Crystal Growth and Dielectric Properties of New Ferroelectric Barium Titanate: BaTi2O5

Single crystals of the ferroelectric BaTi₂O₅ and BaTiO₃ were prepared from a solution of 33-mol% BaO and 67-mol% TiO₂ by a rapid cooling method. The dielectric constant () and dielectric loss tangent (tan) were measured in a wide temperature range of 10–860 K and in a frequency range of 0.1–3,000 kHz. The along the b-axis of the BaTi₂O₅ crystal, prepared in air, shows a sharp dielectric anomaly reaching 30,000 at the ferroelectric Curie temperature of T_C = 752 K. By contrast, the crystal prepared in a reducing atmosphere shows a diffuse phase transition near T_C = 703 K. The values of and tan are compared between these three crystals consisting of two kinds of BaTi₂O₅ and one BaTiO₃.     

Preparation and ferroelectric properties of MnO2 doped BaTi2O5 ceramics by spark plasma sintering from the solid-state-calcined powder

Dense BaTi₂O₅ are fabricated from the conventional calcined powder by using spark plasma sintering and by adding MnO₂ as a dopant. The effects of the sintering temperature and the amount of MnO₂ on the phase purity are symmetrically investigated. A pure BaTi₂O₅ phase is obtained under a condition with the sintering temperature of 1,055 °C and the amount of MnO₂ doping of 0.2 wt% from the conventional powder calcined at 950 °C. The relative density of that ceramics is 98 %. The temperature dependence of dielectric property shows the Curie temperature (T _c) of 446 °C with the peak value of 450. Besides, the ceramics polarization of 0.63 μC/cm² and the coercive field of 2.0 kV/cm at room temperature, respectively.     

Isolation and characterization of a lipid-degrading bacterium and its application to lipid-containing wastewater treatment

To construct an efficient lipid-containing wastewater treatment system, microorganisms that degrade lipids efficiently were isolated from various environmental sources. Strain DW2-1 showed the highest rate of degradation of 1% (w/v) salad oil among the isolated strains. Strain DW2-1 was identified as Burkholderia sp. and designated Burkholderia sp. DW2-1. The rate of degradation of salad oil, olive oil, sesame oil, and beef tallow by strain DW2-1 were 96.7%, 92.3%, 90.1% and 77.4%, respectively, during a 48-h cultivation. Strain DW2-1 grew well in a synthetic wastewater medium (>1 x 10(10) colony forming unit [CFU]/ml) between 20 degrees C and 38 degrees C, and its rate of degradation of salad oil was above 90% after a 48-h cultivation. The lipase and biosurfactant (BSF) activities of strain DW2-1 after a 48-h cultivation were 1720 U/l and 480 U/ml, respectively. In continuous cultures for lipid-containing wastewater treatment, DW2-1 was stably maintained and degraded more than 90% of salad oil during a 7-d cultivation.     

Effect of spark plasma sintering temperature on the phase equilibria and dielectric properties of BaTi2O5 ceramics

The effect of sintering temperature (ranging from 1055 to 1200 °C) on the phase ingredient and dielectric property of the nominal BaTi₂O₅ ceramics (starting with the Ba/Ti of 1:2) fabricated by a spark plasma sintering method were systematically studied. At the first stage, BaTi₂O₅ component was enhanced in the sintering temperature range of 1055–1120 °C; it turned out to be the dominant phase. For these BaTi₂O₅ phase dominated ceramics, the Curie temperature T _c rised on increasing the sintering temperature and saturated around 440 °C with the maximum dielectric constant of 500. Further increasing the sintering temperature, the decomposition of the obtained BaTi₂O₅ into BaTiO₃ extensively happened; the ceramics turned to be the BaTi₂O₅ and BaTiO₃ coexisting state. These ceramics can be characterized by two dielectric anomalies. One at ~420 °C stood for the phase transition of BaTi₂O₅ while the other at ~150 °C stood for the transition of BaTiO₃, which is exceptionally high as the normal BaTiO₃ ceramics. Further increasing the sintering temperature (until 1200 °C) would dramatically enhance the BaTiO₃ phase; the ceramics showed T _c at 130 °C with the maximum dielectric constant of 1800.     

Raman scattering study on ferroelectric (Ba0.32Sr0.68)2Nb2O7 ceramics

Raman scattering technique was applied to examine the Ba-doping effect to the two low temperature phase transitions of Sr₂Nb₂O₇ (SN) in the temperature range from −190 to 600 °C. The line shape of Raman spectra can be well fitted by multidamped harmonic oscillator model. We did not observe any soft mode related to the two low temperature phase transitions corresponding to those of the pure SN. It is correlated to the disappearance of the incommensurate phase in (Ba_0.32Sr_0.68)₂Nb₂O₇ ceramics. However, the temperature dependence behavior of the three low frequency modes indicates another new structural phase transition around 270 °C. It is considered that the reduction of the interlayer interaction caused by partial replacement of Sr-site by Ba-site, whose ionic radius is larger than that of Sr, may be the reason for the disappearance of the incommensurate phase transition in (Ba_0.32Sr_0.68)₂Nb₂O₇ ceramics.     

Dielectric properties and heating effect of multiferroic BiFeO3 suspension

Bismuth ferrite (BiFeO₃) ceramic particles of micro-meter size were prepared by a solid-state route. This study revealed an appropriate method to measure the dielectric properties of BiFeO₃ particle suspension using a system designed by ourselves. The heating effect of the BiFeO₃ suspension with applied AC voltage was confirmed. Application of this material in hyperthermia treatment of biological tissues with the goal of tumor therapy may be possible.     

BiFeO3 ceramics synthesized by spark plasma sintering

Phase-pure BiFeO₃ particles were synthesized by an improved solid state technique. High density BiFeO₃ ceramics were prepared using these particles by spark plasma sintering (SPS). The dielectric permittivity and loss of SPS samples were measured as functions of sintering temperature, frequency, and annealing conditions. Dielectric spectra of the ceramics annealed at 650 °C were characterized in a broad range of temperature (300–725 K) and frequency (100 Hz to 20 MHz). Two kinds of dielectric relaxation following the Arrhenius law were detected in low and high temperature ranges, respectively. The low temperature dielectric relaxation could be almost completely removed by annealing in vacuum and it should be assigned to be a valence fluctuation of Fe ions, while the high temperature dielectric relaxation was proposed to stem from the short-range motion of oxygen vacancies.