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ABSTRACT: Effects of oxygen content on the transport behavior of epitaxial La2/3Sr 1/3MnO
3-d_{3-\delta}
films on (110) NdGaO3 and (001) SrTiO3 substrates have been experimentally studied. A quantitative relation between the temperature of metal-to-insulator transition (T
p
) and the content of oxygen vacancies is established, and it is found that oxygen non-stoichiometry causes a monotonic decrease of T
p
. A comparison to crystals La1-x
Sr
x
MnO3 indicates that the reduction of hole concentration due to the incorporation of anionic vacancies dominates the variation of T
p
, while the vacancies themselves influence the detailed features of the T
p
-
d\delta
dependence. Strain in the film affects the effects of oxygen deficiency, and the metal-to-insulator transition disappears at a smaller
d\delta
value in tensily stressed films. In the temperature region above T
p
, oxygen vacancies affect the resistive behavior of the films mainly by modulating the content of Mn4 + . In contrast, extra effects due to the scattering of oxygen vacancies become important at low temperatures, causing an exponential increase of resistivity with
d\delta
. A further analysis indicates that oxygen deficiency enhances magnetic scattering, and leads to a resistivity upturn of the form
-ln(T)-\ln(T)
when
d\delta
is significant.
Physics of Condensed Matter 09/2003; 35(4):481-491. · 1.53 Impact Factor
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ABSTRACT: Formation of interfacial phase in the La0.82Ca0.18MnO3/La0.18Ca0.82MnO3 composite and associated effects have been experimentally studied. Interfacial phase appears when the composite is sintered at temperatures above 950°C, and its composition experiences a considerable change during the sintering according to the x-ray diffraction analysis. Compared with magnetization, the transport property is relatively insensitive to the phase constitution of the composite. The appearance of the third phase and the resulted extra grain boundaries produce only a weak enhancement of magnetoresistance at the percolation point (~26% in volume fraction) of the new phase.
Journal of Physics D Applied Physics 01/2002; 35(3):173. · 2.54 Impact Factor
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ABSTRACT: Effects of oxygen content on the resistivity of epitaxial (110) La <sub> 2/3 </sub> Sr <sub> 1/3 </sub> CoO <sub>3-δ</sub> film have been experimentally studied. The oxygen release, measured by the change of lattice parameter, was controlled by annealing the film at different temperatures in vacuum. Significant oxygen loss can take place at temperature as low as ∼200 ° C . A quantitative relation between resistivity ρ and oxygen deficiency δ was established. For δ≪0.07, a linear decrease of the resistive transition temperature with δ was found. The temperature dependence of the low temperature resistivity follows ρ∝T<sup>2</sup> for δ≪0.046, and ρ∝ exp [(T<sub>0</sub>/T)<sup>1/2</sup>] for 0.067≪δ≪0.16. A transition from T<sup>1/2</sup> variable-range hopping to T<sup>1/4</sup> variable-range hopping takes place for δ≫0.17, which may be a result of the absence of Co <sup> 4+ </sup> which are the nuclei of metallic clusters. Compared to La <sub>1-x</sub> Sr <sub>x</sub> CoO <sub> 3 </sub> with similar Co <sup> 4+ </sup> content, the resistivity of the La <sub> 2/3 </sub> Sr <sub> 1/3 </sub> CoO <sub>3-δ</sub> film is significantly low, which may be the consequence of a larger quantity of Sr in the film. © 2001 American Institute of Physics.
Journal of Applied Physics 10/2001; · 2.17 Impact Factor
