The effect of internal pressure on charge-ordered rare earth manganates of the compositionLn 1−x A x MnO3(Ln=La, Pr, Nd andA=Ca, Sr) has been studied by varying the average radius of theAsite cations (〈r A 〉). Increasing 〈r A 〉 is generally accompanied by an increase in the ferromagnetic transition temperature and a decrease in the charge-ordering transition temperature. On increasing the size of theAsite cations by appropriate substitution, charge-ordered insulators such as Pr0.7Ca0.3MnO3and Nd0.5Ca0.5MnO3become ferromagnetic, accompanied by an insulator-metal transition. In Pr0.5Sr0.5MnO3, substitution of La in place of Pr destroys the antiferromagnetic transition and favors the ferromagnetic metallic state.
C. N. R. Rao and R. Sen, Chem. Commun., 1998, 1525 DOI: 10.1039/A802258E
Single crystalline nanorods and nanowires of t-Te have been prepared by a simple solution route. The procedure involves the disproportionation of NaHTe, prepared by the reduction of Te with NaBH4. By carefully controlling the reaction conditions, the diameter of the nanorods could be varied in the 20–300 nm range. Nanowires of 10 nm diameter were obtained in the presence of sodium dodecylbenzenesulfonate. Te nanobelts and nano junctions were obtained by employing hydrothermal and solvothermal conditions. The nanorods have been characterized by a variety of microscopic and spectroscopic techniques. UV-Visible spectra reveal two absorption bands, one around 300 nm which is size-sensitive and the other at 600 nm insensitive to size.
Au, Pt and Au–Pt alloy nanocrystals have been prepared in thin SiO2 film matrices by sol–gel spin-coating, followed by heating at 450 °C in 10% H2–90% Ar. X-Ray diffraction patterns reveal that the Au and Au–Pt nanocrystals have a preferential (111) orientation. Upon increasing the Pt concentration, part of the Pt does not alloy with Au, but instead forms a shell around the Au–Pt alloy core. The alloy composition itself goes up to Au(50) : Pt(50), and the Pt shells are formed around the alloy above an alloy composition of Au(75) : Pt(25). The surface plasmon resonance (SPR) band at 544 nm of Au gradually disappears due to the formation of Au–Pt alloys and core–shell structures.
No abstract is provided for this article.
Phase transitions of CsNO3 (II-I), RbNO3 (IV-III-II) and NH4NO3 (V-IV-III-II-I) have been studied by i.r. spectroscopy. The study has provided useful information on the changes in the dispositions of the ions during the phase transitions.
No abstract is provided for this article.
Electrochemical reduction of CO2 to produce value-added fuels is an effective strategy for capturing and utilizing atmospheric CO2. The development of an electrocatalyst for efficient and selective reduction of CO2 is highly desirable. However, most of the research focuses on metal-based catalysts, which suffer from drawbacks such as high cost, limited resource availability, and competing hydrogen evolution. Herein, we study the electrochemical reduction of CO2 on metal-free borocarbonitride (BxCyNz) catalysts in an aqueous electrolyte. BC1.2N0.8 catalyst exhibits high selectivity for CO, reaching a CO faradaic efficiency of 98% at −0.45 V (vs RHE). Thus, we have tuned the composition of BxCyNz to study the effects of incorporating B and N in a carbon lattice. This work provides insights into the effects of codoping heteroatoms in a carbon lattice on the surface area, CO2 uptake, and electrochemical reduction of CO2. A linear correlation was observed between FECO and N content, specifically pyridinic N content, shedding light on the active site for the electrochemical reduction of CO2.
In order to investigate the factors determining the relative stabilities of layered perovskite and pyrochlore structures of transition metal oxides containing trivalent bismuth, several ternary and quaternary oxides have been investigated. While d 0 cations stabilize the layered perovskite structure, cations containing partially-filled d orbitals (which suppress ferroelectric distortion of MO6 octahedra) seem to favor pyrochlore-related structures. Thus, the vanadium analogue of the layered perovskite Bi4Ti3O12 cannot be prepared; instead the composition consists of a mixture of pyrochlore-type Bi1.33V2O6, Bi2O3, and Bi metal. The distortion of Bi1.33V2O6 to orthorhombic symmetry is probably due to an ordering of anion vacancies in the pyrochlore structure. None of the other pyrochlores investigated, Bi2NbCrO7, Bi2NbFeO7, TlBiM2O7 (M = Nb, Ta), shows evidence for cation ordering in the X-Ray diffraction patterns, as indeed established by structure refinement of TlBiNb2O7.
No abstract is provided for this article.
In the Tl1-yPbyCaSr2Cu2O7 system, monophasic superconducting compositions are formed in the range 0.25 < y < 0.60 and the minimum Pb content required to stabilize the tetragonal 1122 phase is about 25%. Maximum Tc is found when y = 0.5, at which composition the hole concentration is optimal. Metallic compositions of Tl1−yPbyCaSr2Cu2O7 (y = 0.25) and Tl0.75Pb0.25Y1−xCaxSr2Cu2O7 (0.80 ⩽ X ⩽ 1.0) become superconducting on decreasing the oxygen content by vacuum annealing.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
