Studies On Giant Dielectric-permittivity Properties Of NaCu₃Ti₃Sb_xNb_1-xO₁₂ And NaCu₃Ti₃Sb_xTa_1-xO₁₂ Ceramics

Dielectric materials are widely used to fabricate capacitive devices such as capacitance, resonators and filters. With the increasing miniaturization and integration of microelectronic devices, the high dielectric permittivity material has a wide application prospects in microelectronic industry, especially in the high-capacity electrical appliances and dynamic random access memory?DRAM?.In recent years, a body-centered cubic perovskite CaCu₃Ti₄O₁₂?CCTO? material has received wide attention because of its giant dielectric properties. Its dielectric permittivity is up to 104, with a good temperature stability over a large temperature range. As a new giant dielectric material, CCTO has very large potential practical value. However, the mechanism?s? of its giant dielectric properties still remain controversial, and its relatively high dielectric loss and the sensitive dependence to the fabrication processes become a bottleneck for its practical applications. Therefore, lots of researchers do some work to improve the dielectric properties of CCTO ceramics through doping, or other chemical methods. In addition, some researchers study on various of CCTO-like ceramics material in the hope of finding new ceramic materials which have the high dielectric permittivity and low dielectric loss.In this paper, NaCu₃Ti₃Sb_xNb_1-xO₁₂?x = 0¹? ceramics were successfully obtained by solid-state method and their electrical properties were studied. Similar to the literature results of CCTO ceramics, the abnormal large dielectric permittivity over 104 have been observed in all of these ceramics. Within the measuring frequency range of 20 Hz² MHz, a single dielectric relation with the characteristic frequency around 1 MHz is seen at room temperature. Because all of these ceramics were experimentally found to be quantitatively similar, the ceramic of x = 0.5 was selected to be studied as a representative, and its crystal lattice structure and microstructure are measured. The existence of the second phase of CuO was observed directly through the X ray diffraction. The NaCu₃Ti₃Sb_0.5Nb_0.5O₁₂ ceramic sintered at 1333 K was chosen as the representative to be further investigated detailedly. Similar to the results of CCTO ceramics, another dielectric relaxation emerges in the frequency range below 100 kHz at higher temperatures. Complex impedance spectrum analysis proved that the grain is semiconductive and the grain boundary is insulated Cu2+/Cu+, Ti4+/Ti3+, Sb5+/Sb3+ and Nb5+/Nb4+ aliovalences has been directly confirmed by X-ray photoelectron spectroscopy analysis.Similarly, NaCu3Ti3SbxTa1-xO12?x = 0¹? ceramics were prepared by solidstate method and the electrical properties were measured. Then, NaCu3Ti3Sb0.5Ta0.5O12 ceramic was further detailed investigated as the representative. Similar to the literature results, giant dielectric-permittivity phenomena with low-frequency e? larger than 104 have been observed in all of these ceramics. Within the measuring frequency range of 20 Hz² MHz, a single dielectric relaxation with the characteristic frequency around 1MHz is seen at room temperature and an additional one in low frequency region is also observed at high temperatures. Complex impedance spectrum analysis proved that the grain is semiconductive and the grain boundary is insulated, Cu2+/Cu+, Ti4+/Ti3+, Sb5+/Sb3+ and Ta5+/Ta4+ aliovalences has been directly confirmed by X-ray photoelectron spectroscopy analysis.In general, the results can be explained by the similar mechanism of internal barrier layer capacitance?IBLC? effect formerly proposed for CaCu₃Ti₄O₁₂ ceramics and indicate that the giant-e? phenomena should be quite common in the large family of compositionally and structurally CaCu₃Ti₄O₁₂-like oxide ceramics.