REPLACED SITE OF Eu^(2+) ION IN THE COMPLEX FLUORIDES WITH THE PEROVSKITE CRYSTAL STRUCTURE

The replaced site of Eu^(2+) ion is dependent on the electronegativity difference of the cations in complex fluorides.In the mixed fluoride KMgF_3:Eu^(2+),Eu^(2+) ion occupies K^+ site,its emission spectrum is a sharp line and its valence-state is stable.

Synthesis and Electrocatalytic Properties of Complex Oxides Containing Lanthanum

A series of perovskite-type complex oxides LaNi1-xRuxO3 were prepared and studied by means of XRD. The effects of some factors on th complex oxides were discussed. Each kind of those perovskite-type complex oxides was used to prepare cathode by composite-electroplating technique. The cathodes were electrochemically charactrized. The results show that these novel cathode exhibit high activities and excellent stabilities during long-term continuous electrolysis with some current interruptions.

Effect of Sn^(4+) B-Site Substitution on the Microstructure and Dielectric Properties of Ba(Mg_(1/3)Ta_(2/3))O_3 Microwave Ceramics

The effect of Sn^4＋ （BaSnO3） B-site substitution on the microstructure and dielectric properties of Ba（Mg1/3Ta2/3）O3 microwave ceramics was investigated. X-ray diffraction shows that a complex perovskite material Ba（Mg1/3Ta2/3）O3 was prepared. As Sn^4＋ content x increases in the （1-x） Ba（Mg1/3Ta2/3）O3-xBaSnO3 （x=0.00～0.20） system, the dielectric constant generally keeps unchanged, while TCF changes from positive to negative. Although the addition of Sn^4＋ reduces the ordering degree, Q f0 is still increased when the ceramics density increases. This trend implies that Q f0 of this system is mostly determined by ceramics density rather than ordering degree. After sintering at 1500℃ for 3 h, the system with x=0.15 was found to have excellent dielectric properties as follows：ε≈25, Q f0≥300,000 GHz at 7 GHz, TCF=-0.6×10^-6/℃.

Microwave dielectric properties and microstructure of a new kind Eu-based Eu(Mg_(0.5)Ti_(0.5))O_3 ceramic

A new Eu-based microwave dielectric ceramic,Eu(MgTi)O(EMT for short), was prepared through conventional solid-state reactions. The EMT ceramics were well densified at 1425 ℃ and exhibit good microwave dielectric properties with permittivity of 23.92, high quality factor(Q*f) of 66,957 GHz at 8.93 GHz and relatively low-temperature coefficient of resonant frequency of-20.3 10/K. Additionally, the variations of dielectric constants among Ln(MgTi)O(Ln represents rare earth elements, LMT) compounds were analyzed. Ionic radii of Ln, associated with the tolerance factors of the perovskite structure of LMT, were investigated to be the key factor to influence the permittivity. These results indicate that EMT ceramics might be one of the promising candidates as microwave resonators.

Order-Disorder Phase Transition and Dielectric Mechanism in Relaxor Ferroelectrics

An overview is presented on the order-disorder structural transitions and the dielectric mechanism in the complex-perovskite type relaxor ferroelectrics, i.e., the relaxors. Emphasis is put on the theoretical understanding of the structural transitions, the macroscopic dielectric properties, and the relationship between them. The influences of the composition, the temperature, and the atomic interactions on the order-disorder microstructures can be well understood in the cluster-variation-method calculations. The criterion drawn from theoretical analysis is successful in predicting the order-disorder structure of relaxors. Among various physical models about relaxors, the dipole glassy model that described the dielectric response as the thermally activated flips of the local spontaneous polarization under random interactions is discussed in details. The Monte Carlo simulation results of this model are consistent with the linear and nonlinear experiments of relaxors.

Modification of physical properties of Ba(Ni_(1/3)Nb_(2/3))O_(3) ceramics through ordered domain engineering

Ordered domain engineering has been further developed for modifying and improving physical prop-erties in complex perovskite ceramics. In the present work, Ba(Ni_(1/3)Nb_(2/3))O_(3) ceramic is taken as a typicalexample for ordered domain engineering, in which the sintering temperature lies above the order-disorder transition temperature. Though the well-ordered structure could not be obtained in as-sintered samples, high ordering degree could be achieved together with preferred ordered domainstructures in Ba(Ni_(1/3)Nb_(2/3))O_(3) ceramics through long-time annealing, and subsequently the physicalproperties such as electrical resistivity, thermal conductivity, dielectric strength and energy storagedensity are significantly enhanced, where the ordering degree, ordered domain structure and ordereddomain boundary play the critical rules. The present work provides an effective approach for developingcomplex perovskite dielectric ceramics with superior physical properties.

Polarized Raman scattering study of PSN single crystals and epitaxial thin films

This paper describes a detailed analysis of the dependence of Raman scattering intensity on the polarization of the incident and inelastically scattered light in PbSc_(0.5)Nb_(0.5)O_(3)(PSN)single crystals and epitaxially compressed thin films grown on(100)-oriented MgO substrates.It is found that there are significant differences between the properties of the crystals and films,and that these differences can be attributed to the anticipated structural differences between these two forms of the same material.In particular,the scattering characteristics of the oxygen octahedra breathing mode near 810 cm^(-1) indicate a ferroelectric state for the crystals and a relaxor state for the films,which is consistent with the dielectric behaviors of these materials.