| In order to explore new function materials in niobates and tantalates, series new compounds and ceramics of the filled and unfilled tungsten bronze structures were synthesized and prepared using high purity powders by solid state reaction method, according to the characteristics of the structure and the cations in A and B site (radii, valence and electronegativity) in this dissertation. Their composition, structure and dielectric and impedance properties were systematically investigated, and the relationship between composition, structure and properties were analyzed.Series new compounds and ceramics of Sr5RETi3M7O30 and Sr4RE2Ti4M6O30 (RE=Pr,Eu;M=Nb,Ta) with filled tungsten bronze structure were prepared respectively. All the compounds except Sr4Pr2Ti4Ta6O30 exhibit weak ferroelectric at room temperature. Among them, Sr5PrTi3Nb7O30 and Sr4Eu2Ti4Ta6O30 are relaxor ferroelctrics, and the others are diffuse transition ferroelectrics.The transition temperature of Pr-containing compounds is lower than that of Eu-containing compounds. Sr5PrTi3Nb7O30 and Sr4Pr2Ti4Nb6O30 exhibit high dielectric constant and low dielectric loss, and contrary temperature coefficient of dielectric constant. The mixtures of Sr5PrTi3Nb7O30 and Sr4Pr2Ti4Nb6O30 at the ratio of 1:4 and 1:8 exhibit exceptional temperature stability which meet require of X7R capacitor.Series new K3A2RENb10O30 (A=Ba, Sr; RE=La, Pr, Nd, Sm, Eu, Gd) with filled tungsten bronze structure compounds and ceramics were prepared respectively.The influence of rare earth on the density, phase transition temperature and relaxor behavior of the compounds were investigated. The two formers increase with the decrease of the rare earth atomic radii, while the latter disappears with the incease of the difference of cationic radii at A site. K3Ba2LaNb10O30, K3Sr2LaNb10O30 and K3Sr2PrNbio03o are relaxor, while the other ceramics exhibit diffuse transition behavior. K3Sr2LaNb10O30 and K3Sr2PrNb10O30 are paraferroelectrics, the other ceramics show weak ferroelectricity. Among them K3Ba2LPrNb10O30 has the highest remnant polarization (2Pr) of 9.56μC/cm2. The abnormity of dielectric properties above 400℃attributes to the increase conducting electrons created by oxygen vacancy. The phase transition diffuseness degree of compounds of 1-2, and the Curie constant with the magnitude of 105 suggest these compounds are displacement type ferroelectrics. The fitting of experimental curve by Vogel-Fulcher relationship suggests that, the relaxor behavior of K3Sr2LaNb10O30 and K3Sr2PrNb10O30 are analogous to a spin glass with polarization fluctuations above a static freezing temperature. The combination effects of the free conduction electrons results from the first-ionization of oxygen vacancies and the reorientation of the off-center Nb ion will contribute the dielectric relaxor. All the impedance characteristic of K3Sr2RENb10O30 (RE=La, Pr, Nd, Sm, Eu, Gd) compounds are similar. The activation energy of ac impedance is approximately same as the one required for the motion of oxygen vacancies. This result confirms that the observed conductivity is due to a movement of oxygen vacancy in these ceramics.Series new KBa3RENb10O30 (RE=La, Pr, Nd, Sm, Eu, Gd) compounds and ceramics with unfilled tungsten bronze structure were prepared respectively. KBa3GdNb10O30 is a classical ferroelectric, while the other ceramics are relaxor. Phase transit temperature increase with the decrease of the rare earth atomic radii. The former three are paraferroelectrics while the latter three show weak ferroelectricity, and among them KBa3GdNb10O30 has the highest remnant polarization (2Pr) of 8.2μC/cm2. According to the fitting of experimental curve by Vogel-Fulcher relationship, the activation energy of KBa3LaNb10O30, KBa3PrNb10O30 and KBa3NdNb10O30 are 0.148 eV,0.129 eV,0.16 eV, respectively. This suggests that the relaxor behavior is analogous to a spin glass with polarization fluctuations above a static freezing temperature. The impedance properties of KBa3LaNb10O30, KBa3PrNb10O30 and KBa3NdNb10O30 ceramics are similar and can be fitting by Arrhenius relationship. The activation energy of them is approximately the same as the one required for the motion of oxygen vacancies. This confirms that the observed conductivity is due to a movement of oxygen vacancies in these ceramics.Series new Ba4RETiNb9O30 (RE=La, Pr, Nd, Sm, Eu, Gd) compounds and ceramics with unfilled tungsten bronze structure are prepared respectively. These former four ceramics are relaxor, while the latter two show diffuse phase transition. The phase transit temperature increase with the decrease of the radii of rare earth. The Curie constant larger than the magnitude of 105 suggest these compounds as displacement type ferroelectrics. All these compounds show weak ferroelectricity. Among them Ba4GdTiNb9O30 has the highest remnant polarization (2Pr) of 5.12μC/cm2. Dielectric loss increase with the increase frequency due to the forming disordered state, because the number of larger cations is not equal to the interstics in the tungsten bronze structure. The relaxor behaviors of these ceramics obey the dipole-glass model. The activation energy of Ba4LaTiNb9O30, Ba4PrTiNb9O30, Ba4NdTiNb9O30 and Ba4SmTiNb9O30 are 0.174,0.096,0.074 and 0.12 eV, respectively, which suggests that the relaxor behavior is attribute to the combination effect of the free conduction electrons results from the first-ionization of oxygen vacancies and the reorientation of the off-center Nb ion. The freezing temperature(62, 243,276,304 K, respectively) increases with the decease of the radii of rare earth ion of the value. All the impedance properties of Ba4PrTiNb9O30, Ba4SmTiNb903o and Ba4GdTiNb9O30 ceramics are similar and follow the Arrhenius relationship. The activation energy of impedance relaxation is approximately the same as the one (-1eV) required for the motion of oxygen vacancies, which confirm that the observed conductivity are due to movement of oxygen vacancies.
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