Broadband spectroscopy of dielectrics and oxygen-ion conductors

The frequency response of the permittivity of oxides is described by the dielectric dispersion of four contributions: the interfacial, dipole, ionic, and electronic polarizations. Our recent studies related to the broadband dielectric and conductivity spectroscopy of oxides are reviewed herein. Two methods, i.e., the micro-sized planar electrode and ring resonator techniques, were developed to measure the microwave dielectric properties of specimens having a large permittivity. Using these methods, we developed the complex permittivity of a paraelectric SrTiO₃ (ST) single crystal up to a few GHz. We also investigated the polarization contribution to the microwave tunability, T, of ferroelectric Ba_0.8Sr_0.2TiO₃ (0.8-BST). The apparent tunability of 0.8-BST was determined by the domain wall density; a higher domain wall density resulted in a larger dipole polarization. A modified Kohlrausch-Williams-Watts model was used for the dipole relaxation function. Ionic polarization was analyzed using the fourparameter semi-quantum phonon dispersion model. The dielectric function combining these two relationships was used for broadband spectroscopic analysis of the dielectrics. The dipole and ionic polarizations and electronic contributions were simultaneously quantified for the ferroelectric BaTiO3 ceramic and ST single crystal. The broadband conductivity spectrum of 8 mol% yttria-stabilized zirconia, a fast oxygen-ion conductor, was also acquired to quantify all conduction contributions, i.e., the interfacial, grain boundary, and bulk contribution.