Chemical Principles And Properties

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Electric and Magnetic Anomalies At the Charge-Density-Wave Transition in Niobium-Substituted Vanadium Diselenides

A systematic study has been made of the effect of niobium substitution on the CDW transition in VSe2, especially in the low-doping region. Transitions were monitored by measurements of static magnetic susceptibility, which has been found to be particularly sensitive for both onset and lock-in discontinuities, and by measurements on resistivity and Hall effect. Results, discussed in terms of the model of Chan and Heine and in terms of McMillan\u27s phenomenological model, suggest that structural changes due to the presence of the niobium dopant lead to enchanced electron-phonon coupling thus raising the CDW onset temperature

Crystal Data for Mixed-Anion Molybdenum Dichalcogenides

The layered dichalcogenides1 MoS2 and MoSe2 are of special interest as lubricants, 2 catalysts, and catalyst supports for hydrodesulfurization reactions, 3 precursors of intercalation superconductors, 4 and possible electrodes for photoelectrolysis.5 In the pure, stoichiometric state they are moderate-gap semiconductors (1.75 eV for MoS2 and 1.4 eV for MoSe2), 5 presumably because the characteristic trigonal splitting of the d orbitals leads to filled d subbands. As part of a larger study on how small changes in chemical parameters affect superconductivity, we have had occasion to prepare the full solid solution series MoS2-xSex (0 \u3c × \u3c 2). The end compounds form both 2H and 3R polytypes. In each case, molybdenum atoms occupy trigonal-prismatic sites within the layers. In addition, in the system MoS2-xSex, a continuous series of solid solutions can be prepared, all having the same 2H two-layer hexagonal structure (space group P63/mmc). We report in this communication the evolution of lattice parameters of the mixed-anion system

The Effect of Niobium Substitution on Charge Density Wave Anomalies in Vanadium Diselenide

Precise measurements of the static magnetic susceptibility have been made by the Faraday method over a range of temperature from 1.6 to 300 K on a series of niobium-substituted vanadium diselenides. The kink anomaly associated with onset of the charge density wave at 117 K in VSe2 is observed to move to higher temperatures as the niobium concentration is increased. In addition, plateaus appear in the susceptibility versus temperature curve below the onset temperature. It is suggested that the plateaus are due to stepwise destruction of the Fermi surface. A transition to the commensurate state is observed at about 75 K in pure VSe2; it is relatively insensitive to the doping level and is observed as an anomaly in the magnetic susceptibility even at a 10% doping level

Chemistry

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Chemistry

xii, 654 p. illus. (part col.) 25 cm

Chemistry

xiv,623; 24 cm

Chemistry

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Experimental chemistry

xi, 439 p.; 21 cm

A textbook of chemistry for university students /

"This book is based on tape recordings of lectures in the large introductory chemistry course at Cornell University"--Pref.Mode of access: Internet