Secondary-tertiary acetylenic δ-glycols in the mannich reaction

Conclusions Some acetylenic bis(diethylaminomethyl) ethers were obtained by the reaction of secondary-tertiary acetylenic -glycols with diethylamine by the Mannich reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2824–2825, December, 1970.     

Magnetic phase transitions in the iron-doped Pr<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>Mn<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>Fe<Subscript>y</Subscript>O<Subscript>3</Subscript> manganites at high pressures

The atomic and magnetic structures of the iron-doped Pr_0.7Ca_0.3Mn_1?yFe_yO₃ manganites (y=0, 0.1) have been studied at high pressures of up to 4 GPa in the temperature range 16–300 K. At normal pressure, Pr_0.7Ca_0.3MnO₃ undergoes a phase transition from the paramagnetic to an antiferromagnetic (AFM) state of the pseudo-CE type and Pr_0.7Ca_0.3Mn_0.9Fe_0.1O₃ undergoes a phase transition from the paramagnetic to the ferromagnetic state at low temperatures. Partial substitution of Mn atoms by Fe brings about a noticeable decrease in the average magnetic moment per atom. A new A-type AFM state was observed to form in Pr_0.7Ca_0.3MnO₃ at a pressure P≈2.2 GPa and in Pr_0.7Ca_0.3Mn_0.9Fe_0.1O₃ at 2.7 GPa. This phenomenon may originate from the anisotropy in the compressibility, which causes uniaxial contraction of the oxygen octahedra MnO₆ in the structure and provides favorable conditions for the formation of an A-type AFM state. The structural parameters obtained were used to calculate the pressure dependence of bandwidth in the compounds under study.     

Chemical shifts in the x-ray emission spectra of MgB<Subscript>2</Subscript> and their correlation with the electronic structure

The x-ray emission spectra of magnesium diboride MgB₂ are measured. It is found that the Mg L_2,3 and B K_α emission lines are shifted with respect to the spectra of the pure metals toward the low-energy range. The band calculations of the MgB₂ diboride in the framework of the full-potential linearized muffin-tin orbital (LMTO) method demonstrate that the electron populations of the shells in both components of MgB₂ are higher than those of pure metals. This increase in the electron populations is associated with the crystal contraction and manifests itself in low-energy shifts of the emission lines.     

Electronic origin of solid solution softening in bcc molybdenum alloys

The intrinsic mechanism of solid solution softening in bcc molybdenum alloys due to 5d transition metal additions is investigated on the basis of ab initio electronic-structure calculations that model the effect of alloying elements on the generalized stacking fault (GSF) energies. We demonstrate that additions with an excess of electrons (Re, Os, Ir, and Pt) lead to a decrease in the GSF energy and those with a lack of electrons (Hf and Ta) to its sharp increase. Using the generalized Peierls-Nabarro model for a nonplanar core, we associate the local reduction of the GSF energy with an enhancement of double kink nucleation and an increase of the dislocation mobility, and we reveal the electronic reasons for the observed dependence of the solution softening on the atomic number of the addition.     

Role of embedded clustering in dilute magnetic semiconductors: Cr doped GaN

Results of extensive density-functional studies provide direct evidence that Cr atoms in Cr:GaN have a strong tendency to form embedded clusters, occupying Ga sites. Significantly, for larger than 2-Cr-atom clusters, states containing antiferromagnetic coupling with net spin in the range 0.06-1.47 muB/Cr are favored. We propose a picture where various configurations coexist and the statistical distribution and associated magnetism will depend sensitively on the growth details. Such a view may elucidate many puzzling observations related to the structural and magnetic properties of III-N and other dilute semiconductors.     

Synthesis of Iron(II,III)-containing Derivatives of Arabinogalactan

A synthesis of iron(II, III) derivatives of arabinogalactan, involving formation in an alkaline solution of a hydrated iron(II, III) oxide biopolymer, is proposed. Optimal conditions of the synthesis are determined.