The electrical resistivity of some uranium tellurides

Electrical resistivity of U₃Tein4, U₂Te₃ (cubic) and UTe₃ has been measured over temperature range 4.2–300 K. The two former compounds appear to be semimetallic conductors while the last one has semiconducting character. The results are discussed in the terms of available magnetic data.     

Parallel organization of contralateral and ipsilateral prefrontal cortical projections in the rhesus monkey

Background  

The neocortical commissures have a fundamental role in functional integration across the cerebral hemispheres. We investigated whether commissural projections in prefrontal cortices are organized according to the same or different rules as those within the same hemisphere, by quantitatively comparing density, topography, and laminar origin of contralateral and ipsilateral projections, labeled after unilateral injection of retrograde tracers in prefrontal areas.     

Optical and electrical properties of Be doped GaN bulk crystals

Highly resistive GaN : Be was obtained by means of synthesis of Ga+Be with atomic nitrogen under high nitrogen pressure. Activation energy of resistivity is about 1.5 eV. This material exhibits features very different from those observed in highly resistive bulk GaN : Mg. Up to 300 K strong yellow band dominates photoluminescence spectrum in resistive GaN : Be crystals. Positron annihilation studies point to the presence of gallium vacancies, V_Ga. In highly resistive GaN:Mg neither yellow band with considerable intensity, nor detectable concentration of V_Ga was found. We also discuss the puzzling findings in highly resistive bulk GaN : Be of morphological features typical for highly conducting bulk n-GaN material.     

Electron paramagnetic resonance of impurities in uranium trichalcogenides

Uranium trichalcogenides US₃ and UTe₃ were examined by EPR. The measurements were performed at the X-band over temperature range 4.2–300K and with the magnetic field applied perpendicular and parallel to the (001) plane. The EPR spectra consist of two lines with g-factors about 2 and 4 respectively. Results are discussed in terms of interactions of the U⁴⁺ ion with impurities. A magnetic ordering in US₃ below 50 K is suggested.     

Magnetic structure of the cubic U2Te3 with a non-stoichiometric Th3P4 type of structure

The neutron diffraction patterns of the cubic U₂Te₃ have been obtained at 15 and 150 K. There are no extrapeaks of magnetic origin below the Curie point T_c = 70 ± 5 K. Thus the ordering corresponds to a collinear ferromagnetic structure. The value of the magnetic moment is 1.78 μ_B which is close to those values determined for a few cubic uranium pnictides and chalcogenides.     

High pressure phase transition in PbSnTe

The high pressure structural phase transition in the alloy series Pb_{1 ? x}Sn_xTe has been investigated using resistivity and Hall coefficient measurements. With increasing of tin content the critical pressure decreases linearly and the phase transition becomes less drastic. The anomalous behavior of the resistivity in the phase transition region is explained by band structure changes. It is suggested that the high pressure phase transition in Pb_{1 ? x}Sn_xTe is a metallic-covalent transition.     

Pressure induced phase transition in PbSnTe

Hall coefficient R_H and resistivity ? for Pb_0.56Sn_0.44Te crystal were measured as a function of temperature and pressure in the region of the ferroelectric phase transition. It enabled to obtain the pressure dependence of the phase transition temperature. Analysis of the experimental data showed that the lattice anharmonicity gives the dominant contribution to the phase transition mechanism.