John C. Jamieson

Formation of Diamond by Explosive Shock

Samples of graphite have been recovered after exposure to explosive shocks of 300,000-atm estimated intensity. X-ray and electron-diffraction examinations prove the existence of diamond in this material. The mechanism proposed for the formation of diamond under these conditions is simple compression in the c-axis direction of the rhombohedral form of graphite.

Crystal Structures of Titanium, Zirconium, and Hafnium at High Pressures

At high pressures, as determined by x-ray analysis, titanium and zirconium metal have a distorted, body-centered-cubic structure. This phase persists on pressure release. The normal hexagonal close-packed structures are recovered when the metals are heated. An electronic shift must occur in the transition. Hafnium metal showed no such transition.

Crystal Structures Adopted by Black Phosphorus at High Pressures.

Black phosphorus undergoes two reversible structural transitions at high pressures. The first is to a structure of the type arsenic A7. This structure is transformed to a simple cubic structure at higher pressures. The reversibility between the A7 and simple cubic structures at 111 kilobars indicates that the transition obtainable at this pressure provides a good calibration point by which high-pressure x-ray data may be united with volumetric or resistance measurements, or both.

Shock-Wave Compression and X-Ray Studies of Titanium Dioxide

The Hugoniot of the rutile phase of titanium dioxide has been determined to 1.25 megabars, and data show the existence of a phase change at about 0.33 megabar. The volume decrease associated with this transformation appears to be quite large (approximately 21 percent). Rutile, when recovered from shockloading in excess of the transformation pressure, is found to be irreversibly transformed to the orthorhombic lead dioxide structure (a distortion of the fluorite structure) with parameters a, 4.529; b, 5.464; and c, 4.905 angstroms and a calculated density of 4.374 grams per cubic centimeter. The new phase reverts to rutile at temperatures above 450�C. It is suggested that the new phase may be another diagnostic indicator of meteorite impact on the earths surface.

Phase Equilibrium in the System Calcite‐Aragonite

The equilibrium curve for two of the phases of CaCO3, calcite‐aragonite, has been determined as a function of temperature and pressure over the range 25–80°C and several thousand kg/cm2, using the electrical conductivity of aqueous solutions of each form. Aragonite is proved to be the high pressure modification. From the determined equilibrium curve, various thermodynamic quantities are obtained in a more accurate fashion than previously possible. All normal natural occurrences of aragonite must be due to metastable formation rather than equilibrium, since the geothermal gradient lies completely in the calcite field.

Crystal Structures at High Pressures of Metallic Modifications of Compounds of Indium, Gallium, and Aluminum

X-ray diffraction shows that the high-pressure modifications (at 22 to 130 kilobars) of the antimonides of indium, gallium, and aluminum are analogous to white tin. The arsenide and phosphide of indium transform to NaCl type. The transformation of these semiconductors to their metallic states is empirically related to their energy gap under normal conditions.

Crystal Structure of Tellurium at High Pressures

Powder x‐ray‐diffraction studies on tellurium up to 150 kbar show only two structural transitions at 40 and 70 kbar in agreement with Bridgmans work. The structure of the 40–70‐kbar phase is unsolved. Above 70 kbar, it is proposed that tellurium is isomorphous with β‐polonium and is rhombohedral with a=3.002±15 A, α=103.3°±3° (P=115 kbar), space group R3m with an atom in 1a (0, 0, 0).

New Device for Obtaining X‐Ray Diffraction Patterns from Substances Exposed to High Pressure

A device is described for obtaining powder diffraction patterns of thin sheets pressed between opposing diamond pistons. The pressure, initially applied by a small auxiliary laboratory press, is clamped onto the sample by a lock‐nut. The whole unit is designed to replace the sample mount of a standard x‐ray diffraction unit. Sample patterns taken on two of the high pressure modifications of bismuth are exhibited.

High-Pressure Polymorphism of Titanium Dioxide

X-ray diffraction studies made in situ under conditions of high pressure and high temperature revealed the direct transition of rutile to the alpha lead dioxide form in titanium dioxide. Compressibility studies of this alpha lead dioxide form at room temperature showed anomalous behavior in that its molar volume converges close to, but not equal to, that of the rutile form. Under this circumstance an unexpectedly large error appears in the calculations of the equilibrium pressure for the two forms at 298�K.

Elastic constants of nonmetamict zirconium silicate

Two independent reports in the literature for the elastic constants of zircon (zirconium silicate) are in disagreement by an order of magnitude and are reported without specifying the conditions of the mineralogical specimens. However, natural zircon crystals frequently contain uranium and thorium atoms as an impurity so that zircon can exist in a metamict (radiation damaged) condition. A redetermination of the elastic constants has been carried out on small synthetic crystals and on high‐purity natural single crystals of nonmetamict zircon of lattice parameters ao = 6.606(2) A, co = 5.980(2) A by ultrasonic pulse superposition and also by phase comparison methods. The values in 1012 dyn/cm2 are c11 = 4.237, c33 = 4.900, c44 = 1.136, c66 = 0.485, c12 = 0.703, and c13 = 1.495. The estimated uncertainty in the measurements are 0.4% for c11, c33, c44, and c66, and 3% for c12 and c13. Wave velocity measurements have also been carried out on a metamict zircon crystal (density 4.531 g/cm3) and it is shown that ...