No abstract

A thermodynamic analysis of the vaporization of the substoichiometric plutonium dioxide phase [~1.6 O/Pu 5$ 2.0] is presented. The results are based on measurements of the vapor pressure of known compositions in tungsten, rhenium, and tantalum effusion cells over the range of temperature 1650 to 2100°K. The vapor pressures are interpretable in terms of Pu02(g), PuO(g), and oxygen as the important vapor species; the partial pressure of the gaseous dioxide is relatively insensitive to the composition of the solid phase whereas the partial pressures of gaseous monoxide and oxygen (both atomic and molecular) show a marked dependence and become predominant near the lower and upper phase boundaries, respectively. Known thermodynamic data for the solid phase are combined with the vapor pressure data to yield equations for the standard free energies of formation of gaseous dioxide and monoxide: A(7f0[(Pu02(g)] = -113,100 + 4.35T and &G°[ (PuO(g) ] = -29,000 -12.1 T. The congruently vaporizing composition is calculated to vary from O/Pu = 1.92 at 1600°K to 1.84 at 2400°K. ently vaporizing composition (minimum vapor pressure) was shown to exist for the Pu02_z phase although(1) Based on work performed under the auspices of the U. S. Atomic Energy Commission.(2) T. E. Phipps, G. W. Sears, and O. O. Simpson, J, Chem. Phys 18, 724 (1950).

The magnetic behaviour of ruthenium dioxide up to 1000°K is interpreted in terms of J being ca. -3000 cm.-l in dioxo-bridged chains of ruthenium atoms. The high electrical conductivity as well as certain structural features imply that the average oxidation state of the ruthenium atoms is substantially greater than +4.The oxide hydrate has a high surface area ; it is formulated as Ru02+,, yH,O since there can be an excess (chemisorbed) of oxygen particularly after removal of some of the water. Values of x up to 0.1 2 have been found whereas y is often 1 to 1.3. The susceptibility, though generally similar to that of RuO,, varies from sample to sample: its behaviour is discussed in relation both to the influence of adsorbed groups and also to some terminal ruthenium atoms behaving as mononuclear Ru(V), i.e., being in the d3 state. Expected spectral bands in the infrared have not been detected owing to the presence of electronic conductance bands. Solid State Physics Divisions, A.E.R.E., Harwell. Berkshire IN a recent note,l Cotton and Mague conclude that ruthenium dioxide has the rutile structure ; however, they point out that the closest Ru-Ru distance (3.107 A) excludes metal-metal coupling as the cause of the very of this second term and certain other properties to strong super-exchange, via the dioxo-bridges, in the chains (A) which exist in the c direction. Strong bondlow magnetic susceptibility. In this paper we report \RU/O\ /OARL,/ magnetic susceptibility measurements from 1.3 to from 298-673"~ together with other properties of the / \o/Ru\o/ \ 1033"~, supplementing previously available values (A) dioxide. The susceptibility per g.-atom of ruthenium, defined as XA-Xdia, has a temperature independent term ( N a ) which is relatively large, about 185 x lo* e.m.u. ; the temperature dependent term is small, about 20 x e.m.u. at room temperature and about 85x lo4 e.m.u. at 1000"~. We attribute the smallness ing within the chains is also indicated by the contraction along the c axis with increase of temperature that we have observed.The shape of the susceptibility-temperature curve is completely different from that predicted3 for a mononuclear 4d4 svstem in an octahedral environment but 1 F.

Implementation of electronic ground states and singlet and triplet excitation energies in coupled cluster theory with approximate triples corrections

MTDATA embodies the principle that equilibria in multicomponent, multiphase systems can be calculated from a knowledge of the thermodynamic data for the subsystems. A number of modules are incorporated for manipulating and retrieving the data, making various types of calculation and plotting binary, ternary, multicomponent, and predominance area diagrams. The principles and operation of MTDAT A are illustrated by reference to systems of practical importance.