Field-Induced Strain in Single-Crystal BaTiO3

The electric-field-induced strain in single-crystal BaTiO₃ was investigated. For crystals relatively free of twinning, a longitudinal strain of 0.35% can be induced just above the ferroelectric-paraelectric phase transition temperature (T_c1) primarily by field-forced paraelectric-ferroelectric phase transition. For heavily twinned crystals, 90° domain reorientation under the applied electric field plays an important role in the induced strain below T_c1, and an induced strain of 0.6% is observed a few degrees below T_c1. Above T_c1, the electrostrictive property measured by a weak excitation field is purely intrinsic. When the excitation field is large, so that a field-forced paraelectric-ferroelectric phase transition is involved, the x₃₃/P²₃ value (where x₃₃ and P₃ are the induced strain and polarization along the z axis, respectively) is intrinsic at higher temperature, but may be modified at temperatures just at and slightly above T_c1 by residual 90° twin structure.     

A safer and more effective treatment regimen for eclampsia

The purpose of our investigation was twofold: to provide normative data for the ratios between head circumference and cerebellum, abdominal circumference and cerebellum, and femur length and cerebellum; and to evaluate the predictive accuracy of an abnormal ratio in the detection of growth retardation and macrosomia. Data on 675 women with normal gestations between 14 and 42 weeks were used to estimate reference curves for the three ratios to be evaluated. We then compared the ratios of 34 fetuses with intrauterine growth retardation and 28 macrosomic fetuses to the control group. Of the three ratios that we investigated, abdominal circumference to transverse cerebellar diameter was the most efficacious. However, the sensitivity of this ratio for the detection of intrauterine growth retardation and macrosomia was only 52.9% and 46.6%, respectively. A ratio between head circumference, abdominal circumference, or femur length and the transverse cerebellar diameter cannot reliably distinguish between normally growing fetuses and those that are growth retarded or macrosomic.     

Study of the biodegradation behavior of soy protein‐grafted polyethylene by the soil burial method

In this article, we report on the biodegradation of soy‐protein‐grafted polyethylene, which was successfully synthesized by a graft copolymerization method with benzoyl peroxide as the radical initiator. The biodegradation behavior of the grafted polyethylene was ascertained by a soil burial test. The weight‐loss percentage was measured as a function of the number of days, and it was observed that the percentage weight loss increased with increasing number of days. To further substantiate the degradation, microanalysis of the soil containing the samples was carried out. An increase in microorganism colonies was observed with increasing number of days. The hydrolysis of the samples taken from the soil after a specified number of days also corroborated the findings and revealed a continuous loss of weight. The effect of the degradation of the grafted samples on the growth of plants (wheat and soybean) was studied, and we observed that the products of degradation were not harmful to the growth of the plants. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Growth and dielectric properties of Ta_2O_5 single crystals grown by laser heated pedestal growth technique

Ta2O5 single crystals have been grown by the laser heated pedestal growth (LHPG) technique up to several centimeters length with diameter of 1.1 mm. The crystal, characterized by X-ray diffraction, dielectric measurement, and thermal expansion analysis, has Htri-Ta2O5 symmetry. Dielectric permittivity, loss tangent along [001] and [110] direction were investigated over the temperature range from -80 ℃ to 100 ℃. Large dielectric anisotropy in Ta2O5 single crystal was observed. At room temperature, the dielectric permittivities (1 MHz) along [001] and [110] are 33.2 and 231.9, respectively. The reason of dielectric enhancement in Ta2O5 crystal grown by LHPG was also discussed.     

Sol–Gel Synthesis of Strontium Pyroniobate and Calcium Pyroniobate

Strontium and calcium pyroniobates were prepared by a sol–gel process, using strontium/calcium metal and niobium ethoxide as precursors. The formation of Sr₂Nb₂O₇ occurred at 750°C via an intermediate perovskite phase of composition close to Sr_0.82NbO₃. The crystallization of Ca₂Nb₂O₇ occurred at 600°C directly without any intermediate phases. Sintered Sr₂Nb₂O₇ and Ca₂Nb₂O₇ pellets showed a preferred grain orientation. Microstructural studies revealed an increase in grain growth and associated orientation with sintering temperature.     

Dielectric properties of densified hardened cementitious materials

Relative permittivity (K′) and loss factor (tan D) of densified hardened cementitious materials with w/c=0.20 and heat treated to 500°C prepared with type I, type III, and a special microfine high silica content (MC500) cement have been compared as a function of temperature and frequency. These K′ and tan D values were found to be considerably lower for materials with microfine silicate cement than those with portland cements.

Activation energies (Q) and relaxation times for the loss mechanism values were related to an ionic jump relaxation process. Lower K′ and tan D values have been measured for cement/polymer composites prepared with a methyl cellulose polymer and a lower w/c ratio of 0.17. The relative permittivity and loss factor of materials with a 60 vol. % of silica microspheres prepared with the silicate cement ranged from 5.4 to 5.1 and from 0.035 to 0.012 respectively.     

Electrostrictive and Dielectric Response in Lead Magnesium Niobate–Lead Titanate (0.9PMN · 0.1PT) and Lead Lanthanum Zirconate Titanate (PLZT 9.5/65/35) under Variation of Temperature and Electric Field

In situ measurements of electrostrictive strain and effective dielectric constant for two ferroelectric relaxor materials, lead magnesium niobate–lead titanate (0.9PMN · 0.1PT) and lead lanthanum zirconate titanate (PLZT 9.5/65/35), were performed in the temperature ranges near their respective mean Curie points under the variation of applied electric field. The measurement results show that the polarization-related electrostrictive coefficients Q_ij are not constant under variation of temperature and electric field. The observed anomaly in Q_ij indicates the dynamic behavior of the existing micropolar domains and its coupling to local defect structure. The data also support the idea that at temperatures far above the mean Curie point, there is still a substantial amount of micropolar domain and the response of the relaxor materials at the experimental temperature range is from the combined contributions due to induced polarization and micropolar domain flipping.