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A study of the (1-x)BiFeO3-(x)Ba1/2Na1/2TiO2.75 (BFO-BNT) solid solutions obtained using the solid state reaction method, for different molar relative concentration of Ba1/2Na1/2TiO2.75 in the 0.0 ≤ x ≤ 0.12 composition range, is presented. The crystal structure and the dielectric and ferroelectric properties are studied in detail. Results of the Rietveld refinement of the X-ray diffraction data demonstrate that the system is single phase with R3c symmetry up to x = 0.09 while for x = 0.12, a small quantity of a secondary phase with P4mm symmetry appears. Scanning electron microscopy demonstrates that BNT presence promotes grain growth resulting in larger grains. Raman spectroscopy shows that, with increasing x, some of the A and E Raman modes slightly reduce their intensity while shifting in frequency, evincing the structural changes caused by the Ba, Na, and Ti incorporation on the BFO lattice. The X-ray photoelectron spectroscopy study confirms the successful substitution and gradual structural distortion in the samples. The improvement in dielectric properties with increasing BNT concentration can be attributed to stable dipole moment formation. Compared with pure BFO ceramics, doped BFO samples exhibit remarkably enhanced ferroelectric properties.

A novel magnetic semiconductor nanocomposite based on functionalized magnetite nanoparticles (MNPs) embedded in a matrix of bismuth ferrate compound (BFO) was obtained in a single step for the first time using the microwave-assisted hydrothermal synthesis. The synthesis method allows obtaining multiferroic BFO small particles and MNPs–BFO nanocomposites with optical activity in the near-infrared region (1.6 eV) due to d–d charge transfer transitions on Fe(III) ion orbitals. The functionalized MNPs exhibit strong superparamagnetic behavior with blocking temperature TB near room temperature and high saturation magnetization of MS = 59 emu/g, attributed to ferrimagnetic nano-monodomains with critical size. Meanwhile, the synthesized BFO shows an unusual superparamagnetic behavior with TB = 20 K and an interesting magnetic transition from the blocked superparamagnetic state to quantum superparamagnetic state at a critical temperature Tc = 11 K, attributed to ferromagnetic very small, critical size nano-monodomains. As result, the MNPs–BFO nanocomposite shows a superparamagnetic behavior at room temperature which, in close connection with its optical properties, makes it an excellent candidate for infrared magneto-optical applications.

In the last few years, the quantum superparamagnetic (QSP) phenomenon has been reported in isolated ultrasmall nanoparticles. In this work, a QSP state and superparamagnetic (SP) state in nanostruc...

In this paper, the multiferroic ceramics Bi0.80La0.10Ca0.10Fe1-xMnxO3 (0.0 ≤x ≤ 0.12) are synthesized via conventional solid-state reaction route and their structural, Raman spectroscopy and magnetic properties are explored. Rietveld analysis carried out for all samples, revealed that the system exhibits coexistence of mainly two crystalline phases with symmetries R3c and Pbnm throughout the whole composition range. The presence of two structural phases is further supported by Raman spectroscopy analysis. The magnetic parameters, that is, magnetization, remanency, coercivity and squareness ratio are found to be enhanced by the Mn incorporation into Bi0.80La0.10Ca0.10FeO3. This is basically due to the structural modification, breaking of the incommensurate spin structure and inter-grain magnetostatic interaction in the Bi0.80La0.10Ca0.10Fe1-xMnxO3 ceramic samples. The exchange bias effect (~734 Oe) is observed for the Mn doped sample only with 6 at. %. Such high value may be extremely useful for technological applications including magnetoresistive read heads and sensors.

Multiferroic materials show great academic and technological interest for their role in new generation devices due to the coexistence of magnetic, ferroelectric and elastic ordering. In this article the fabrication of SrRuO3 (SRO) thin films by the RF magnetron ion sputtering technique is presented where the deposition conditions, namely deposit time, substrate temperature and RF power were optimized. The growth of the SRO phase was evaluated using X-ray diffraction. The homogeneity of the films was analysed using energy dispersive X-ray spectroscopy. Film thickness and optical properties were determined by ellipsometry.

A novel ferromagnetic state coexisting with ferroelectric ordering at room temperature in strained BiFeO 3 (BFO) thin films grown using a sputtering technique on La 0.7 Sr 0.3 MnO 3 /SiO 2 /Si(100) (LSMO/SOS) substrates is reported. The properties of BFO films with different thicknesses ( t BFO = 15, 50, 70, 120, and 140 nm) on 40 nm LSMO layers are explored. [012] out-of-plane highly textured BFO/LSMO stacks grew with rhombohedral structures. LSMO layers are nanostructured in nature, constituted by ferromagnetic single-domain nanoregions induced by the constrain of the SiO 2 surface, with T C ∼200 K and high coercive field ( H C ) of ∼1100 Oe at 2.5 K. BFO films grew epitaxially nanostructured on LSMO, exhibiting ∼4 nm spherical nanoregions. The BFO layers show typical antiferromagnetic behavior (in a greater volume fraction) when made thicker ( t BFO > 70 nm). The thinner films ( t BFO T C > 400 K, H C ∼ 1600 Oe for 15 nm and ∼1830 Oe for 50 nm. We propose that such ferromagnetic behavior is originated by the establishment of a new magnetic configuration in the Fe 3+ O Fe 3+ sublattice of the BFO structure, induced by strong hybridization at the interface as consequence of superexchange coupling interactions with the ferromagnetic Mn 3+ O Mn 3+ /Mn 4+ sublattice of LSMO. All BFO layers show excellent ferroelectric and piezoelectric properties (coercive field ∼ 740 kV/cm, and d 33 = 23 p.m./V for 50 nm; ∼200 kV/cm and 55 p.m./V for 140 nm), exhibiting 180° and 109° DWs structures depending on the thickness. Such multiferroic properties predict the potential realization of new magneto-electronic devices integrated with Si technology.

The optical, electronic, and vibrational properties of quaternary CdxZnyOγSδ (CdZnOS) semiconductor nanoparticles grown on mordenite-type zeolite (MOR) were studied using infrared, Raman, photoluminescence in emission and excitation modes, and cathodoluminescence spectroscopy. Semiconductor–mordenite (CdZnOS-MOR) composites were prepared utilizing low-cost and scalable methods: 1) Ion-exchange with as-synthesized sodium-mordenite and 2) a one-pot direct synthesis of zinc/cadmium-mordenite using a modified sol–gel technique, which were followed by sulfidation under a flow of H2S. The results of our vibrational studies have revealed the characteristic signals for the zinc-blende-type phase of the quaternary nanoparticles. From our photoluminescence analysis, the CdZnOS-MOR nanocomposites exhibits an up-conversion phenomenon, which is strongly related to the quantum confinement effect, while a high energy cathodoluminescence response established that the diversity of the transitions in this up-conversion process is associated to the wide distribution of size and stoichiometry of the nanoparticles. The luminescent, photoluminescent, and cathodoluminescent properties make the nanocomposite a promising photoactive material for application in photocatalysis.

Photocatalysts based on silver or gold metallic and CdS semiconductor nanoparticles embedded on a mordenite matrix (M-CdS/MOR), was successfully synthesized and tested to obtain glucuronic acid by photoconversion of glucose. The M-CdS/MOR photocatalyst exhibited a synergistic interaction between the plasmonic behavior from metallic nanoparticles and the photoactive properties of semiconductor nanoparticles, which leads to the photoconversion of the glucose (38% in 60 min). The reaction mechanisms are presented and discussed.

Multifunctional materials such as the multiferroic compound Pb(Fe1/2Nb1/2)O3, are of great interest from the academic and technological points of view. However, the occurrence of Fe2+ and oxygen vacancies originated during the sintering process increase the dielectric loss and electrical conductivity, detrimental to optimal device performance. Here, a report on the effects of a saturated O2 atmosphere used during the calcination and sintering stages is presented. A comparative study of structural, morphological, and physical properties with those obtained for samples sintered in air or in its own atmosphere, is presented. The O2 atmosphere enhances the dielectric constant by ~180 % (with maximum e r of 12700 at T C = 103 °C and dielectric loss smaller than 0.01 independent of frequency and temperature below 100 kHz and T C, respectively), the maximum and remanent polarization by ~275 % (P max from 6.2 to 16.8 µC/cm2 and P r from 2.4 to 6.7 µC/cm2 at 16 kV/cm), and reduces the electrical conductivity by one order of magnitude (from ~1 × 10−7 to ~3 × 10−8/Ω cm at 1 kHz at room temperature). Additionally, a pronounced ac positive temperature coefficient of resistivity effect, strongly dependent on frequency and with potential barrier values from 0.2 eV at 1 kHz to 0.71 eV at 500 kHz, is associated with the highly resistive and capacitive behavior of the grain boundary.

In this work, an effort has been made to show the effect of Er doping on the dielectric, electrical, ferroelectric, and optical properties of BiFeO3 (BFO) nanoparticles prepared by the sol-gel route. XRD of Bi1-xErxFeO3 samples revealed that the rhombohedral (R3c) structure is stable for 0 ≤ x ≤ 0.08 with distortional changes, whereas a co-existence of two phases, rhombohedral (R3c) and orthorhombic (Pn21a) is present for x = 0.12. At room temperature, dielectric properties are slightly improved with the appearance of defects at a higher temperature. The ln σac vs. 1000/T plots revealed the presence of different Arrhenius-type thermally activated mechanisms and, for their analysis, were divided in five regions: the low temperature regions (I and II), followed by a small polaron hopping (intermediate region III) and a single and a double oxygen vacancies regions in the high temperature side (IV and V). Er doped BFO displays an improvement of the dielectric properties with respect to those of BFO, clearly reflected in better P-E loops. UV–Vis spectroscopy revealed the optical band energy lies in the 2.10 eV–1.70 eV interval, suggesting possible applications in the visible range of the spectrum. The multiferroic properties at room temperature make it a good candidate for future potential application in memory devices.

The present studies are focused on the effect of divalent Ca2+ ion on the structural, magnetic, and optical properties of Bi0.80La0.20FeO3 (BLFO) ceramic samples, synthesized via conventional solid-state reaction route. The addition of Ca2+ ion into BLFO substituting Bi, creates distortion in the structure and leads a phase transition from rhombohedral (R3c) to orthorhombic (Pbnm) crystal symmetry, confirmed by Rietveld analysis and further supported by Raman spectroscopy, attributed to a decrease in tilt angle for anti-phase rotation of BO6 octahedra. Weak ferromagnetic ordering was observed for all Bi0.80-xCaxLa0.20FeO3 samples with Ca at.% of 0.03 (BCLFO3), 0.06 (BCLFO6) and 0.12 (BCLFO12), associated to changes in Fe–O–Fe angle. The remnant magnetization has been found to increase from 1.2×10−3 emu/g for BLFO to 9.1x10−3 emu/g for BCLFO12. Similar trends were found in the deconvoluted ferromagnetic contribution with Ca2+ ion doping. Moreover, Arrott plot analysis suggests a second order meta-magnetic transition for all samples. Room temperature dielectric properties were improved with Ca2+ ion substitutions. The optical band gap significantly reduced from 2.10 eV for BLFO to 1.93 eV for BCLFO12, indicating the distortion induced by the Ca2+ ion.

A highly efficient photocatalyst based on Ag-metal and CdZnSO-semiconductor nanoparticles, grown on a zeolitic matrix, was successfully synthesized by a solvent- and template-free procedure, and tested on the photodegradation of recalcitrant disperse orange 30 dye. The Ag-CdZnSO/ZM nanocomposite showed great synergistic interaction between the surface plasmon resonance of the Ag nanoparticles, the photoactive properties of CdZnSO nanoparticles, and the catalytic properties of the zeolitic, which leads to the degradation of the dye (99.5% in 90 min, from optical absorbance). The reaction mechanisms are presented and discussed. Also, the small amount of acetone required as sensitizer was eliminated during the process.

This work demonstrates that the rf-sputtering technique, combined with appropriate heat treatments, is potentially effective to develop new materials and devices based on oxide-interface and strain engineering. We report a study of the structural-physical properties relationship of high crystalline quality, highly oriented and epitaxial thin films of the lead-free (K0.5Na0.5)0.985La0.005NbO3 (KNNLa) compound which were successfully deposited on Nb-doped SrTiO3 substrates, with orientations [100] (NSTO100) and [110] (NSTO110). The crystalline growth and the local ferroelectric and piezoelectric properties were evaluated by piezoresponse force microscopy combined with transmission electron microscopy and texture analysis by X-ray diffraction. Conditioned by the STO surface parameters, in the KNNLa films on NSTO100 coexist a commensurate [001]-tetragonal phase and two incommensurate [010]-monoclinic phases; while on NSTO110 the KNNLa films grew only in an incommensurate [101]-monoclinic phase. Both samples show excellent out-of-plane polarization switching patterns consistent with 180° domains walls; while for KNNLa/NSTO100 ferroelectric domains grow with the polarization pointing down, for KNNLa/NSTO110 they prefer to grow with the polarization pointing up. Comparing with previous reports on epitaxial KNN films, we find our samples to be of very high quality regarding their crystalline growth with highly ordered ferroelectric domains arrangements and, consequently, great potential for domain engineering.

Atomic, electronic, and compositional structure of quaternary CdxZnySδOγ semiconductor nanoparticles grown on synthesized mordenite-type zeolite (MOR) is discussed in this work. Semiconductor–MOR composites were synthesized using two different methods: by Cd2+-Zn2+-ion exchange with synthesized sodium-mordenite, and by direct synthesis of zinc/cadmium-mordenite through a variant of the sol–gel technique, both followed by sulfidation treatment in H2S flow. We show that CdxZnySδOγ semiconductor nanoparticles grow strongly bonded, revealing a core–shell-type arrangement with a wide-open (a = 8.33 A) cubic fcc structure, and constrained by the MOR surface structure. Because of the core–shell-type nanoparticles and their observed structural and optical properties, these photoactive composites are promising candidates for applications in the fields of photocatalysis and optoelectronics.

Systems for optical analysis use vacuum chambers, where low pressures are reached. Remaining water molecules are the prevalent contaminant in high vacuum chambers. For this reason measurement of water levels is an important task that allows correct equipment operation. In this work, a different approach is presented for detecting and quantifying the water molecules inside a the vacuum chamber used in optical systems. A zeolite coated quartz crystal microbalance is used for detecting the water molecules, and the change in the resonance frequency is measured using a novel technique known as the principle of rational approximations. Theoretical results show how nanograms of adsorbed molecules are measured, and the number of molecules are quantified.

A study of the ferroelectric and magnetic properties and of the magnetoelectric coupling effects of Pb(Fe0.5Nb0.5)O3 (PFN) thin films, grown on SrRuO3/Si [(100) or (111)] substrates by the rf-magnetron sputtering technique, is presented. Structural, morphological, and compositional characterization was realized using the XRD, AFM, XPS, and TEM techniques. Highly textured single phase films with different thickness (from 45 to 270 nm) were successfully grown without Fe2+ presence. A vertically [110] oriented grainy structure was observed. Polarization vs. electric field (P-E) hysteresis loops exhibit excellent and almost constant values of the maximum (∼ 60 μC/cm2) and remanent (∼ 22 μC/cm2) polarizations in the temperature range from 4 K to room temperature; small values of the coercive field, characteristic of soft ferroelectric materials, are observed in these samples. Measurements of the zero-field cooled (ZFC) and field cooled (FC) magnetization behavior and magnetic (M-H) hysteresis loops were realized at different temperatures between 5 and 300 K. Proof of the existence of ferromagnetic order in the low temperature region (below to 50 K) is discussed and reported for the first time. Values of the maximum (∼ 3 emu/g) and remanent (∼ 1.5 emu/g) magnetizations were obtained. dc magnetic field dependence of the ferroelectric hysteresis loops are shown as evidence of the magnetoelectric coupling.

"Successful synthesis of metal–, semiconductor–, and metal/semiconductor–mordenite nanocomposites, using geothermal solid waste as precursor is reported. Powders of nanostructured composites, consisting of metal and/or semiconductor nanoparticles grown on a mordenite-type zeolitic matrix surface, were synthesized by a one-step solvent-free and organic template-free process. The developed methodology is capable of controlling and tuning the final properties of composites from their synthesis and is also reproducible and repeatable. For comparison and demonstration of the application of the final products, dye photocatalysis degradation tests were done using commercial TiO 2 as reference (degradation reached ∼ 75% in 215 min, k = 0.004 min − 1 ), [M]–S–MOR samples revealed better performance ( ≥ 95% in 100 min, k = 0.009 min − 1 ). All Rights Reserved © 2016 Universidad Nacional Autónoma de México, Centro de Ciencias Aplicadas y Desarrollo Tecnológico. This is an open access item distributed under the Creative Commons CC License BY-NC-ND 4.0."

Frequency domain sensors (FDS) are important elements in control, data acquisition and monitoring systems. Such sensors have some outstanding characteristics like output of quasi-digital signals, high sensitivity, high resolution, wide dynamic range, anti-interference capacity and good stability. A FDS converts a physical variable (measurand) into a frequency domain ouput. When the measurand changes, the output has a proportional frequency shift. In systems that use FDS, measuring the frequency shift is desirable. Accuracy of most frequency measurement techniques is limited by measurement time, and if more precision is required, longer times for measuring are needed. In this work, a novel approach using the rational approximations principle for measuring frequency shift in the output of a FDS is introduced. Also algorithms for simulating the mathematical model of frequency measurement process are proposed, and resolution of measurement is improved by analyzing the data obtained.

In all the real-time control systems used on autonomous navigation systems (ANS), a computing system is used. In such, the proper functioning depends of the correct operation of a reference oscillator. Unfortunatelly, the stability of frequency standards is barely explored in ANS, and due the importance it has, more attention is needed. In this work, a new method for measuring frequency-time reference in autonomous navigation systems is proposed. Basics about instability sources is briefly reviewed, and a new frequency suited for measurement technique for ANS is explained; also a brief review of frequency measurement techniques is presented. Analysis of measurements in frequency standard values is carried on, and measurement error is introduced.

The antimicrobial activity of silver nanoparticles (AgNPs) is currently used as an alternative disinfectant with diverse applications, ranging from decontamination of aquatic environments to disinfection of medical devices and instrumentation. However, incorporation of AgNPs to the environment causes collateral damage that should be avoided. In this work, a novel Ag-based nanocomposite (CEOBACTER) was successfully synthetized. It showed excellent antimicrobial properties without the spread of AgNPs into the environment. The complete CEOBACTER antimicrobial characterization protocol is presented herein. It is straightforward and reproducible and could be considered for the systematic characterization of antimicrobial nanomaterials. CEOBACTER showed minimal bactericidal concentration of 3 μg/ml, bactericidal action time of 2 hours and re-use capacity of at least five times against E. coli cultures. The bactericidal mechanism is the release of Ag ions. CEOBACTER displays potent bactericidal properties, long lifetime, high stability and re-use capacity, and it does not dissolve in the solution. These characteristics point to its potential use as a bactericidal agent for decontamination of aqueous environments.

Multifunctional materials such as the single phase compound Pb(Fe0.5Nb0.5)O3 (PFN), where ferroelectric and magnetic order coexist, are very promising and have great interest from the academic and technological points of view. However, as was established in previous work, the occurrence of Fe2+ and oxygen vacancies originated during the sintering process increase electrical conductivity, dielectric loss, and space-charge accumulation at the grain boundary, all of them detrimental to optimal device performance.1-3 Here, a report on the effects of an O2 atmosphere during the calcination and sintering stages of the preparation process using the traditional ceramic method is presented. A comparative study of structural, morphological and small signal dielectric frequency-temperature response study, where appropriate microstructural and equivalent circuit models were established using the impedance spectroscopy technique is presented. Big differences in the hysteret!ic behavior of the samples prepared in the presence and without the O2 atmosphere were observed and are discussed. The O2 atmosphere improves the dielectric and ferroelectric properties largely, in comparison with previous reports on PFN ceramics where other methods such as sintering in air, Pb atmospheres or fabricated from sol-gel-derived powders were used. 1 O. Raymond et al, J. Appl. Phys. 97, 084107 (2005). 2 O. Raymond et al. J. Appl. Phys. 97, 084108 (2005). 3 O. Raymond et al. J. Appl. Phys. 99, 124101 (2006). This work was partially supported by DGAPA-UNAM Project IN109305-3 and CoNaCyT Projects No. 47714-F and 49986-F. The authors thank E. Aparicio, P. Casillas, I. Gradilla, and J. Peralta for their technical assistance.

Las propiedades multiferroicas del compuesto BiFeO3 (BFO) han recibido gran atención durante décadas. Hasta la fecha, existen muchos estudios teóricos y experimentales detallados sobre la coexistencia en el BFO del ordenamiento ferroeléctrico (FE) que muestra una alta polarización espontánea con un ordenamiento antiferromagnético (AFM) que, bajo ciertas circunstancias, puede aparecer como ferromagnetismo (FM) débil. Sin embargo, en la literatura se encuentran pocos reportes sobre ordenamientos FM en el BFO los cuales se refieren a fenómenos en la interfaz de heteroestructuras y, aparentemente, ninguno sobre el BFO en bulto y/o película delgada con ordenamiento FM. Recientemente, se ha reportado un nuevo estado FM que coexiste con un ordenamiento FE a temperatura ambiente en películas delgadas de BFO (de grosor ≤ 50 nm) depositadas sobre substratos de La2/3Sr1/3MnO3/SiO2/Si(100) usando la técnica de erosión iónica (Ramirez-Camacho et al., 2017). Siguiendo este trabajo, estudiamos por primeros principios, las propiedades multiferroicas tanto en las partes como en el todo de heteroestructuras de BiFeO3/La2/3Sr1/3MnO3 (BFO/LSMO) enfocados en la explicación de las propiedades ferromagnéticas y ferroeléctricas observadas. Para este fin, usamos diferentes celdas de construcción: una celda romboédrica de 40 átomos con simetría R3c para el BiFeO3 , mientras para el LSMO se empleó una celda de 120 átomos con simetría R3 ̅c conteniendo el número de iones de La3+ y Sr2+ requeridos por la estequiometría. En cada caso se estudian las propiedades estructurales, el enlace químico y la estructura electrónica, empleando el formalismo de la teoría del funcional de la densidad (DFT) conjuntamente con el potencial de Hubbard (U) y el uso de una combinación de diferentes representaciones como la densidad de estados, la estructura de bandas, la densidad electrónica, la función de localización de electrones y los orbitales moleculares. La polarización espontánea Ps se calculó usando la teoría moderna de la polarización. El trabajo de tesis demuestra que es posible el ordenamiento FM estable en el BFO coexistiendo con el ordenamiento FE, como consecuencia de un pequeño aumento de las distorsiones romboédricas, fuertemente asociado a un mayor grado de covalencia de los orbitales eg de espín-arriba con los orbitales O-2p en los enlaces Fe-O. Con ello, el ordenamiento FM se establece mediante interacciones de intercambio indirecto como de super-intercambio y/o doble intercambio... The multiferroic properties of the BiFeO3 (BFO) compound have received great attention for decades. To date, there are many detailed theoretical and experimental studies on the coexistence of ferroelectric ordering (FE) that show a high spontaneous polarization and antiferromagnetic (AFM) ordering in BFO which, under certain circumstances, can show up a weak-ferromagnetism (FM). However, there are only a few reports in the literature of FM ordering in BFO at the interface in heterostructures and, apparently, none on FM BFO bulk and/or thin film. Recently, a novel FM state coexisting with FE ordering at room temperature has been reported in BFO thin films (thickness ≤ 50 nm) on La2/3Sr1/3MnO3/SiO2/Si(100) substrates grown by the sputtering technique (Ramirez-Camacho et al., 2017). Following this work, the multiferroic properties in both, the parts and the whole of BiFeO3/La2/3Sr1/3MnO3 (BFO/LSMO) heterostructures were studied by first principles, focusing on the explanation of the observed ferromagnetic and ferroelectric properties. For this purpose, different construction cells are used: a rhombohedral cell of 40 atoms with R3c symmetry for BiFeO3, while for the LSMO a cell with 120 atoms with R3 ̅c symmetry containing the number of La3+ and Sr2+ ions required for stoichiometry is used. In each case, structural properties, chemical bond and electronic structure are studied, using the density functional theory (DFT) + Hubbard potential (U) formalism using a combination of different representations such as density of states, band structure, electron density, electron localization function and molecular orbital. The spontaneous polarization Ps is calculated using the modern theory of polarization. The thesis shows that stable FM ordering in FE BFO is possible. It is a consequence of a small increase of the rhombohedral distortions and is strongly associated to a higher degree of covalence of the spin-up Fe-eg orbitals with the O-2p orbitals in the Fe-O bonds, and it is established by indirect exchange interactions such as superexchange and/or double exchange interactions which are mediated by the oxygen ions located between the Fe ions. The calculated Ps values are very similar independently of the magnetic ordering (AFM-G or FM), and are in good correspondence with those reported experimentally. For the LSMO, it is demonstrated that the ferromagnetic arrangement with the randomly distributed La3+ and Sr2+ ions is more stable than that with an ordered...

Las heteroestructuras multiferroicas compuestas de materiales ferroicos, al acoplarse eléctrica, magnética, y/o estructuralmente, dan como resultado efectos de ferroelectricidad y ferromagnetismo simultáneo. El gran potencial tecnológico, junto con la abundancia de fenómenos físicos en las interfaces, han provocado una intensa investigación en heteroestructuras multiferroicas. Estas heteroestructuras pueden ser explotadas para mejorar significativamente el rendimiento y/o añadir nuevas funcionalidades a muchos dispositivos existentes o emergentes, tales como dispositivos de memorias de múltiples estados, dispositivos sintonizables de microondas, sensores y transductores magnetoeléctricos, etc. Este trabajo reporta un nuevo estado ferromagnético (FM) que coexiste con el ordenamiento ferroeléctrico a temperatura ambiente en películas de BiFeO3 (BFO) crecidas sobre sustratos de La0.7Sr0.3MnO3/SiO2/Si(100) (LSMO/SOS), por medio de la técnica de erosión iónica. Se estudiaron las propiedades de los sistemas de películas de BFO con diferentes espesores (tBFO = 15, 50, 70, 120 y 140 nm) sobre películas de LSMO con un espesor fijo de 40 nm. Se crecieron bicapas de BFO/LSMO altamente texturadas con orientación [012] en la dirección perpendicular al plano, ambas con estructuras romboédricas. Las películas de LSMO fueron crecidas nanoestructuradamente, conformadas por nanoregiones de monodominios FM inducidas por la superficie del SiO2, con TC ~ 200 K y altos campos coercitivos (Hc) (~ 1100 Oe a 2.5 K). Las películas del BFO crecieron nanoestructuradas epitaxialmente sobre el LSMO, exhibiendo nanoregiones esféricas de ~ 4 nm de diámetro. Las películas más gruesas de BFO (tBFO > 70 nm) presentan un comportamiento típico antiferromagnético. Las más delgadas (tBFO < 50 nm) despliegan un comportamiento FM con TC > 400 K, HC ~ 1600 Oe para 15 nm de espesor y ~1830 Oe para 50 nm. Proponemos que tal comportamiento FM se origina por el establecimiento de una configuración electrónica de espín inusual en la subred Fe3+-O-Fe3+ de la estructura del BFO, inducida por una fuerte hibridación en la interfaz como consecuencia de un acoplamiento de interacciones de superintercambio con la subred Mn3+-O-Mn3+/Mn4+ FM del LSMO. Todas las películas de BFO presentan propiedades ferroeléctricas y piezoeléctricas excelentes (con campos coercitivos del orden de ~ 740 kV/cm y 200 kV/cm, y valores de d33 = 23 pm/V y 55pm/V para 50 nm y 140 nm, respectivamente), exhibiendo estructuras de paredes Multiferroic heterostructures are made of materials that have coupled electric, magnetic, and structural order parameters that result in simultaneous ferroelectricity and ferromagnetism. The exciting technological potential, along with the wealth of physical phenomena at the interface, has sparked intensive research on multiferroic heterostructures. It can be exploited to significantly improve the performance of or/and add new functionalities to many existing or emerging devices such as multistate memory devices, tunable microwave devices, sensors and magnetoelectric transducers, etc. We report a novel ferromagnetic (FM) state coexisting with ferroelectric ordering at room temperature (RT) in strained BiFeO3 (BFO) thin films grown on La0.7Sr0.3MnO3/SiO2/Si(100) (LSMO/SOS) substrates, using a sputtering technique. The properties of BFO films with different thicknesses (tBFO = 15, 50, 70, 120, and 140 nm) on 40 nm LSMO layers were explored. [012] out-of-plane highly textured BFO/LSMO stacks grew with rhombohedral structures. LSMO layers grew nanostructured, constituted by FM single-domain nanoregions induced by the constrain of the SiO2 surface, with TC ~ 200 K and high coercive field (HC) of ~ 1100 Oe at 2.5 K. BFO films grew epitaxially nanostructured on LSMO, exhibiting ~ 4 nm spherical nanoregions. The thicker BFO layers (tBFO > 70 nm) show typical antiferromagnetic behavior. The thinner ones (tBFO < 50 nm) display FM behavior with TC > 400 K, HC ~ 1600 Oe for 15 nm and ~ 1830 Oe for 50 nm. We propose that such FM behavior is originated by the establishment of an unusual electronic-spin configuration in the Fe3+-O-Fe3+ sublattice of the BFO structure, induced by strong hybridization at the interface as consequence of superexchange coupling interactions with the ferromagnetic Mn3+-O-Mn3+/Mn4+ sublattice of LSMO. All BFO layers show excellent ferroelectric and piezoelectric properties (coercive field ~ 740 kV/cm, and d33 = 23 pm/V for 50 nm; ~ 200 kV/cm and 55 pm/V for 140 nm), exhibiting 180˚ and 109˚ DWs structures depending on the thickness. Such multiferroic properties envisage the potential realization of new magneto-electronic devices integrated with Si technology.

La fotocatálisis plasmónica ha recibido atención recientemente como una tecnología de alto rendimiento en la producción de compuestos de alto valor agregado como sorbitol y acido glucurónico, al usar metales nobles como oro, plata y cobre soportados en nanocompuestos. Estos compuestos juegan un papel importante en la industria farmacéutica y la industria de los hidrocarburos. El presente estudio reporta los resultados obtenidos en la conversión de la glucosa a productos de valor agregado, empleando nanocompuestos basados en nanopartículas de metales y/o semiconductoras contenidas en el interior y en la superficie de matrices zeolíticas tipo mordenita. Se desarrollaron nanocompuestos metal-mordenita como 30Ag-MOR, 30Au-MOR, semiconductor-mordenita como 20CdS-MOR y metal/semiconductormordenita como 30Au/20CdS-MOR y 10Ag/20CdS-MOR. Los nanocompuestos fueron caracterizados detalladamente en su morfologia, estructura cristalina, composición superficial, área superficial, porosidad y composición química. La difracción de rayos X mostró el crecimiento de la zeolita tipo mordenita de alta cristalinidad. Las microscopias electrónicas de transmisión y de barrido presentaron los aspectos morfológicos de los polvos caracterizados por granos de empaquetamientos de cristalitos en forma de agujas. Las nanopartículas metálicas y/o semiconductoras se observan distribuidas homogéneamente dispersas en la superficie de los cristalitos. La espectroscopia fotoelectrónica de rayos X confirmó el contenido de los valores predichos para los nanocompuestos. El análisis de adsorción de N2 junto con la técnica BET y las curvas-t proporcionaron los valores del área superficial y el volumen de los mesoporos de cada uno de los nanocompuestos. Por otra parte, las propiedades ópticas se caracterizaron por espectroscopia de absorción UV-Visible, mostrando las propiedades de absorción (fotoactivas) de cada uno de los nanocompuestos empleados. Las propiedades fotocatalíticas plasmónicas de los nanocompuestos fueron evaluadas al aplicar radiación ultravioleta en un fotorreactor con una longitud de onda de 254 nm y con agitación de 200 rpm. Los nanocompuestos se sometieron a prueba en diferentes tiempos de radiación de 15 minutos, 2 horas y 4 horas en soluciones de glucosa en agua y acetonitrilo mostrando su alta capacidad fotocatalítica en la conversión de la glucosa. The plasmonic photocatalysis has recently received attention as a high performance technology in the production of high added value compounds such as sorbitol and glucuronic acid, using noble metals such as gold, silver and copper supported in nanocomposites. These compounds play an important role in the pharmaceutical and hydrocarbons industry. The present study reports the results obtained in the conversion of glucose to value-added products, using nanocomposites based in nanoparticles of metal and /or semiconductor supported on and in the structure of zeolites type mordenite. Metal-mordenite nanocomposites were developed as 30Ag-MOR, 30Au-MOR, semiconductor-mordenite as 20CdS-MOR and metal/semiconductor-mordenite as 30Au/20CdS-MOR, 10Ag /20CdS-MOR. All nanocomposites were characterized in detail in their morphology, crystalline structure, surface composition, surface area and mesoporous volume and chemical composition. X-ray diffraction showed the growth of the high crystallinity mordenite zeolite. The transmission and scanning electron microscopes presented the morphological aspects of the powders characterized by grains of packing of crystallites in the form of needles. The metallic and / or semiconducting nanoparticles are observed distributed homogeneously dispersed on the surface of the crystallites. The X-ray photoelectron spectroscopy confirmed the content of nanoparticles embedded in the surface of nanocomposites. The analysis of N2 adsorption and the BET technique together with the t-plot report showed that the nanocomposites have a surface area and mesoporous volume. On the other hand, the optical properties were characterized by UV-Visible absorption spectroscopy showing the absorption (photoactive) properties of each of the nanocomposites. The plasmonic photocatalytic properties of all nanocomposites were evaluated, using ultraviolet radiation in a photoreactor with a wavelength of 254 nm and with agitation of 200 rpm. Nanocomposites were tested for different time of radiation of 15 minutes, 2 hours and 4 hours in glucose solutions of water and acetonitrile, showing its high photocatalytic ability in the conversion of glucose. The determination of glucose conversion products using nanocomposites and UV radiation was carried out by liquid chromatography to determine the concentration of sorbitol and glucuronic acid.

Las películas delgadas piezoeléctricas han tenido un gran interés en los últimos años por sus potenciales aplicaciones en sistemas micro-electro-mecánicos (MEMS, del inglés). Los MEMS son ampliamente aplicados en micropropulsores, motores ultrasónicos, resonadores, transductores de alta frecuencia, entre otras. La mayoría de las producciones en artículos industriales que emplean las propiedades físicas de materiales ferroeléctricos en su funcionamiento, se basan fundamentalmente en el compuesto Pb(ZrxTi1-x)O3 (PZT). Sin embargo, el óxido de plomo, que se desprende durante el procesamiento de las materias primas para elaborar el compuesto PZT, es altamente tóxico. Como resultado, la ciencia y la tecnología moderna se han propuesto desarrollar materiales libres de plomo debido a la exigencia de la protección del medio ambiente. El compuesto niobato de potasio y sodio (KxNa1-x)NbO3 (KNN) es considerado uno de los candidatos más promisorios entre los compuestos ferroeléctricos libres de plomo. Con base en la literatura existente sobre materiales libres de plomo y con la experiencia del Grupo de Ferroeléctricos del CNyN, en este trabajo nos propusimos desarrollar películas delgadas del compuesto (K0.5Na0.5)0.985La0.005NbO3 (KNNLa) con buenas propiedades dieléctricas, ferroeléctricas y piezoeléctricas empleando la técnica de depósito por erosión iónica que puedan sustituir al PZT en el mercado ferroeléctrico; reduciendo de esta manera la contaminación por plomo. En la tesis se describen las condiciones óptimas para el depósito de películas delgadas de KNNLa. El estudio estructural y de composición química se realizó empleando las técnicas de difracción de rayos-X; microscopía electrónica de barrido; espectroscopia por energía dispersiva y microscopía de fuerza atómica; mientras las propiedades físicas se evaluaron por microscopia de piezo-fuerza, medidas de histéresis eléctrica, medidas de permitividad, pérdidas dieléctricas e impedancia en función de la frecuencia, y medidas de corriente-voltaje. Como resultados principales, se reporta el crecimiento de películas con estructura perovskita de alta calidad cristalina sobre sustratos de SrRuO3/SiOx/Si[100], y con muy alta textura cristalográfica sobre sustratos de SrTiO3:Nb[100] caracterizadas por la coexistencia de las fases tetragonal y ortorrómbica y sobre SrTiO3:Nb[110] con solo fase tetragonal. Aun cuando las películas exhiben valores altos de corrientes de fuga debido a la presencia, especialmente en las fronteras de grano, de vacancias de Na, K y de oxígeno originadas en los procesos de depósitos por la alta volatilidad del Na fundamentalmente, a nivel local las películas presentan buena repuesta ferroeléctrica con una estructura de dominios predominantemente de 180° fáciles de ser conmutada en la dirección fuera-del-plano. Piezoelectric thin films have had great interest in recent years due to their potential applications in micro-electro-mechanical systems (MEMS). MEMS are widely applied in microthrusters, ultrasonic motors, resonators, high frequency transducers, among others. Most industrial products based on the physical properties of ferroelectric materials in their operation are mainly based on the compound Pb (ZrxTi1-x)O3 (PZT). However, lead oxide, which is released during the processing of raw materials for making PZT, is highly toxic. As a result, science and modern technology have taken up the task of developing lead-free materials driven by the requirement of environmental protection. The compound potassium and sodium niobate (KxNa1-x)NbO3 (KNN) is considered one of the most promising candidates among lead-free ferroelectric compounds. Based on the literature on lead-free materials and the experience of CNyN Ferroelectrics Group, in this work we set out to develop thin films of the (K0.5Na0.5)0.985La0.005NbO3 (KNNLa) compound with good dielectric, ferroelectric and piezoelectric properties using the sputtering deposition technique, such that they can substitute PZT in the ferroelectric market; thereby reducing lead contamination. In this thesis work, the optimum conditions for the deposition of thin films KNNLa are described. The structural and the chemical composition study was carried out using Xray diffraction; SEM; energy dispersive spectroscopy and atomic force microscopy; while the physical properties were evaluated by piezoelectric force microscopy, electrical hysteresis measurements, permittivity, dielectric loss and impedance as a function of frequency, and current-voltage measurements. As main results of this work, the growth of high quality film with perovskite crystalline structure on substrates of SrRuO3/SiOx/Si[100], and highly textured film on SrTiO3:Nb[100] substrates, characterized by the coexistence of tetragonal and orthorhombic phases and on SrTiO3:Nb[110] with only tetragonal phase. Even though the films exhibit high leakage currents values due mainly to the presence of Na, K and oxygen vacancies at the grain boundaries, originating from the deposits processes by the high volatility of Na, mainly, films locally exhibit good ferroelectric response with a predominantly 180° domain structure easily to switch in the out-of-plane direction.

Recientemente, la síntesis de materiales fotoactivos se ha llevado en la dirección de diseñar estructuras en la nanoescala con funciones fisicoquímicas específicas. Se han reportado diversos procesos para sintetizarlos, tal como su crecimiento en soportes porosos afines como las zeolitas. Por otra parte, en los últimos años han proliferado los métodos de síntesis asistida por el calentamiento de la radiación de microondas porque en muchos casos, permite sintetizar compuestos más rápido y con mayor eficiencia que los métodos convencionales de calentamiento por lo cual representa un campo prometedor para la obtención de materiales fotoactivos basados en soportes porosos. El objetivo principal de esta tesis es la investigación en la síntesis de materiales porosos del tipo zeolita a partir de geles precursores obtenidos de soluciones molares de silicato de sodio (Na2SiO3) y sulfato de aluminio (Al2(SO4)3) siguiendo una variante de la técnica sol-gel y empleando las microondas como método de calentamiento. La síntesis se llevó a cabo en un horno de microondas de Anton Paar Synthos 3000 a diferentes condiciones de temperatura (entre 125 y 240 °C) y tiempo (de 1 a 6 h). Las propiedades morfológicas, estructurales y químicas se caracterizaron por difracción de rayos X, microscopía electrónica de barrido, microscopía electrónica de transmisión de alta resolución, difracción de electrones, espectroscopía de energía dispersiva y adsorción física de N2. La respuesta óptica se caracterizó por espectroscopia de absorción en el espectro UV-Vis. En el trabajo, se demuestra cómo a partir de un mismo gel estandarizado, se obtienen polvos de zeolitas tipo mordenita y/o analcima, así como polvos nanoestructurados de una mezcla de ambas zeolitas en dependencia de las condiciones de síntesis. Se presenta un diagrama de fases de los materiales obtenidos que describe las diferentes fases cristalinas obtenidas, morfologías, tamaños de grano, así como la evolución cristalina en función de la temperatura del proceso y el tiempo de reacción. Se determinó que los materiales obtenidos son microporosos caracterizados por un diámetro de poro promedio de 18 A y valores de área superficial característicos del tipo de zeolitas sintetizadas. Se demuestra que la ruta de síntesis empleada asistida por la radiación de microondas es una técnica de gran potencialidad para la fabricación de materiales porosos con gran control de sus propiedades y alta repetibilidad. In recent years photoactive materials synthesis has been directed into nanoscalestructures design with specific physicochemical features. Many synthesisprocesses have been reported to obtain them such as growth on porous supportsas zeolites. On the other hand, in last years many synthesis methods have beenassisted by the heating from microwave radiation which allow synthesizing differentmaterials faster and with more efficiently than conventional heating methods andalso they represent a promising field for obtaining photoactive materials ontoporous supports.The main aim of this thesis is the research on porous materials synthesis aszeolite-type materials from reagent gels prepared from sodium silicate (Na2SiO3)and aluminum sulfate (Al2(SO4)3) in molar solutions according to a varying sol-gelmethod and using the microwave heating. The synthesis was carried out in anAnton Paar Synthos 3000 microwave oven at different temperature (from 125 to 240 °C) and time (1 to 6 h) conditions. Morphological, structural and chemicalproperties were characterized by X-ray diffraction, scanning electron microscopy,high-resolution transmission electron microscopy, electron diffraction, energydispersive spectroscopy and physical adsorption of N2. The optical response wascharacterized by UV-Vis absorption spectroscopy.Powders of mordenite and analcime type zeolites, as well as a mixed ofthem were obtained from a standard single reagent gel depending on the synthesisconditions.A phase diagram as a function of process temperature and reaction timedescribes the differences between the crystalline phases, morphologies, grainsizes as well as the crystalline evolution of the synthesized materials. Porousmaterials obtained in the present work were microporous sized that werecharacterized by an average pore size of 18 A and surface area valuescharacteristic of the zeolite types synthesized. It´s demonstrated that microwaveassisted synthesis as the synthesis route employed in this work is a great potentialtechnique to obtain porous materials with greater control of their properties andhigh repeatability.

Este trabajo reporta el crecimiento de zeolitas tipo mordenita (MOR) por síntesis directa, así como el crecimiento de nanocúmulos semiconductores del sistema ternario CdxZnyS crecidos en las zeolitas sintéticas mediante la sulfuración con H2S. Los análisis de composición química, morfología y estructura fueron realizados por difracción de rayos X, microscopía electrónica de transmisión (MET) y barrido (MEB), espectroscopia de dispersión de energía, espectroscopia de plasma inducido, espectroscopia fotoelectrónica de rayos X y adsorción física. La difracción de rayos X mostró la fase correspondiente a la mordenita bien definida; La espectroscopia de dispersión de energía nos mostró la composición química de la matriz y el porcentaje en peso relativo de Cd, Zn y S. MET y MEB mostraron una morfología de granos en forma de discos ovalados con un empaquetamiento de mordenitas en forma de agujas crecidas en la dirección (001) con diámetro promedio de 70 nm. La espectroscopia de emisión de plasma nos indicó la estequiometría real de los compuestos desarrollados en este trabajo, mientras que la espectroscopia fotoelectrónica de rayos X nos indicó que ambientes químicos tienen los diferentes elementos que contiene nuestro material. Esta serie de resultados nos permitió proponer la estructura de los nanocúmulos semiconductores que se han crecido sobre la superficie volumétrica de las mordenitas sintetizadas. Por otro lado, se llevaron a cabo mediciones de las propiedades ópticas espectrales; algunos resultados notables son los corrimientos en los bordes de absorción en los espectros de UV-Vis de las muestras con respecto a los de ZnS y CdS en bulto, los efectos de confinamiento cuántico observado en los espectros de fotoluminiscencia, así como el carácter protónico de los nanocompuestos mostrado en espectroscopia de infrarrojo. Los efectos anteriores nos indican que los nanocompuestos desarrollados son altamente fotoactivos y que son fuertes candidatos a usarse en procesos fotocatalíticos. The growth and optical spectra properties of mordenite-type zeolites by direct synthesis and semiconductor nanoclusters of the ternary CdxZnyS system growth by treatment in hydrogen sulphide flow, is reported. Compositional, morphological and structural studies were realized by XRD, SEM, TEM, energy dispersive spectroscopy (EDS), induced coupled plasma optical emission spectrometry (ICPOES), X-ray photoelectron spectroscopy (XPS) and surface area and pore size distribution. XRD shows well-crystallized mordenite and the absence of secondary phases; EDS gives us the chemical composition of the matrix host and the relative weight percent of Cd, Zn and S. TEM and SEM show the disc-shaped grain morphology made by needle-shaped mordenite crystals growth in (001) with average diameters of 70 nm. ICP-OES shows a real stoichiometry of our compounds. XPS gives us as the chemical environments of different ions containing in our material and we propose a cluster formation within the channels and surface of mordenite from these results. On the other hand, were carried out measurements of spectral optical properties; some results are the shifts of absorption edges in the UV-Vis spectra of the samples with respect to those of ZnS and CdS in bulk, the quantum confinement effects observed in the spectra of photoluminescence, and protonic nature of the nanocomposite was showed in infrared spectroscopy. The above effects indicate that the nanocomposites are highly photoactive developed and are strong candidates to be used in photocatalytic processes.

Los materiales multiferroicos son de gran interés académico y tecnológico por sus potenciales aplicaciones en una nueva generación de dispositivos donde se conforman diferentes ordenamientos de naturaleza eléctrica, magnética y elástica. En este trabajo se reporta la obtención de películas delgadas del compuesto multiferroico (ferroeléctrico, antiferromagnético) de formula estequiométrica PbFe0.5Nb0.5O3 (PFN) obtenidas durante procesos de depósito por erosión iónica en régimen de radio frecuencia, a partir de un blanco de PFN+10%Pb en exceso. El objetivo de este trabajo es investigar las condiciones óptimas para obtener películas delgadas de alta textura del compuesto de PFN y el estudio de sus propiedades físicas. Dicho estudio se realizó utilizando una técnica de espectroscopia óptica in situ para analizar los espectros del plasma producido en el proceso de depósito, de manera que las películas texturadas se crecieron controlando la relación de intensidad de dos de las líneas espectrales, IPb(405.78nm)/IFe(404.59nm). La evolución del crecimiento cristalino de las películas delgadas y la optimización de los parámetros de depósito se evaluaron por la técnica de difracción de rayos X, el análisis de tamaño de grano y rugosidad se realizó mediante imágenes obtenidas de microscopia de fuerza atómica, la composición y análisis superficial y morfológico se analizó por microscopia electrónica de barrido, el grosor de las películas delgadas se determinó por perfilometría y el ambiente químico de los elementos se determinó por espectroscopia fotoelectrónica de rayos X y espectroscopía electrónica Auger. También se analizaron las medidas de histéresis ferroeléctrica, medidas de magnetización y susceptibilidad en regímenes de magnetización sin campo y magnetización con campo. Se obtuvieron películas delgadas con alta textura cristalográfica, ciclos de histéresis de alta polarización máxima (100 μC/cm2) y remanente (47 μC/cm2), además de una respuesta ferromagnética a temperaturas criogénicas (debajo de 25 K). Multiferroic materials are of great academic and technological interest for their potential applications in a new generation of devices where electrical, magnetic and elastic order coexist. In this work we report the production of multiferroic thin films (ferroelectric, antiferromagnetic) with stoichiometric formula PbFe0.5Nb0.5O3 (PFN) deposited by radio frequency ion sputtering, of a 10% Pb excess PFN target. The aim of this study is to investigate the physical properties and determine the optimal conditions to obtain highly textured thin films of the PFN compound. Such study was performed using a technique of in situ optical spectroscopy to analyze the spectrum of the plasma produced in the deposition process, so the epitaxial films were grown by controlling the intensity ratio between two spectral lines: IPb (405.78nm) / IFe (404.59nm). The crystalline evolution of the thin film growth and the parameters for deposition were evaluated by X-ray diffraction; grain size and surface roughness were analyzed via Atomic Force Microscopy; composition, surface and morphological analyses were performed by Scanning Electron Microscopy, while film thickness was determined by profilometry; the chemical environment of the constituent elements was analyzed by X-ray photoelectron spectroscopy and Auger Electron Spectroscopy. Ferroelectric hysteresis, magnetization and susceptibility measurements were performed with and without applied external magnetic field. The obtained thin films were highly textured, with hysteresis loops showing high maximum and remnant polarization (100μC/cm2, 47 μC/cm2) and a ferromagnetic response at temperatures below 25 K.