Investigation On The Structure-properties Relationship Of Novel Phosphor-based Microwave Dielectric Ceramics

Due to the low intrinsic sintering temperature,low permittivity,high quality factor and good chemical compatibility with commonly used electrodes,LiMPO₄（M=Mg,Ni）ceramics have become potential and promising materials for LTCC applications.In this paper,LiMPO₄（M=Mg,Ni）ceramics were synthesized via the traditional solid-state reaction route.The phase composition,microstructure and microwave dielectric properties were systematically studied.On the basis of the XRD data,the chemical bond characterizations were deeply investigated.The intrinsic factors on microwave dielectric properties were also discussed.1.The effects of processing technique on phase composition,microstructure and microwave dielectric properties of LiMgPO₄ ceramics were systematically investigated.The chemical bond parameters including ionicity,lattice energy and bond energy were obtained and the crystal structure of LiMgPO₄ ceramics was analyzed.And the relationship between chemical bond parameters and microwave dielectric properties was also discussed.When the pre-sintering temperature was 700^oC,LiMgPO₄ ceramics sintered at 825^oC for 2h could obtain the excellent microwave dielectric properties ofε_r⁶.53,Q×f⁷2,777GHz,τ_f^-44.4ppm/^oC.2.The effects of ion substitution on the structure and microwave dielectric properties of LiMgPO₄ ceramics were investigated.The Li(Mg_1-xA_x)PO₄(A=Mn²⁺,Ca²⁺)ceramics were prepared and different divalent ions(Mn²⁺,Ca²⁺)were introduced to substitute Mg²⁺ion of LiMgPO₄ ceramics.The effects of different divalent ions on the phase composition,microstructure and microwave dielectric properties were studied.The polarizability and packing fraction were calculated by formulas and the relationship between these parameters and microwave dielectric properties was discussed.LiMg(P_1-xNb_x)O₄ ceramics were prepared by substituting Nb⁵⁺for P⁵⁺.The phase composition,microstructure and microwave dielectric properties of LiMg(P_1-xNb_x)O₄ ceramics were systematically investigated.LiMg(P_0.96Nb_0.04)O₄ ceramics possessed the highest Q×f value of 86,848 GHz.3.The phase composition,microstructure and microwave dielectric properties of LiNiPO₄ ceramics were investigated.The sintered samples were indexed as orthorhombic phase and its space group was Pnma（62）.The lattice parameters of LiNiPO₄ ceramics were a=10.025（?）,b=5.860（?）,c=4.676（?）and V=274.69（?）³.According to the complex chemical bond theory,the relationship between chemical bond parameters and microwave dielectric properties was established.LiNiPO₄ ceramics sintered at 825^oC for 2h exhibited good microwave dielectric properties:ε_r⁷.2,Q×f²7,754GHz,τ_f^-67.7ppm/^oC.4.In order to adjust theτ_f value to near zero,TiO₂ was added as temperature coefficient regulator.The phase composition,microstructure and microwave dielectric properties of sintered samples were systematically investigated.In addition,the chemical compatibility between LiNiPO₄ ceramics and Ag electrode was also studied.The results demonstrated that the LiNiPO₄-15wt%TiO₂ ceramics could obtain the good microwave dielectric properties ofε_r¹1.49,Q×f¹0,792GHz,τ_f^-2.8ppm/^oC when sintered at 900^oC for 2h.