The use of Mössbauer spectroscopy in stable isotope geochemistry

Equilibrium Iron Isotope Fractionation Factors of Minerals: Reevaluation from the Data of Nuclear Inelastic Resonant X-ray Scattering and Mossbauer Spectroscopy

Iron isotope fractionation between pyrite (FeS2), hematite (Fe2O3) and siderite (FeCO3): A first-principles density functional theory study

Transport properties of La 2- x Sr x CuO 4 , YBa 2 Cu 3 O 6+ x and Bi 1.6 Pb 0.5 Sr 1.9- y La y Cu 1.05 O z have been studied over wide temperature regions. Drastic temperature variations of the Hall coefficients R H found in the underdoped region of the hole carriers suggest that there exists a crossover-like change of the electronic state above room temperature. Temperature dependence of other transport properties studied at high temperatures is also discussed in relation to this anomalous behavior of R H . These results elucidate the formation process of the abnormal metallic state of high- T c oxides at low temperatures, the existence of which characterizes the metal-insulator transition of the Cu-oxide system as a new-type Mott-Hubbard transition.

Transport Anomalies of High-T c Oxides above Room Temperature

The NiS{sub 2{minus}x}Se{sub x} system represents one of the best examples of a Mott-Hubbard system, i.e., a system in which, under appropriate conditions of concentration, temperature, or pressure, a metal-insulator transition driven by electron-electron interaction takes place. Here, the metallic phase is either antiferromagnetic (for 0.44 {le} x {le} 1) or paramagnetic (for x {ge} 1), whereas the insulating phase is as a rule antiferromagnetic (including the spin-canted phases). In this paper the authors review both the physical properties and outline the basic features of the theoretical approach to those correlated electron systems. Emphasis is placed on a qualitative understanding of the observed transformation of the system from semiconductor (or magnetic insulator) to metal.

Electronic Properties of NiS2-xSex Single Crystals: From Magnetic Mott−Hubbard Insulators to Normal Metals

Specific heats of FeS 2 -CoS 2 -NiS 2 Solid solutions and of Ni 0.95 Cu 0.05 S 2 have been measured from 10 K to 350 K. Debye temperatures, coefficients of electronic contribution γ, magnetic ordering temperatures, and magnetic entropies have been determined. The magnetic entropy of ferromagnetic Fe 1- x Co x S 2 is proportional to cobalt concentration and is 40% of that expected for a localized spin 1/2 per Co atom, suggesting an itinerant character of e g electrons. The magnetic entropy of NiS 2 is smaller than that of a localized spin 1 and is in good agreement with that expected for the magnetic moment observed by neutron diffraction. The magnetic entropy of antiferromagnetic Co 1- x Ni x S 2 Suggests that only Ni atoms have magnetic moment in Ni-rich phase. The density-of-states curve of e g band for NiS 2 has been constructed from γ values assuming a rigid band. The band width of lower half of e g band is 0.6 eV. The Debye temperature decreases monotonously from 605 K of FeS 2 to 455 K of NiS 2 .

Shinji Ogawa

Papers

Specific Heat Study of Magnetic Ordering and Band Structure of 3d Transition Metal Disulfides Having the Pyrite Structure