Ana Gabriela Leyva

Electrical current effect in phase-separated La5∕8−yPryCa3∕8MnO3: Charge order melting versus Joule heating

We have studied the effect of electric field on transport properties of the prototypical phase-separated manganite La5∕8−yPryCa3∕8MnO3 with y=0.34. Our results show that the suggested image, in which the charge ordered state is melted by the appliance of an electric current and∕or voltage, has to be revised. We explain the observed resistivity drop in terms of an artifact related to Joule heating and the particular hysteresis that the system under study displays, common to many other phase-separated manganites.

Nonvolatile Multilevel Resistive Switching Memory Cell: A Transition Metal Oxide-Based Circuit

We study the resistive switching (RS) mechanism as a way to obtain multilevel cell (MLC) memory devices. In an MLC, more than 1 b of information can be stored in each cell. Here, we identify one of the main conceptual difficulties that prevented the implementation of RS-based MLCs. We present a method to overcome these difficulties and to implement a 6-b MLC device with a manganite-based RS device. This is done by precisely setting the remnant resistance of the RS device to an arbitrary value. Our MLC system demonstrates that transition metal oxide nonvolatile memory devices may compete with currently available MLCs.

Phase diagram of La_{5/8-y}Nd_{y}Ca_{3/8}MnO_3 manganites

We report a detailed study of the electric transport and magnetic properties of the La(5/8-y)Nd(y)Ca(3/8)MnO(3) manganite system. Substitution of La(3+) by smaller Nd(3+) ions reduces the mean ionic radius of the A-site ion. We have studied samples in the entire range between La-rich and Nd-rich compounds (0.1<y<0.625). Results of dc magnetization and resistivity show that doping destabilizes the ferromagnetic (FM) character of the pure La compound and triggers the formation of a phase-separated state at intermediate doping. We have also found evidence of a dynamical behaviour within the phase-separated state. A phase diagram is constructed, summarizing the effect of chemical substitution on the system.

Modeling electronic transport mechanisms in metal-manganite memristive interfaces

We studied La0.325Pr0.300Ca0.375MnO3-Ag memristive interfaces. We present a pulsing/measuring protocol capable of registering both quasi-static i-v data and non-volatile remnant resistance. This protocol allowed distinguishing two different electronic transport mechanisms coexisting at the memristive interface, namely space charge limited current and thermionic emission limited current. We introduce a 2-element electric model that accounts for the obtained results and allows predicting the quasi-static i-v relation of the interface by means of a simple function of both the applied voltage and the remnant resistance value. Each element of the electric model is associated to one of the electronic transport mechanisms found. This electric model could result useful for developing time-domain simulation models of metal-manganite memristive interfaces.

Tuning the electronic properties at the surface of BaBiO3 thin films

The presence of 2D electron gases at surfaces or interfaces in oxide thin films remains a hot topic in condensed matter physics. In particular, BaBiO3 appears as a very interesting system as it was theoretically proposed that its (001) surface should become metallic if a Bi-termination is achieved (Vildosola et al., PRL 110, 206805 (2013)). Here we report on the preparation by pulsed laser deposition and characterization of BaBiO3 thin films on silicon. We show that the texture of the films can be tuned by controlling the growth conditions, being possible to stabilize strongly (100)-textured films. We find significant differences on the spectroscopic and transport properties between (100)-textured and non-textured films. We rationalize these experimental results by performing first principles calculations, which indicate the existence of electron doping at the (100) surface. This stabilizes Bi ions in a 3+ state, shortens Bi-O bonds and reduces the electronic band gap, increasing the surface conductivity. Our results emphasize the importance of surface effects on the electronic properties of perovskites, and provide strategies to design novel oxide heterostructures with potential interface-related 2D electron gases.

Performance of Ag/La0.6Sr0.4Co1-xFexO3 (x = 0 - 0.8) Nanotube Composite Cathodes for IT-SOFCs

We investigated the performance of Ag/La0.6Sr0.4Co1-xFexO3 (x = 0;0.8) nanotube composite cathodes using samaria-doped ceria as electrolyte. These composites were prepared by mixing a commercial Ag paste and La0.6Sr0.4Co1-xFexO3 (x = 0;0.8) nanotubes synthesized by the pore wetting technique using plastic templates. Electrochemical impedance spectroscopy analyses showed that the incorporation of La0.6Sr0.4Co1-xFexO3 nanotubes significantly enhances the performance of the cathode in comparison to pure Ag due to their high specific surface area.

Magnetic properties of cobalt doped ZrO2 nanoparticles: Evidence of Co segregation

We synthesized pure and Co-doped (6.25 12.5 at.) ZrO

Influence of particle size and agglomeration in solid oxide fuel cell cathodes using manganite nanoparticles

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Nanostructured LnBaCo2O6−&#x1d739; (Ln = Sm, Gd) with layered structure for intermediate temperature solid oxide fuel cell cathodes

nanopowders in order to study their magnetic properties.We analyzed magnetic behavior as a function of the amount of Co and the oxygenation, which was controlled by low pressure thermal treatments. As prepared pure and Co-doped samples are diamagnetic and paramagnetic respectively. Ferromagnetism can be induced by performing low pressure thermal treatments, which becomes stronger as the dwell time of the thermal treatment is increased. This behavior can be reversed, recovering the initial diamagnetic or paramagnetic behavior, by performing reoxidizing thermal treatments. Also, a cumulative increase can be observed in the saturation of the magnetization with the number of low pressure thermal treatments performed. We believe that this phenomenon indicates that cobalt segregation induced by the thermal treatments is the responsible for the magnetic properties of the ZrO

Performance of La0.6Sr0.4Co1−yFeyO3 (y=0.2, 0.5 and 0.8) nanostructured cathodes for intermediate-temperature solid-oxide fuel cells: Influence of microstructure and composition

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