Spin-orbit Distortion Research Articles

The effects of spin-orbit distortion in deuteron stripping reactions

Proton differential cross-section and polarization are calculated for the rreactions C 12(d, p)C 13 (1st excited state) and Si 28(d, p)Si 29 at deuteron energies of 6 MeV and 15 MeV, respectively. The D.W.B.A. is employed and spin-dependent proton distortion is taken into account. Spin-orbit distortion is found to leave a small effect on the cross-sections, but the polarization is found to be large. In the case of the Si 28 reactions good agreement with the experimental polarization is obtained. An approximate treatment of both deuteron and proton spin-dependent distortion is developed and partially justified. Relatively simple expression for the polarization effects are obtained.

Direct Cation- -Cation Interactions in Several Oxides

It is pointed out that interactions between octahedral-site cations are cation-anion-cation interactions if the cation-occupied octahedra share a common corner, but may be primarily cation- -cation (no anion intermediary) if the cation-occupied octahedra share either a common edge or a common face. It is further pointed out that cation- -cation interactions may be naturally classified as "strong" or "weak" since there is a critical cation separation below which the interacting electrons are best described by a collective-electron model, above which by a Heitler-London model. The characteristics of the different interactions under varying conditions are summarized. In the case of strong cation- -cation interactions, covalent-type bonds may be formed at low temperatures. The resulting phase transitions are marked by the following features: (1) the transitions may be noncooperative (isolated cation-cation pairing introducing no symmetry change to the structure) and extend over a considerable temperature interval ($\ensuremath{\Delta}T\ensuremath{\sim}100\ifmmode^\circ\else\textdegree\fi{}$C), or cooperative, occurring at a definite temperature and exhibiting thermal hysteresis. (2) Bonded cations are displaced from the center of symmetry of their anion interstice (in contrast to Jahn-Teller or spin-orbit distortions). (3) Bonding electrons are spin-paired so that they make no contribution to the atomic moment unless localized, unpaired $d$ electrons are simultaneously present to weaken the covalent-type bond via intra-atomic exchange. (4) Bonding electrons cannot contribute to metallic-type conductivity so that if the bond-forming phase ties up all of the outer $d$ electrons in covalent-type bonds, the transition is semiconducting \ensuremath{\rightleftharpoons} metallic. The physical properties of several compounds that illustrate the importance of the cation- -cation interactions are discussed.