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Metal Transition (metal + transition)
Selected AbstractsThe ,-to-, Transition in BiFeO3: A Powder Neutron Diffraction StudyADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Donna C. Arnold Abstract High-temperature powder neutron diffraction experiments are conducted around the reported ,,, phase transition (,930,°C) in BiFeO3. The results demonstrate that while a small volume contraction is observed at the transition temperature, consistent with an insulator,metal transition, both the ,- and ,-phase of BiFeO3 exhibit orthorhombic symmetry; i.e., no further increase of symmetry occurs during this transition. The ,-orthorhombic phase is observed to persist up to a temperature of approximately 950,°C before complete decomposition into Bi2Fe4O9 (and liquid Bi2O3), which subsequently begins to decompose at approximately 960,°C. [source] Electronic properties and phase transitions in Si, ZnSe, and GaAs under pressure cycling up to 20,30 GPa in a high-pressure cellPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009Sergey V. Ovsyannikov Abstract An automated high-pressure setup employing anvil-type cells is applied for investigation of phase transitions and elec- tronic properties (the thermoelectric power (Seebeck effect), the electrical resistivity) of silicon, zinc selenide and gal lium arsenide under pressure cycling within the range of 0,20(30) GPa. The "correlation" dependencies of a pressure value of the semiconductor,metal transition in Czochralski-grown silicon (Cz-Si) on the concentrations of both carriers and residual interstitial oxygen are discussed. In all Si samples a decompression of the high-pressure metal phase produces the semimetal p-type phases: the rhombohedral r8 (Si-XII) and the body-centred cubic bc8 (Si-III) lattices. Re- pressurization cycles reveal two features in the semimetal phase, near 2 GPa and 5 GPa. The transitions into the metal phase at higher pressure resemble those in pristine silicon. For ZnSe and GaAs, it is found that decompression from the high-pressure phases (NaCl and Cmcm, respectively) can follow different paths, producing the zincblende, the cinnabar and the wurtzite lattices. Advantages of the characterization method are discussed, in comparison with both the traditional techniques (X-ray diffraction, Raman spectroscropy, etc.) and the more recent ones (such as nanoindentation). (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic and transport properties of the Co-doped manganite La0.7Sr0.3Mn1,xCoxO3 (0 , x , 0.5)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2005B. C. Zhao Abstract The effect of Co doping on the magnetic and transport properties of La0.7Sr0.3Mn1,xCoxO3 (0 , x , 0.5) is investigated. The Co doping at Mn sites dilutes the double-exchange interaction between Mn3+ and Mn4+ ions and changes the long-range ferromagnetic (FM) order of La0.7Sr0.3MnO3 (LSMO) to the spin glass (SG) or cluster glass (CG) state for samples with x , 0.1. For x , 0.3, the paramagnetic (PM) metal to FM metal transition of LSMO disappears and the temperature dependence of resistivity ,(T) follows semiconducting behavior in the whole measured temperature region with the resistivity increasing by orders of magnitude. An interesting result is that ,(T) exhibits an obvious anomaly at T* , 100 K, which is ascribed to the spin-state transition of Co ions. For samples with x = 0.1 and 0.3, magnetoresistance (MR) effects are markedly enhanced in the low-temperature region compared with undoped LSMO, which is suggested to originate from the appearance of spin-dependent tunneling magnetoresistance. However, for samples with x = 0.5, the MR effect is suppressed over the entire temperature region measured and an obvious exchange anisotropy phenomenon, characterized by the shift of the hysteresis loop, is also observed, which is ascribed to the marked increase of the antiferromagnetic insulating phase. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanostructured antiferromagnetic spin glass in doped Ge near the insulator,metal transitionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008A. G. Zabrodskii Abstract It is shown that, on the insulator side of the insulator , metal transition, the single spin density exponentially disappears as T , 0. Such spins are bound into pairs to give an antiferromagnetic (AFM) phase. Upon an increase in temperature the AFM phase is destroyed, the single-spin density, and, as a result, ESR absorption signal becomes stronger. The temperature dependencies of the densities of the pairs and single spins are typical of a chaotic distribution of neutral donors. In this case, there is no Neel temperature. In low degree of compensation, the crystal lattice of Ge with the AFM phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AFM phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Insulator to metal transition induced by substitution in the nearly two-dimensional compound CuCr1,xVxS2PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006N. Tsujii The cover picture of this issue of physica status solidi (c) has been taken from the article [1]. [source] Raman phonons and Raman Jahn,Teller bands in perovskite-like manganitesJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2001Milko N. Iliev The perovskite-like manganites R1,xAxMnO3, where R is a trivalent rare earth or Y and A is a divalent alkaline earth element, are characterized by a strong interplay of magnetism, electric transport and crystallographic distortion. At doping levels 0.15 < x < 0.45 the materials exhibit colossal magnetoresistance near the concomitant ferromagnetic and insulator,metal transitions. At a fractional doping level, such as x = 0.5, the crystallographic and magnetic environment is strongly modified and charge ordering between Mn3+ and Mn4+ or phase separation takes place. In this work, the polarized Raman spectra of the orthorhombic and rhombohedral phases of parent RMnO3 compound were analyzed in close comparison with results of lattice dynamic calculations. We argue that the strong high-wavenumber bands between 400 and 700 cm,1, which dominate the Raman spectra of rhombohedral RMnO3 and magnetoresistive La1,xAxMnO3 are not proper Raman modes for the R3c or Pnma structures. Rather, the bands are of phonon density-of-states origin and correspond to oxygen phonon branches activated by the non-coherent Jahn,Teller distortions of the Mn3+O6 octahedra. The reduction of these bands upon doping of La1,xAxMnO3 and their disappearance in the ferromagnetic metallic phase support the model. The variation with temperature of the Raman spectra of La0.5Ca0.5MnO3 is also discussed. The results give a strong indication for charge and orbital ordering and formation of superstructure at low temperatures. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||