Wen Zhi Yang

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.

Structure, magnetic, and dielectric characteristics of Ln2NiMnO6 (Ln = Nd and Sm) ceramics

In the present work, the structure, magnetic, and dielectric characteristics of Nd2NiMnO6 and Sm2NiMnO6 have been investigated with comparison to those for La2NiMnO6. The magnetic and dielectric properties of the present ceramics vary with decreasing lanthanide ionic radius (RLn). Both Nd2NiMnO6 and Sm2NiMnO6 are ferromagnetism with the monoclinic symmetry (space group P21/n). The Curie temperature TC of Nd2NiMnO6 and Sm2NiMnO6 is 194 K and 156 K, respectively, and it decreases with decreasing 〈Ni-O-Mn〉 bond angle which depends on RLn. Meanwhile, the dielectric constant e′ monotonically decreases with decreasing RLn. The similar variation tendency of magnetic and dielectric characteristics with RLn indicates that the structural origins for the magnetic and dielectric response should be closely linked with each other.

Structure, magnetic, and dielectric properties of La2Ni(Mn1-xTix)O6 ceramics

In the present work, the effects of Ti-substitution for Mn upon the structure, magnetic and dielectric properties in La2NiMnO6 ceramics have been investigated. Ti-substitution for Mn strongly affects the crystallographic, magnetic, and dielectric properties of La2NiMnO6 double perovskite ceramics. Refinements of the x-ray diffraction data show that all compositions investigated here have the monoclinic perovskite structure in space group P21/n with a partially ordered arrangement of Ni and Mn/Ti cations. The magnetic nature of the present ceramics with x up to 0.8 is ferromagnetic (FM), while that is antiferromagnetic for La2NiTiO6. The Curie temperature and the spontaneous magnetization, or FM component, decrease with increasing x. These ferromagnetic states are attributed to the Ni2+-O-Mn4+ superexchange interaction. The dielectric constant monotonically decreases and the relaxor-like behavior is suppressed with x. The similar variation tendency of magnetic and dielectric properties with increasing x ca...

Giant dielectric response in (Sm1−xNdx)1.5Sr0.5NiO4 ceramics: The intrinsic and extrinsic effects

(Sm1−xNdx)1.5Sr0.5NiO4 solid solution ceramics with K2NiF4-type structure have been synthesized in the entire range of 0.2 ≤ x ≤ 0.8. All compositions can form the single orthorhombic phase in a space group of Bmab (64). With increasing x, the crystal structure has a tendency of transforming from orthorhombic to tetragonal phase, and this transformation should be related to the average radius of ions in K-site. The relationships between the low temperature dielectric relaxations and the adiabatic small polaronic hopping processes in all compositions are confirmed. Because of the inhomogeneity and fluctuation of the constituent and structure, the dielectric relaxations above room temperature are originated from extrinsic Maxwell-Wagner effect in the compositions with x = 0.4, and 0.6. The low-frequency dielectric relaxation observed in the sample of x = 0.8 is attributed to grain boundary effect.