Investigation Of Structure-properties Relationship On ZnZrNb₂O₈ Microwave Dielectric Ceramics

Recently,great attentions have been paid on the ZnZrNb₂O₈-based ceramics for their excellent microwave dielctric properties.In order to further optimize the performance in the above wolframite-sturctured ceramics,different A-site ions were used to substitute Zn²⁺ions,and the Zn_1-xMn_xZrNb₂O₈ and Zn_1-xNi_xZrNb₂O₈ ceramics were prepared by the conventional solid-state method.The effects of ionic substitution on the sintering characteristic,phase composition and microwave dielectric properties of the matrix were systematically investigated.The corelation between bonding characteristics,crystal structure and microwave dielctric properties were also characterised by bond ionicity,lattice energy,bond energy and thermal expansion coefficient obtained from the complex chemical bond theory.The main research contents are as follows.?1?The Zn_1-xMn_x ZrNb₂O₈?0.02?x?0.1?cermaics were prepared by the convential solid-state method,and the temperature coefficient of resonant frequency was expected to be adjusted by Mn²⁺substitution.The investigation indicated that the dense Zn_1-xMn_xZrNb₂O₈ceramics could be obtained at 1200?,and the properties were mainly affected by the Mn²⁺content under the above situation.With the x value increasing from 0.02 to 0.10,the dielectric constant of Zn_1-xMn_x ZrNb₂O₈ ceramics increased from 29.12 to 29.43,the quality factor decreased from 51,300 GHz to 44,900 GHz,while the temperature coefficient increased from-23.94 ppm/?to-5.61 ppm/?.The Zn_0.9Mn_0.1ZrNb₂O₈ ceramics sintered at 1200°C could possess best microwave dielectric properties of?_r=29.43,Q·f=44,900 GHz and?_f=-5.61ppm/°C??2?The Zn_1-xNi_x ZrNb₂O₈?0?x?0.1?cermaics were prepared by the convential solid-state method,and the temperature coefficient of resonant frequency as well as dielcteric loss were expected to be adjusted by Ni²⁺substitution.The investigation indicated that the dense Zn_1-xNi_xZrNb₂O₈ ceramics could be obtained at 1150?,and the properties were mainly affected by the Ni²⁺content under the above situation.As the Ni²⁺doping amount graually increased,the dielectric constant of Zn_1-xNi_x ZrNb₂O₈ decreased from 28.06 to 26.35,the quality factor increased to around 60,000 GHz,and the temperature coefficient increased from-42.68 ppm/°C to around-10 ppm/°C.Excellent microwave dielctric properties of?_r=27.10,Q·f=62,700 GHz and?_f=-14.72 ppm/°C could be obtained in Zn_0.96Ni_0.04ZrNb₂O₈ ceramics sintered at 1150°C.?3?The chemical bond properties in ZnZrNb₂O₈ microwave dielctric ceramics were analysed by using Rietveld refinefiment and complex chemical bond theory.The results indicated that the Nb-O bond could possess higher bond ionicity,lattice energy,bond energy and near-zero thermal expansion coefficient.Hence,the variation of Nb-O properties could paly an important role on crystal structure and microwave dielctric properties.In addtion,both the A-O and B-O octahedron could be affected by the substitution of A-site ions.?4?The mechanism of A-site ionic substitution on the properties of ZnZrNb₂O₈ ceramcis was investigated by combining chemical bond vibration characteristics,crystal structure and the bond stability.The dielectric constant witnessed the similar trend with molecular polarizability and bond ionicity,and there is a proportional relationship between quality factor and lattice energy.The variation trend of temperature coefficient of resonant frequency might be associated with factors such as bond energy,octahefra distortion and bond valence.