_(2)O_(3) ceramics was detected.Experimental data revealed that all samples have a uniform microstructure,while the average grain sizes increase with the increase of the sintering temperatures.Impressively,the optimum in-line transmittance of Yb:Sc_(2)O_(3) ceramics,pre-sintered at 1550℃after HIP post-treatment,reaches 78.1%(theoretical value of 80%)at 1100 nm.Spectroscopic properties of the Yb:Sc_(2)O_(3) ceramics reveal that the minimum population inversion parameterβ2 and the luminescence decay time of 5%Yb:Sc_(2)O_(3) ceramics are 0.041 and 0.49 ms,respectively,which demonstrate that the optical quality of the Yb:Sc_(2)O_(3) has been improved.Meanwhile,their best vacuum sintering temperature can be controlled down to a lower temperature(1550℃).In conclusion,Yb:Sc_(2)O_(3) nano-powders are successfully synthesized by co-precipitation method,and good optical quality transparent ceramics are fabricated by vacuum pre-sintering at 1550℃and HIP post-treatment.
