Min Min Mao

Structure and dielectric relaxation of double-perovskite La2CuTiO6 ceramics

Dielectric properties of La2CuTiO6 ceramics were investigated in a broad frequency and temperature range. There is only one dielectric relaxation in the curve of temperature dependence of dielectric properties for La2CuTiO6 ceramics. This dielectric relaxation is a thermal activated process. The bulk and grain boundary resistances can be obtained from results of the least-mean-square fitting on impedance spectra. The conduction mechanism of the present ceramics is also a thermal activated process. The activation energy of dielectric relaxation is almost same as that of electrical conductivity and this indicates the closely correlation between the dielectric relaxation and electrical conductivity. The dielectric relaxation in the present ceramics should be attributed to the mixed-valent structure (Cu+/Cu2+ and Ti3+/Ti4+), which is induced from the oxygen vacancy.

Characterization of Microstructures and Defects in SrSmAlO4-Based Microwave Dielectric Ceramics by TEM

The microstructures and defects in SrSmAlO4-based microwave dielectric ceramics were investigated by TEM. The layer sequence defect was observed in Sm-rich SrSmAlO4 ceramics. The other type of intergrowth defect was observed in Sr/Ti co-substituted SrSmAlO4 ceramics, where the inhomogeneity of local area also appeared. The dislocation and secondary phase were present in Ti substituted (Sr0.3Ca0.7)SmAlO4 ceramics. In addition, the secondary phases were observed in the SrSmAlO4 ceramic with ZrO2 pollution and that was sintered at the elevated temperature. All these defects lead to an increase in extrinsic dielectric loss, which should be prevented by microstructural engineering.

Structures and microwave dielectric characteristics of compounds in vicinity of CaNdAlO4 in CaO–Nd2O3–Al2O3 ternary system

Abstract Abstract Single phase ceramics in the vicinity of CaNdAlO4 in CaO–Nd2O3–Al2O3 ternary system, such as ternary oxide compound CaNdAl3O7 and binary oxide compounds NdAlO3, CaAl2O4, Ca3Al2O6 and Ca12Al14O33, were prepared by the standard solid state reaction route. The phases and structure of the ceramics were analysed through X-ray diffraction and scanning electron microscopy. The microwave dielectric characteristics of the ceramics were studied using a network analyser. High Qf values were obtained in CaNdAlO4, CaNdAl3O7, NdAlO3 and CaAl2O4, while the Qf values in Ca3Al2O6 and Ca12Al14O33 were much lower. The best microwave dielectric characteristics (ϵr = 8·9, Qf = 90 800 GHz at ∼9·40 GHz and τf≈−55·2 MK−1) were achieved for CaAl2O4 ceramics sintered at 1425°C in air for 3 h. It could be expected as a promising new candidate for microwave dielectric ceramics. Moreover, the present results showed the direction for modification of CaNdAlO4 microwave dielectric characteristics through composition tailoring.