Composite materials based on Poly(3,4-ethylenedioxythiophene) (PEDOT) and CoFe_2O_4 magnetic nanoparticles (NP) were synthesized by chemical oxidative polymerization with varying monomer and surfactant (DBSA) concentrations, and were compared to PEDOT samples synthesized without NP. Electrical conductivity measurements were performed, which revealed that the composites are more conductive than the pure PEDOT samples, with this effect depending on EDOT and DBSA contents. Characterizations by SEM and TEM microscopies, UV-Vis, FTIR and Raman spectroscopies, X-ray diffraction and dynamic light scattering were carried out in order to associate the morphology and structure of these materials to their electrical conductivity, and to explain how EDOT and DBSA concentrations, and also the presence of NP, affects those properties. It was found that the NP play a significant role in the polymerization of EDOT, influencing the formation and arrangement of polymer chains, as well as their conjugation length, oxidation state, and resonant structures. These effects are also dependent on the DBSA content. To describe the conductivity of the composites, a two-phase model based on general effective media theory was introduced. The analysis revealed that, at low reactant concentrations, the NP increase the conductivity of the adjacent PEDOT by over two orders of magnitude.

We report on the characterization of Pt-YBa2Cu3O7-delta interfaces, focusing on how oxygen vacancies content (delta) affects electrical transport mechanisms. Our study examines four Pt-YBa2Cu3O7-delta samples with varying delta (0.12 <=delta <= 0.56) using voltage-current measurements across a temperature range. We successfully model the electrical behavior using a Poole-Frenkel conduction framework, revealing that oxygen vacancies create potential wells that trap carriers, directly influencing conduction. We observe that the energy of these traps increases as delta rises, in agreement with a peak previously detected in optical conductivity measurements. This result supports earlier interpretations, strengthening the proposed connection between oxygen vacancies and the ionization energy associated with impurity bands in oxygen-depleted YBa2Cu3O7 - (delta).

A rapid method using a magnetic ionic liquid (MIL) in the effervescence-assisted liquid-liquid microextraction (EA-LLME) was developed for the separation and determination of inorganic and organic species of Hg in beverage samples. A chlorocomplex was formed with Hg(II) for its extraction in 75 mu L of the MIL trihexyl(tetradecyl)phosphonium tetrachloroferrate ([P-6,P-6,P-6,P-14]FeCl4). CO2 bubbles disperse the MIL phase, followed by phase separation with a magnetic rod and the MIL dilution with chloroform. A rapid back-extraction was performed by an ultrasonic bath with 6 mol L-1 HCl solution. The inorganic Hg(II) species was determined by cold vapour atomic fluorescence spectrometry (CV-AFS), while total Hg quantification involved a photooxidation step prior to preconcentration. Thus, organic species was calculated by the difference between the concentrations of total Hg and Hg(II). The extraction conditions were optimized achieving a maximum extraction efficiency of 98 % for Hg(II). The analytical performance included a relative standard deviation of 1.6 %, a limit of detection (LOD) and limit of quantification (LOQ) of 0.096 mu g L-1 and 0.113 mu g L-1 for Hg(II), respectively. The linear calibration range was 0.113-4 mu g L-1. The results showed that the proposed methodology was efficient and selective for Hg speciation analysis in water and wine samples.

In this work, the resistive switching and the conducting mechanism of forming-free TiO2 thin films between Ti and Pt electrodes were investigated. The devices were fabricated employing Physical Vapor Deposition (PVD) methods. Ti/TiO2 films were prepared with a cathodic arc system while Pt contacts were deposited by sputtering. Different TiO2 structures (amorphous, anatase, rutile) and thicknesses (60-240 nm) were analyzed through current-voltage (IV) characteristic curves and resistance hysteresis switching loops (RHSL). Amorphous TiO2 produced more conductive devices, with a circulation path, both in IV and RHSL, opposite to that of crystalline TiO2. From these results, the TiO2-Ti was found to be the active interface in devices based on the amorphous phase, while the Pt-TiO2 interface was the active one for anatase and rutile. The results showed that the selection of the TiO2 growth conditions allows to tune which will be the active interface that produces the resistive changes by choosing the structure of the films, as well as the degree of non-linearity of the electrical conduction of the device by varying the thickness of the TiO2 (anatase) film.

Dipolar and RKKY interactions, tuned by intercluster separation, play a significant role in the magnetic behaviour of PEDOT:DBS–Fe 3 O 4 composites.

Memristors are expected to be one of the key building blocks for the development of new bio-inspired nanoelectronics. Memristive effects in transition metal oxides are usually linked to the electromigration at the nanoscale of charged oxygen vacancies (OV). In this paper we address, for Pt/TiOx/TaOy/Pt devices, the exchange of OV between the device and the environment upon the application of electrical stress. From a combination of experiments and theoretical simulations we determine that both TiOxand TaOylayers oxidize, via environmental oxygen uptake, during the electroforming process. Once the memristive effect is stabilized (post-forming behavior) our results suggest that oxygen exchange with the environment is suppressed and the OV dynamics that drives the memristive behavior is restricted to an internal electromigration between TiOxand TaOylayers. Our work provides relevant information for the design of reliable binary oxide memristive devices.

10 MeV proton-irradiation effects on a YBCO-based test structure were analyzed by measuring its current-voltage (IV) characteristics for different cumulated fluences. For fluences of up to - 80.109 p/cm2 no changes in the electrical behavior of the device were observed, while for a fluence of - 300.109 p/cm2 it becomes less conducting. A detailed analysis of the room temperature IV characteristics based on the ? power exponent parameter [? = dLn(I)/dLn(V)] allowed us to reveal the main conduction mechanisms as well as to establish the equivalent circuit model of the device. The changes produced in the electrical behavior, in accordance with Monte Carlo TRIM simulations, suggest that the main effect induced by protons is the displacement of oxygen atoms within the YBCO lattice, particularly from oxygen-rich to oxygen-poor areas, where they become trapped.

The possibility to develop neuromorphic computing devices able to mimic the extraordinary data processing capabilities of biological systems spurs the research on memristive systems. Memristors with additional functionalities such as robust memcapacitance can outperform standard devices in key aspects such as power consumption or miniaturization possibilities. In this work, we demonstrate a large memcapacitive response of a perovskite memristive interface, using the topotactic redox ability of La0.5Sr0.5Mn0.5Co0.5O3-delta (LSMCO, 0 <= delta <= 0.62). We demonstrate that the multi-mem behavior originates at the switchable n-p diode formed at the Nb:SrTiO3/LSMCO interface. We found for our Nb:SrTiO3/LSMCO/Pt devices a memcapacitive effect C-HIGH/C-LOW similar to 100 at 150kHz. The proof-of-concept interface reported here opens a promising venue to use topotactic redox materials for disruptive nanoelectronics, with straightforward applications in neuromorphic computing technology.

Composites of magnetic CoFe2O4 nanoparticles (MNP) in a poly(3,4-ethylenedioxythiophene) matrix at different ratios have been synthesized. Composites were characterized by electron microscopy, X-ray diffraction, thermal analysis, electrical conductivity, magnetization, and magnetoresistance studies. In the composites the MNP appear clustered, with an interparticle distance essentially constant, but where two regimes are distinguished for cluster separation: for high MNP concentrations an intercluster separation similar to the interparticle distance is found, while for low MNP contents the distance between clusters is larger than the interparticle separation. The electrical conductivity increases with polymer content, but being always far lower than general effective medium theory expectations. This indicates that the effect of MNP effect on polymer conduction is probably related to the generation of mechanical stress both by introducing additional scattering centers and by producing different arrangement of the polymer chains, compared with the pure PEDOT. The magnetization studies reveal the existence of the RKKY interaction, which couples ferromagnetically the MNP located in a cluster, while the dipolar interaction dominates the interaction between clusters. Magnetoresistance was studied for these composites, with a maximum value close to 0.7% at 0.7 T for the lowest polymer content. The magnetoresistance correlates very well with the reversible part of the magnetization, indicating that its possible origin should be associated with polymer mechanical deformation due to the magnetic-field-induced rotation of the MNP.

Magnetite superparamagnetic nanoparticles (MNP) are becoming one of the firsts nanocommodity products. MNP find a number of applications and they are been produced at relatively large scale. The co-precipitation method presents many technical and economical advantages among alternative processes. However, the relationships between physical and chemical reaction conditions during the co-precipitation process and the resulting properties of obtained MNP are not yet fully understood. The novelty of this contribution is the establishment of the cross-dependency effects of the main physical and chemical parameters of the co-precipitation reaction on the properties of resulting MNP. The conditions were varied by following an experimental design. The crystallite size, particle size and magnetization of the MNP and the Z-potential and size of their aggregates were selected as main response properties. A set of equations in the form of 4D surface responses in the space of co-precipitation process variables was obtained and analyzed in terms of the resulting properties. The set of equations is useful to predict, optimize and tailor very precisely the properties of resulting MNP as a function of reaction conditions.

Current-voltage characteristics of Au/YBa2Cu3O[Formula: see text] interfaces (Au/YBCO), built on optimally-doped YBCO thin films, grown by pulsed laser deposition, were measured as a function of temperature in the 50 K to 270 K range, for two different resistance states. A non-trivial equivalent circuit model is proposed, which reveals the existence of a highly inhomogeneous scenario composed by two complex layers: one presenting both a non-linear Poole-Frenkel conduction as well as variable range hopping localization effects (probably associated with YBa2Cu3O6) mixed with a minor metallic phase, while the other is also composed by a mixture of YBCO with different oxygen contents, where a metallic ohmic phase still percolates. A microscopic description of the effects produced by the resistance switching is given, showing the evolution of carrier traps, localization effects and dielectric behavior for each state. The dielectric behavior is interpreted in terms of a Maxwell-Wagner scenario.

Los materiales termocrómicos, con propiedades ópticas variables con la temperatura, optimizan el aprovechamiento de la energía solar por la envolvente del edificio para mejorar su eficiencia energética. El objeto de este estudio es determinar el impacto de un revestimiento de mortero termocrómico (MT) en fachada sobre la eficiencia energética del edificio en un clima mediterráneo. Se propone una metodología de cálculo para implementar las propiedades ópticas variables del mortero en la simulación energética. Se estudia un revestimiento de MT con absortancia solar entre 0,65 y 0,60, y una temperatura de transición entre 20ºC y 35ºC. El mortero muestra color gris oscuro para temperaturas bajas y color claro para temperaturas altas. El edificio presenta una demanda energética anual un 3 % inferior que con revestimiento de propiedades ópticas no variables. La reducción de demanda de calefacción puede llegar a un 8%.

Thermochromic materials, with optical properties changing with temperature, optimize the use of solar energy by the building envelope for the improvement of energy efficiency. The purpose of this research is to determine the impact of a thermochromic mortar (TM) facade coating on the building energy performance in a Mediterranean climate. A new calculation methodology is proposed to implement the dynamical optical properties of the mortar in conventional energetic simulation tools. This study considers a coating with variable optical properties that move from 0,65 to 0,60 solar absorptance value, and a transition temperature moving from 20 degrees C to 35 degrees C. The mortar shows a dark grey colour for low temperatures and a light colour for high temperatures. The building with TM coating shows a 3 % lower yearly energy demand than the building with non-variable optical properties, with a maximum heating demand reduction reaching 8 %.

The possibility to develop neuromorphic computing devices able to mimic the extraordinary data processing capabilities of biological systems spurs the research on memristive systems. Memristors with additional functionalities such as robust memcapacitance can outperform standard devices in key aspects such as power consumption or miniaturization possibilities. In this work, we demonstrate a large memcapacitive response of a perovskite memristive interface, using the topotactic redox ability of La_0.5Sr_0.5Mn_0.5Co_0.5O_3-δ (LSMCO, 0 ≤ δ ≤ 0.62). We demonstrate that the multi-mem behaviour originates at the switchable n-p diode formed at the Nb:SrTiO3/LSMCO interface. We found for our Nb:SrTiO_3/LSMCO/Pt devices a memcapacitive effect C_HIGH/C_LOW   100 at 150 kHz. The proof-of-concept interface reported here opens a promising venue to use topotactic redox materials for disruptive nanoelectronics, with straightforward applications in neuromorphic computing technology.

The development of novel devices for neuromorphic computing and non-traditional logic operations largely relies on the fabrication of well controlled memristive systems with functionalities beyond standard bipolar behavior and digital ON-OFF states. In the present work we demonstrate for Ta2O5-based devices that it is possible to selectively activate/deactivate two series memristive interfaces in order to obtain clockwise or counter-clockwise multilevel squared remanent resistance loops, just by controlling both the electroforming process and the (a)symmetry of the applied stimuli, and independently of the nature of the used metallic electrodes. Based on our thorough characterization, analysis and modeling, we show that the physical origin of this electrical behavior relies on controlled oxygen vacancies electromigration between three different nanoscopic zones of the active Ta2O5-x layer: a central one and two quasi-symmetric interfaces with reduced TaO2-h(y) layers. Our devices fabrication process is rather simple as it implies the room temperature deposition of only one CMOS compatible oxide-Ta-oxide-and one metal, suggesting that it might be possible to take advantage of these properties at low cost and with easy scability. The tunable opposite remanent resistance loops circulations with multiple-analogic-intermediate stable states allows mimicking the adaptable synaptic weight of biological systems and presents potential for non-standard logic devices.

We measured and analyzed the dynamic and remnant current-voltages curves of Al/TiO2/Au and Ni/TiO2/Ni/Au memory devices in order to understand the conduction mechanisms and their synapse-like memory properties. Current levels and switching threshold voltages are strongly affected by the metal used for the electrode. We propose a non-trivial circuit model which captures in detail the current-voltage response of both kinds of devices. We found that, for the former device, the voltage threshold can be maintained constant, independently of the applied voltage history, while for the latter, a limiting resistor controls the threshold voltages behavior, being the origin of their dependence on the resistance value previous to the switching. The identification of the conduction mechanisms across the device allows optimizing the memristor performance and determining the best electrode choice to improve the device synapse-emulation abilities.

The development of novel devices for neuromorphic computing and non-traditional logic operations largely relies on the fabrication of well controlled memristive systems with functionalities beyond standard bipolar behavior and digital ON-OFF states. In the present work we demonstrate for Ta_2O_5-based devices that it is possible to selectively activate/deactivate two series memristive interfaces in order to obtain clockwise or counter-clockwise multilevel squared remanent resistance loops, just by controlling the (a)symmetry of the applied stimuli and independently of the nature of the used metallic electrodes. Based on our thorough characterization, analysis and modeling, we show that the physical origin of this electrical behavior relies on controlled oxygen vacancies electromigration between three different zones of the active Ta_2O_5-x layer: a central – bulk – one and two quasi-symmetric interfaces with reduced TaO_2-h(y) layers. Our devices fabrication process is rather simple as it implies the room temperature deposition of only one CMOS compatible oxide – Ta-oxide – and one metal, suggesting that it might be possible to take advantage of these properties at low cost and with easy scability. The tunable opposite remanent resistance loops circulations with multiple – analogic – intermediate stable states allows mimicking the adaptable synaptic weight of biological systems and presents potential for non-standard logic devices.

The development of reliable redox-based resistive random-access memory devices requires understanding and disentangling concurrent effects present at memristive interfaces. We report on the fabrication and electrical characterization of TiOx/La1/3Ca2/3MnO3−x microstructured interfaces and on the modeling of their memristive behavior. We show that a careful tuning of the applied external electrical stimuli allows controlling the redox process between both layers, obtaining multilevel non-volatile resistance states. We simulate the oxygen vacancies dynamics at the interface between both oxides, and successfully reproduce the experimental electrical behavior after the inclusion of an electronic effect, related to the presence of an n-p diode at the interface. The formation of the diode is due to the n- and p-character of TiOx and La1/3Ca2/3MnO3−x, respectively. Our analysis indicates that oxygen vacancies migration between both layers is triggered after the diode is polarized either in forward mode or in reverse mode above breakdown. Electrical measurements at different temperatures suggest that the diode can be characterized as Zener-type. The advantages of our junctions for their implementation in RRAM devices are finally discussed.