Polarization Relaxation Time Research Articles

Anisotropic Polarization Relaxation Time Observed by Light Scattering in KD2PO4

Light scattering spectra in KD 2 PO 4 were observed just above the transition temperature with the HH-scattering geometry and the right angle scattering in the a b -scattering plane. The linewidth of the broad central component depends upon the direction of the scattering wave vector q and decreases as \(\hat{\textbf{\itshape q}}\) approaches [100] or [010]. This \(\hat{\textbf{\itshape q}}\) dependence is shown to be the frst observation of the \(\hat{\textbf{\itshape q}}\) dependent polarization relaxation time due to the piezoelectric coupling to acoustic waves.

Brillouin Scattering Studies of the Polarization Relaxation Time in Rubidium Hydrogen Sulfate

The Brillouin spectra associated with the pure longitudinal acoustic mode (elastic stiffness c 22 E ) of rubidium hydrogen sulfate RbHSO 4 have been studied in the temperature range between -40° and +20°C. The frequency shift and the full width at half maximum of Brillouin satellites show the anomalous behavior near the transition temperature ( T c =- 8.76^° C ) and below. From the anomalous parts of them, the temperature dependence of the polarization relaxation time is evaluated within a phenomenological framework and is determined as (1.9 ±0.3) ×10 -11 /( T c - T ) sec in the ferroelectric phase.

Measurements of T2 in excited vibrational states of HCN

Polarization relaxation times (T2) have been measured for the J=6, 9, and 10 l-doublet transitions in the (0110) vibrational level of HCN by means of microwave transient emission. Also, T2 values for relaxation induced by He, H2, and CH3F are obtained for the J=6 transition. The dephasing cross sections for foreign gas collisions are consistent with the force laws operative in each case. The HCN–H2 result provides a comparison with the recently measured cross section of the isoelectronic molecular ion system, HCO+–H2, and confirms the prediction of Green that rotational relaxation rates are only moderately faster for molecular ions.

Dielectric and NMR studies of the molecular movements in comb-like polyfluoro-alkyl acrylates and polyfluoro-alkyl methacrylates

The characteristics of the molecular movements have been studied in a series of polyacrylate and polymethacrylate homologues containing fluoro-alkyl fragments in the branches. The ability of the secondary groups to arrange themselves in an orderly fashion and to crystallize has been shown to apply to the lower homologues; the transition to the highly-elastic state and the melting have shifted into higher temperature ranges when compared with those of the polyalkyl acrylates (PAA) and polyalkyl methacrylates (PAMA). Relaxation processes due to the mobilities of the ester and the polar end groups in the branches, the α-methyl groups, and also the fluoromethylene fragments, have been detected at low temperatures. The comb-like homologues in the series with differing compositions have been found to have dipolar polarization relaxation times of the ester groups at low temperatures which depend to a large extent on the interactions and the arrangement of the side chains.

PYROELECTRIC PROPERTIES OF CHIRAL SMECTIC PHASES

The temperature dependences of the pyroelectric coefficient y(T) of ferroelectric liquid crystalline L-p-decyloxyand L-p-nonyloxybenzylidene-p'-amino-2-methylbutylcinnamate and their mixture were calculated from the measurements of their responses to heat pulses with durations of 2 x and 3 x lo-' s. The frequency dispersion of y and the spontaneous polarization P, was discovered which is consistent with the corresponding dispersion of dielectric permittivity over a frequency range lo4-2 x 10' Hz. The direct measurements of the relaxation time for spontaneous polarization (2) were performed and sharp increase in z near the SmC-SmA phase transition was observed. The effect of dipolar admixtures on ymax and Py was also discussed.

Interaction of papain with derivatives of phenylalanylglycinal: fluorescence studies.

Fluorescence studies have been performed on the interaction of papain with active-site-directed inhibitors of the type mansyl-(Gly)n-Phe-glycinal, where n = 0, 1, 2. It has been found that whereas the mansyl [6-(N-methylantilino)-2-naphthalene sulfonyl] fluorescence of mansyl-Phe-glycinal is greatly enhanced, that of the two longer mansyl compounds is not, although all three are equally effective as inhibitors of papain action. Measurements of fluorescence polarization and rotational relaxation time support the conclusion that the fluorescent probe group of the two longer mansyl compounds protrudes into the solvent to a greater degree than that of mansyl-Phe-glycinal. Considerable energy transfer from papain tryptophan to the mansyl group is evident for all three inhibitors, however, although it is most marked with mansyl-Phe-glycinal. Stopped-flow fluorescence measurements have shown that, after initial rapid interaction, the first-order conformational changes in the active-site region of papain in the complex with mansyl-Phe-glycinal are approximately 1/10(4) those observed with comparable mansyl oligopeptide substrates, and approximately 1/10(2) those with acetyl-Phe-glycinal.

Effect of relaxation processes on the coherent interaction between radiation and a two-level medium

Numerical integration of a system of equations describing the coherent interaction between radiation and a two-level medium (e.g., a semiconductor) is employed to analyze the effect of relaxation processes on the energy characteristics and dynamics of radiation pulses of duration τpΣ T '2 (T '2 is the irreversible polarization relaxation time). It is shown that the interaction of these pulses with the medium is strongly dependent on their area on entry to the medium and the attenuation of the pulses as a result of relaxation processes decreases with increasing pulse input power. This may be utilized for probing the medium in the resonant absorption range for short polarization relaxation times, in solution 42.65.Gv.

Brillouin Scattering Studies of the Uniaxial Ferroelectric Phase Transition in TGS and TGSe

The Brillouin spectra of the ferroelectric triglycine sulfate (TGS) and its isomorphous selenate (TGSe) crystals have been observed in three cases of orientations of the longitudinal or quasi-longitudinal phonon vector q ; (1) q // c -axis, (2) q // b -axis and (3) q deviates 5° from b -axis in the (100) plane. The temperature dependence of both the frequency shift and the spectral width shows a remarkable anisotropy near T c . In the case (1) the temperature at which the width becomes maximum shifts to the lower temperature than T c which has simultaneously been determined by an accompanied measurement of dielectric constant. The polarization relaxation time is determined from this temperature shift using the phenomenological relation. In the case (2) and the case (3), the decrease in the anomaly is explained as the depolarization field effect of the long range dipole-dipole interaction which is characteristic in the ferroelectric phase transition.

Dynamic polarization of protons in 1, 2-cyclohexanediol: A target material solid at room temperature

An investigation was made of the polarization behaviour of the Cr(V) complex with 1,2-cyclohexanediol. Dynamic proton polarization and spin-lattice relaxation times were measured at magnetic fields of 8.5 kG and temperatures 4.2 K and 1.4 K. High enhancement factors were obtained, which may in some cases surpass the enhancement factors attained in 1,2-ethanediol. On the basis of the experimental proton relaxation rates an estimate is made as regards the applicability of this diol as a material for frozen spin polarized proton target.

Dielectric properties of KDP at the critical point

Bias effects on the first-order transition in KDP have been studied dielectrically. The bridge method for dielectric constant showed unexpectedly a reduction of the value under bias field. Polarization responses to stepwise changes of the external field E ⇄ E + ΔE were measured, and the static dielectric constant showed a dominant increase at Ecr and Tcr. This was considered to be the critical state. The direct method gave also the relaxation time of polarization. It showed a peak of several tens sec at the critical point. This large relaxation time explained the substantial difference between 1 kHz dielectric constant and static dielectric constant.

Electrical Conductivity of KH2AsO4and KD2AsO4

Measurements of the electrical conductivity of K${\mathrm{H}}_{2}$As${\mathrm{O}}_{4}$ and its deuterated isomorph have been performed from room temperatures to the temperature of their respective ferroelectric transitions. Activation energies of 0.66 and 0.64 eV have been found to characterize the temperature dependence of the conductivity for K${\mathrm{H}}_{2}$As${\mathrm{O}}_{4}$ and K${\mathrm{D}}_{2}$As${\mathrm{O}}_{4}$, respectively. Further evidence that these materials display anomalously long polarization relaxation times near the temperature of their ferroelectric transition is presented and discussed. The nature of this behavior remains unexplained.

Ultrasonic Velocity and Attenuation in Ammonium Dihydrogen Phosphate

The velocity and attenuation of ultrasonic shear waves have been investigated as a function of temperature in single-crystal ammonium dihydrogen phosphate (ADP). Particular emphasis was placed in the region near the antiferroelectric critical temperature. As the antiferroelectric transition is approached from high temperature, the dielectric polarization relaxes from the paraelectric to the antiferroelectric configuration. This relaxation process causes the shear velocity and attenuation to shift anomalously. This change in velocity can be described in terms of an elastic Curie-Weiss law with a negative absolute critical point. For the first time the ultrasonic attenuation measured near an antiferroelectric transition will be reported. The anomalous attenuation shift is used to calculate the polarization relaxation time associated with the transition and the relaxation time will be compared to existing microwave and Raman spectrum experiments.

Passage of an ultrashort coherent light pulse through a semiconductor

A theory is given of the resonant interaction between an ultrashort coherent light pulse and a semiconductor, which occurs when the pulse duration is less than the polarization or phase memory relaxation time. It is shown that, under certain conditions, a stationary 2? pulse can form. Numerical estimates of the velocity of propagation of a stable pulse are obtained for a typical semiconductor.

Ultrasonic Investigation of the Ferroelectric Transition Region in KH2PO4

The velocity and attenuation of 15-MHz ultrasonic shear waves have been investigated as a function of the temperature and the electric field applied along the polar axis of potassium dihydrogen phosphate single crystals. These data are analyzed to give the free dielectric susceptibility ${\ensuremath{\chi}}^{X}$ and the constant-stress polarization relaxation time ${\ensuremath{\tau}}_{X}$. The ${\ensuremath{\chi}}^{X}$ values are in fairly good agreement both above and below ${T}_{c}$ with the predictions of the Silsbee-Uehling-Schmidt model. However, the ${\ensuremath{\tau}}_{X}$ values show a temperature dependence which cannot be readily interpreted in terms of the Silsbee-Uehling-Schmidt model. Comparison with comparable data for K${\mathrm{D}}_{2}$P${\mathrm{O}}_{4}$ strongly suggests that proton tunneling plays an important role in K${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$.

Anomalous propagation of longitudinal ultrasonic waves in KD 2PO 4

The temperature dependence of the Young modulus C 33 E and of the polarization relaxation time in KD 2PO 4 are determined below the transition temperature. The results are compared with the corresponding data in KH 2PO 4, obtained by similar measurements. The striking difference between the “Curie constants” associated with the relaxation time is confirmed.

Sound propagation in the polar phase of KH2 PO4

Abstract The propagation of longitudinal ultrasonic waves along the ferroelectric c axis has been investigated in the close vicinity of the transition temperature of KH 2 PO 4 . Data on the elastic anomaly and the polarization relaxation time are obtained and analyzed.

On the magnetic moment of the isotope 12B

Measurements of relaxation times of the nuclear polarization of the isotope 12B have been performed in several host metals. The nuclear magnetic moment as determined by the resonant NMR frequencies is corrected by assuming the validity of the Korringa relation for the Knight shift.

Dielectric Properties of Water Adsorbed on Silica Gel and Alumina Gel

Observations were made of the dielectric properties of water film adsorbed on silica and alumina gels to investigate the structural conditions of adsorbed water films which may cause non-Newtonian behaviour and thixotropic characteristics in these dispersions.The following results have been obtainedWhen the amount of water in the adsorbed film was increased:(1) Contribution to the dielectric polarization of dissolved and adsorbed ions in the moisture film decreased(2) The relaxation time of interfacial polarization due to the adsorbed ions decreased(3) The width of the distribution of relaxation time became a little narrower. When the compression was applied to the gels:(4) The interfacial polarization due to the adsorbed ions in the adsorbed moisture layer increased.(5) The relaxation time decreased to a small extent(6) Little variation of width has been detected in the distribution of relaxation time.From these results investigated, it can be concluded that the water molecules in the adsorbed water layers have different properties from those of free water molecules. The adsorption forces on the surface of gel powder decrease with the distance from the powder surface. When the electrical field is applied, the adsorbed ions have a tendency to move through the outer layers where the adsorption forces are small.

Analysis and performance of a light-sensitive capacitor

A comprehensive study has been made of a duo-dielectric capacitor in which one of the dielectrics is photoconducting and the other inert. Under dark conditions, device capacitance per unit area is set by the respective dielectric coefficients, conductivities, and thicknesses. Illumination causes device capacitance to change, and decreases the interfacial polarization relaxation time. Analysis reveals the means to optimize device performance, and the existence of a light-dark capacitance ratio-cutoff frequency limitation. A fabricated unit, utilizing CdS with BaTiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , exhibited a capacitance change of 2500 times and a frequency span extending to 0.22 Mc/s. A CdS:silicone plastic unit showed a maximum capacitance change of 20 times and a frequency span of ∼10 Mc/s, but had degraded dark performance attributed to electron traps, and an interesting piezo-electric resonance that affected both capacitance and dissipation factor at 0.315 Mc/s. Applications of this type of a light-sensitive capacitor are limited to specialized situations where a maximizing dissipation factor and a varying frequency bandwidth can be tolerated.

The electric polarization of rod-like, charged macromolecules

The polarizability in the longitudinal direction of rod-like, highly charged macromolecules has been evaluated. A simple model, emphasizing the discrete distribution of the fixed charges along the macromolecule, but neglecting interionic repulsion, has been used to calculate the statistical distribution of the counterions which gives rise to this polarization. For weak electric fields the expression obtained for the polarizability is analogous to that previously derived by Schwarz, although it contains less implicit information about the temperature dependence and the influence of the valency of the counterions. The possibility that saturation effects may appear with high electric fields is left open. An approximate formula for the relaxation time of the longitudinal polarization is also derived.