"ReBaCo4O7(Re = Y,Er,Ho) ReBaCo4O7(Re = Y,Er,Ho)及MgV2O4化合物之介電性質研究"

Abstract

The synthesis, characterization and dielectric properties of polycrystalline ReBaCo4O7 (Re = Y , Er , Ho ) and MgV2O4 compounds were investigated in this thesis. Powder X-ray diffraction patterns reveal that all ReBaCo4O7 are single phase hexagonal structure with P63mc space group and MgV2O4 is single phase cubic structure with Fm3m space group. The refined lattice parameters and volume of ReBaCo4O7 obey the Lanthanide contraction rule. The dielectric properties of these compounds were studied in the frequency range from 20 Hz to 1 MHz between 20 K and 320 K. The ErBaCo4O7 sample exhibits a high dielectric permittivity (e' ~ 104) at room temperature with frequency dispersion. In addition, e'(T) also show a step like increases at low temperature. The corresponding loss tangent(T) curve exhibits a dielectric relaxation at T < 100 K. The peak temperature TP of loss tangent shifts to a higher temperature as the frequency increases in dielectric relaxation. The dielectric properties of Re = Y and Ho exhibit a similar relaxation behavior. The observed dielectric response of ErBaCo4O7 was explained in terms of internal (grain boundary) barrier layer capacitance (IBLC) effect and relaxation at ~ 98 K is related to the development of long-range antiferromagnetic order. On the other way, the MgV2O4 sample exhibits a dielectric permittivity (e' ~ 103) at room temperature with frequency dispersion . e'(T) of the sample MgV2O4 also show a step like increases at low temperature. The corresponding loss tangent(T) curve exhibits a dielectric relaxation at T < 65 K. The peak temperature TP of loss tangent shifts to a higher temperature as the frequency increases in dielectric relaxation. The observed dielectric response of MgV2O4 was explained in terms of internal (grain boundary) barrier layer capacitance (IBLC) effect and relaxation at ~ 62 K is related to the development of long-range antiferromagnetic order.