Showing papers on "Charge ordering published in 1970"

Collective Electron Theory of the Metal‐Semiconductor Transition in Magnetite

Abstract: The Verwey transition in magnetite is described on a band model, with the electrons self‐consistently breaking the symmetry by ordering in the self‐induced Coulomb potential. The order parameter is the difference in occupation numbers on alternate sites. There is a gap in the single‐particle excitation spectrum, and the gap and order parameter undergo a second‐order phase transition. The theory is BCS‐like, with the Verwey temperature being given in the weak‐coupling limit by an exponential in the reciprocal of the density of states at the Fermi level.

Metal-insulator transition in transition metal oxides

Abstract: The metal-insulator transition in the V2O3 system is discussed. A recent series of experiments on V2O3 and (V1-xCrx)2O3 is reviewed. The phase diagram fort he system is described. The Cr-doped mixed oxides are insulating at room temperature for x ≥ 0.009 and transform to a metal with the application of pressure. This phase transition is identified as a Mott transition. A comparison is made between the experimental results and theoretical predictions of the Mott transition.

Observation of a phase transformation in Eu3S4 at 168°K

Abstract: A phase transformation in EU3S4 at 168°K has been established by several different experimental methods. Electrical conductivity and Seebeck coefficient measurements show a discontinuity through the transition. Above the transition temperature, the activation energy for conduction is 0.163 eV and the resistivity is about 3 × 10 4 Ωcm , while below the transition the activation energy is 0.21 eV and the resistivity is about 106 Ωcm. Differential thermal analysis thermograms reveal an endothermic peak on heating with a hysteresis of 5°C. X-ray diffraction experiments show a change in symmetry accompanied by a lattice parameter change of approximately 0.4% for the transition. Measurements of the magnetic susceptibility show the transition not to be magnetic in origin. It is proposed that the transformation in EU3S4 is due to charge ordering which produces tetragonal symmetry in the unit cell.