The lattice parameters of seven oxides and two sulfides have been measured as a function of pressure to several hundred kilobars. FeO, CoO, NiO, MnO, and MnS have the NaCl structure or slight distortions thereof. The data can be fit by a Born—Mayer equation. For FeO, CoO, and NiO the crystal-field stabilization term contributes 5% to 15% of the total attractive pressure. FeS2 (pyrites) has a cubic structure which can be related to the fcc lattice. Its compressibility is much less than MnS and more comparable to the oxides. The binding is appraently covalent. SnO2, MnO2, and TiO2 all have the same tetragonal structure. For SnO2 and MnO2 the c axis actually expands with increasing pressure at low pressure, then passes through a maximum and ultimately contracts. The compressibilities of these two compounds are low at low pressure and increase at pressures beyond the maximum in c. TiO2 behaves more normally. It is apparent that central forces, and therefore ionic binding, contribute little to the cohesion of these crystals.

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The effect of pressure up to several hundred kilobars has been measured on the lattice parameters of a number of hep metals and alloys including magnesium and six dilute alloys, cadmium and two alloys, two alloys of silver with indium and two with antimony, and the rare-earth metals holmium, erbium, and thulium. For magnesium and its alloys the x-ray data combined with resistance data give rather clear evi dence for a transition at high pressure from hep to dhep (ABABAB---to ABACABAO ••)• Electrical resistance measurements on pure cadmium indicate a similar event. No transition is noted for the cadmium alloys. All four silver alloys underwent a similar transition at high pressure. The rare earths show a highpressure transition accompanied by an increase in the lattice parameter с with increasing pressure, which may be related to those appearing in the group II metals and the silver alloys.T HE effect of pressure to several hundred kilobars has been measured on the lattice parameters of 17 metals and alloys having the hexagonal-close-packed structure (hep) at 1 atm and 25 °C. The materials studied include magnesium and six dilute alloys of mag nesium, cadmium and two alloys, four alloys of silver, and three rare-earth metals. The magnesium and alloys were obtained from C. S. Smith of Case Institute of Technology and from R. S. Busk of Dow Chemical Company. The cadmium, silver, antimony, and indium were 99.99% material from A. D. Mackay. The cad mium alloys with silver were prepared by melting mixed powders of the two in vacuo in a resistance furnace at 650°C. The alloys were annealed for 21 days at 300°C. The samples were filed and the filings reannealed for 48-72 h at 290°C. The silver alloys were prepared by melting in an argon atmosphere in an induction furnace, annealed in vacuo for 23 days at 550°C. The filings were reannealed for 72 h at 550°C. All alloy samples were checked for weight loss at each stage. The compositions of the alloys, the electron to atom ratios, and the one atmosphere lattice parameters for both pure metals and alloys are summarized in Table I.

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The effect of high pressure has been measured on a series of alloys, including Fe plus 8 at. % Si, which has a (disordered) bcc structure, Fe3Al and Fe3Si, which have an ordered bcc structure, and FeAl and AgMg, which have the CsCl structure. The compressibilities of all the alloys except Fe3Si decrease with increasing pressure and lie between those of the pure components. For Fe3Si the compressibility increases slightly with increasing pressure and is less than that either of pure iron or pure silicon.