Study On The Dielectric Properties Of New Niobate Function Materials

With the development of the industry in micro-electronics and energy-storage materials, dielectric functional materials have become a new frontier domain between the most popular technologies in 21st:biotechnology, nanotech and new materials, new energy resources, environment protection. By now, most scientists and researchers, high-tech corp. have invested a large quantities of money, experiment apparatus, human beings into it to find a materials with all of the premium properties: colossal dielectric constant, high resistance, low loss tangent, low-priced, low-sintering temperature, keeping steady in a wide temperature and frequency range. Although, Several colossal dielectric materials have been reported by different authors, for example, CaCu3Ti4O12, LuFe2O4, La15/8Sr1/8NiO4, Li- and Ti- doped NiO. These materials have some flaws somewhere more or less. For this reason, several physical mechanisms related to the outstanding dielectric phenomenon have been revealed to help improve the whole properties. That is, to have a deep understanding of the interior physical law is of highly meaningful. By the way, some scientists ever reported that M2+Nb2O6 (Ca, Nb, Ni, Mg, Zn) have good dielectric properties in microwave frequencies. Here, as a representation, M2+Nb2O6 (Ca, Zn) are studied in detail in the low-frequency range (under 10 MHz). Some interesting results are as follows:1. CaNb2O6 ceramics exhibit an intrinsic dielectric response with a dielectric constant of 18.06 below 400 K. In the temperature range from 400 to 1023 K, the sample successively shows a relaxor-like peak and an increasing ramp, which were having closely relationship with oxygen vacancies. Annealing treatment in N2 and O2 atmospheres revealed that the relaxor-like peak is consisted of two different relaxations (R1 and R2) and the ramp is evidenced to be another relaxation (R3). Our results demonstrated that the low-temperature relaxation (R1) belongs to Maxwell-Wagner-type dielectric relaxation caused by surface-layer effect and the high-temperature relaxations (R2 and R3) are conduction relaxation due to hopping motions of oxygen vacancies. A phase transition was revealed to have affinity relationship with oxygen vacancies.2. ZnNb2O6 ceramics exhibit an intrinsic dielectric response with a dielectric constant of -20.9 below 150℃ followed by two thermally activated relaxations (R1 and R2) at higher temperatures. Both R1 and R2 are related to oxygen vacancies inherent in the sample. At temperatures higher than-550℃, an external relaxation (R3) induced by dc bias was observed. By means of the dielectric permittivity, electric modulus, impedance and admittance, R1 was attributed to be a dipole-type relaxation due to the hoping motions of oxygen vacancies. R2 and R3 were ascribed to be a Maxwell-Wagner-type relaxation resulting from the space charge due to the hoping vacancies blocked by grain boundaries and electrodes, respectively.