Natsuko Noda

Electrokinetic Study of Migration of Anions, Cations, and Water in Water-Saturated Compacted Sodium Montmorillonite

Electromigration studies of 36Cl− ions and 22Na+ ions, and electro-osmosis of water traced with HTO and H2 18O were conducted with water-saturated compacted sodium montmorillonite having dry densities from 0.8 to 1.6 Mg/m3. The mobilities and dispersivities for each species were obtained from the apparent electromigration velocities and hydrodynamic dispersion coefficients, respectively. When corrected by water flow, the apparent diffusion coefficients of Cl− ions obtained from the Einstein relation are in good agreement with the coefficients obtained from an earlier conventional diffusion experiment in the high dry densities (above 1.3 Mg/m3,). This result suggests that the migration pathways of Cl− ions are nearly identical to those of water above 1.3 Mg/m3. The former diffusion coefficient is smaller than the latter in the low dry densities (below 1.3 Mg/m3), suggesting that Cl− ions migrate in the region distant from the montmorillonite sheets. In contrast, for Na+ ions, the obtained Da values without water flow correction are in good agreement with conventional values at all dry densities. This suggests that Na+ ions migrate mainly in the interlayer and the vicinity of montmorillonite sheets. The dispersivities increase with increasing dry densities for all species. This corresponds to a geometrical complexity that increases with increasing dry density.

Broadband characterization of high-dielectric constant films for power-ground decoupling

We evaluated the broadband dielectric permittivity and impedance characteristics of high dielectric constant films for decoupling capacitance applications at frequencies of 100 to 10 GHz. In order to extend the measurements to the microwave range, we developed an appropriate expression for the input admittance of a thin-film capacitance terminating a coaxial line. The theoretical model treats the capacitance as a distributed network and correlates the network scattering parameter with complex permittivity of the specimen. The method eliminates the systematic uncertainties of the lumped element approximations and is suitable for high-frequency characterization of low-impedance substrates.

Broadband dielectric metrology for polymer composite films

We evaluated the dielectric permittivity and relaxation in polymer composite films filled with ferroelectric ceramics. Such materials are currently being developed for power-ground decoupling in electronic circuits operating at microwave frequencies. In order to extend the measurements to the microwave range, we developed an appropriate expression for the input admittance of a thin film capacitance terminating a coaxial line. The theoretical model treats the capacitance as a distributed network and correlates the network scattering parameter with complex permittivity of the specimen. The method eliminates the systematic uncertainties of the lumped element approximations and is suitable for high frequency characterization of low impedance substrates with high value of the dielectric constant. The complex permittivity was measured at frequencies of 100 Hz to 10 GHz for films 100 /spl mu/m thick, having the dielectric constant of 4 to 40, and was fitted to a dielectric model expressed as a combination of Havriliak-Negami functions. An intrinsic high frequency relaxation process has been identified. It was found that the position of the loss peak depends on the relaxation of polymer matrix, while its magnitude is amplified by the permittivity of the ferroelectric component.

A calorimetric study of the (rochelle salt)1−x - (ammonium rochelle salt)x mixed crystal system

Abstract The specific heat of the (Rochelle salt)1−x - (ammonium Rochelle salt)x mixed crystal system has been measured in the region III (0.18⩽x≲0.90) with an ac calorimetric technique. A very small anomaly has been observed around the transition temperature. It has been found that the transition entropy, roughly estimated from the anomalous specific heat, depends on x.

A calorimetric study of RS1-xARSx mixed crystal system (0.9 ≲ x < 1.0)

The specific heat in the region IV (0.9 ≲ x < 1.0) of RS1-x-ARSx mixed crystal system has been measured between 80 K and 290 K by AC method. The anomaly of the specific heat has a large peak; its apparent height increases with x. Thermal hysteresis between 0.5 K and 1.0 K for the anomalies were observed. This indicates that the phase transition seems to be of the first order. In many cases, the specific heat anomaly with two peaks was observed in the whole range of the region IV. The cause of this phenomenon also is discussed using the results of dielectric measurements.

Characteristic feature of the ferroelectric phase transition in Rochelle salt

Abstract Structural characteristics of the ferroelectric phase transition in Roshelle salt (RS) are presented together with those of the mixed crystals of RS and ammonium Rochelle salt (ARS). Also the specific heat anomaly due to the phase transition in the mixed crystal system is reviewed. Discussions are made on the mechanism of the ferroelectric phase transition of RS, and on the characteristic feature viewed as the terminal substance of the RS1−xARSx, where the behaviour of RS (x=0) is given as the extrapolated behaviour of the mixed crystals having finite x values.

Phase transition and excess specific heat in RS-ARS mixed crystals

Abstract The specific heat of Rochelle salt–ammonium Rochelle salt (RS1−x–ARSx) mixed crystals for 0.18⩽x⩽0.9 (region III) exhibits a finite jump at the transition to the ferroelectric phase. Any critical behaviour like diverging is not observed. We consider the behaviour of the specific heat around the transition on the basis of Landau theory taking account of fluctuation effects. We also give a consideration from a structural point of view.