This study designs and synthesizes highly dense Li2 Mg_(6)ZnTi_(6)O_(20)microwave dielectric ceramics based on a high-entropy strategy,focusing on achieving stable structures,low sintering temperatures,and excellent c...This study designs and synthesizes highly dense Li2 Mg_(6)ZnTi_(6)O_(20)microwave dielectric ceramics based on a high-entropy strategy,focusing on achieving stable structures,low sintering temperatures,and excellent comprehensive performance.The ceramics exhibit a predominant face-centered cubic disordered phase(Fd-3 m)sintered at 1200-1280℃,alongside an increased presence of the second phase MgTiO_(3) at higher temperatures.Remarkably,these ceramics demonstrate excellent microwave dielectric properties(ε_(r)=16.69,Q×f=88,230 GHz,and τ_(f)=−36.5 ppm/℃).Additionally,we have explored the addition of x wt%LiF(1≤x≤5)to the Li2 Mg_(6)ZnTi_(6)O_(20)ceramics to enhance their applicability.The ceramics feature a spinel structure for LiF contents up to 3 wt%,while higher LiF concentrations induce the formation of a secondary phase,LiTiO2,characterized by a rock salt structure.Notably,the lattice distortion induced by LiF leads to a constant decrease in ε_(r).A moderate degree of lattice distortion serves to enhance the lattice stability of ceramics,which is reflected in increased lattice energy.Excellent microwave dielectric properties(ε_(r)=16.23,Q×f=89,728 GHz,τ_(f)=−43.5 ppm/℃)were obtained for x=3 ceramic sintered at 1140℃.Even at x=5,the ceramic retains excellent microwave dielectric properties(ε_(r)=16.02,Q×f=63,079 GHz,τ_(f)=−26 ppm/°C)at a low sintering temperature of 900°C.This work realizes the multiple effects of LiF and confirms good chemical compatibility with silver for LTCC(low-temperature co-fired ceramics)applications.展开更多
Research on doping modification of ZnTiO_(3) ceramics to enhance microwave dielectric properties has been hindered by poor performance,unclear structure-function mechanisms.To expand the applicability of ZnTiO_(3) cer...Research on doping modification of ZnTiO_(3) ceramics to enhance microwave dielectric properties has been hindered by poor performance,unclear structure-function mechanisms.To expand the applicability of ZnTiO_(3) ceramics,this study explores Zn_(1-x)Li_(2x)TiO_(3)(O≤×≤1)ceramics using a phase engineering strategy.Our findings reveal that the introduction of Lit into the ZnTiO_(3) system initiates a multiple phase transition,starting at x=0.1.Initially,ilmenite ZnTiO_(3) transforms into a cubic ordered spinel phase(space group P4332).Subsequently,a transition to a disordered spinel phase(space group Fd3m)occurs at x=0.5,culminating in the formation of a monoclinic rock salt-structured LizTiO3 phase.Significantly,two sets of ceramics with near-zero temperature coefficients of resonance frequency(t:)were obtained at x=0.1 and 0.75.Moreover,the quality factor(Qxf)demonstrated a 4.4-fold increase compared to that of ZnTiO_(3) ceramics at x=0.25(105,013 GHz).Additionally,it was observed that the Ti4 polarization in Zn_(1-x)Li_(2x)TiO_(3) ceramics was underestimated by 11.3%-13.3%,causing the measured dielectric constant(e.)exceeding the theoretical dielectric constant(eth).The ionic polarizability of Ti*was adjusted to stabilize around 3.29 A.Evaluation using multiple methods,including Phillips-van Vechten-Levine(P-V-L)theory,Raman vibrational mode analysis,bond valence,bond energy theory,and octahedral distortion,confirms that the Ti-O bonds within the octahedron predominantly affect&r,the increasing lattice energy(U)contributes to the enhancement of Qxf,and the strengthened Li-O bond energy effectively regulates Tr.展开更多
This study introduces a novel microwave dielectric ceramic,MgAl_(5/4)(Li_(1/3)Ti_(2/3))_(3/4)O_(4),tailored for modern communication technologies.MgAl_(5/4)(Li_(1/3)Ti_(2/3))3/4O4 ceramics feature a composite spinel s...This study introduces a novel microwave dielectric ceramic,MgAl_(5/4)(Li_(1/3)Ti_(2/3))_(3/4)O_(4),tailored for modern communication technologies.MgAl_(5/4)(Li_(1/3)Ti_(2/3))3/4O4 ceramics feature a composite spinel structure(Fd-3m space group)comprising MgAl_(2)O_(4)and Li_(4)Ti_(5)O_(12)type phases.By substituting Al^(3+)of MgAl_(2)O_(4)ceramic with the composite ion(Li_(1/3)Ti_(2/3))^(3+),differences in elemental diffusion induced by sintering temperature(1200-1280℃)significantly affect the microwave dielectric properties:a lowεr(11.83)and enhanced microwave properties(Q×f=79,381 GHz and tf=-28.5×10^(-6)/℃)at 1240℃.With further optimization of the ceramics,a near-zero tf is realized in 0.93MgAl^(5/4)(Li_(1/3)Ti_(2/3))_(3/4)O_(4)-0.07CaTiO_(3)ceramics with excellent comprehensive performance(εr=14.36,Q×f=44,144 GHz).Building on this,a multiband dielectric resonant antenna(DRA)was designed for applications in communication and aeronautical radio navigation,featuring a wide relative bandwidth of 39.37%(5.97-6.49 GHz and 7.19-9.83 GHz).This study presents an optimization strategy for obtaining microwave dielectric ceramics with lowεr,high Q×f,excellent frequency-temperature stability,low sintering temperature,and low density.展开更多
基金supported by the National Natural Science Foundation of China(No.52102129)the Hunan Provincial Natural Science Foundation of China(No.2023JJ30138)the Science and Technology Innovation Program of Hunan Province(No.2023RC3094).
文摘This study designs and synthesizes highly dense Li2 Mg_(6)ZnTi_(6)O_(20)microwave dielectric ceramics based on a high-entropy strategy,focusing on achieving stable structures,low sintering temperatures,and excellent comprehensive performance.The ceramics exhibit a predominant face-centered cubic disordered phase(Fd-3 m)sintered at 1200-1280℃,alongside an increased presence of the second phase MgTiO_(3) at higher temperatures.Remarkably,these ceramics demonstrate excellent microwave dielectric properties(ε_(r)=16.69,Q×f=88,230 GHz,and τ_(f)=−36.5 ppm/℃).Additionally,we have explored the addition of x wt%LiF(1≤x≤5)to the Li2 Mg_(6)ZnTi_(6)O_(20)ceramics to enhance their applicability.The ceramics feature a spinel structure for LiF contents up to 3 wt%,while higher LiF concentrations induce the formation of a secondary phase,LiTiO2,characterized by a rock salt structure.Notably,the lattice distortion induced by LiF leads to a constant decrease in ε_(r).A moderate degree of lattice distortion serves to enhance the lattice stability of ceramics,which is reflected in increased lattice energy.Excellent microwave dielectric properties(ε_(r)=16.23,Q×f=89,728 GHz,τ_(f)=−43.5 ppm/℃)were obtained for x=3 ceramic sintered at 1140℃.Even at x=5,the ceramic retains excellent microwave dielectric properties(ε_(r)=16.02,Q×f=63,079 GHz,τ_(f)=−26 ppm/°C)at a low sintering temperature of 900°C.This work realizes the multiple effects of LiF and confirms good chemical compatibility with silver for LTCC(low-temperature co-fired ceramics)applications.
基金This work was supported by the National Natural Science Foundation of China(No.52102129)the Hunan Provincial Natural Science Foundation of China(No.2023JJ30138)the science and technology innovation Program of Hunan Province(No.2023RC3094).
文摘Research on doping modification of ZnTiO_(3) ceramics to enhance microwave dielectric properties has been hindered by poor performance,unclear structure-function mechanisms.To expand the applicability of ZnTiO_(3) ceramics,this study explores Zn_(1-x)Li_(2x)TiO_(3)(O≤×≤1)ceramics using a phase engineering strategy.Our findings reveal that the introduction of Lit into the ZnTiO_(3) system initiates a multiple phase transition,starting at x=0.1.Initially,ilmenite ZnTiO_(3) transforms into a cubic ordered spinel phase(space group P4332).Subsequently,a transition to a disordered spinel phase(space group Fd3m)occurs at x=0.5,culminating in the formation of a monoclinic rock salt-structured LizTiO3 phase.Significantly,two sets of ceramics with near-zero temperature coefficients of resonance frequency(t:)were obtained at x=0.1 and 0.75.Moreover,the quality factor(Qxf)demonstrated a 4.4-fold increase compared to that of ZnTiO_(3) ceramics at x=0.25(105,013 GHz).Additionally,it was observed that the Ti4 polarization in Zn_(1-x)Li_(2x)TiO_(3) ceramics was underestimated by 11.3%-13.3%,causing the measured dielectric constant(e.)exceeding the theoretical dielectric constant(eth).The ionic polarizability of Ti*was adjusted to stabilize around 3.29 A.Evaluation using multiple methods,including Phillips-van Vechten-Levine(P-V-L)theory,Raman vibrational mode analysis,bond valence,bond energy theory,and octahedral distortion,confirms that the Ti-O bonds within the octahedron predominantly affect&r,the increasing lattice energy(U)contributes to the enhancement of Qxf,and the strengthened Li-O bond energy effectively regulates Tr.
基金supported by The Science and Technology Innovation Program of Hunan Province,China(2023RC3094)Scientific Research Fund of Hunan Provincial Education Department(24B0047).
文摘This study introduces a novel microwave dielectric ceramic,MgAl_(5/4)(Li_(1/3)Ti_(2/3))_(3/4)O_(4),tailored for modern communication technologies.MgAl_(5/4)(Li_(1/3)Ti_(2/3))3/4O4 ceramics feature a composite spinel structure(Fd-3m space group)comprising MgAl_(2)O_(4)and Li_(4)Ti_(5)O_(12)type phases.By substituting Al^(3+)of MgAl_(2)O_(4)ceramic with the composite ion(Li_(1/3)Ti_(2/3))^(3+),differences in elemental diffusion induced by sintering temperature(1200-1280℃)significantly affect the microwave dielectric properties:a lowεr(11.83)and enhanced microwave properties(Q×f=79,381 GHz and tf=-28.5×10^(-6)/℃)at 1240℃.With further optimization of the ceramics,a near-zero tf is realized in 0.93MgAl^(5/4)(Li_(1/3)Ti_(2/3))_(3/4)O_(4)-0.07CaTiO_(3)ceramics with excellent comprehensive performance(εr=14.36,Q×f=44,144 GHz).Building on this,a multiband dielectric resonant antenna(DRA)was designed for applications in communication and aeronautical radio navigation,featuring a wide relative bandwidth of 39.37%(5.97-6.49 GHz and 7.19-9.83 GHz).This study presents an optimization strategy for obtaining microwave dielectric ceramics with lowεr,high Q×f,excellent frequency-temperature stability,low sintering temperature,and low density.
