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Optical And Mechanical Properties Of Highly Transparent Spinel And ALON Domes
Optical and mechanical properties of aluminum oxynitride (ALON) and magnesium aluminate spinel (MgA1<sub>2</sub>0<sub>4</sub>) are presented as well as some optical properties of spinel and ALON hemispherical domes. These materials are transparent in the visible and mid IR and are durable polycrystalline ceramics.
Gravimetric Electrochemical Voltage Spectroscopy:In SituMass Measurements during Electrochemical Doping of the Conducting Polymer Polypyrrole
A new technique is described for direct measurement of mass changes of a conducting polymer electrode during electrochemical cycling. A quartz microbalance is used, with one of its contacts serving as the working electrode. Its high sensitivity permits resolution of mass changes less than 100 ng/${\mathrm{cm}}^{2}$. T…
Quasicrystals: A New Class of Ordered Structures
A quasicrystal is the natural extension of the notion of a crystal to structures with quasiperiodic, rather than periodic, translational order. We classify two- and three-dimensional quasicrystals by their symmetry under rotation and show that many disallowed crystal symmetries are allowed quasicrystal symmetries. We…
Thermal conductivity of polyacetylene
The thermal conductivity of polyacetylene has been measured in the temperature range of 0.8 to 300 K. For T&lt;70 K we present also data of AsF5-doped samples and of doped samples which have been compensated with (CH3)2NH into the insulating state. The undoped sample shows a T2-temperature dependence up to 12 K fo…
EPR of Mn2+ in polycrystalline dolomite
The EPR spectrum at 9.1 GHz of the M=1/2↔-1/2 transition for Mn2+ in polycrystalline dolomite has been studied using a detailed computer simulation of the line shapes in the powder pattern spectrum. The accuracy of the analytical procedure was verified for the spectrum of Mn2+ in calcite, yielding magnetic constants w…
Structural characterization of soft-core and hard-core glasses by Delaunay tessellation
Methods of the Delaunay and Voronoi tessellation are applied to investigate significant structures and structural differences among liquids, glasses, and crystals of the soft-core (inverse 12th power potential) and hard-core models for which molecular dynamics (MD) techniques are used. With particle configurations obt…
Measurements of the interfacial tension between nematic and isotropic phase of some cyanobiphenyls
The interfacial tension γeq between nematic and isotropic phases of some cyanobiphenyls has been measured by using the sessile drop method. Values of γeq ranging from 0.7×10−2 to 1.8×10−2 erg/cm2 are obtained. In a recent paper we measured the optical reflectivity coefficients at the nematic–isotropic interface of 7CB…
The time dependence of luminescence in solids
A review of experimental data on the time dependence of luminescent decay in solids shows very few examples of the classically expected exponential dependence and none of the bimolecular law. The prevailing long-term time dependence obeys power laws in time with exponents between -1 and -2. It is suggested that the wi…
Optical studies of the structure of porous silicon films formed in p-type degenerate and non-degenerate silicon
The detailed structure of porous Si (PS) layers formed in p-type wafers with resistivities 0.01-25 Omega cm has been investigated using reflectance, transmission, ellipsometry and photoluminescence techniques. Marked differences were observed in the optical properties of PS formed in degenerate or non-degenerate Si an…
Vibrational Decoupling of Rings in Amorphous Solids
It has been proposed that the sharp Raman lines seen in vitreous Si${\mathrm{O}}_{2}$ and other glasses are the signatures of highly regular rings of bonds connected into a more disordered network. We derive a condition for vibrational decoupling of the appropriate ring modes from the surrounding network, and thereby…
Ionic conductivity in AgI1−xClx
Experimental results are presented for the ionic conductivity of AgI1−xClx (0 < x < 0.1) in the temperature range 60 to 200 °C. It is found that the substitution of Cl− ions for I− ions in AgI leads to a substantial decrease in the temperature for β–α phase transition and also a large increase in the ionic conductivit…
On the nature of various stacking defects in 18R martensite in CuAl alloys A study by high resolution electron microscopy
A high resolution study of the defects in the 18R martensite of the Cu-Al alloys enables a detailed analysis of the basal plane stacking faults and two other particular types of nearly planar defects observed in martensite phases. One type of defect is parallel with the martensite habit plane, another type, more frequ…
Dielectric Dispersion in KH2PO4Single Crystal at Low Temperatures
Complex dielectric constants of KH 2 PO 4 single crystals along the a - and the c -axes have been measured in the temperature range from 2.5 K to 30 K at frequencies between 10 Hz and 20 kHz. Dielectric dispersions with small loss peaks are observed in both directions. The dispersion along the c -axis (dispersion C) i…
Factor group splitting and dispersion on internal vibrational modes: A qualitative discussion
Factor group splittings, of common occurrence in the infrared and Raman spectra of crystals, and dispersion, usually encountered in discussions of lattice modes, are shown to be closely related phenomena. Their relationship is elucidated by a model comprising a linear array of four vibrating units. A correlation betwe…
Resistivity Anomalies in Pb1-xGexTe at Low Temperatures
Electrical measurements of n- and p-Pb 1- x Ge x Te have been made between 4.2 K and 300 K. Below 40 K, resistivity exhibits anomalous behaviours similar to the Kondo effect in a dilute magnetic alloy. The anomaly is strongly correlated with the phase transition temperature. The formation of the pseudo-spins and the e…
High-pressure Raman study of two ferroelectric crystals closely related to PbTiO3
We report high-pressure Raman measurements of the zone-center phonons in two ferroelectric crystals that closely resemble the $\mathrm{AB}{\mathrm{O}}_{3}$ perovskite crystal PbTi${\mathrm{O}}_{3}$. These crystals are (${\mathrm{Pb}}_{0.22}$${\mathrm{Ba}}_{0.78}$)Ti${\mathrm{O}}_{3}$, i.e., Ba replacing Pb on the $A$…
Electron-energy-loss-spectroscopy study of oxygen chemisorption and initial oxidation of Fe(100)
The initial stages of the interaction of oxygen with an Fe(100) surface have been investigated at 300 K mainly by electron-energy-loss spectroscopy (EELS) with in situ combined low-energy-electron-diffraction, Auger-electron and secondary-electron-emission spectroscopy, and workfunction---change measurements ($\ensure…
Bremsstrahlung isochromat spectra and density-of-states calculations for the3dand4dtransition metals
We present the results of a systematic investigation of the empty electronic states up to 10 eV above ${E}_{F}$ in the $3d$ and $4d$ transition metals with the use of bremsstrahlung isochromat spectroscopy (BIS). We compare these data to calculations of the unoccupied densities of states. The agreement between theoret…
Structure studies of thortveitite-like dimanganese diphosphate, Mn2P2O7
Cristallisation dans C2/m avec a=6,633, b=8,584 et c=4,546 A, β=102,67°, Z=2; affinement jusqu'a R=0,083 (diffraction RX sur poudre), R=0,040 (diffraction RX sur monocristal) et R=0,051 (diffraction de neutrons sur poudre). Confirmation de l'isomorphisme avec la thortveitite Sc 2 Si 2 O 7 , mais avec un oxygene pourta…