No abstract available

[en] The present work reports on the influence of CO₂ on the chemical constitution and catalytic properties for the oxidative dehydrogenation of ethane (OXDE) of the praseodymium oxide (Pr₆O₁₁. When the reaction is run in a flow of He praseodymia behaves like ceria, whereas in a flow of CO₂ its behaviour is closer to that of lanthana. In the latter case, Pr(III) ions become stabilized as monocarbonate dioxide (Pr₂O₂CO₃), thus explaining the differences of selectivity observed between reducible rare earth oxides, and the sesquioxides or CO₂ treated praseodymia

[en] Electron microscope images obtained at about 3A resolution for Pr₇O₁₂ (and isomorphous Zr₃Sc₄O₁₂) are in excellent agreement with calculated images based upon the structure determined separately by total profile neutron powder diffraction analysis. The image calculation programs establish the efficacy of lattice image interpretation in structural terms for these types of related phases whose structures are as yet beyond conventional means to determine. Such images for several other intermediate phases are interpreted and structures proposed. Finally, images of crystals which can be made to undergo reaction within the microscope are interpreted according to the structures involved. These studies reveal the role of intergrowth and topotaxy in these systems

No abstract available

No abstract available

[en] Doped manganites with bilayer structure La_2-2xSr_1+2xMn₂O₇ have attracted the considerable interest by having more than one physical phenomena such as broad metallic region, Jahn-Teller distortion, etc. Keeping the hole concentration at x = 0.4 in La_1.2Sr_1.8Mn₂O₇, the doping of 60 % small ionic radius Pr³⁺ (1.126 A) on the larger La³⁺ (1.160 A) site, Viz. (La_1-zPr_z)_1.2Sr_1.8Mn₂O₇, which causes the mismatch in the cationic size, in turn modifies the crystal field. Hence, (La_0.4Pr_0.6)_1.2Sr_1.8Mn₂O₇ (LPSMO) becomes an insulator for all range temperature. Gordon et al., studied the effect of magnetic field on LPSMO and found the first-order insulator-metal transition at 50K and it is increased as 100K, 125K, 150K by further increase of field. The magnetic field and hydrostatic pressure has the same nature on manganites of making the more ferromagnetic metal due to the enhancement of interlayer coupling by ferromagnetic double exchange phenomena through favoring of 3d_x²_-y² states with respect to 3d_z²_-r². In this paper, we have carried out a systematic investigation of hydrostatic pressure effect on the insulating state of (La_0.4Pr_0.6)_1.2Sr_1.8Mn₂O₇ system

[en] To study the electronic structure of CeP crystal (and its two analogs) a cluster approach, realized within the framework of the scattered waves X_α (MSX_α) with a local exchange operator and MT-approximation for density and potential, is used. Due to additions, introduced into the calculation program according to the MSX_α, ions charges have been correlated depending on their values, obtained as a result of the MSX_α procedure. The reasonable parameter values of crystal fields of the fourth and sixth orders are determined

[en] The mixing method was used in the temperature range 400--2200⁰K to conduct the first systematic study of the enthalpy of sulfides of the praseodymium-sulfur system. Temperature dependences of the enthalpy, heat capacity, entropy, and corrected Gibbs energy of the investigated compounds were obtained and are recommended for practical use. It was established that enthalpy and heat capacity decrease from PrS to PrS₂ due to an increase in the degree of covalence of the sulfides with an increase in the ratio [S]/[Pr]

[en] Method of X-ray diffraction analysis was used to investigate the structure of praseodymium oxide films, prepared by Pr₆O₁₁ vacuum precipitation. Formation of nonstoichiometric PrO_1.83-x phase, A- and C- forms of Pr₂O₃, depending on precipitation temperature was established. Precipitation temperature, leading to formation of equilibrium Pr₂O₃ structure in films, is equal to 900 deg C

[en] Published in summary form only