Crystalline Solid Solutions Research Articles

Mesomorphism in the System Disodium Chromoglycate-Water

Abstract The system has been studied by a combination of polarization microscopy, using a hot stage, and X-ray diffraction analysis. The sequence of condensed phases occurring at room temperature with increasing concentration of disodium chromoglycate (DSCG) is: (i) a mesophase N; (ii) a mesophase M; (iii) crystalline solid solutions SS. A variety of evidence has shown that the molecule of DSCG retains an essentially planar configuration throughout the system. The mesomorphic phases are optically negative, indicating a parallel, or approximately parallel, arrangement of the molecular planes. (A parallel arrangement of these planes in the SS solid solutions had been previously indicated by a preliminary X-ray analysis, which pointed to there being only one molecule in the unit cell; and in conformity with such an arrangement the crystals were found to be optically negative.) The transformations between the N and M phases and between the M and SS phases take place pseudomorphically, and on reversal the original textures are recovered. The N phase appears to be genuinely nematic in structure, in contrast to other cases of lyotropic systems showing nematic-like textures that have been reported, but which are believed to be deformed lamellar phases. The M phase gives X-ray reflections corresponding to a “middle” structure, of the M 1 type, i.e., one in which the DSCG is clustered into rods separated by a water continuum, and with the polar —COONa groups occupying the surfaces of the rods. Considerations based on calculations of the diameter of the rods indicate that some water is associated with the DSCG molecules within the rods.

The effect of fine structure appearance in laser-excited fluorescence spectra of organic compounds in solid solutions

Some experiments with excitation of the perylene fluorescence at 4.2°K in the region of the 0-0 transition by a cadmium laser ( λ=4415.6 A ̊ ) were made. It was found that with the laser excitation, narrow lines (≈1 cm -1 appear instead of broad bands (≈200 cm -1) in the fluorescence spectrum of both the crystalline and glass-like solid solutions. A similar effect was observed with some other molecules. A rapid decrease of the intensity of the narrow lines with increase of temperature was found. A possible model of the formation of the wide spectral bands suggested by the new results obtained is discussed.

Transient Photoconductivity Effects in an Insulator-Semiconductor Powder System

An investigation of transient photoconductivity effects associated with semiconductor particles suspended in a transparent insulator has been carried out. II-VI compound crystalline solid solutions of CdSxSe1−x and CdSeyTe1−y were used as the photoconductors and poly (N-vinyl carbazole), PVK, as the transport medium, or matrix. Interparticle distances (∼ 5 μ) were large compared with particle diameters (∼ 1 μ). Transient photoconductivity as well as xerographic discharge measurement techniques were employed to study the quantum yield of the system as a function of applied electric field, wavelength of the incident radiation, temperature, and certain surface parameters of the components. Ideal geometry samples, consisting of single-crystal semiconductor-PVK-metal capacitors, were also studied to observe directly the photoemission of holes from the semiconductor into the PVK. The magnitude of the injection efficiency is found to depend upon the surface parameters of the components as well as the applied electric field. The data indicate the electric field dependence of the discharge in these systems to be due to electric field penetration of the surface of the semiconductor.

蒸気圧により組成制御した液相からのGaAs<SUB>1−<I>x</I></SUB>P<I><SUB>x</SUB></I>化合物の調製

Crystalline solid solutions between GaAs and GaP compounds were prepared from the melt under controlled vapour pressures. The experimental results were found to agree with the theoretical formulae derived in order to calculate the pseudo-equilibrium in a heterogeneous system consisting of two parts with different temperatures. It was assumed that all condensed phases would be regular or sub-regular and that the gas phase is ideal. In addition, some of the thermodynamic properties of the Ga-As-P ternary system were discussed. It was found that one can apply the concept of pseudo-equilibrium to the preparation of crystalline solid solutions of III-V compounds containing two volatile components.

Gas Adsorption Studies on the (100) Plane of Vanadium by Low-Energy Electron Diffraction

Gas adsorption studies were conducted on the (100) plane of a vanadium single crystal using low-energy electron diffraction (LEED). The crystal was exposed to hydrogen and to oxygen, in the pressure range from 10−6–10−9 torr, with the substrate held at temperatures between 25°–1400°C. A procedure for cleaning the surface of vanadium is described. Several important conclusions were reached: (1) the adsorption of hydrogen is random, i.e., amorphous; (2) the adsorption of oxygen is ordered; a (1 × 1) structure is formed and the intensity of the (00) beam is substantially higher than that from the clean surface; (3) when the temperature of the oxygen adsorbed crystal is raised to 1100°C, a (2 × 2) structure is formed; (4) on further heating of the oxygen-adsorbed crystal to 1400°C, all structures due to oxygen disappear; (5) with prolonged heating satellite spots appear on the (00) and the (10) beams, and cannot be removed by heating or argon ion bombardment. Thermal faceting takes place, and patches of a crystalline solid solution of tantalum (from the crystal support) and vanadium appear to form.

Metastable evaporated thin films of CuAg and CoAu alloys—I occurrence and morphology of phases

Metastable solid solutions of the CuAg and CoAu systems have been prepared by “vapor quenching” i.e. simultaneous vacuum evaporation of the two components onto a substrate held at liquid nitrogen temperature. The films so obtained are studied by resistivity measurements and by transmission electron microscopy and diffraction. The pure metals and dilute alloys are crystalline as deposited, while concentrated alloys (35–65% Ag for CuAg and 25–65% Au for CoAu) are amorphous when deposited on an amorphous substrate but crystalline when deposited onto a pure metal. The resistivity in the asdeposited state is almost independent of composition, but the annealing behavior of the various compositions is quite different. In particular, the high resistivity of the amorphous alloys anneals out in two distinct stages. In the first stage (near 370°K for CuAg and 430°K for CoAu) a transformation from amorphous to a metastable single-phase crystalline solid solution occurs in a narrow temperature range. The second stage, which is broader, involves the transformation to the equilibrium two-phase state. Structures at various stages of anneal are studied in detail by transmission microscopy and diffraction. A qualitative discussion is given of the reasons for the occurrence of the amorphous structure, for its relatively high metastability, and for its transformation first into a single-phase crystalline structure.

Transfer Processes in Irradiated Crystalline Solid Solutions

First Page

Metastable Alloy Films

Metastable alloy films of a number of binary alloy systems with limited terminaI solubilities were prepared by simultaneous vapor deposition of the two components onto a cold substrate. The resulting structures are either crystalline solid solutions (of concentrations higher than the terminal solubility) or amorphous solutions. Several examples for both types of structures are described. The conditions for occurrence of the amorphous structure are found to be a difference of atomic radii of the components in excess of 10% and a sufficiently low substrate temperature. The composition range of the amorphous structure increases with increasing difference of the atomic size of the components. Amorphous structures generally decompose at about 0.3 Tm (where Tm is the average melting temperature), while metastable crystalline structures decompose near 0.45 Tm. Thus, for many of the alloys studied, the metastable structure persisted to room temperature and above.

The infrared spectrum of ammonium thiocyanate from 90 to 300°K

The infrared absorption spectra of NH 4NCS, ND 4NCS, and of a mixture of partially deuterated species has been studied between 300–4000 cm −1 in the form of polycrystalline films at temperatures ranging from about 90–300°K. Initially amorphous films were annealed, and after crystallization exhibited splittings of all the degenerate modes of the ammonium and thiocyanate ions. A previously unknown phase (II) was observed which transformed irreversibly into the room temperature phase (I) at about 207°K in NH 4NCS and 189°K in ND 4NCS. Approximate compliance constants were evaluated and used to predict the frequencies of the partially deuterated species of ammonium ion. A crystalline solid solution containing a mixture of these species revealed extensive fine structure, which is attributed to the fact that in addition to the site group splittings of the degenerate species of NH 3D + and NH 2D 2 +, the isotopic C 3 υ molecules occupy their sites in four distinguishable ways and NH 2D 2 + occupies its site in six distinguishable orientations.

Molecular rotation and translation in crystals of compounds formed between highly branched hydrocarbons

Highly branched hydrocarbons rotate in the solid state and form solid solutions with compound formation. The compounds have a characteristic rotational transition replacing entirely the first order rotational transition of the components. The rotating crystalline solid solutions with the composition of the compound can be supercooled. The supercooled rotating solid behaves exactly like a glass. Certain deductions are made from these facts.

Molecular Rotation and Translation in Crystals. Nuclear Magnetic Resonance Absorption, Heat Capacity, and Entropy of Crystalline Solid Solutions of 2,2-Dimethylbutane in 2,3-Dimethylbutane from 10°K to 273°K

The nuclear magnetic resonance absorption of solid solutions of 2,2-dimethylbutane (A) and 2,3-dimethylbutane (B) has been studied as a function of composition. The melting range is clearly marked, but the rotational transition is absent. There is a maximum in the melting point diagram at the composition B2 A3. Thermal data have been determined on this complex from 10°K to 265°K from which the zero-point entropy has been deduced. The heat capacity curve and zero-point entropy of the crystals are those of a glass which indicates translational freedom in the rotating crystals.

Bakerian lecture.—On the constitution of the copper-tin series of alloys

This paper is an attempt to fill a very serious gap in the study of alloys. As a rule, an alloy begins to be interesting when the temperature of the liquid alloy has fallen to its freezing point. This point, which records the moment when solid first appears in the liquid, is easily observed on account of the evolution of latent heat that occurs on the formation of solid, and if the freezing points of all the alloys of a series are determined, we can plot the freezing-point curve. Many such curves have been traced in the last ten years: that of the copper-tin alloys is given by the upper line in our diagram. The curve consists of several branches cutting each other in angular points. The one thing that these curves record without ambiguity is the number of different solids that can crystallise out of the liquid alloys, for each branch corresponds to the crystallisation of a different substance. But this is almost all that such curves tell us with certainty. They do not tell us whether the solids forming are the pure metals, or pure compounds, or crystalline solid solutions of the metals. Other experiments are needed to decide such questions.