Bertha Oliva Aguilar Reyes

• PhD
• National Autonomous University of Mexico

La retención de metales pesados en el suelo tiene una relación directa con sus propiedades como el contenido de materia orgánica, pH y capacidad de intercambio catiónico. Con estas propiedades se desarrolló un índice de amortiguamiento (IA) a la contaminación y un mapa de distribución para Morelia Michoacán. Las propiedades del suelo presentaron...

Graphene oxide (GO), a two-dimensional material with exceptional properties such as high mechanical strength and electrical conductivity, has attracted considerable attention in materials science and engineering. This study introduces a novel GO synthesis method using benzoyl peroxide (BPO) as the oxidizing agent, which offers simplicity, scalabili...

In recent years, the hybrid perovskite CH3NH3PbI3 has been widely studied because of its potential application in the fabrication of high efficiency solar cells. The main challenge is to avoid destabilization of this compound under working conditions. Indeed, the MAPbI3 begins to decompose into the precursor phases, a few hours or days after being...

Airborne particulate matter is a serious threat to human health, especially in fast-growing cities. In this study, we carried out a magnetic and elemental study on tree leaves used as passive captors and urban dust from various sites in the city of Santiago, Chile, to assess the reliability of magnetic and elemental measurements to characterize par...

Antarctica is a natural research laboratory thanks to its unique climate, geography, flora and fauna. The conservation of Antarctica's environment is monitored through the Madrid Protocol; however, there are local pollution problems associated with human activities such as research and tourism; in particular, there are negative impacts on air quali...

The interplay between magnetic, megneto-transport and structural properties of Nd-doped double perovskite Sr2−yNdyFe1+xMo1−xO6, in the range 0.05 < y < 0.45 for x = y/2 and synthesized by solid state reaction, has been investigated. Specifically, it has been shown that the observed tetragonal to monoclinic crystallographic phase transition at the N...

The effect of microwave radiation on the hydrothermal synthesis of the double perovskite Sr2FeMoO6 has been studied based on a comparison of the particle size and structural characteristics of products from both methods. A temperature, pressure, and pH condition screening was performed, and the most representative results of these are herein presen...

The ferromagnetic double perovskite Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeMoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (SFMO) system with half-metallicity and fairly high Curie temperature points to the possibility of...

The nanostructure materials are a prefer option to the high-growth technological changes. The remarkable nanotubes and other carbon nanostructure properties have been theoretically and experimentally tested. These nanostructures can be used as reinforcement materials in composites; the research main challenge is the dispersion of these carbon mater...

Organic-inorganic hybrid perovskites have been studied in recent years because of their potential application in the fabrication of high efficiency solar cells. One of the disadvantages of these compounds is the chemical instability to environmental conditions. In the present work, thin films of CH3NH3PbI3 were obtained from a single-step depositio...

Curie temperature (TC) of the ferromagnetic compound Sr2FeMoO6 can be modified by increasing the itinerant electrons at the Fermi level. Nd doping increases the electron density but the charge neutrality should be taken into account. In this work, a series of double perovskites Sr2−yNdyFe1+xMo1−xO6 (y=0.0, 0.25, 0.5, 0.75 and 1.0) for both cases, t...

In this work an experimental study on the synthesis and magnetic and structural properties of double perovskite compounds Sr2−xLaxFeMoO6 fabricated via a sol-gel process is presented. This method allowed to prepare doped systems with x values of 0, 0.25, 0.5, 0.75 and 1.0. The tetragonal crystalline structure was confirmed by X-ray diffraction expe...

The double perovskite compound Sr2FeMoO6 has a half-metallic ferromagnetic character and a high Curie temperature (420 K). Fe-Mo usually present some degree of disorder in either Fe or Mo ions, it is therefore fundamental to understand the role of electronic and structural parameters controlling the half-metallic character together with a Curie tem...

Emissions from motor vehicles are considered to be one of the main sources of airborne particulate matter in Santiago. International researchers have shown that particulate matter contains metal oxides and magnetic particles, both of which are emitted mainly from vehicles exhaust pipes. On the other hand, trees are effective in reducing such contam...

Soils contain variable amounts of Fe oxides, which may be used as indicators of pedogenic processes and the environments related to soil formation. Also, their presence affects soil properties and functions, because it influences the color, aggregation, cation exchange capacity, and phosphorus retention in soils. Since Fe oxides are ferrimagnetic m...

Soils contain variable amounts of Fe oxides, which may be used as indicators of pedogenic processes and the environments related to soil formation. Also, their presence affects soil properties and functions, because it influences the color, aggregation, cation exchange capacity, and phosphorus retention in soils. Since Fe oxides are ferrimagnetic m...

Rock-magnetic investigations of environmental samples, such as soils, dust and leaves, can provide useful information on environmental stress. Aim of this paper is to report on the first magnetic survey carried out on environmental samples from Bogotá, Colombia, which is the fifth most populated city of Latin America. We studied three kinds of samp...

We report the results of a rock magnetic and archeointensity study on pottery fragments recovered at the archaeological site of Puertas de Rolón, Capacha culture (Colima), that is considered one of the most important pre-Classic cultural developments of western Mesoamerica, Mexico. Standard rock magnetic experiments were carried out in order to inv...

The Pacific coast of Mexico has repeatedly been exposed to destructive tsunamis. Recent studies have shown that rock magnetic methods can be a promising approach for identification of tsunami- or storm-induced deposits. We present new rock magnetic and anisotropy of magnetic susceptibility (AMS) results in order to distinguish tsunami deposits in t...

[1] The firm relationship between archeomagnetic samples and their absolute ages, which is usually determined or estimated using a variety of methods (archaeological context, thermoluminiscense, C14, etc.), is crucial in any archaeomagnetic investigation. In this paper, we report 18 successful (from 65 analyzed) archaeointensity determinations of h...

En el presente trabajo, investigamos la correlación entre algunos parámetros magnéticos y el nivel de contaminación por metales pesados en suelos urbanos de la ciudad de Morelia, en el occidente de México. El estudio magnético fue llevado a cabo en 98 muestras urbanas provenientes de diferentes tipos de uso de suelo. La mayoría de las muestras cont...

We report a detailed palaeomagnetic investigation of 28 lava flows (221 standard palaeomagnetic cores) collected from the Paraguayan part of the Paraná flood basalts (the Alto Paraguay Formation). The initial aims of our study were to (i) document variability of the Earth's magnetic field during the time interval sampled, (ii) obtain a new Early Cr...

A rock-magnetic and paleomagnetic investigation was carried out on eleven Pleistocene and Pliocene 40Ar/39Ar dated lava flows from the Tepic-Zacoalco rift region in the western sector of the Trans-Mexican Volcanic Belt (TMVB) with the aim of obtaining new paleomagnetic data from the study region and information about the Earth’s magnetic field reco...

RESUMEN Se reportan los resultados del primer estudio magnético en líquenes de la ciudad de Montevideo, Uruguay. El interés de éste estudio radica en el papel de los biomonitores en la evaluación del nivel de contaminación atmosférica. Se empleó la metodología magnética para determinar niveles relativos de contaminación en la zona más transitada de...

RESUMEN Los depósitos de tsunamis han sido ampliamente estudiados en latitudes de climas templados, pero las dificultades asociadas al trabajo en ambientes tropicales y la intensidad de bioturbación en estos hábitats limitan las oportunidades para analizar estos depósitos. Hasta ahora, no hay una una técnica analítica que por sí sola identifique a...

We present a diagnostic study to evaluate the suitability of Ficus benjamina tree leaves as a captor of heavy metal particles from atmospheric dusts in urban areas. Leaf samples were taken at 16 localities within three areas in Morelia, state of Michoacán (Mexico’s medium size city, 830000 inhabitants). Measurements of magnetic susceptibility were...

This article presents the first palaeomagnetic results from 13 independent cooling units in the Chiapanecan Volcanic Arc (ChVA). Six sites were directly dated by Ar–Ar or K–Ar methods: their dates range from 2.14 to 0.23 Ma. We isolated the characteristic palaeodirections for all 13 lavas. Eleven non-transitional directions yield a mean direction w...

We report a detailed rock-magnetic and archaeointensity analysis of four pottery fragments and a burned floor recovered from the Tzintzuntzan archaeological site in western Mexico. Results from rock-magnetic experiments (x-T curves and first-order reversal curves [FORC] diagrams) indicate the suitability of most of these materials as faithful geoma...

Quantitative assessment of the vibrational features of nanocrystalline hydrated silicas is still not yet ascertained, although this is a relevant issue in silica physics. In this work, we examine the vibrational states in two generic opaline silicas. PM3 semiempirical calculations on finite SiO2hydrated clusters prove that the low-frequency Raman l...

This paper focuses on the study of the correlation between magnetic parameters with the level of contamination by heavy metals in urban soils. We report a magnetic investigation of urban soil samples from Merida, state of Yucatan, Southern Mexico. It appears that most of our samples contain ferrimagnetic minerals as the magnetic carriers, probably...

The paleosecular variation (PSV) and polarity transitions are two major features of the Earth’s magnetic field. Both PSV and reversal studies are limited when age of studied units is poorly constrained. This is a case of Central and western Mexico volcanics. Although many studies have been devoted to these crucial problems and more than 200 paleoma...

For long time the western-central Mexico has been affected by oblique subduction caused by Farallon plate beneath North America. As result, smaller plates (e.g. Cocos Plate), several fault systems outlining crustal blocks (e.g. Michoacán block) and magmatic arcs (e.g. Paleocene-Early Oligocene magmatism and the Trans-Mexican Volcanic Belt) were dev...

Montevideo as well as any Latin-American capital city is confronted to air pollution and human health problems. However, the limited number of monitoring stations does not allow the production of high-resolution pollution maps. In order to contribute to the air pollution monitoring and to better characterize health pollutants in Montevideo, the pre...

We present rock-magnetic and paleomagnetic results obtained on samples belonging to a Neogene sequence of 11 successive lava flows and a dyke from La Gomera (Canary Islands, Spain). Analysis of thermomagnetic curves allows to distinguish three types of samples: (i) Type H samples with low-Ti titanomagnetite as the only carrier of remanence; (ii) ty...

Despite of the impressive cultural heritage and abundant archaeological sites, absolute geomagnetic intensity data from Mesoamerica are still sparse. Archeointensity determinations using the Coe variant of the Thellier and Thellier method have been carried out on some selected pottery fragments from the El Opeño archeological site which has the ear...

The search for materials having complete spin polarization and high Curie temperature have received a lot of attention in view of spintronics applications, especially the ferromagnetic (F) Sr2FeMoO6, because of its fairly high Curie temperature (TC= 450 K), half-metallic character, large magnetoresistance and potential applications. On the other ha...

The western-central part of Mexico is segmented by several structural systems bounding crustal blocks, two of them are the Jalisco and Michoacan blocks. In an oblique convergent margin system the deformation induced is partitioned into an arc normal component, accommodated at the trench, and an arc-parallel component, accommodated at the magmatic a...

Ordered Sr2FeMoO6 is expected to have complete spin polarization, however all samples usually present some degree of Fe/Mo disorder which reduces the tunneling magnetoresistance in granular samples. It can be inferred that disorder is detrimental to the half-metallicity. We present an electronic approach of this disorder using a model based on a co...

Este estudio presenta los resultados paleomagnéticos del Volcán Tancitaro, (perteneciente al Campo Volcánico Michoacán Guanajuato), en el oeste de México, como una contribución a la base de datos de promediados en el tiempo del campo global. Se realizó el estudio paleomagnético y de magnetismo de roca en once flujos de lava. Se colectaron 120 núcle...

We studied urban soils samples from Merida Yucatan Mexico using magnetic methods. Measurements of magnetic susceptibility (X) at high and low frequencies allowed us to obtain Xfd, whose values indicate a high SP grains content in most samples. We calculated S-200 and S-20 ratios from IRM measurements. These parameters are the Isothermal remanent ma...

Results of detailed paleomagnetic studies from Tecalitlan area are reported. Sexteen sites (about 150 oriented samples) were collected including one Ar-Ar dated ignimbrite. Rock-magnetic experiments permitted identification of the magnetic carriers and assessment of the paleomagnetic stability. Continuous susceptibility measurements vs temperature,...

We sampled eleven fresh, apparently not altered outcrops out of 26 sites reported recently while 27 independent cooling units were collected at Tacambaro area belonging to the Michoacan Guanajuato Volcanic Field. All studied sites were dated by means of state-of-the-art 40Ar-39Ar geochronological method and span from 1.23 ± 0.2 ma to present. Low-f...

We report a detailed archeomagnetic and micro-Raman spectroscopy investigation on pre-Columbian pottery fragments from Cuanalan (a formative village in the valley of Teotihuacan, central Mexico). Available radiocarbon ages range from 2320 ± 80 to 2060 ± 90 B.P. Continuous low-field susceptibility versus temperature curves performed in air indicate...

aBstract The microstructure of nearly 200 common gem opal-A and opal-CT samples from worldwide localities was investigated using scanning electron microscopy (SEM). These opals do not show play-of-color, but are valued in the gem market for their intrinsic body color. Common opal-AG and opal-CT are primarily built from nanograins that average ~25 n...

Thellier paleointensity experiments are carried out on the Early Cretaceous Arapey Formation, which belongs to the Parana Magmatic Province (PMP) in northern Uruguay. Twenty-seven samples out of 225 analyzed yield reliable absolute intensity determinations. For these samples the NRM fraction f used for determination ranges between 0.33 to 0.83 and...

Reportamos una investigación arqueomagnética detallada de algunas cerámicas pre–Colombinas de Quiahuiztlan (Veracruz, Golfo de México). Las muestras estudiadas pertenecen al intervalo de ~900 D.C. a 1521 D.C. Las muestras, analizadas por técnicas magnéticas modernas, parecen portar esencialmente una magnetización termoremanente estable y univectori...

Recently, the double perovskites family A2MM′O6 (A being a divalent or trivalent cation and M, M′ two transition metals) has attracted considerable interest with the view of using these materials in spin electronics. This has been triggered but the fact that some members, in particular SrFe2MoO6, present a Curie temperature TC above room temperatur...

We study the double perovskite Sr2FeMO6 using a tight-binding model with the renormalized perturbation expansion technique. An analysis of the antiferromagnetic (AF) phase shows that the electronic energy remains larger than in the ferromagnetic (F) state but the difference decreases with increasing charge transfer energy. Therefore, with increasin...

This is the first NMR study of the destabilization through whitening of paracrystalline opal-CT (SiO2, nH2O). The aim of this study is to understand the process leading to the degradation, particularly any changes in the structure and bonding of this material. 29Si and 27Al NMR signals are not significantly modified. In contrast, using for the firs...

The double perovskites Sr2FeMO6 have received a lot of attention, especially Sr2FeMoO6 because of its fairly high Curie temperature (TC = 450 K), half-metallic character, large magnetoresistance and potential applications. On the other hand, Sr 2FeWO6 is insulating and antiferromagnetic with T N = 37 K. With a double exchange type model it has been...

We study the ordered double perovskite of the type Sr2FeMO6 using a tight-binding model with the renormalized perturbation expansion technique. In the ferromagnetic phase (F), we determine the behavior of the critical temperature as a function of the band filling and the Fe–M charge transfer energy. In the antiferromagnetic phase (AF) as in Sr2FeWO...

Este trabajo presenta los resultados del primer estudio mineralógico del fenómeno de desestabilización por blanqueamiento en ópalos mexicanos de origen volcánico. En los espectros Raman de las muestras de ópalo estudiadas se observan bandas características de grupos moleculares de H2O en dos regiones diferentes: alrededor de 3,200 cm-1 para la part...

This paper presents the first mineralogical study of the destabilization phenomena by whitening in Mexican opals. The Raman spectra of the opal samples are characterized by the well-resolved bands assigned to molecular H2O, at 3,200 cm-1 and at 2,900 cm-1 for the unaltered (orange) and for the destabilized (whitened) parts, respectively. The shape...

A Mexican opal from the state of Jalisco has a bidisperse, perfectly ordered structure with framboid silica lepispheres of two different diameters. Its structure has been determined by the observation of a vicinal section, close to a dense plane. Fresh breaks along a vicinal plane emphasized regular steps, which were studied by means of SEM. We hav...

A Mexican opal from the state of Jalisco has a bidisperse, perfectly ordered structure with framboid silica lepispheres of two different diameters. Its structure has been determined by the observation of a vicinal section, close to a dense plane. Fresh breaks along a vicinal plane emphasized regular steps, which were studied by means of SEM. We hav...

This paper presents the first mineralogical study of the destabilization phenomena by whitening in Mexican opals. The Raman spectra of the opal samples are characterized by the well-resolved bands assigned to molecular H2O, at 3,200 cm -1 and at 2,900 cm -1 for the unaltered (orange) and for the desta- bilized (whitened) parts, respectively. The sh...

Recently, the double perovskites family A2MM'O6 (A being a divalent or trivalent cation and M, M' two transition metals) has attracted considerable interest with the view of using these materials in Spin Electronics. This has been triggered but the fact that some members, in particular Sr2FeMoO6, present a Curie temperature TC above room temperatur...