A. von Hippel

Structure and Conductivity in the VIb Group of the Periodic System

In the sequence oxygen, sulfur, selenium, tellurium, and polonium a systematic alteration takes place from diatomic molecules, through ring and chain molecules, to a simple cubic lattice structure formed by atoms. This transition is paralleled by a modification in the electrical behavior from insulator (O,S), to semiconductor (Se,Te), to metal (Po). This paper is concerned with this progressive change in structure and conductivity and with the interrelation of the two phenomena. It discusses first the stability of ring and chain molecules and how the chain lattices of Se and Te may be derived by a simple distortion of the Po structure. Next, it considers schematically the electronic conductivity of selenium from the standpoint of the band picture, and finds that metallic Se is probably an intrinsic P‐type conductor. Finally an alternative approach is suggested which connects structure and conductivity by extending qualitatively the concept of quantum‐mechanical resonance from molecular structures to lattice structures and makes use of Paulings resonating bond. The actual structure and conductivity of Se and Te thus appear as the outcome of a resonance between an insulating chain structure held by van der Waals cohesion and a metallic lattice of simple cubic structure, in which for Se the chain structure and for Te the Po lattice makes the stronger contribution.

Transfer of Protons through “Pure” Ice Ih Single Crystals. I. Polarization Spectra of Ice Ih

After a short introduction of the subject “proton transfer in ice” and some background information on previous polarization measurements, the growing and preparation of our single crystals and the instrumentation for a–c measurements from 105–8 × 10−3 Hz, 0 to − 180°C, are briefly described. By rigorous control of error limits and an improved computerized evaluation procedure it was possible to resolve the dielectric spectrum of these “pure” ice single crystals into several significant components: the intrinsic Debye spectrum, two weak spectra preceding it at a high frequency, and “space‐charge‐polarization” spectra. Important characteristics of these spectra and inherent difficulties in quoting their “accurate” parameters are presented. The interpretation of these data requires new molecular models; they are developed in Part II; the analysis of polarization data is resumed in Part III in conjunction with new transconductance measurements.

Transfer of Protons through “Pure” Ice Ih Single Crystals. II. Molecular Models for Polarization and Conduction

Neither the polarization of pure ice single crystals can be understood on the basis of rotating H2O molecules nor the conduction through such crystals by assuming migrating H3O+ and OH− ions. Bjerrums concepts of L‐, D‐defect and ionic‐defect formation are a useful starting point, but the subsequent development of double‐well models leads into serious difficulties. A new interpretation of the intrinsic polarization of ice Ih visualizes L, D pair formation as a one‐step process: a proton shifted by near‐infrared phonon excitation to an empty corner of its H2O tetrahedron. Subsequent intramolecular proton transfers, slightly field directed, inscribe a dipole moment into the disordered proton system of the ice crystal; the defects die off by recombination. Thus the polarization builds up from a statistically triggered pulse spectrum; its correlation period is the waiting time, until the same H2O molecule forms again a defect pair. This waiting period, the relaxation time of the Debye spectrum, connects the ...

Piezoelectricity, ferroelectricity, and crystal structure

By visualizing polar crystals as a network of permanent dipole moments, the piezo- and ferroelectric properties of dielectrics may be derived from the standpoint of molecular symmetry. This approach is used to clarify the relation between the sphalerite and wurtzite structures, the ferroelectric feedback effect in barium titanate, aspects of domain formation, and the interrelationship between ferro and piezoelectricity.

Transfer of Protons through “Pure” Ice Ih Single Crystals. III. Extrinsic versus Intrinsic Polarization; Surface versus Volume Conduction

In order to analyze the charge transport through ice Ih single crystals and over their surfaces, the a–c polarization studies of Part I were supplemented by d–c and transient measurements ranging from 10−2‐4 × 104 V/cm, from nanoamperes to microamperes, and from 100μsec–3 h. After a brief description of techniques, the research focuses on “conductivity” as represented by an activation energy equation. In the literature, the activation energies quoted range from 33 ↔ 0 kcal/mole. Investigating the reasons for this confusion we found: (1) The value 33 kcal/mole is caused by surface conduction and can be reduced to ∼ 20 kcal/mole by pumping. (2) Zero activation energy characterizes the “initial” currents in the milli‐second range. (3) Intermediate values (e.g., 12 kcal/mole) stem from apparent conductivities in space‐charge distorted fields. The saturation current at high fields, measured by Eigen and co‐workers (activation energy ∼ 22 kcal/mole), seems to be an extrinsic current produced by multicrystallini...

The dielectric relaxation spectra of water, ice, and aqueous solutions, and their interpretation. I. Critical survey of the status-quo for water

A summarizing critical analysis is given of the present understanding of the dielectric relaxation spectrum of pure water. The author starts with a classical description of this spectrum and proceeds through the various molecular interpretations by electrostatic models (Debye, Onsager, Kirkwood, Lennard-Jones, and Pople) and by dynamic-statistical models, including their relations to infrared spectroscopy. It is concluded that there is at present no valid theory for the static permittivity or for the relaxation time. >

The Electroplating of Metallic Selenium

The electroplating of metallic selenium from acid baths has been achieved and reduced to practice. The paper discusses in succession the polymorphism of selenium; selenium ions in selenious acid solution; cathodic deposition as the amorphous and metallic phase; the nucleation characteristic and crystal growth of the metallic modification; the properties of various types of plating baths; a selenium‐carbon anode for the stabilization of the bath composition; and finally a number of influences affecting the crystallization habit of the deposit. The current density of 200 amp./ft.2 attainable in a well‐balanced plating bath compares favorably with standard baths for true metals.

The dielectric relaxation spectra of water, ice, and aqueous solutions, and their interpretation. III. Proton organization and proton transfer in ice

For pt.II see ibid., vol.23, no.5, Oct. 1988, p.817-23. After a short presentation of the various ice phases and of the oxygen sublattices for ice I, the proton array of ice I is considered, simple approximate derivation of the zero-point entropy for random distribution given, and evidence examined from some proton ordering along the hexagonal axis of ice I/sub h/. Next, the experimental facts are summarized on orientation polarization and conduction, and N. Bjerrums ideas (1951) are given about defect-pair and ion-pair formation. The double-well model for polarization and conduction in ice, is used to describe the behavior of the individual defects and ions, after the pairs have formed, drifted apart, and settled down. The author argues that this model seems in conflict with the observed dielectric relaxation time when the proper activation energy is used. Therefore, another model is presented, linking the formation and separation of defects to the dielectric relaxation spectrum and to infrared spectroscopy. >

Distortable Double Well. A Prototype for the Analysis of Relaxation Spectra

The origin of dielectric relaxation spectra is frequently not the rotation of dipoles as visualized in the Debye and Onsager models but the reversible transfer of ions or electrons between equilibrium sites. The displacement of such charge carriers corresponds to a reversal of dipole moments and had been treated previously as a shifting of charges between fixed equal or unequal double wells. The reversal of dipole moments in condensed phases, however, frequently has decisive after effects: The electrical unbalance created leads to a compensating action of the surroundings, lowering the free energy and tending to freeze in the charge in the occupied well site. Thus the double well becomes unequal because of the reaction of the embedding medium. This model of a distortable double well is here treated, first in its stationary state with and without superposed dc field and then in its ac response, under the simplifying assumption that the surroundings react by an exponentially decaying distortion described by a time constant and final well depth. The characteristics of the model are that it incorporates the equal and unequal fixed double well as special cases but in addition shows an inherent distribution of relaxation times and—for long observation periods—an anomalously large polarizability, since eventually the wells can be turned with their deepened sites in the favorable field direction.

The dielectric relaxation spectra of water, ice and aqueous solutions, and their interpretation. II. Tentative interpretation of the relaxation spectrum of water in the time and frequency domain

For pt.I see ibid., vol.23, no.5, Oct. 1988, p.801-16. A qualitative discussion on the relaxation spectrum of water in the time and frequency domains is presented. According to the picture that emerges, quantum jumps, induced by thermal phonon excitation in the near infrared, disconnect water dipoles sufficiently from their surroundings to allow reorientation of these dipoles and a subsequent reorganization of their near-surroundings. In an applied electric field, these jumps can be measured as polarization spike signals in the time domain. The statistical correlation time between the consecutive jumps of the same water molecule determines the relaxation time tau in the frequency domain. With increasing temperature, the statistical average of the required activation energy moves from the intramolecular into the intermolecular region, and the effect deuterium substitution on vibration frequency and tau consequently falls from the mass ratio square root D/H toward square root D/sub 2/O/H/sub 2/O. >