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Showing papers on "Dielectric published in 1971"


Journal ArticleDOI
Michio Matsuoka1
TL;DR: In this paper, the non-ohmic properties of ZnO ceramics with five additives of Bi2O3, CoO, MnO, Cr2O 3, and Sb 2O3 are studied in relation to sintering temperature, additive content, and temperature dependence.
Abstract: Nonohmic properties of ZnO ceramics with five additives of Bi2O3, CoO, MnO, Cr2O3, and Sb2O3 are studied in relation to sintering temperature, additive content, and temperature dependence. The observation of electron photomicrographs and X-ray microanalysis proves a ceramic microstructure such that ZnO and these five oxides form, at the grain boundaries, segregation layers which are responsible for the nonohmic properties. The electrical resistivity and dielectric constant of segregation layers are estimated to be 1013 ohm-cm, and 170, respectively by using a simple model. The electric field strength corresponding to the steep rise in the current is also estimated to be 104 V/cm by taking account of the concentration of applied voltage at the segregation layer. In view of these data and simple model, a possible explanation for nonohmic properties is discussed.

1,054 citations


Journal ArticleDOI
TL;DR: In this article, the dielectric constant of saline water was represented by an equation of the Debye form and the parameters for the parameters were given as functions of the water temperature and salinity.
Abstract: The dielectric constant of saline water may be represented by an equation of the Debye form. Equations for the parameters in the Debye expression are given as functions of the water temperature and salinity.

715 citations


Journal ArticleDOI
TL;DR: In this paper, the elastic, piezoelectric, and dielectric constants, and their temperature dependence within the range 0°-110°C, have been determined for single crystals of lithium tantalate and lithium niobate.
Abstract: The elastic, piezoelectric, and dielectric constants, and their temperature dependence within the range 0°–110°C, have been determined for single crystals of lithium tantalate and lithium niobate. For each material, the constants were extracted from a combination of many ultrasonic phase‐velocity measurements, the measured resonant and antiresonant frequencies of a single length‐extensional bar resonator, and the measured low‐frequency capacitances of two thin flat‐plate specimens. For lithium tantalate, the normalized first temperature derivatives of the elastic constants range from −0.4 to −6.7×10−4/°C, while the derivatives for the piezoelectric stress constants range from −1.3 to +1.5×10−4/°C. In the case of lithium niobate, the elastic constant temperature derivatives are all on the order of −2×10−4/°C, while the piezoelectric temperature derivatives are all positive in the range 0.8–8.9×10−4/°C. The dielectric or permittivity temperature derivatives are positive for both materials.

606 citations


Journal ArticleDOI
TL;DR: Conduction through thin dielectric films sandwiched between metal and semiconductor electrodes is reviewed in this article, where the authors show that the dielectrics can be used to conduct the circuit.
Abstract: Conduction through thin dielectric films sandwiched between metal and semiconductor electrodes is reviewed.

460 citations


Journal ArticleDOI
TL;DR: The empirical dielectric decay function ϕ(t)= exp −(t/τ0)β, 0 0, but significant corrections may have to be applied for β > 0.5 and log ωτ0 < 0.
Abstract: The empirical dielectric decay function ϕ(t)= exp –(t/τ0)β, 0 0, but significant corrections may have to be applied for β >0.5 and log ωτ0 < 0.

431 citations


Journal ArticleDOI
TL;DR: In this paper, the dispersions of resistivity and dielectric constant of fine oxides over a frequency range from 10 Hz to 1 MHz in the temperature range from 77°K to 300°K were studied.
Abstract: A study is made on the dispersions of resistivity and dielectric constant of α-Fe2O3, γ-Fe2O3, Fe3O4, Zn ferrite, Mn ferrite, and MnZn ferrite fine particles over the frequency range of 10 Hz to 1 MHz in the temperature range from 77°K to 300°K. The Maxwell-Wagner interfacial polarization arising from the heterogeneity of oxidation is observed in the fine particles of the oxides, except α-Fe3O3, which are prepared from aqueous solutions of divalent metal salts as well as in the powders of ferrites containing ferrous ions which are prepared by the calcination at high temperatures. The structures of heterogeneity in the fine particles are explained by the model that there are high resistivity shells with poor ferrous ions on the surfaces of the particles.

415 citations


Journal ArticleDOI
TL;DR: In this article, an extension of the Helfrich theory of hydrodynamic instabilities to the case of alternating electric fields is presented, where the electrohydrodynamic effects are described by two coupled equations for the charge density (q) and the local curvature of the molecular alignment (ψ).
Abstract: We present an extension of the Helfrich theory of hydrodynamic instabilities to the case of alternating electric fields. The electrohydrodynamic effects are described by two coupled equations for the charge density (q) and the local curvature of the molecular alignment (ψ). The relaxation time for q is the dielectric relaxation time τ (∼ 10-2 s in typical samples). The relaxation time T for ψ is strongly dependent on the field magnitude. Provided that the sample thickness d is above a certain limit dc, the nature of the instability is very different, depending on the ratio of the field frequency ω to a critical frequency ω c. For ω ωc the situation at threshold corresponds to a constant q and an oscillating ψ. These predictions, together with the calculated curves of threshold voltage vs ω and d, are in reasonable agreement with a number of recent experiments.

236 citations


Journal ArticleDOI
TL;DR: In this article, the elastic constants and the dispersion curves for phonons propagating along (0,0, xi ) and ( xi, xi, 0) are calculated using a rigid ion model with short range central axially symmetric forces and long range Coulomb forces which gives satisfactory agreement with the experimentally observed frequencies.
Abstract: For Pt. II see abstr. A71824 of 1970. The polarized infrared reflection absorption and laser Raman spectra have been recorded at both 300K and 100K for single crystals of SnO2. The dielectric parameters epsilon ' and epsilon " have been derived and the optically active transverse and longitudinal k=0 phonon frequencies found. The elastic constants and the dispersion curves for phonons propagating along (0,0, xi ) and ( xi , xi ,0) are calculated using a rigid ion model with short range central axially symmetric forces and long range Coulomb forces which gives satisfactory agreement with the experimentally observed frequencies. The principal force constants and the effective charges on the ions are compared with those for other crystals with the rutile structure. The multiphonon infrared absorption is compared with theoretical predictions based on selection rules and the calculated phonon dispersion curves. The hydroxyl ion impurities are shown to be oriented parallel to the crystal's optic axis.

226 citations


Journal ArticleDOI
TL;DR: In this paper, the temperature dependence of the dielectric constants for single-domain SrTi${\mathrm{O}}_{3}$ crystals was measured and deviations from the simple Curie-Weiss law were discussed in connection with the structural phase transitions at 110 and 65 degrees.
Abstract: We have measured the temperature dependence of the dielectric constants for single-domain SrTi${\mathrm{O}}_{3}$ crystals. Dielectric anisotropies and deviations from the simple Curie-Weiss law have been observed and are discussed in connection with the structural phase transitions at 110 and 65\ifmmode^\circ\else\textdegree\fi{}K.

214 citations


Journal ArticleDOI
TL;DR: In this paper, the 36 k=0 modes of vibration were classified using group theoretical methods using kramers-kronig theory and the dielectric parameters were derived from the reflection spectrum using kramer-krusig theory.
Abstract: This paper reports polarized infrared and raman studies on zircon, zrsio4. The 36 k=0 modes of vibration are classified using group theoretical methods. The dielectric parameters epsilon minutes and epsilonseconds have been derived from the reflection spectrum using kramers-kronig theory. Measurements have also been made on the elements of the raman polarizability tensor, and the angular dependence of the scattered intensity has been studied for several bands. The crystal field splittings of the vibrational levels of the silicate ions are large, but some simple force constant considerations lead to the conclusion that the silicate ions are essentially molecular units.

212 citations



Journal ArticleDOI
TL;DR: In this paper, a piezoelectric ceramic material has been prepared from PbTiO3 incorporated with 2.5 mol% LaO12 and 1.0 mol% MnO2.
Abstract: A piezoelectric ceramic material having low dielectric constant, high thickness coupling factor, high mechanical quality factor, high stability, and high operating temperature, has been prepared from PbTiO3 incorporated with 2.5 mol% of LaO12 and 1.0 mol% of MnO2. Typical electromechanical constants of this material are as follows: dielectric constant e11T/e0 230, e33T/e0 170; coupling factor k33 0.46, kt 0.46, k15 0.28, kp 0.07, k31 0.04; mechanical quality factor Q 1100, Poisson's ratio σE 0.20. Frequency constants Nt and N3t of the fundamental and third‐harmonic thickness vibrations have temperature coefficients of −1.1 × 10−4°C−1 and −2 × 10−5°C−1, respectively. Aging rates of Nt and N3t, are +0.02% and −0.02%/time decade at 30°C, respectively. The Curie point of this material exists at 470°C, and k33 and kt increase gradually with temperature up to 400°C. This material has grain size of 2–3 μ and bending strength of 2 × 107 kg/m2, and can be polished into very thin plate. The PbTiO3 ceramics have a h...

Journal ArticleDOI
TL;DR: In this paper, a theory of orientation polarization in nematic liquid crystals is developed for a molecular dipole moment parallel to the long axis of the molecule, which is essentially an extension of the Debye model for normal polar liquids to take into account the strong intermolecular potential.
Abstract: A theory of orientation polarization in nematic liquid crystals is developed for a molecular dipole moment parallel to the long axis of the molecule. The theory is essentially an extension of the Debye model for normal polar liquids to take into account the strong intermolecular potential which is responsible for the nematic state. It is shown in detail that the relaxation time depends strongly on the nematic potential and also on whether the polarization takes place parallel or perpendicular to the symmetry axis of the crystal. In the first case, the relaxation time increases from its value in the isotropic liquid phase by a “retardation factor” which may amount to several orders of magnitude, depending on the strength of the nematic potential. In the second case, the relaxation time decreases slightly. The calculated retardation factor is smaller than the experimental one. It is suggested that this discrepancy is due to the neglect of molecular short-range order.

Journal ArticleDOI
TL;DR: In this paper, a method for the measurement of permittivity at microwave frequencies using an open resonator is proposed, and an experimental procedure is developed, and a thorough experimental study of the method has shown that experimental errors can be made very small indeed.
Abstract: A method for the measurement of permittivity at microwave frequencies using an open resonator is proposed. The theory of the method is developed, and an experimental procedure is evolved and justified. It is shown that the present method has advantages over other open resonator methods which have been proposed, and a thorough experimental study of the method has shown that experimental errors can be made very small indeed. Since the very beginnings of modern microwave techniques in the 1940s, many alternative methods of measuring the complex permittivity of gases, liquids and solids have been devised. Most of these have employed a cavity resonator or a length of waveguide as a means of defining the configuration of the electromagnetic field with the precision needed for accurate quantitative analysis of the experimental results. Although very satisfactory results have been obtained using such methods, they become increasingly difficult to apply as the wavelength decreases. For the solid dielectric materials with which the present paper is exclusively concerned, a major problem is the accurate machining of a specimen of the material to fit closely into the resonator or waveguide. Even very small air gaps between the dielectric material and the metal wall can cause large errors, and this problem is obviously more serious at shorter wavelengths since the fractional error corresponding to a given absolute error in the dimensions of the specimen is inversely proportional to the wavelength. Another difficulty is encountered at very high frequencies in the resonant cavity method of measurement of the loss tangent of a dielectric material when this has a small value. The accuracy of measurement begins to decrease when the loss tangent falls below the reciprocal of the Q factor of the empty resonant cavity. Since this Q factor varies as fo , where f0 is the resonant frequency it is clear that the method is unsatisfactory for low-loss materials at high frequencies. The pioneer work of Culshaw & Anderson (I962) on the measurement of permittivity and dielectric loss with a millimetre wave Fabry-Perot interferometer was the first successful attempt to use an open resonator for this purpose. However, the use of parallel-plane mirrors rather than spherical mirrors gives rise to a field distribution within the resonator which is not readily amenable to mathematical analysis. Moreover, the diffraction losses are much larger than is the case when spherical mirrors are used in a suitable configuration.

Journal ArticleDOI
TL;DR: In this article, a model anisotropic system, suggestive of the graphite structure, is investigated: it consists of a series of equally spaced parallel planes, and a finite two-dimensional density of electrons in each plane is allowed to move freely in the plane, but tunneling between planes does not take place.
Abstract: A model anisotropic system, suggestive of the graphite structure, is investigated: It consists of a series of equally spaced parallel planes. A finite two-dimensional density of electrons in each plane is allowed to move freely in the plane, but tunneling between planes does not take place. The dielectric screening of a point charge is evaluated exactly in the random-phase approximation. For realistic electron densities and interlayer separations the screened potential drops off very rapidly both in the plane of the charge and perpendicular to it. The induced charge density is determined, and validity of the Thomas-Fermi approximation is discussed.

Journal ArticleDOI
TL;DR: In this article, a perturbation theory for coupling between degenerate modes of dielectric waveguides (optical fibers, etc) is presented. But the authors only consider the case of coupling between two parallel dielectrics.
Abstract: Two parallel dielectric waveguides can exchange energy if the field carried by one guide reaches the other guide. We consider only the case of coupling between degenerate modes of dielectric waveguides (optical fibers, etc). Degenerate modes have equal phase velocities, but their transverse field distributions need not be identical. The coupling theory presented in this paper applies to dielectric waveguides of arbitrary shape and arbitrary distribution of refractive index. The dielectric media of the guides as well as the surrounding medium are allowed to be lossy. The coupling coefficient is obtained by means of perturbation theory. It is shown that whereas lossless degenerate modes can exchange their power completely, lossy modes tend to equalize their power. The theory is applied to the problem of crosstalk between cladded dielectric slab waveguides and cladded optical fibers embedded in a lossy medium. Since a lossy surrounding medium also causes an increase in the loss of the guided modes, formulas for this additional loss are presented. It is shown that additional mode loss results even for a lossless surrounding medium if n 3 k > β. (n 3 = index of surrounding medium, k = free space propagation constant, β = propagation constant of guided mode.)

Journal ArticleDOI
TL;DR: In this paper, the effects of temperature and hydrostatic pressure on the ferroelectric (FE) properties of PbTiO3 and on certain properties of Ba TiO3 which have not been treated or emphasized earlier were investigated.
Abstract: The effects of temperature and hydrostatic pressure on the ferroelectric (FE) properties of PbTiO3 and on certain properties of BaTiO3 which have not been treated or emphasized earlier were investigated. For PbTiO3, the FE-paraelectric (PE) transition is of first-order, and the transition temperature, Tc, decreases with pressure with an initial slope of -8.4 ± 0.3°K/kbar. It is estimated that the latent heat associated with the transition is 350 ± 45 cal/mole, with a corresponding entropy change of 0.46 ± 0.05 cal/mole°K. In the PE phase, the static dielectric constant, e, obeys the Curie-Weiss law e = C/(T- T0) over a wide temperature range. Both C and T0 decrease with pressure. At constant % e varies with pressure according to e = C*/(p-po), where p0 decreases strongly with increasing T while C* is very weakly T-dependent. The results can be explained in terms of an increase of the frequency of the soft FE mode with pressure, and the Gruneisen parameter and its Tdependence are determined for this mode. ...

Journal ArticleDOI
TL;DR: In this paper, a more generalized form of potential barrier than the coulombic one usually chosen in the Schottky law was adopted to obtain consistent agreement with experiment, and the form of barrier chosen appears to refer to the cathode-dielectric interface and is probably determined by space charge in the dielectric.
Abstract: Electrical conduction is studied in polyethylene terephthalate and to a limited extent in polyethylene over a range of fields up to 12×106 V cm−1. In common with previous investigations, it is found that the current decays with time according to an inverse power law, but this can be obviated by a conditioning procedure which then allows steady values of current to be measured over a range of temperature and field. The results suggest that the current has an activation energy which is field dependent, but attempts to fit the results to a Schottky-type law are not very successful. By adopting a more generalized form of potential barrier than the coulombic one usually chosen in the Schottky law, it is possible to obtain consistent agreement with experiment. The form of potential barrier chosen appears to refer to the cathode-dielectric interface and is probably determined by space charge in the dielectric. Values of the metal-dielectric contact potential for the samples of polyethylene terephthalate and polyethylene investigated were 258 and 214 eV respectively for aluminium electrodes. It is suggested that the time dependence observed before conditioning is completed is due to the slow build-up of the full interfacial barrier.

Journal ArticleDOI
TL;DR: In this article, the authors show that the width of the impulse response gets narrower when coupling between guided modes and that the intensity response width increases as the square root of the guide length for sufficiently long guides.
Abstract: In dielectric waveguides operating at optical frequencies, the primary cause of time dispersion of narrow pulses can be mode conversion. In this paper we argue that under certain assumptions a dielectric waveguide acts as a linear system in intensity. That is, given the intensity input, the intensity output is equal to the input convolved with an intensity impulse response. We show that contrary to intuition, the width of the impulse response gets narrower when coupling between guided modes increases. Using the perturbation results of D. Marcuse, we obtain an interesting model of energy propagation down imperfect guides. We conclude that the intensity response width increases as the square root of the guide length for sufficiently long guides and approaches a gaussian shape for sufficiently long guides. We conclude from the theory that the dispersion in dielectric wave-guides may be orders of magnitude below that which was previously expected in guides of sufficiently long length having properly controlled large amounts of mode conversion. These theoretical results have not yet been verified experimentally.

Journal ArticleDOI
TL;DR: In this paper, the real and imaginary parts of the ac conductivity are shown to increase with frequency according to power law σ=Aωs, where s=0.85 to 0.95, and it is found that the dielectric behavior can be described by a Debye-type relaxation behavior only if a broad distribution of relaxation times exists.
Abstract: Conductivity and dielectric properties of semiconducting glass of composition 80% V2O5:20% P2O5 have been measured as a function of frequency from dc to 3.6 GHz over a temperature range from 77°K to 420°K. A fit of the dc results to a model of polaronic hopping conduction leads to an activation energy due to disorder ΔW=0.09 eV at 77°K and an optical phonon energy of 0.053 eV compared to a calculated Miller‐Abrahams energy of approximately 0.12 eV. The real and imaginary parts of the ac conductivity are shown to increase with frequency according to power law σ=Aωs, where s=0.85 to 0.95, and it is found that the dielectric behavior can be described by a Debye‐type relaxation behavior only if a broad distribution of relaxation times exists. The results are shown to be consistent with a model of ac conduction normally applied to impurity‐doped broad‐band semiconductors, and differences between the temperature dependence of the dc and ac conductivity are attributed to a distribution of site energies in the gl...

Journal ArticleDOI
TL;DR: In this article, the long-wavelength dielectric constant with lattice vibrations neglected e∞ is determined to be 8.16 ± 0.02, and the resulting static dieectric constant e0 is 10.06 ± 0.04.
Abstract: The refractive index of AlAs at 300 °K has been measured in the 0.5‐ to 2.2‐eV range of photon energy. The long‐wavelength dielectric constant with lattice vibrations neglected e∞ is determined to be 8.16 ± 0.02, and the resulting static dielectric constant e0 is 10.06 ± 0.04.

Journal ArticleDOI
TL;DR: In this article, it was shown that even if the waves produced correspond to a uniform distribution of directions of wave vector, there may be a large enhancement of energy flow in some crystallographic directions compared to the average.
Abstract: The generation of thermal acoustic waves by a heated metallic film on the surface of a dielectric crystal at low temperatures is discussed. It is shown that even if the waves produced correspond to a uniform distribution of directions of wave vector, there may be a large enhancement of energy flow in some crystallographic directions compared to the average. This effect arises because of elastic anisotropy. Explicit expressions are given for the enhancement expected in the principal directions of cubic crystals.

Journal ArticleDOI
TL;DR: In this article, a model for electrohydrodynamic alignment effects in cholesteric liquid crystals is proposed and a formula for the threshold voltage of such alignment, starting from the planar texture between two conducting plates.
Abstract: A model is proposed for electrohydrodynamic alignment effects in cholesteric liquid crystals. We derive and discuss a formula for the threshold voltage of such alignment, starting from the planar texture between two conducting plates. An improved formula for the threshold of the dielectric deformation of this orientation pattern is also given.

Journal ArticleDOI
TL;DR: In this paper, the dielectric constants and refractive indices of a 5PbO · 3GeO2 crystal, which was grown from the melt by by the Czochralski method, were measured as a function of temperature.
Abstract: Dielectric constants and refractive indices of a 5PbO · 3GeO2 crystal, which was grown from the melt by by the Czochralski method, were measured as a function of temperature. The crystal was identified as a new type of ferroelectric with spontaneous polarization Ps = 0.046 C/m2, coercive field Ec ∼ 2.3 × 106 V/m at room temperature, and Tc = 177°C.

Journal ArticleDOI
TL;DR: In this article, it is shown that when an arbitrary external field is applied, the constitutive relation P=(e−1)/4 πE between the local polarization and the local macroscopic electric field is valid under some completely acceptable restrictions.
Abstract: A molecular fluid of identical molecules with a rigid dipole moment in an arbitrarily shaped volume is considered. The volume may or may not be embedded in a dielectric continuum. It is shown that when an arbitrary external field is applied, the constitutive relation P=(e−1)/4 πE between the local polarization and the local macroscopic electric field is valid under some completely acceptable restrictions. In the establishment of this relation a crucial role is played by a long‐range part of the two‐particle correlation function, for which an explicit expression is obtained. One term in this long‐range part is explicitly dependent on the shape of the sample volume and on the surroundings. The resulting dielectric constant of the molecular fluid can be formally expressed in only the local interactions of the molecules and is thus independent of the surroundings and the shape of the sample.


Patent
14 Jul 1971
TL;DR: In this article, the radiating structure is made of a non-magnetic dielectric and a ferrimagnetic material, and the magnetic part is associated with magnetizing coils energized from an aperture control current source.
Abstract: In order to obtain wide aperture and high directivity radiation patterns from the same antenna, the radiating structure is made of a non magnetic dielectric and a dielectric ferrimagnetic material. The magnetic part is associated with magnetizing coils energized from an aperture control current source. When the antenna is of the rod type, the rod is made of the non magnetic dielectric which is covered at least partly with a magnetic coating. When the antenna is of the spherical type, a magnetic material core is surrounded with a non magnetic dielectric shell.

Journal ArticleDOI
TL;DR: In this article, the dielectric β relaxation of polyvinyl chloride has been studied in the ranges of temperature, pressure and frequency, 296 to 353 K, 1 × 105 to 3 × 108 N m 2 and 1 to 105 Hz.
Abstract: The dielectric β relaxation of polyvinyl chloride has been studied in the ranges of temperature, pressure and frequency, 296 to 353 K, 1 × 105 to 3 × 108 N m–2 and 1 to 105 Hz. Detailed results are discussed in terms of current concepts of the α, β and (αβ) relaxations which occur in amorphous polymers and in small molecule glass forming systems.

Journal ArticleDOI
TL;DR: In this paper, a critical examination of four Debye equations for dilute solutions is presented, which can be used to determine the relaxation time of a polar solute molecule, especially two representative formulas which are mutually independent.
Abstract: There are four Debye equations for dilute solutions which can be used to determine the relaxation time of a polar solute molecule. This paper offers a critical examination of these equations, especially two representative formulas which are mutually independent. If the solute molecule has a non-rigid configuration and has two relaxation times, τ1 and τ2, for overall and internal rotations, respectively, average relaxation times will be obtained from these equations based on measurements at a single frequency. However, the analysis of this paper shows that under a certain condition (if a proper frequency for the measurement and a suitable equation for the calculation are employed) one may make a crude estimate regarding one of the two relaxation times. Further, the ratio of two relaxation times seems to afford a clue for investigating the mechanism of internal rotation. In addition, Cole-Cole dispersion and atomic polarization problems are also discussed.

Journal ArticleDOI
TL;DR: In this article, the authors measured the permittivity and loss of solutions of tri(n-butyl)ammonium picrate and iodide in various polar solvents at a number of frequencies between 0.2 and 3.0 GHz.
Abstract: The permittivity and loss of solutions of tri(n-butyl)ammonium picrate and iodide in various polar solvents have been measured at a number of frequencies between 0.2 and 3.0 GHz. The relative static permittivities of the pure solvents used range from 3.37 to 20.7 at 25°C. For all the solutions investigated, the observed dispersion of permittivity is adequately described by a single relaxation time, which for a given solvent depends on the concentration as well as the nature of the solute. Apparent dipole moments evaluated from the dispersion amplitude by means of Bottcher's theory, on the assumption that the dipole occupies a spherical cavity, are 12.3±0.4 D and 11.2±0.6 D for the picrate and iodide respectively. These values indicate that the relaxing dipole is an ion pair. Dielectric relaxation times corrected for internal field effects by different relations are compared with those calculated from the partial molar volume of the solute and the viscosity of the solvent by means of the Debye-Stokes equation. Density data for solutions of the two salts in 1,2-dichloroethane are included and from these data, partial molar volumes of the salts have been evaluated.