The effect of pressure to 200 kbar has been measured on the Mössbauer resonance in a number of high-spin ionic ferrous and ferric compounds. The isomer shift and quadrupole splitting characterize the ionic state and spin state of iron. In general, there is a decrease in the iosmer shift with increasing pressure correspinding to an increase of electron density at the iron nucleus. This can amount to 8%—20% of the difference in isomer shift between typical ferrous and ferric compounds. The pressure effect is usually larger in ferrous than in ferric compounds, and is associated with changes in the 3d−3s shielding. The quadrupole splitting usually increases with pressure. A quantitative interpretation depends on knowledge of changes in local symmetry and of spin—orbital coupling factors, as well as local compressibility. For six of the eight ferric compounds, we observed a significant amount of reduction to the ferrous state at high pressure. This phenomenon was definitely reversible. It appears to be associated with a general tendency for the ground state of the ferrous ion to decrease in energy relative to the ligands with increasing compression. Thus, electron transfer is facilitated. Some evidence exists that strong light also reduces iron compounds. These results tend to broaden the analogy previously noted between photochemical and high-pressure reactions.

The effect of pressure to 200 kbar has been measured on the Mössbauer resonance in potassium ferrocyanide, potassium ferricyanide, and insoluble Prussian blue. The ferrocyanide exhibits a decrease of isomer shift with pressure large compared with typical high-spin ionic ferrous compounds. The ferricyanide exhibits an initial shift with pressure twice as large as the ferrous material. These large changes can be associated with changes in ``back donation'' and in 4s admixture in the binding. The ferricyanide reduces to ferrous compound with increasing pressure, paralleling to behavior of many high-spin ferric compounds. As in the case of the high-spin material, the phenomenon reverses with decreasing pressure. Near 50 kbar a first-order phase transition occurs which apperantly relieves the internal compression of the ferricyanide ion. It is accompanied by an increase in the isomer shift of the ferric ion and the pressure-induced ferrous ion as well as a decrease in the quadrupole splitting of the former. It is also accompanied by a large decrease in the percentage of Fe2+ ion present. This definitely relates the reversible reduction of ferric iron to overlap of the wavefunctions of metal and ligand. Insoluble Prussion blue contains high-spin ferric ion and low-spin ferrous ion. This compound also shows a reversible reduction of high-spin ferric ion with increasing pressure.

Uniaxial shock-compression studies were conducted on Teflon in the stress region between 2.5 and 25 kbar using a compressed-gas gun and quartz-gauge instrumentation. Measurements of stress and particle velocity at the impact surface show that a transition occurs at 5.0 * O. 2 kbar with an associated volume change of approximately 2.2 * 0.2%. Measurements of the stress wave profiles after transmission through the samples show an attenuation of peak stresses and suggest a visoelastic behavior of Teflon.

The effect of shock stress amplitude and duration on the hardness and microstructure of Hadfield steel has been investigated over the pressure range of 5–480 kbar. Electron microscopy techniques were used to examine the microstructure and measure the dislocation density of shock loaded specimens. Stacking fault and twin fault probabilities were estimated from x-ray diffeaction experiments. For a given peak shock stress the time duration of the stress pulse greatly affected the hardness and microstructure of the shocked material. The Hugoniot equation of state of Hadfield steel is reported for shock stresses of 5–500 kbar.

An apparatus has been developed which permits high pressure Mössbauer resonance studies to 300 kbar. It can be operated with either the source or the absorber under pressure. The pressures are established by x-ray diffraction measurements, and calibration curves are presented for both the supported taper and Bridgman anvils cells. A motion device involving magnets and phosphor bronze springs, with an adjustable mount, is described. Circuits necessary to control the motion, and to distribute the signals from two devices operating in parallel, are outlined.