The Effect of Oxygen Vacancies on the Dielectric Responses of BaTiO3 Based Ceramics in the Ultra-Wide Frequency Range

The effect of oxygen vacancies and their migrations on the dielectric responses of BaTiO3 (BT) ceramics and (Ba, Ca)(Ti, Zr)O3 (BCTZ) ceramics was studied using wideband dielectric spectroscopy. Both dipole and ionic polarization of BT ceramics after annealing in a reducing atmosphere markedly decreased. To elucidate the decrease of dipole and ionic polarization, we observed the domain width and the crystal structure of BT ceramics annealed in different PO2. The mass fractions of constituted phases in 90o domain were calculated using the refinement of XRD patterns to explain the degradation of ionic polarization by oxygen vacancies. From the results above, we judged that the decrease of dipole polarization was due to the domain wall clamping by oxygen vacancies, while that of ionic polarization was attributable to the lattice hardening by the incorporation of oxygen vacancies into the BT lattice. In the case of BCTZ ceramics, dipole polarization showed the same way as BT ceramics with annealing conditions but the ionic polarization was independent of PO2 in annealing because of anti-reducing behavior of BCTZ ceramics. On the basis of the effect of oxygen vacancy in BT ceramics and BCTZ ceramics, we could clarify the oxygen vacancy migration in BCTZ ceramics under high direct-current voltage (DCV).

Rational Design of Organic Electro-Optic Materials

ABSTRACTA number of material properties must be optimized before organic electro-optic materials can be used for practical device applications. These include electro-optic activity, optical transparency, and stability including both thermal and photochemical stability. Exploiting an improved understanding of the structure/function relationships, we have recently prepared materials exhibiting electro-optic coefficients of greater than 50 pm/V and optical loss values of less than 0.7 dB/cm at the telecommunication wavelengths of 1.3 and 1.55 microns. When oxygen is excluded to a reasonable extent, long-term photostability to optical power levels of 20 mW has been observed. Photostability is further improved by addition of scavengers and by lattice hardening. Long-term (greater than 1000 hours) thermal stability of poling-induced electro-optic activity is also observed at elevated temperatures (greater than 80°C) when appropriate lattice hardening is used. The successful improvement of organic electro-optic materials rests upon (1) attention to the design of chromophore structure including design to inhibit unwanted intermolecular electrostatic interactions and to improve chromophore instability and (2) attention to processing conditions including those involved in spin casting, electric field poling, and lattice hardening. A particularly attractive new direction has been the exploitation of dendrimer structures and particularly of multi-chromophore containing dendrimer structures. This approach has permitted the simultaneous improvement of all material properties. Development of new materials has facilitated the fabrication of a number of prototype devices and most recently has permitted investigation of the incorporation of electro-optic materials into photonic bandgap and microresonator structures. The latter are relevant to active wavelength division multiplexing (WDM). Significant quality factors (greater than 10,000) have been realized for such devices permitting wavelength discrimination at telecommunication wavelengths of 0.01 nm.