Hiroshi Ikushima

Electrical Properties of Ag-Doped Barium Titanate Ceramics

Temperature dependence of electrical conductivity, thermoelectric motive force and Hall effect, electron spin resonance, X-ray analyses, voltage-current characteristics and voltage dependence of capacitance of the Ag-doped BaTiO3 ceramics were studied. The semiconducting specimens were obtained by firing the ceramic in nitrogen atmosphere. Charge carriers in the specimens are electrons in view of the sign of Hall electric and thermoelectric motive force. The electron spin resonance spectra of oxygen vacancy with electron capture were observed at solid nitrogen temperature. The g-values of the spectra were 1.946±0.001, 1.932±0.0005 and 1.922±0.003. It is suggested that the anomalous temperature dependence of resistivity is due to the decrease of carrier mobility. A tentative model is proposed also for rectification and capacitance action.

Electron Spin Resonance of Mn2+ in BaTiO3 Single Crystal

The paramagnetic resonance of Mn 2+ in BaTiO 3 single crystals has been studied. The bivalent manganese ion seems to be located at the barium site in the unit cell. The “forbidden” transition lines in the hyperfine spectrum were most clearly observed in the tetragonal phase, while in the cubic phase the intensities of the forbidden lines were very small compared to those of the allowed lines. The value of the cubic field splitting parameter a in the tetragonal phase was somewhat larger than that in the cubic phase. In the tetragonal phase, the value of E has been verified to be vanishingly small in contrast to the large value of D . The hyperfine constant is anisotropic. Theoretical explanations are tried to the third-order perturbation for the splittings and the intensities of the “forbidden” lines.

Electrical properties of BaPbO3 ceramics

Abstract A new type semiconductor of perovskite structure, BaPbO 3 , was studied. The electrical conduction of BaPbO 3 is metallic and the carrier concentration is ∼ 2 × 10 20 electrons/cm 3 . The type of charge carrier was determined from the sign of the Hall field and thermoelectromotive force. The ESR was observed below solid nitrogen temperature. A broad and asymmetric differential curve appeared clearly at liquid helium temperature. The g -value was 2.057 ± 0.005 and its line width was 141.5 ± 10 G. The electrical properies are compared with those of oxygen-deficient BaTiO 3 semiconductor.

Electrical Conduction in Reduced Single Crystals of Barium Titanate

Temperature dependence of electrical conductivity and Hall effect of the barium-titanate crystals reduced by hydrogen were studied at temperatures -195~165°C. The hydrogen reduction was carried out at above 800°C. The optical absorption in the reduced crystals was observed. Electron spin resonance absorption due to oxygen vacancy with a captured electron was observed in the slightly reduced crystals. Thermal activation energies obtained from temperature dependence of electrical conductivity showed different values in each phase of BaTiO3 crystal. Carrier concentration calculated from Hall coefficient is 1017~1019/cc and Hall mobility ranges from 10-2 to 1 cm2 v-1s-1 at room temperature. A hydrogen-atom-like model is proposed for the captured electron in oxygen vacancy in the reduced barium-titanate crystals. The electrical conduction seems to be reasonably explained by a band model theory.

Electron Spin Resonance of Mn2+ in Reduced BaTiO3 Single Crystals

The interaction between bivalent manganese ion (Mn 2+ ) and oxygen vacancy with a captured electron (F-center) in BaTiO 3 is investigated via electron spin resonance (ESR). The resonance intensity of hyperfine structure (h.f.s.) of Mn 2+ decreases with the degree of reduction. The fine structure is not observed in strongly reduced specimens. The narrowing and broadening of line widths of the h.f.s. in reduced crystals are observed below room temperature and above Curie temperature, respectively. The hyperfine splittings in reduced specimens are slightly less than those in unreduced ones. The changes of ESR spectra in reduced crystals are reasonably explained in terms of the interaction between Mn 2+ and the F-center.

Observation of Chladni Figures in Piezoelectric Ceramic Plates of Rectangular Form

Observation of the Chladni figures was made on a piezoelectric ceramic plate which may be used as a piezoelectric transformer. Many spurious vibration modes were easily excited besides the normal mode. Those spurious modes were found to be the thickness flexure mode. The position where the transformer is to be supported could be determined from the Chladni figures. The resonant frequencies of the spurious mode were in better agreement with the calculated values from the frequency equation of a rectangular beam vibration in the flexure mode rather than with those from Rayleigh-Lamb equation.