| Recently the complex perovskite ceramics with the formula of (A=Ba,Sr；=Mg,Zn,Co,Ni,Mn；=Nb,Ta) have gotten much attention because of its good dielectric properties: moderate high permittivity, high quality value Q (low dielectric loss) and low temperature coefficient of resonant frequency ,which can be used as microwave dielectric ceramic materials and be developed as filters and resonators. Presently compounds have been studied overseas and abroad, but Ta2O5 is too expensive own to its high purity and high sintering temperature(1500℃-1600℃),so its usage is limited .While Nb2O5 is a compounds with low cost and can be developed as a substitution to Ta2O5, so Ba(Zn1/3Nb2/3)O3(BZN)is promising .This thesis studied Ba(Zn1/3Nb2/3)O3 ceramics—modulated its temperature coefficient of capacitance toward zero and higher quality value Q so as to make it be used in practice. Furthermore, we studied the effect of additives and non-stoichiometry on properties and structure. Three ways are adopted to modulate the properties of system, moreover, the ordered structure of system with B- site ions, Zn2+,Nb5+,departuring stoichiometry, is researched ,too.The substitution of Sr2+ to A site Ba2+ in Ba(Zn1/3Nb2/3)O3 ceramics.The structure of Ba(Zn1/3Nb2/3)O3 and Sr(Zn1/3Nb2/3)O3 are reported as complex perovskite with opposite temperature coefficient. When Sr(Zn1/3Nb2/3)O3 is added to Ba(Zn1/3Nb2/3)O3 , solid solution is formed. Temperature coefficient of resonant frequency is good with enough Sr(Zn1/3Nb2/3)O3 in solid solution. It stated that anomaly of permittivity and was found because of phase transition. To lower sintering temperature, some additives are added to solid solution and good achievements gotten correspondingly. 2. The substitution of Sn4+ ,Zr4+ to B site ions in Ba(Zn1/3Nb2/3)O3 ceramics.The structure of BaSnO3 is cubic perovskite with =+190×10-6/℃,so when some of it is added to Ba(Zn1/3Nb2/3)O3 ceramic, can be modulated to zero. In the same time, the average radius of B-site ions of ABO3 increased with the addition of Sn2+ ,Zr4+ ions to Ba(Zn1/3Nb2/3)O3 ,since Sn2+ ,Zr4+ ions have a larger ionic radius, the spacings between ions become smaller in solid solution and the anharmonic interaction and dampening constants, , are decreased, so the dielectric loss is lowered.3. The substitution of Ni2+ to B site ions in Ba(Zn1/3Nb2/3)O3 ceramics.The structure of Ba(Ni1/3Nb2/3)O3 and Ba(Zn1/3Nb2/3)O3 are cubic perovskite and temperature coefficient of resonant frequency of Ba(Ni1/3Nb2/3)O3 is negative, -18×10-6/℃.According to the logarithmic mixing rule, with moderate contents of Ba(Ni1/3Nb2/3)O3 added to Ba(Zn1/3Nb2/3)O3 , solid solution is formed and will be modulated to zero. Weak superstructure is formed when system is sintered at 1350℃ or annealing at 1300℃/12h after sintered at 1350℃, and ordered structure increased after annealing. It indicated that mutual diffusion of Ni2+, Nb5+ ions in B-site will increase with thermal energy and sintering time. Nb-rich liquid phase is formed after sintered at 1550℃. The formation of a Nb-rich liquid phase is accompanied by defects (vacancies) concentration because the increase of lattice constant means the increase of defects. The generation of vacancies in the structure probably gives rise to the disordering, since the interdiffusion of Ni2+,Nb5+ ions can be facilitated by the vacancies.4. The ordered structure change of Ba(Zn1/3Nb2/3)O3 ceramic when Ni2+,Nb5+ ions in B-site are non-stoichiometry.Because ordering structure is sensitive to stoichiometry in B-site, we change the percentage of B-site ions and make it to be compounds of Zn-rich (BZNZ) or Nb-rich (BZNN) ,that is , non-stoichiometry , so as to research structure change. Dielectric loss is sensitive to the ratio of B-site ions: when Zn2+/Nb5+ is 1:2 accurately, loss is minimal, but when the ratio of it deviates from1:2 ,loss will decrease greatly. If the composition is adjusted to be zinc rich as BZNZ, the overall composition is inclined towards...
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