E. L. Wagner

Bio: E. L. Wagner is an academic researcher. The author has contributed to research in topics: Ion. The author has an hindex of 1, co-authored 1 publications receiving 319 citations.

The Vibrational Spectra of Molecules and Complex Ions in Crystals III. Ammonium Chloride and Deutero‐Ammonium Chloride

Abstract: The infra‐red spectra of thin non‐scattering films of NH4Cl and ND4Cl were obtained at 28°, −78° and −190°C. A convenient low temperature transmission type cell usable for such films is described. No indication of fine structure due to free rotation of the NH4+ ions was found. Instead, evidence is presented for the existence, both above and below the λ‐point, of a torsional lattice mode involving the NH4+ ions. The limiting frequencies of the torsional oscillations were observed at about 390 and 280 cm−1 for NH4Cl and ND4Cl, respectively. These values agree quite well with the frequencies calculated on the basis of a purely electrostatic potential function. The spectra of the low temperature modifications indicate strongly that the structures belong to the space group Td1 in which the NH4+ ion symmetry is Td. Of the eight observed bands, two are assigned to the triply degenerate fundamentals ν3 and ν4, one to the overtone 2ν4, one to the combination ν2+ν4 which resonates strongly with ν3, one to the combi...

Infrared Spectra of Ferrites

Abstract: The infrared spectra of 7 ferrites of the formula $M{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$, where $M$ designates a divalent metal, are presented and analyzed. Electronic absorption was observed in the visible and near-infrared regions. Two absorption bands arising from interatomic vibrations were measured and force constants calculated for the stretching of bonds between octahedral or tetrahedral metal ions and oxide ions. These force constants are in agreement with the elastic and thermodynamic properties of these compounds and are sensitive to distribution of metal ions between the alternate sites. The integrated vibrational band intensities were measured: they are compatible with predominantly ionic bonding for these structures.

Infrared Spectra and Characteristic Frequencies of Inorganic Ions

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Soft-mode spectroscopy: Experimental studies of structural phase transitions

Abstract: This paper reviews the experimental studies of displacive phase transitions in solids. Primary emphasis is upon inelastic light scattering and neutron scattering; related infrared reflectivity measurements, as well as x-ray and EPR analyses are also summarized. Several prototype structures are considered in detail: (1) the rocksalt IV-VI semiconductors PbTe, SnTe, and GeTe; (2) the ferroelectric perovskites exemplified by PbTi${\mathrm{O}}_{3}$ and BaTi${\mathrm{O}}_{3}$; (3) perovskites which exhibit cell-doubling transitions, such as LaAl${\mathrm{O}}_{3}$, SrTi${\mathrm{O}}_{3}$, and KMn${\mathrm{F}}_{3}$; (4) crystals having the $\ensuremath{\alpha}$-quartz structure, including Ge${\mathrm{O}}_{2}$, Si${\mathrm{O}}_{2}$, and AlP${\mathrm{O}}_{4}$; (5) the "improper ferroelectrics" ${\mathrm{Gd}}_{2}$${(\mathrm{M}\mathrm{o}{\mathrm{O}}_{4})}_{3}$ and ${\mathrm{Tb}}_{2}$${(\mathrm{M}\mathrm{o}{\mathrm{O}}_{4})}_{3}$; (6) the V-VI-VII semiconductors typified by SbSI; (7) the hydrogen-bonded ferroelectrics of the K${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$ family; (8) Jahn-Teller systems such as DyV${\mathrm{O}}_{4}$ and RbCo${\mathrm{F}}_{3}$, in which structural distortions occur as secondary effects; (9) order-disorder systems such as NaN${\mathrm{O}}_{2}$ and the ammonium halides (N${\mathrm{H}}_{4}$Cl, N${\mathrm{H}}_{4}$Br), in which no "soft mode" occurs in the spectral region ($\ensuremath{\omega}g{10}^{11}$ Hz) probed by ir, Raman, and neutron spectroscopy; (10) $\ensuremath{\beta}$-tungsten ($A\ensuremath{-}15$) structures such as ${\mathrm{V}}_{3}$Si and ${\mathrm{Nb}}_{3}$Sn, which exhibit high-temperature superconductivity. These crystal categories are used to illustrate several phenomena of current physical interest: Specifically, we discuss harmonic and anharmonic mode coupling; "critical exponents" $\ensuremath{\beta}$ differing from one-half in the temperature dependences of the order parameter $\ensuremath{\phi}(T)={\ensuremath{\phi}}_{0}{(T\ensuremath{-}{T}_{0})}^{\ensuremath{\beta}}$ and of the soft-mode frequency $\ensuremath{\omega}(T)={\ensuremath{\omega}}_{0}{(T\ensuremath{-}{T}_{0})}^{\ensuremath{\beta}}$; and the recently discovered "central" modes centered at zero frequency, which grow in intensity as the transition temperature ${T}_{0}$ is approached from above or below. The review covers the period 1940-1972. A few 1973 works are mentioned for which the author had preprints in 1972 or very early 1973. This review is in no sense a comprehensive survey of ferroelectricity. Readers are referred to the following earlier reviews on that subject: Silverman (1966, 1969), Cochran and Cowley (1967), Blinc (1968), Murzin et al. (1968), Nettleton (1970), and Blinc and Zaks (1972).

Physical properties and atomic arrangements in crystals

Abstract: A survey is given of the relation between four physical properties of crystals and their structural characters. The properties discussed are the magnetic, optical, piezoelectric and elastic. The well-established relations between (a) diamagnetic anisotropy and molecular orientation and (b) paramagnetic anisotropy and the environment of complex ions are briefly reviewed. The more recent study of paramagnetic resonance absorption at high frequencies in a magnetic field is also included. The work on antiferromagnetic crystals is discussed in connection with the spinels. The study of optical activity and Raman spectra are considered under the heading of optical properties. The experimental confirmation by X-rays of the original convention concerning atomic configurations and the sign of optical activity in a molecule are described and also the connection between special features of the structures of tartrates, of sodium chlorate and of quartz and the handedness of the rotatory power is analysed. The piezoelectric properties of zinc blende, quartz, tourmaline, Rochelle salt and potassium dihydrogen phosphate are considered in relation to their structures. In the study of quartz and tourmaline the origin of the piezoelectric charge is attributed to tetrahedra of SiO4 stressed in a direction from one corner to the opposite face. The spontaneous electric polarization of Rochelle salt and KH2PO4 is attributed to cooperative movements of hydrogen ions. Broad generalizations concerning the relation between elastic constants and the crystal structure are given. It is shown that the hardness increases in a regular way with the elastic constant c11 (or an average of c11, c22, c33) and also that there is a close connection between directions of strong interatomic bonds and a large value of the corresponding elastic constant.

Tunneling States of Defects in Solids

Abstract: The various optical, caloric, dielectric, elastic, and microwave investigations which have been used to study the tunneling states connected with the motion of atomic and molecular impurities in alkali halides are reviewed.