Electrical anisotropy of dielectric and DC/AC conduct ing properties of single crystals of barium bismuth titanate (BaBi4Ti4O15), which is a member of bismuth layer-structured ferroelectrics, has been studied and compared with those of polycrystalline samples. It was found that BaBi4Ti4O15, when measured at 1MHz, showed about 6 times and 58 times higher dielectric permittivity in the direction parallel to bismuth layer (crystallographic a (b)-axis) than those in the perpen dicular direction (c-axis) at room temperature and the Curie temperature, respectively. DC/AC conductivity showed a higher value in the direction parallel to the bismuth layer than those in the perpendicular direc tion. On the other hand, the activation energy for elec tric conduction in the direction parallel to the bismuth layer showed a lower value. Polycrystalline samples had intermediate properties of those of the two direc tions in single crystals. Complex impedance measure ments also showed anisotropy in the dielectric and the DC conducting properties even for paraelectric phase. Thus, the bismuth layer was thought to act as an in sulating and paraelectric layer in BaBi4Ti4O15.

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Photoluminescence and photocurrent characteristics of Eu 2+ activated MAl 2 O 4 (M = Ba, Ca, Sr) phosphors during and after Ultraviolet ray and visible light irradiation have been investigated. The photoluminescence (PL) and the photocurrent (PC) of the phosphors, in order to elucidate the relationship between the PL and the PC, were measured simultaneously on the same samples within a specially designed measuring box. Composition effects, such as a presence of Dy 3+ as a co-activator and Al-rich composition on the PL and PC characteristics have been investigated. Also, sensing characteristics on UV and visual light have been tested.The simultaneous measurement of PL and PC on the same sample clearly indicated that the presence of co-activator and vacant site, namely Al-rich composition, acted as a hole trap; the introduction of co-activator and vacant site decreased the PC and increased the PL during and after UV and visible light irradiation, whose PC was much lower than that of MAl 2 O 4 with only Eu 2+ as an activator. The electrical intensity affected on the PL characteristics after UV and visual light irradiation(afterglow); with increasing in the electrical intensity, the afterglow lasted more longer and intensively. The PC of MAl 2 O 4 showed a good proportional relationship to UV and visible light intensity. Especially, SrAl 2 O 4 showed an excellent linearity within 1-5 mW/cm 2 , but showed somewhat delayed response and hysterisis as seen in CdS photoelectric cell.

In this study, we have investigated the effects of Mn and Co co-doping on defects, J-E curves and grain boundary characteristics of ZnO-Bi2O3 (ZB) varistor. Admittance spectra and dielectric functions show two bulk defects of   •• (0.17∼0.18 eV) and   • (0.30∼0.33 eV). From J-E characteristics the nonlinear coefficient (α) and resistivity (ρgb) of pre-breakdown region decreased as 30 to 24 and 5.1 to 0.08 GΩcm with sintering temperature, respectively. The double Schottky barrier of grain boundaries in ZB(MCo) (ZnO-Bi2O3-Mn3O4-Co3O4) could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.64 eV at lower temperature to 1.06 eV at higher temperature. It was revealed that a co-doping of Mn and Co in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against an ambient temperature (α-factor= 0.136).