Search

Effects of cation disorder and strain on the surface morphologies and transport properties of thin films with different A-site cation disorder, which was achieved by Y and Sr codoping into La2/3Ca1/3MnO3, have been investigated. A metal-insulator transition (MIT) was observed on all films except that on MgO, which indicates that large strain increases insulator phase. With increasing cation disorder, the resistivity increases while MIT and Curie temperature decrease, which reveal that cation disorder suppresses the long-range ferromagnetic metallic phase. The spin-glass state and ferromagnetic-metallic state coexist in low temperature. Cation disorder induces more insulator phases in the large strain films. A Kondo-like transport behavior was observed in the large cation disordered films. [ABSTRACT FROM AUTHOR]

Polycrystalline manganite oxides with different A-site cation disorder were synthesized. The hole concentration and average radius of A-site cation are kept unchanged while the A-site cation disorder increases linearly by Y and Sr co-doped in La2/3Ca1/3 MnO3. All these samples exhibit a paramagnetic insulator to ferromagnetic (FM) metal transition, and the transition temperature TC and TMI decrease while the transition width increases with increasing the A-site cation disorder. TMI is usually 10 K higher than TC for the small cation disorder samples. However, with increasing the cation disorder, TMI is about 60 K lower than TC, and the resistivity increases in magnitude while the magnetization decreases. The metal-to-insulator transition for samples with small cation disorder can be well described by a percolative model, which indicates FM-metal state and antiferromagnetic insulator state assuredly coexist in the transition interval. It reveals that cation disorder suppresses the long-range FM-metal state which results in the phase separation behavior in samples with large cation disorder. [ABSTRACT FROM AUTHOR]

Y and Sr co-doped La2/3Ca1/3MnO3 films with different A-site cation disorder were deposited on Yttrium-stabilized ZrO2 (YSZ) single crystal substrate by modified off-axis rf magnetron sputtering technology. The influences of A-site cation disorder and biaxial strain on the surface morphologies and transport properties are discussed in detail. At high temperature, the mechanism of conduction is changed from the small polaron hopping model to the variable-range hopping model with increasing cation disorder, which reveals that cation disorder induces carrier localization. The Curie temperature and the magnetoresistance decrease with the increase of cation disorder. It reveals the variation of phase separation to be caused by the increasing cation disorder which suppresses the long-range FM metal state. [ABSTRACT FROM AUTHOR]

Abstract: A novel compound Ba2ZnV2O8 has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P21/c with , , , . It builds up from 1-D branchy chains of [ZnV2O84-]∞, and the Ba2+ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba2ZnV2O8 is an insulator with direct band gap of 3.48eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V–O bonds are mostly covalence characters and Zn–O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba–O than between the Zn–O. The refractive index of nx, ny, and nz is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060nm for Ba2ZnV2O8 crystal. [Copyright &y& Elsevier]

Structural and magnetocaloric properties for the perovskite manganite La2/3-xYxCa1/3-ySryMnO3 (x<0.2) have been studied. These compounds with the fixed A-site average ionic radii of 1.204 Å and Mn4+/Mn3+ ratio were prepared by conventional solid-state reaction technique. The lattice parameters were obtained from refining x-ray diffraction diagrams preformed by Rietveld refinement method. The ferromagnetic ordering temperature TC increases abruptly owing to the increase in the competition between A-site size-disorder degree σ2 and double-exchange interaction resulting from Mn–O–Mn bond angle. Phase transition may be broadened due to the cation disordering at A-site. Sample with x=0.01 appears a large magnetic entropy ΔSM=3.3 J kg-1 K-1 at the Curie temperature TC=274 K, which may be used as a promising candidate for magnetic refrigerant near room temperature. [ABSTRACT FROM AUTHOR]