Dielectric properties of porous aluminum oxide with inclusions of triglycine sulphate and Rochelle salt

The dielectric properties of composite structures based on porous aluminum with inclusions of triglycine sulphate and Rochelle salt were investigated. The effect of structured and adsorbed water on the dielectric behavior of the nanocomposite under study was found.     

<Superscript>23</Superscript>Na spin-lattice relaxation in powder Rochelle salt

The temperature dependence of ²³Na spin-lattice relaxation in the polycrystalline Rochelle salt was studied by NMR within the range from 235 to 320 K covering both Curie points. The spin-relaxation time t ₁ versus temperature curve showed noticeable dips near the phase transitions against the background of the regular decrease in the relaxation time upon increasing temperature. The dips observed were ascribed to critical contributions to sodium spin-lattice relaxation caused by the slowdown of the correlation time for one of two relaxation modes in the Rochelle salt. The ²³Na NMR parameters were also measured for the melted Rochelle salt. This article was submitted by the authors in English.     

Dielectric studies of nanoporous alumina films filled with the Rochelle salt

Dielectric studies of nanoparticles of the Rochelle salt embedded in pores of porous alumina have been performed in the temperature range from 80 K to the decomposition temperature of the bulk Rochelle salt. It has been revealed that the permittivity exhibits an anomaly corresponding to the lower structural transition to the paraelectric phase, whereas the upper ferroelectric transition is shifted above the decomposition temperature in agreement with the recently published data. The temperature of the lower transition for nanoparticles in pores is found to decrease by 10 K. Possible physical factors that can be responsible for the broadening of the region of existence of the ferroelectric phase have been discussed.     

Dielectric properties of deuterated ammonium Rochelle salt

The dielectric constant of deuterated ammonium Rochelle salt along the three crystallographic axes as well as the pyroelectric charge density developed on the crystal surface perpendicularly to the b-axis have been measured with a high temperature resolution. The para- to ferroelectric transition at T_c = ?159°C shows a thermal hysteresis of ΔT = 0.15°C. This and the discontinuities in the dielectric constant along all three axes show that the phase transition is of the first-order. No phase intermediate between the para- and the ferroelectric phases could be detected.     

Properties of nanoporous aluminum oxide with triglycine sulfate and Rochelle salt inclusions

The possibility of producing the ferroelectric state in nanoporous aluminum oxide loaded with triglycine sulfate and Rochelle salt has been studied. Our dielectric, pyroelectric and emission measurements give grounds to suggest that this state persists in the composites under study up to temperatures exceeding the Curie point of bulk crystals by several tens of degrees.     

Room temperature ferroelectric effect and enhanced dielectric permittivity in Rochelle salt/PVA percolative composite films

Rochelle salt (RS) filled polyvinyl alcohol (PVA) composite films have been prepared via a simple solution casting technique. The transport, dielectric and ferroelectric properties of the samples have been studied. The dielectric permittivity decreases slowly with increasing frequency and rise gradually with increasing temperature and RS contents in the composites. As the volume fraction of the RS reaches to percolation threshold (f_c ～0.0538), an abrupt increase in the dielectric permittivity (～403 almost 80 times higher compared to pure PVA with low loss ～0.18 at 1 kHz and room temperature) occurs in the RS/PVA composite film, which is attributed to the formation of the conductive network in the matrix. Ferroelectric loops up to room temperature (300 K) and the slight increase in Curie temperature from 297 to 300 K have also been observed for percolative composite film. The developed composite material with low loss high dielectric permittivity and room temperature ferroelectric behaviors might be applied in the technological fields.     

Effect of electric field on the longitudinal ultrasonic waves in Rochelle salt

The temperature dependence of velocity and attenuation for the longitudinal ultrasonic waves propagating along the (100) direction has been measured in the vicinity of the upper transition temperature under the various electric conditions in Rochelle salt.     

Dielektrische Relaxationen und Kristallwasserhaushalt des Seignettesalzes

Various dispersions of the dielectric permittivity of Rochelle Salt, which are caused by crystal imperfections, are known to occur at low frequencies. On the other hand some properties of Rochelle Salt point out that at room temperature rather high concentrations of crystal water defects are present. Therefore the dependence of the relaxation strengths on the content of crystal water is investigated in the case of two different dispersions. One of them shows no connection with the stoichiometry as far as the water of crystallization is concerned, whereas the relaxation strength of the other decreases by about two decades, if the relative humidity, at which the crystals are stored, is increased from 9 to 54 per cent. This dependence is explained quantitatively by concentration changes of water vacancies in the lattice. The energy of activation of the corresponding dielectric relaxation and the energy necessary to create a water vacancy are determined as 0.5 eV.     

Thermal conductivity of Rochelle salt

The temperature dependence of the anisotropic thermal conductivity of a Rochelle salt single crystal was investigated in different crystallographic directions in the range from −35 to +40°C. No anomalous behaviour was found near the Curie points.     

On the specific heat anomaly in ferroelectric Rochelle salt

The temperature dependence of the “ferroelectric” contribution to the specific heat in Rochelle salt has been calculated for the two sublattice model. In contrast to single order parameter models it is found that the specific heat anomaly has the same sign at the lower and at the upper Curie point.     

Zur Frequenzabhängigkeit der ferroelektrischen Koerzitivfeldstärke

Measurements of the coercive field of Rochelle salt, triglycine sulfate and ammonium sulfate were performed in the frequency range from 0,007 cps to 1200 cps. The use of a trapezoidal electric field results in a decrease of the coercive field with increasing frequency. It is shown that this decrease is caused generally by an intrinsic bias field, which is believed to be an expression for the polarization induced ordering of certain lattice defects. In the case of Rochelle salt a quantitative explanation for this frequency behaviour is given.     

Polarization relaxation in Rochelle salt crystals

The relaxation behavior of the domain structure of a Rochelle salt crystal during its repolarization by a static electric field was studied over a wide temperature range (from ?18 to +24°C). The field and temperature dependences of the relaxation time are found. It is shown that the difference between the activation energies determined far from and near the lower and upper phase transition points is due to the different mechanisms of interaction between domain boundaries and defects.     

Photoelastic studies on ammonium Rochelle salt single crystal

Elastooptic measurements at room temperature on single crystals of ammonium Rochelle salt (ARS) which belongs to the Class 222 (D₂) of orthorhombic system and is isomorphous with Rochelle salt in its non-polar phase, have been made at 5890 Å. The values of all the photoelastic tensors, q_ij and p_ij of (ARS) at 5890 Å are reported. These constants have been determined from the measurements of relative and absolute path retardations produced in crystal prisms of various orientations when subjected to linear stresses using the birefringent compensator method and a modified form of Rayleigh refractometer respectively. The effect of hydrostatic pressure on the principal refractive indices and birefringences of (ARS) has also been deduced.     

Proton dynamics in Rochelle salt

The investigation of the frequency spectra of Rochelle salt was performed by inelastic incoherent scattering of thermal neutrons using beryllium detector method. The neutron spectra were measured above the upper ferroelectric transition temperature at 307 K and in the polarized phase at 291 K, in the energy range 17–83 meV. Tentative conclusions concerning proton dynamics are drawn from the analysis of the spectra.     

On order parameter fluctuations in Rochelle salt detected by Brillouin scattering

In both of the nonpolar phases of ferroelectric-ferroelastic Rochelle salt frequency and linewidth of the quasilongitudinal acoustic phonon propagating along [011] have been investigated in a high resolution Brillouin- scattering experiment. Softening and damping of this mode can be quantitatively explained by a piezoelectric coupling to the fluctuations of the polarization along the ferroelectric axis, P₁.     

23Na nuclear magnetic resonance study of the phase transition in ammonium rochelle salt,NaNH4C4H4O6 • 4H2O

The satellite NMR spectrum of ²³Na in ammonium Rochelle salt (NaNH₄C₄H₄O₆ ? 4H₂O) is investigated near the transition temperature. Each line in the paraelectric phase splits discontinuously into four lines at the transition temperature; this fact is compatible with the first-order phase transition and reveals the existence of the superstructure in the ferroelectric phase.     

Phase transition of the aqueous solution of the rochelle salt

Summary Thermal measurements of the aqueous solution of the Rochelle salt were carried out with slow evaporation. It is found that the phase transition occurs from the transparent-solution state of strong viscosity to a white solid state with exothermic peak.     

Two curie points in Rochelle salt and other ferroelectric or ferromagnetic substances

A simple model for Rochelle salt or other ferroelectric and ferromagnetic substances is presented. It yields a ferroelectric (ferromagnetic) phase with two phase transitions to paraelectric (paramagnetic) states. The dependence on the parameter of the theory is discussed in molecular field approximation.     

First photoconductivity measurement following photoionization of rare-earth dopant in a dielectric powder

Transient response of the dielectric permittivity of dielectric powder of LSO:Ce³⁺ under pulsed laser excitation were recorded by the 8-mm microwave resonator technique at room temperature. The signal in absorption mode is the signature of Ce³⁺ photoionization and photoconductivity effect in the rare-earth-doped dielectric grains. The signal in dispersion mode results from surface defects around each grain leading to electronic traps. This opens new perspectives for photoconductivity measurements on rare-earth-doped insulating nanopowders.     

Messung der komplexen Dielektrizitätskonstanten von Seignette-Salz bei 10 GHz in Abhängigkeit von der Temperatur

We determined the complex dielectric constant of Rochelle Salt at 9.61·10⁹ Hz and its temperature dependence using a microwave interferometer. In thex-direction of the crystal which becomes its ferroelectric axis between ?18°C and +24°C, the real part of the dielectric constant shows distinct minima at the transition points according to our measurements. We find agreement with results ofJäckle but discrepancies to older measurements. Neither the humidity of the surrounding atmosphere nor the position of the sample in the growing crystal proved to have an effect. In they- andz-directions, we observed no anomaly of the dielectric constant.