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Etude magnetique du compose intermetallique NdCo5
Vol. 4, No. 4
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
halides. The greatest effects are apparently associated with an absorption band edge which, for CrBr3, is located in the green. This paper presents the spectral variation of that rotation and of the corresponding absorption band edge. We consider a model consisting of a Cr~ ion in an octahedron of Br ions, subjected to a molecular field. It is shown that the absorption band edge in CrBr3 corresponds to charge transfer transitions in which an electron in a bromine orbital is promoted into an orbital localized on the central chromium ion. The rotation arises as a consequence of the splitting of the excited energy levels by the spin orbit coupling and the trigonal crystal field. (Received 31 December 1965) 10.
ETUDE MAGNETIQUE DU COMPOSE INTERMETALLIQUE NdCo6. H. Bartholin, B. Van Laar, R. Lemaire et J. Schweizer (CEN, Grenoble).
Les mesures magnótiques sur le compos~ NdCo5 montrent tine anomalie sur In courbe d’aimantation champ constant au voisinage de Ia température ambiante.
a
Une etude aux rayons-X sur des ~chantil1ons de poudre orient~set figés sons champ dtff~rentes temp~ratures indiquent une rotation de l’axe de facile aimantation entre 230°Ket 290°K. D’une etude aux neutrons diff~rentestemperatures, on deduit un arrangement ferromagn~tique et une decroissance reguli~redes moments lorsque Ia temperature croit.
a
a
La mesure des coefficients d’anisotropie magn~tiqueK~et K2 a ete faite stir une poudre orientée et colle’e sous champ. La variation thermique de ces coefficients permet d’ expliquer l’anomalie des courbes d’aimantation. (Received 26 January 1966) 11.
THEORY OF DOMAIN WALLS IN ORDERED STRUCTURES III J.W. Cahn and R. Kikuchi (Department of Metallurgy, Massachusetts Institute of Technology, Cambridge, Mass,)
mi
geneous system using the Bragg-Williams and the pair approximations. Thermodynamic selfconsistency requirements, similar to the Gibbs adsorption equation for interfaces, are derived and proved to hold for either approximation. The surface free energy is zero at T = 0°K, goes through a maximum as T increases, and comes back to zero again at the order-disorder transition temperature. The chemical potential and the surface excess values of free energy, energy, entropy and amount of each species are given as a function of temperature and composttion. (Received 13 January 1966) 12. FUSION BEHAVIOR AND PHASE CHANGES AT HIGH PRESSURES IN SOME INTERMETALLIC COMPOUNDS WITH FLUORITE STRUCTURE. A.R. Storm, J.H. Wernick, and A. Jayaraman (Bell Telephone Laboratories, Incorporated, Murray Hill, New Jersey). The fusion behavior at pressures to 50 kbars has been determined for AuA12, AuGa2 and AuIn2, all of which crystallize in the fluorite-type structure. The melting points of AuGa2 and AUA12 decrease with increasing pressure to 50 kbars. The fusion curve of AuIn2 has essentially zero slope to about 30 Icbars and then acquires a positive slope with further increase in pressure, suggesting the occurrence of a pressure induced phase change. The high pressure phase could not be retained on release of pressure. A technique for carrying out DTA with the belt apparatus is described. (Received 31 January 1966) 13. SYNTHESIS AND STABILITY OF A HIGH-PRESSURE POLYMORPH OF SULFUR. C. B. Sciar, L. C. Carrison, W. B. Gager, and 0. M. Stewart (Battelle Memorial Institute, Columbus Laboratories, Columbus, Ohio).
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The structure of an equilibrium CI 00) domain wall between two antiphase domains of a B.C. C. binary ordered alloy of non-stoichiometric composition is investigated by minimizing the appropriate free energy in the inhomo-
A new quenchable polymorph of sulfur has been prepared under high pressure and elevated temperature. It is stable between aoo C and the liquidus in the pressure range 30 to 60 kb, and is characterized by unique X-ray powder dtffraction data and optical properties. The strongest powder diffraction lines are 4. 04 A (100), 3.22 1 (35), 2. 90 A (20), 2.27 1 (20), and 1. 34 A (15). The phase is uniaxtal positive and shows essen-
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
halides. The greatest effects are apparently associated with an absorption band edge which, for CrBr3, is located in the green. This paper presents the spectral variation of that rotation and of the corresponding absorption band edge. We consider a model consisting of a Cr~ ion in an octahedron of Br ions, subjected to a molecular field. It is shown that the absorption band edge in CrBr3 corresponds to charge transfer transitions in which an electron in a bromine orbital is promoted into an orbital localized on the central chromium ion. The rotation arises as a consequence of the splitting of the excited energy levels by the spin orbit coupling and the trigonal crystal field. (Received 31 December 1965) 10.
ETUDE MAGNETIQUE DU COMPOSE INTERMETALLIQUE NdCo6. H. Bartholin, B. Van Laar, R. Lemaire et J. Schweizer (CEN, Grenoble).
Les mesures magnótiques sur le compos~ NdCo5 montrent tine anomalie sur In courbe d’aimantation champ constant au voisinage de Ia température ambiante.
a
Une etude aux rayons-X sur des ~chantil1ons de poudre orient~set figés sons champ dtff~rentes temp~ratures indiquent une rotation de l’axe de facile aimantation entre 230°Ket 290°K. D’une etude aux neutrons diff~rentestemperatures, on deduit un arrangement ferromagn~tique et une decroissance reguli~redes moments lorsque Ia temperature croit.
a
a
La mesure des coefficients d’anisotropie magn~tiqueK~et K2 a ete faite stir une poudre orientée et colle’e sous champ. La variation thermique de ces coefficients permet d’ expliquer l’anomalie des courbes d’aimantation. (Received 26 January 1966) 11.
THEORY OF DOMAIN WALLS IN ORDERED STRUCTURES III J.W. Cahn and R. Kikuchi (Department of Metallurgy, Massachusetts Institute of Technology, Cambridge, Mass,)
mi
geneous system using the Bragg-Williams and the pair approximations. Thermodynamic selfconsistency requirements, similar to the Gibbs adsorption equation for interfaces, are derived and proved to hold for either approximation. The surface free energy is zero at T = 0°K, goes through a maximum as T increases, and comes back to zero again at the order-disorder transition temperature. The chemical potential and the surface excess values of free energy, energy, entropy and amount of each species are given as a function of temperature and composttion. (Received 13 January 1966) 12. FUSION BEHAVIOR AND PHASE CHANGES AT HIGH PRESSURES IN SOME INTERMETALLIC COMPOUNDS WITH FLUORITE STRUCTURE. A.R. Storm, J.H. Wernick, and A. Jayaraman (Bell Telephone Laboratories, Incorporated, Murray Hill, New Jersey). The fusion behavior at pressures to 50 kbars has been determined for AuA12, AuGa2 and AuIn2, all of which crystallize in the fluorite-type structure. The melting points of AuGa2 and AUA12 decrease with increasing pressure to 50 kbars. The fusion curve of AuIn2 has essentially zero slope to about 30 Icbars and then acquires a positive slope with further increase in pressure, suggesting the occurrence of a pressure induced phase change. The high pressure phase could not be retained on release of pressure. A technique for carrying out DTA with the belt apparatus is described. (Received 31 January 1966) 13. SYNTHESIS AND STABILITY OF A HIGH-PRESSURE POLYMORPH OF SULFUR. C. B. Sciar, L. C. Carrison, W. B. Gager, and 0. M. Stewart (Battelle Memorial Institute, Columbus Laboratories, Columbus, Ohio).
-
The structure of an equilibrium CI 00) domain wall between two antiphase domains of a B.C. C. binary ordered alloy of non-stoichiometric composition is investigated by minimizing the appropriate free energy in the inhomo-
A new quenchable polymorph of sulfur has been prepared under high pressure and elevated temperature. It is stable between aoo C and the liquidus in the pressure range 30 to 60 kb, and is characterized by unique X-ray powder dtffraction data and optical properties. The strongest powder diffraction lines are 4. 04 A (100), 3.22 1 (35), 2. 90 A (20), 2.27 1 (20), and 1. 34 A (15). The phase is uniaxtal positive and shows essen-