| B-site ordered complex perovskite ceramics have important applications in microwave communication systems as the core of medium dielectric constant microwave dielectric ceramics. In this thesis, the order-disorder transition, ordering domain structures and ordering domain boundary of 1:2 ordered complex perovskites have been systematically investigated toghther with the microwave dielectric characteristics. Moreover, a primary exploration is conducted on the tailoring of ordering domain structure and microwave dielectric properties of 1:1 ordered complex perovskites.As-sintered Ba[(Co, Zn, Mg)1/3Nb2/3]O3 ceramics are well ordered since Mg substitution significantly increased the order-disorder transition temperatures to above the densification temperatures. The significantly improved Qf value is obtained in the present ceramics with increasing Mg content, while the dielectric constant decreases slightly together with some increase of temperature coefficient of resonant frequency. After Mg-substitution, the increased ordering degree and fine ordering domain structure are obtained by tailoring the order-disorder transition temperature and the sintering temperatire, thus the ultra-low loss microwave dielectric ceramics are explored in Ba(Zn1/3Nb2/3)O3-Ba(Mg1/3Nb2/3)O3-Ba(Co1/3Nb2/3)O3 ternary system.Long-time annealing at temperatures below the order-disorder transition temperature enhances the B-site ordering degree and promotes the ordering domain growth. The most significant improvement of Rvalue is obtained after annealing at 1400℃ for 12 h, together with a slight decrease of dielectric constant and temperature coefficient of resonant frequency. The Qf value of ceramics annealed at 1400℃ mainly attributes to the enhanced cation ordering degree, the uniform ordering domain structure and the low-ernergy domain boundaries. As the annealing temperature increases, coarse ordering domains with high-energy boundaries are formed, and then the Qf value steadily decreases because of the inferior domain structure, even the cation ordering degree increases. The Qf values of samples are affected by the common function of ordering degree and domain structure.The atomic configurations of 1:2 ordered domain boundaries in Ba(5’1/3B"2/3)03 perovskite ceramics have been comprehensively studied by taking "Ba-B"-Ba-B"-Ba-B’" array as a basic unit, the energy of different boundaries and the corresponding effect on Qf values are predicted. The energy of four types of twin boundaries is proved to be "A-type & B-type< C-type< F-type" according to the magnitude of the destabilization to the system. A-type and B-type boundary, which lie along (001)c and (110)c planes, respectively, show good coherence with both sides of the ordered domains, the cation disruption is quite small. C-type boundary parallels to (111)c plane, while F-type boundary is perpendicular to (111)c plane. At C-type and F-type boundary, atomic intersection leads to a buffer layer, among which the B-site cations are generally disordered. The width of F-type boundary is larger than that of C-type boundary, so is the perturbation to the system. When a conservative twin boundary is combined with anti-phase boundary, the boundary regions are indeed stabilized by forming an extra ordered structure with a periodicity of 1.24 nm along [001]c direction.The 1:2 ordered structure of Ba(B’1/33B"2/3)03 perovskites has been intensively studied by TEM observation from three special projections. The most informative < 110>c zone gives two sets of< 111>c ordering variants, providing convenience to detect the twin boundaries, which are directly related to Qf values.<112>c zone axis with only one set of<111>C variant, has its own advantage to detect single anti-phase boundaries. In addition,<111>C zone axis, which is parallel to the ordering direction, clearly shows the hexagonal symmetry of 1:2 ordered structure in the corresponding HRTEM (High Resolution Transmission Electron Microscopy) image.Minor substitution of BaZrC>3 on Ba[(Co, Zn, Mg)i/3Nb2/3]O3 ceramics destabilizes the 1:2 ordering, and 1:1 ordered phase began to form. Lower ordering degrees mainly contribute to the lower Qf values of the as-sintered Zr-substituted samples. BaZrC>3 substitution significantly reduces both the annealing temperature and annealing time. The ordering-induced domain structure, which is determined by thermodynamic together with kinetic considerations has a strong impact on the Qf values of annealed samples. As a result, the effects of annealing process upon the improvement of Qf values are significant for the lower substitution levels, while limited for higher ones. Not all Ba(5’1/3,S"2/3)O3 system can get optimized Qf values by BaZrO3 substitution.Sr(Ga0.5Nb0.5)1-xTixO3 solid solutions exhibit local 1:1 ordering in B-site. Ti substitution disrupts the 1:1 ordering between Ga and Nb, and an ordering transition from short coherence, long-range ordering to short-range ordering is observed. The dielectric constant and temperature coefficient of resonant frequency increases nonlinearly as Ti content increases while (Rvalues decrease gradually. The variation trend of Qf value is mainly attributed to the increased vibrational anharmonicity by Ti substitution, and the ordering transition has a certain effect on the Qf value variation.The following microwave dielectric ceramics with excellent properties have been developed:1) Ba[(Co0.6-x/2Zn0.4-x/2Mgx)1/3Nb2/3]O3:(x= 0.1-0.3) εr=33.7～34.4, Qf=79,800～93,800 GHz, τf=7.76～9.56 ppm/℃ (as-sintered) εr=33.2～34.1,Qf=111,000～117,000 GHz, τf=6.10～8.60 ppm/℃ (after annealing)2) Sr(Ga0.5Nb0.5)1-xTiO3 (x= 0.3) εr=46.6, Qf= 42,200 GHz, τf=5.0 ppm/℃... |
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