STRUCTURAL-CHANGE DUE TO THERMAL-TREATMENT AND DIELECTRIC-PROPERTIES OF ANODIC OXIDE-FILMS OF BISMUTH

Anodic oxide films of bismuth were fabricated using glycole borate electrolyte at 298 K and a current density of 150 muA cm-2. With analysis by an ellipsometer, it was found that the thickness increases linearly and the diffractive index has a nearly constant value of 2.3-2.5 in the early stage of film growth. The film thickness increases to 0.33 mum by anodic reaction of about 15 h. The as-grown bismuth anodic oxide films are amorphous but change to a polycrystalline structure (beta'-Bi2O3) at 425 K with increasing temperature. The dielectric dispersion and absorption are characterized by the distribution of the relaxation time caused by polarized charge particles and others in the polycrystallized anodic oxide films. The activation energy DELTAH and the entropy DELTAS for dipole rotation are estimated as 47 kJ mol-1 and 164 J mol-1 K-1 respectively, These values are comparable with those of substances with low molecular weight, and contribute to an examination of the dielectric loss and other dielectric behavior.