Bi₂O₃-B₂O₃ガラスの電気伝導と誘電的性質

抄録

Electric conduction and dielectric properties of the bismuth borate glasses were determined over the entire region of homogeneous glass formation (31-80 Bi₂O₃mol%). The electric conduction is affected by water in the glass. The glasses containing the least amount of water could be obtained when reagent grade chemicals of Bi₂O₃ and B₂O₃ were melted in the vacuum furnace.
The results on the electric conduction are summarized as follows:
1) The temperature dependence of conduction was given by
ε=ε₀exp(-ΔH_dc/kT)
in which ε is conductivity, ΔH_dc activation energy of conduction, T absolute temperature, k Boltzman's constant and ε₀ constant. The activation energies increased from 1.12eV (80Bi₂O₃mol%) to 1.59eV (31mol%). The values of ε₀ were about 10³ohm^-1cm^-1.
2) The dielectric rlaxations with very long relaxation time were observed and the relaxation frequency was given by
f_m=f_m0exp(-ΔH_ac/kT)
in which ΔH_ac is activation energy of relaxation and f_m0 constant. The values of f_m0 were about 10¹³Hz. The following correlations were obtained between the conduction and the dielectric relaxation,
ΔH_dc≅ΔH_ac
ε≅2πε₀Δεf_m
in which ε₀ is dielectric constant of free space and Δε magnitude of the dielectric dispersion.
3) The conductivity decreased as the pressure increased and the frequency of dielectric relaxation was shifted to lower frequency side.
The obtained values of ΔH_dc, ε₀, ΔH_ac and f_m0 were compared with those of the glasses of three different types (alkali oxide glasses, transition metal-containing oxide glasses and chalcogenide glasses). And it was found that those values of bismuth borate glasses were agreed very well with those of the alkali oxide glasses. As described in 3), the conductivity decreased as the pressure increased. The investigations on the pressure dependence of conduction show that the conductivity of alkali oxide glasses decreases by applying pressure, while that of electronic conducting glasses increases. From the facts described above, we concluded that the conduction mechanism of bismuth borate glasses is ionic. From the composition dependence of conductivity and the calculated values of carrier concentration from Δε, the conduction mechanism was ascribed to Bi³⁺ ion migration and not to proton or a trace of alkali ion migration.
On the basis of the experimental results on dielectric properties the following problems were discussed, 1) polarization mechanism, 2) electronic polarizability of Bi³⁺ ion and 3) the temperature dependence of dielectric constant.