A series of nominal compositions MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)(x=0,0.04,0.08,0.12,0.16,and 0.20)ceramics were successfully prepared via the conventional solid-state reaction route.The phase compositions,micros...A series of nominal compositions MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)(x=0,0.04,0.08,0.12,0.16,and 0.20)ceramics were successfully prepared via the conventional solid-state reaction route.The phase compositions,microstructures,and microwave dielectric properties were investigated.The results of x-ray diffraction(XRD)and scanning electron microscopy(SEM)showed that a single phase of MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with a spinel structure was obtained at x≤0.12,whereas the second phase of MgTi_(2)O_(5)appeared when x>0.12.The cell parameters were obtained by XRD refinement.As the x values increased,the unit cell volume kept expanding.This phenomenon could be attributed to the partial substitution of(Li_(1/3)Ti_(2/3))^(3+)for Al^(3+).Results showed that(Li_(1/3)Ti_(2/3))^(3+)doping into MgAl_(2)O_(4)spinel ceramics effectively reduced the sintering temperature and improved the quality factor(Q_f)values.Good microwave dielectric properties were achieved for a sample at x=0.20 sintering at 1500℃in air for 4 h:dielectric constantε_(r)=8.78,temperature coefficient of resonant frequencyτ_(f)=-85 ppm/℃,and Q_(f)=62300 GHz.The Q_(f)value of the x=0.20 sample was about 2 times higher than that of pure MgAl_(2)O_(4)ceramics(31600 GHz).Thus,MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with excellent microwave dielectric properties can be applied to 5G communications.展开更多
通过共沉淀法合成了CuCr_(2)O_(4)黑色颜料。研究了沉淀剂(即尿素、氨水、氢氧化钠)对相组成和颜色性能的影响。同时,计算了以氨水和氢氧化钠为沉淀剂时CuCr_(2)O_(4)的结晶动力学和结晶机制。结果表明,由于两种离子(Cu^(2+)和Cr^(3+))...通过共沉淀法合成了CuCr_(2)O_(4)黑色颜料。研究了沉淀剂(即尿素、氨水、氢氧化钠)对相组成和颜色性能的影响。同时,计算了以氨水和氢氧化钠为沉淀剂时CuCr_(2)O_(4)的结晶动力学和结晶机制。结果表明,由于两种离子(Cu^(2+)和Cr^(3+))的溶解度不同,沉淀过程的最佳pH值为7.5;由于产物中存在Cr2O3,尿素不适合作为沉淀剂。氨水作为沉淀剂时,CuCr_(2)O_(4)结晶的活化能为120.2 k J/mol,氢氧化钠作为沉淀剂时为141.3 k J/mol。CuCr_(2)O_(4)的结晶过程涉及成核和三维生长。较小的结晶活化能得到的CuCr_(2)O_(4)颗粒细小,分散均匀,呈色性能更优异。展开更多
基金the Chengdu University of Technology(Grant No.KYQD201907728)。
文摘A series of nominal compositions MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)(x=0,0.04,0.08,0.12,0.16,and 0.20)ceramics were successfully prepared via the conventional solid-state reaction route.The phase compositions,microstructures,and microwave dielectric properties were investigated.The results of x-ray diffraction(XRD)and scanning electron microscopy(SEM)showed that a single phase of MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with a spinel structure was obtained at x≤0.12,whereas the second phase of MgTi_(2)O_(5)appeared when x>0.12.The cell parameters were obtained by XRD refinement.As the x values increased,the unit cell volume kept expanding.This phenomenon could be attributed to the partial substitution of(Li_(1/3)Ti_(2/3))^(3+)for Al^(3+).Results showed that(Li_(1/3)Ti_(2/3))^(3+)doping into MgAl_(2)O_(4)spinel ceramics effectively reduced the sintering temperature and improved the quality factor(Q_f)values.Good microwave dielectric properties were achieved for a sample at x=0.20 sintering at 1500℃in air for 4 h:dielectric constantε_(r)=8.78,temperature coefficient of resonant frequencyτ_(f)=-85 ppm/℃,and Q_(f)=62300 GHz.The Q_(f)value of the x=0.20 sample was about 2 times higher than that of pure MgAl_(2)O_(4)ceramics(31600 GHz).Thus,MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with excellent microwave dielectric properties can be applied to 5G communications.
文摘通过共沉淀法合成了CuCr_(2)O_(4)黑色颜料。研究了沉淀剂(即尿素、氨水、氢氧化钠)对相组成和颜色性能的影响。同时,计算了以氨水和氢氧化钠为沉淀剂时CuCr_(2)O_(4)的结晶动力学和结晶机制。结果表明,由于两种离子(Cu^(2+)和Cr^(3+))的溶解度不同,沉淀过程的最佳pH值为7.5;由于产物中存在Cr2O3,尿素不适合作为沉淀剂。氨水作为沉淀剂时,CuCr_(2)O_(4)结晶的活化能为120.2 k J/mol,氢氧化钠作为沉淀剂时为141.3 k J/mol。CuCr_(2)O_(4)的结晶过程涉及成核和三维生长。较小的结晶活化能得到的CuCr_(2)O_(4)颗粒细小,分散均匀,呈色性能更优异。
基金National Key R&D Program of China(2016YFB0402101,2017YFB0310500)Key Research Project of the Frontier Science of the Chinese Academy of Sciences(QYZDB-SSW-JSC022)。
