754 research outputs found
Resistive switching effects on the spatial distribution of phases in metal-complex oxide interfaces
In order to determine the key parameters that control the resistive switching
mechanism in metal-complex oxides interfaces, we have studied the electrical
properties of metal / YBa2Cu3O7-d (YBCO) interfaces using metals with different
oxidation energy and work function (Au, Pt, Ag) deposited by sputtering on the
surface of a YBCO ceramic sample. By analyzing the IV characteristics of the
contact interfaces and the temperature dependence of their resistance, we
inferred that ion migration may generate or cancel conducting filaments, which
modify the resistance near the interface, in accordance with the predictions of
a recent model.Comment: 3 pages, 5 figures, to be published in Physica B. Corresponding
author: C. Acha ([email protected]
Electrical transport properties of manganite powders under pressure
We have measured the electrical resistance of micrometric to nanometric
powders of the LaPrCaMnO (LPCMO with y=0.3) manganite
for hydrostatic pressures up to 4 kbar. By applying different final thermal
treatments to samples synthesized by a microwave assisted denitration process,
we obtained two particular grain characteristic dimensions (40 nm and 1000 nm)
which allowed us to analyze the grain size sensitivity of the electrical
conduction properties of both the metal electrode interface with manganite (Pt
/ LPCMO) as well as the intrinsic intergranular interfaces formed by the LPCMO
powder, conglomerate under the only effect of external pressure. We also
analyzed the effects of pressure on the phase diagram of these powders. Our
results indicate that different magnetic phases coexist at low temperatures and
that the electrical transport properties are related to the intrinsic
interfaces, as we observe evidences of a granular behavior and an electronic
transport dominated by the Space Charge limited Current mechanism.Comment: 4 pages, 7 figures, to be published in Physica B Corresponding
author: C. Acha ([email protected]
Transport mechanism through metal-cobaltite interfaces
The resistive switching (RS) properties as a function of temperature were
studied for Ag/LaSrCoO (LSCO) interfaces. The LSCO is a
fully-relaxed 100 nm film grown by metal organic deposition on a LaAlO
substrate. Both low and a high resistance states were set at room temperature
and the temperature dependence of their current-voltage (IV) characteristics
was mea- sured taking care to avoid a significant change of the resistance
state. The obtained non-trivial IV curves of each state were well reproduced by
a circuit model which includes a Poole-Frenkel element and two ohmic
resistances. A microscopic description of the changes produced by the RS is
given, which enables to envision a picture of the interface as an area where
conductive and insulating phases are mixed, producing Maxwell-Wagner
contributions to the dielectric properties.Comment: 13 pages, 5 figures, to be published in APL. Corresponding author: C.
Acha ([email protected]
Non-volatile resistive switching in dielectric superconductor YBCO
We report on the reversible, nonvolatile and polarity dependent resistive
switching between superconductor and insulator states at the interfaces of a
Au/YBaCuO (YBCO)/Au system. We show that the
superconducting state of YBCO in regions near the electrodes can be reversibly
removed and restored. The possible origin of the switching effect may be the
migration of oxygen or metallic ions along the grain boundaries that control
the intergrain superconducting coupling. Four-wire bulk resistance measurements
reveal that the migration is not restricted to interfaces and produce
significant bulk effects.Comment: 4 pages, 4 figures, corresponding author: C. Acha ([email protected]
Electrical resistivity of the Ti4O7 Magneli phase under high pressure
We have measured resistivity as a function of temperature and pressure of
Ti4O7 twinned crystals using different contact configurations. Pressures over
4kbar depress the localization of bipolarons and allow the study of the
electrical conduction of the bipolaronic phase down to low temperatures. For
pressures P > 40 kbar the bipolaron formation transition is suppressed and a
nearly pressure independent behavior is obtained for the resistivity. We
observed an anisotropic conduction. When current is injected parallel to the
principal axis, a metallic conduction with interacting carrier effects is
predominant. A superconducting state was not obtained down to 1.2 K, although
evidences of the proximity of a quantum critical point were noticed. While when
current is injected non-parallel to the crystal's principal axis, we obtained a
logarithmic divergence of the resistivity at low temperatures. For this case,
our results for the high pressure regime can be interpreted in the framework of
interacting carriers (polarons or bipolarons) scattered by Two Level Systems.Comment: 9 Revtex pages, 12 EPS figures included, submitted to The European
Physical Journal B. Contact author: C. Acha (e-mail address: [email protected]
Integrated Modelling of Gas and Electricity Distribution Networks with a High Penetration of Embedded Generation
Gas-based combined heat and power (CHP) has matured enough to be regarded as the next evolutionary step in promoting energy efficiency use in the urban environment. Although its potential market is increasing, little research has been conducted into the combined technical effects that a high penetration of these units may have on both natural gas and electric (G&E) distribution networks. This paper presents a power flow tool that performs a simultaneous assessment on some technical impacts that a high penetration of heat-driven cogeneration units may have on G&E networks. A case study is presented and results show that as expected, the gas demand increases as well as the losses associated with its delivery, while the opposite effects occur in the electrical system. However, less evident is the load profile variations distribution networks will experience and that overall energy losses will vary according to the CHP penetration and the type of technology used. The study shows that an integrated G&E analysis offers a fresh perspective in quantifying the effects cogeneration technologies will have on energy distribution networks
Mechanism for bipolar resistive switching in transition metal oxides
We introduce a model that accounts for the bipolar resistive switching
phenomenom observed in transition metal oxides. It qualitatively describes the
electric field-enhanced migration of oxygen vacancies at the nano-scale. The
numerical study of the model predicts that strong electric fields develop in
the highly resistive dielectric-electrode interfaces, leading to a spatially
inhomogeneous oxygen vacancies distribution and a concomitant resistive
switching effect. The theoretical results qualitatively reproduce non-trivial
resistance hysteresis experiments that we also report, providing key validation
to our model.Comment: Accepted for publication in Physical Review B, 6 twocolumn pages, 5
figure
First-Order Insulator-to-Metal Mott Transition in the Paramagnetic 3D System GaTa4Se8
The nature of the Mott transition in the absence of any symmetry braking
remains a matter of debate. We study the correlation-driven insulator-to-metal
transition in the prototypical 3D Mott system GaTa4Se8, as a function of
temperature and applied pressure. We report novel experiments on single
crystals, which demonstrate that the transition is of first order and follows
from the coexistence of two states, one insulating and one metallic, that we
toggle with a small bias current. We provide support for our findings by
contrasting the experimental data with calculations that combine local density
approximation with dynamical mean-field theory, which are in very good
agreement.Comment: 5 pages and 4 figures. Supplemental material: 2 pages, 2 figure
Pressure effects in the triangular layered cobaltites NaxCoO2
We have measured transport properties as a function of temperature and
pressure up to 30GPa in the NaxCoO2 system. For the x=0.5 sample the transition
temperature at 53K increases with pressure, while paradoxically the sample
passes from an insulating to a metallic ground state. A similar transition is
observed in the x=0.31 sample under pressure. Compression on the x=0.75 sample
transforms the sample from a metallic to an insulating state. We discuss our
results in terms of interactions between band structure effects and Na+ order.Comment: 18 pages, 5 figure
Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals
We report on DC and pulsed electric field sensitivity of the resistance of
mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single
crystals as a function of temperature. The low temperature regime of the
resistivity is highly current and voltage dependent. An irreversible transition
from high (HR) to a low resistivity (LR) is obtained upon the increase of the
electric field up to a temperature dependent critical value (V_c). The
current-voltage characteristics in the LR regime as well as the lack of a
variation in the magnetization response when V_c is reached indicate the
formation of a non-single connected filamentary conducting path. The
temperature dependence of V_c indicates the existence of a consolute point
where the conducting and insulating phases produce a critical behavior as a
consequence of their separation.Comment: 5 pages, 6 figures, corresponding author: C. Acha ([email protected]
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