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1.
Inorg Chem ; 2020 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-32806009

RESUMO

The potential of the perovskite system Nd1-xSrxCoO3-δ (x = 1/3 and 2/3) as cathode material for solid oxide fuel cells (SOFCs) has been investigated via detailed structural, electrical, and electrochemical characterization. The average structure of x = 1/3 is orthorhombic with a complex microstructure consisting of intergrown, adjacent, perpendicularly oriented domains. This orthorhombic symmetry remains throughout the temperature range 373-1073 K, as observed by neutron powder diffraction. A higher Sr content of x = 2/3 leads to stabilization of the cubic perovskite with a homogeneous microstructure and with a higher oxygen vacancy content and cobalt oxidation state than the orthorhombic phase at SOFC operation temperature. Both materials are p-type electronic conductors with high total conductivities of 690 and 1675 S·cm-1 at 473 K in air for x = 1/3 and 2/3, respectively. Under working conditions, both compounds exhibit similar electronic conductivities, since x = 2/3 loses more oxygen on heating than x = 1/3, associated with a greater loss of p-type charger carriers. However, composite cathodes prepared with Nd1/3Sr2/3CoO3-δ and Ce0.8Gd0.2O2-δ present lower ASR values (0.10 Ω·cm2 at 973 K in air) than composites prepared with Nd2/3Sr1/3CoO3-δ and Ce0.8Gd0.2O2-δ (0.34 Ω·cm2). The high activity for the oxygen electrochemical reaction at intermediate temperatures is likely attributable to a large disordered oxygen-vacancy concentration, resulting in a very promising SOFC cathode for real devices.

2.
Dalton Trans ; 48(36): 13651-13661, 2019 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-31465070

RESUMO

The partial substitution of up to 5% Nd+3 by Ca+2 results in the oxide Nd1.90Ca0.10MgTiO5.94 that presents some remarkable structural features with a noticeable influence on its properties. In this oxide with a monoclinic perovskite-like structure and an octahedral tilting scheme (a-a-b+), both A- and B-ions are arranged in a rock-salt like manner, representing therefore the first example of a type of perovskite theoretically predicted. Besides this unprecedented arrangement of A- and B-ions, the oxygen vacancies created through doping with acceptor ions are trapped by association with the acceptor defects and hence the mobility of these vacancies is strongly limited. The oxygen conductivity of the substituted material is lower and the activation energy for oxygen motion is higher than those of the parent oxide, in which the concentration of anion vacancies is only due to intrinsic defects.

3.
ChemSusChem ; 12(17): 4029-4037, 2019 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-31282611

RESUMO

Materials with the formula Sr2 CoNb1-x Tix O6-δ (x=1.00, 0.70; δ=number of oxygen vacancies) present a cubic perovskite-like structure. They are easily and reversibly reduced in N2 or Ar and re-oxidized in air upon heating. Oxidation by water (wet N2 ), involving splitting of water at a temperature as low as 700 °C, produces hydrogen. Both compounds displayed outstanding H2 production in the first thermochemical cycle, the Sr2 CoNb0.30 Ti0.70 O6-δ material retaining its outstanding performance upon cycling, whereas the hydrogen yield of the x=1 oxide showed a continuous decay. The retention of the materials' ability to promote water splitting correlated with their structural, chemical, and redox reversibility upon cycling. On reduction/oxidation, Co ions reversibly changed their oxidation state to compensate the release/recovery of oxygen in both compounds. However, in Sr2 CoTiO6-δ , two phases with different oxygen contents segregated, whereas in Sr2 CoNb0.30 Ti0.70 O6-δ this effect was not evident. Therefore, this latter material displayed a hydrogen production as high as 410 µmol H 2 g-1 perovskite after eight thermochemical cycles at 700 °C, which is among the highest ever reported, making this perovskite a promising candidate for thermosolar water splitting in real devices.

4.
Inorg Chem ; 57(23): 15023-15033, 2018 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-30444118

RESUMO

The BaZr0.7Ce0.2Y0.1O3-δ-BaPrO3-δ perovskite system, of interest for high-temperature electrochemical applications involving mixed protonic-electronic conductivity, forms a solid-solution with a wide interval of Ba substoichiometry in the range Ba(Ce0.2Zr0.7)1- xPr xY0.1O3-δ, 0 ≤ x ≤ 1. Structural phase transitions mapped as a function of temperature and composition by high-resolution neutron powder diffraction and synchrotron X-ray diffraction reveal higher symmetry for lower Pr content and higher temperatures, with the largest stability field observed for rhombohedral symmetry (space group, R3̅ c). Rietveld refinement, supported by magnetic-susceptibility measurements, indicates that partitioning of the B-site cations over the A and B perovskite sites compensates Ba substoichiometry in preference to A-site vacancy formation and that multiple cations are distributed over both sites. Electron-hole transport dominates electrical conductivity in both wet and dry oxidizing conditions, with total conductivity reaching a value of ∼0.5 S cm-1 for the x = 1 end-member in dry air at 1173 K. Higher electrical conductivity and the displacement of oxygen loss to higher temperatures with increasing Pr content both reflect the role of Pr in promoting hole formation at the expense of oxygen vacancies. In more reducing conditions (N2) and at low Pr contents, conductivity is higher in humidified atmospheres (∼0.023 atm pH2O) indicating a protonic contribution to transport, whereas the greater electron-hole conductivity with increasing Pr content results in lower conductivity in humidified N2 due to the creation of protonic defects and the consumption of holes.

5.
Inorg Chem ; 57(19): 12093-12105, 2018 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-30198710

RESUMO

Depending on intrinsic (e.g., radius ratio rule rLn/ rZr) and extrinsic factors (e.g., processing conditions), pyrochlore-type Ln2Zr2O7 oxides achieve variable degrees of structural disorder. We report on a systematic study of the structural and microstructural characteristics of the Gd2- xLn xZr2O7 system, exploring the effect of replacing Gd with a wide range of homovalent lanthanide ions (Ln = Nd, Sm, Dy, Ho, Y, and Er; x = 0.20 and 0.80). All compositions were prepared via a mechanochemical reaction between the corresponding oxides and characterized by X-ray diffraction (standard and synchrotron sources) using the Rietveld method, as well as by Raman spectroscopy. Irrespective of chemical composition, this study reveals that all compositions exhibit a fluorite-like structure. Furthermore, by firing each sample at 800 and 1400 °C, we are able to analyze the transition to pyrochlore-like structures, featuring different degrees of disorder, in all but Gd1.20Y0.80Zr2O7, which retains the fluorite structure even after heating. The structural data are used to assess the existing criteria for predicting the formation and stability of the pyrochlore structure; according to this analysis, the simple radius ratio rule ( rLn/ rZr), provides a useful and sufficiently robust criterion. Because the pyrochlore structure has a strong tendency to disorder, it is not possible to define an empirical index similar to the Goldschmidt tolerance factor for perovskite.

6.
Inorg Chem ; 56(15): 9120-9131, 2017 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-28742340

RESUMO

Members of the perovskite solid solution BaZr1-xPrxO3-δ (0.2 ≤ x ≤ 0.8) with potential high-temperature electrochemical applications were synthesized via mechanical activation and high-temperature annealing at 1250 °C. Structural properties were examined by Rietveld analysis of neutron powder diffraction and Raman spectroscopy at room temperature, indicating rhombohedral symmetry (space group R3̅c) for members x = 0.2 and 0.4 and orthorhombic symmetry (Imma) for x = 0.6 and 0.8. The sequence of phase transitions for the complete solid solution from BaZrO3 to BaPrO3 is Pm3̅m → R3̅c → Imma → Pnma. The structural data indicate that Pr principally exists as Pr4+ on the B site and that oxygen content increases with higher Pr content. Electrical-conductivity measurements in the temperature range of 250-900 °C in dry and humidified (pH2O ≈ 0.03 atm) N2 and O2 atmospheres revealed an increase of total conductivity by over 2 orders of magnitude in dry conditions from x = 0.2 to x = 0.8 (σ ≈ 0.08 S cm-1 at 920 °C in dry O2 for x = 0.8). The conductivity for Pr contents x > 0.2 is attributable to positively charged electronic carriers, whereas for x = 0.2 transport in dry conditions is n-type. The change in conduction mechanism with composition is proposed to arise from the compensation regime for minor amounts of BaO loss changing from predominantly partitioning of Pr on the A site to vacancy formation with increasing Pr content. Conductivity is lower in wet conditions for x > 0.2 indicating that the positive defects are, to a large extent, charge compensated by less mobile protonic species. In contrast, the transport mechanism of the Zr-rich composition (x = 0.2), with much lower electronic conductivity, is essentially independent of moisture content.

7.
ChemSusChem ; 10(14): 2978-2989, 2017 07 21.
Artigo em Inglês | MEDLINE | ID: mdl-28594114

RESUMO

The perovskite series Sr2 CoNb1-x Tix O6-δ (0≤x≤1) was investigated in the full compositional range to assess its potential as cathode material for solid oxide fuel cell (SOFC). The variation of transport properties and thus, the area specific resistances (ASR) are explained by a detailed investigation of the defect chemistry. Increasing the titanium content from x=0-1 produces both oxidation of Co3+ to Co4+ (from 0 up to 40 %) and oxygen vacancies (from 6.0 to 5.7 oxygen atom/formula unit), although each charge compensation mechanism predominates in different compositional ranges. Neutron diffraction reveals that samples with high Ti-contents lose a significant amount of oxygen upon heating above 600 K. Oxygen is partially recovered upon cooling as the oxygen release and uptake show noticeably different kinetics. The complex defect chemistry of these compounds, together with the compositional changes upon heating/cooling cycles and atmospheres, produce a complicated behavior of electrical conductivity. Cathodes containing Sr2 CoTiO6-δ display low ASR values, 0,13â€…Ω cm2 at 973 K, comparable to those of the best compounds reported so far, being a very promising cathode material for SOFC.


Assuntos
Condutividade Elétrica , Fontes de Energia Elétrica , Óxidos/química , Eletrodos , Oxigênio/química , Pressão , Temperatura
8.
Inorg Chem ; 55(24): 12766-12774, 2016 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-27989167

RESUMO

The symmetry of the room-temperature (RT) structure of title compounds La2-xSrxCoTiO6-δ changes with x, from P21/n (0 ≤ x ≤ 0.2) to Pnma (0.3 ≤ x ≤ 0.5) and to R3̅c (0.6 ≤ x ≤ 1). For x = 1 the three pseudocubic cell parameters become very close suggesting a transition to a cubic structure for higher Sr contents. Similar phase transitions were expected to occur on heating, paralleling the effect of internal pressure induced by substitution of La3+ by Sr2+. However, only some of these aforementioned transitions have been thermally induced. The symmetry-adapted modes formalism is used in the structural refinements and fitting of neutron diffraction data recorded from RT to 1273 K. Thus, for x = 1, the out-of-phase tilting of the BO6 octahedra vanishes progressively on heating, and a cubic structure with Pm3̅m symmetry is found at 1073 K. For lower Sr contents this transition is predicted to occur far above the temperature limit of common experimental setups. The analysis of the evolution of the perovskite tolerance factor, t-factor, with both Sr content and temperature indicates that temperature has a limited ability to release structural stress and thus to enable transitions to more symmetric phases. This is particularly true when compared to the effect of internal pressure induced by substitution of La by Sr. The existence of phase transitions in materials for solid oxide fuel cells that are usually exposed to heating-cooling cycles may have a detrimental effect. This work suggests strategies to stabilize the high-symmetry high-temperature phase of perovskite oxides through internal-pressure chemically induced.

9.
Dalton Trans ; 44(16): 7643-53, 2015 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-25811695

RESUMO

A solid solution forms for Sr3NdNb(3-x)Ti(x)O(12-δ) with approximate limits 0 ≤ x ≤ 0.06. The system crystallizes with a 12R-type hexagonal perovskite structure in the space group R3, as determined by neutron diffraction and selected area electron diffraction. The electrical properties of the end members have been investigated by impedance spectroscopy in the temperature range 550-800 °C under various gas atmospheres and as a function of oxygen and water-vapour partial pressure. Proton transport dominates under wet oxidising conditions in the temperature range 550-700 °C, as confirmed by the H(+)/D(+) isotope effect. Acceptor doping considerably enhances proton conductivity with a value of 3.3 × 10(-6) S cm(-1) for the bulk response of x = 0.06 at 700 °C in moistened air. The presence of a -» slope for both doped and undoped samples in the range 10(-19) ≤ pO2 ≤ 10(-8) atm at 900 °C indicates n-type transport under reducing conditions following the extrinsic model attributable to acceptor centres. The conductivity is essentially independent of pO2 at 600 °C under dry oxidising conditions, consistent with oxide-ion transport; a positive power-law dependence at higher temperature indicates extrinsic behaviour and a significant electron-hole contribution. The dielectric constant at RT of nominally stoichiometric Sr3NdNb3O12 is εr ∼ 37, with a moderately high quality factor of Q × f ∼ 16,400 GHz at fr ∼ 6.4 GHz. The temperature coefficient of resonant frequency of x = 0 is τf ∼ 12 ppm °C(-1), which lowers to -3 ppm °C(-1) for the Ti-doped phase x = 0.06.


Assuntos
Compostos de Cálcio/química , Óxidos/química , Titânio/química , Cristalografia por Raios X , Espectroscopia Dielétrica , Condutividade Elétrica , Microscopia Eletrônica de Transmissão , Conformação Molecular , Neodímio/química , Nióbio/química , Estrôncio/química , Temperatura
10.
Inorg Chem ; 54(7): 3172-82, 2015 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-25790238

RESUMO

A new hydrated sodium nickel fluoride with nominal composition NaNiF3·3H2O was synthesized using an aqueous solution route. Its structure was solved by means of ab initio methods from powder X-ray diffraction and neutron diffraction data. NaNiF3·3H2O crystallizes in the cubic crystal system, space group Pn3̅ with a = 7.91968(4) Å. The framework, derived from the ReO3 structure type, is built from NaX6 and NiX6 (X = O, F) corner-shared octahedra, in which F and O atoms are randomly distributed on a single anion site. The 2a × 2a × 2a superstructure arises from the strict alternate three-dimensional linking of NaX6 and NiX6 octahedra together with the simultaneous tilts of the octahedra from the cube axis (φ = 31.1°), with a significant participation of hydrogen bonding. NaNiF3·3H2O corresponds to a fully cation-ordered variant of the In(OH)3 structure, easily recognizable when formulated as NaNi(XH)6 (X = O, F). It constitutes one of the rare examples for the a(+)a(+)a(+) tilting scheme with 1:1 cation ordering in perovskite-related compounds. The Curie-like magnetic behavior well-reflects the isolated paramagnetic Ni(2+) centers without worth mentioning interactions. While X-ray and neutron diffraction data evidence Na/Ni order in combination with O/F disorder as a main feature of this fluoride, results from Raman and magic-angle spinning NMR spectroscopies support the existence of specific anion arrangements in isolated square windows identified in structural refinements. In particular, formation of water molecules derives from unfavorable FH bond formation.

11.
Dalton Trans ; 44(8): 3801-10, 2015 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-25609145

RESUMO

We report the rich magnetic behaviour of Sr2CoNb1-xTixO6 (0 ≤ x ≤ 0.5) oxides as a result of their complex microstructure. Although these oxides show an average simple-cubic perovskite structure, they present a flexible microstructure due to short-range ordering between Co/Ti and Nb cations in the perovskite B-sites. The microstructure consists of double-cubic perovskite domains grown in a simple-cubic perovskite matrix. The size and number of the double-cubic perovskite domains decrease as the Ti content increases. As a result of aliovalent substitution of Nb(5+) by Ti(4+) in the parent Sr2CoNbO6 mixed-valence Co(3+)/Co(4+) oxides are obtained. A spin glass-like state has been observed at low temperatures for all the series, with freezing temperatures increasing with the Ti-content in the range 22 to 33 K. Furthermore, the x = 0.3 and x = 0.5 samples show non-interacting superparamagnetic particle-like dynamics associated with relatively high amounts of Co(4+), with "blocking temperatures" of 13 and ∼16 K, respectively. The complex magnetic behaviour of the title oxides seems to be connected with the clustering of magnetic Co(3+) and the distribution of Co(4+) as a result of the microstructure.

12.
Inorg Chem ; 52(1): 313-20, 2013 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-23259916

RESUMO

The full rare-earth (RE) chromites series (RE)CrO(3) with an orthorhombic distorted (Pnma) perovskite structure and the isostructural compound YCrO(3) can be synthesized through a simple microwave-assisted technique, yielding high-quality materials. Magnetization measurements evidence that the Néel temperature for antiferromagnetic Cr(3+)-Cr(3+) ordering strongly depends on the RE(3+) ionic radius (IOR), and a rich variety of different magnetic spin interactions exists. Dielectric spectroscopy on sintered pellets indicates electronic inhomogeneity in all samples as manifested by the presence of at least two dielectric relaxation processes associated with grain boundary and grain interior bulk contributions. X-ray diffraction, Raman spectroscopy, and temperature-dependent dielectric permittivity data do not indicate potential noncentrosymmetry in the crystal or concomitant ferroelectricity. Strong correlations between the magnetic and dielectric properties were not encountered, and microwave-synthesized (RE)CrO(3) may not be classified as magnetoelectric or multiferroic materials.


Assuntos
Cromo/química , Micro-Ondas , Compostos Organometálicos/química , Ítrio/química , Estrutura Molecular
13.
Dalton Trans ; 40(31): 7908-15, 2011 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-21743906

RESUMO

Substitution of La(3+) by Sr(2+) in the double perovskite La(2)CoTiO(6) yields materials of the La(2-x)Sr(x)CoTiO(6) series showing a significant amount of trivalent cobalt ions when prepared at ambient atmosphere. The as-prepared compounds can be reduced in severe conditions retaining the perovskite structure while inducing the formation of a large amount of oxygen vacancies. The limit of aliovalent substitution in this series was found to extend up to x = 1. For substitution of La(3+) up to 15% cobalt and titanium are ordered, though the order is progressively lost as x increases; for x≥ 0.30 no ordering is observed as evidenced by magnetic measurements. The ability of these materials to present either cobalt ions in a mixed oxidation state or large amounts of anion vacancies depending on the atmosphere makes them interesting to be further investigated regarding their electrical and electrochemical properties, and hence, their usefulness in some electrochemical devices.

14.
Inorg Chem ; 48(16): 7659-66, 2009 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-19591438

RESUMO

Despite being proven to be a good lithium-ion conductor 30 years ago, the crystal structure of the ramsdellite-like Li(2)Ti(3)O(7) has remained uncertain, with two potential models for locating the lithium ions in the structure. Although the model presently accepted states that both lithium and titanium occupy the octahedral sites in the framework, evidence against this model are provided by (6)Li and (7)Li MAS NMR spectroscopy. Thus, about 14% of these octahedral positions are empty since no lithium in octahedral coordination is present in the material. When Li(2)Ti(3)O(7)-ramsdellite is treated with nitric acid a complete exchange of lithium by protons is produced to yield H(2)Ti(3)O(7). The crystal structure of this proton-exchanged ramsdellite has been re-examined combining X-ray diffraction (XRD), neutron powder diffraction (NPD), and spectroscopic ((1)H and (7)Li MAS NMR) techniques. Two kinds of protons are present in this material with different acidity because of the local environments of oxygen atoms to which protons are bonded, namely, low acidic protons strongly bonded to highly charged oxygen atoms (coordinated to two Ti(4+) and a vacancy); and protons linked to low charged oxygen atoms (bonded to three Ti(4+) ions) which will display a more acidic behavior. H(2)Ti(3)O(7) absorbs water; proton mobility is enhanced by the presence of absorbed water, giving rise to a large improvement of its electrical conductivity in wet atmospheres. Thus, it seems that water molecules enter the tunnels in the structure providing a vehicle mechanism for proton diffusion.

15.
Inorg Chem ; 46(13): 5390-7, 2007 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-17539630

RESUMO

The structural characterization of NaNbWO(6), prepared by the ceramic route, has been performed. Electron diffraction has shown the presence of two related phases in a 1:1 ratio, whose lattice parameters correspond to those of the well-known tetragonal tungsten bronzes (TTB) and those of a monoclinically distorted phase. In addition to basic unit cells, the morphology of the two phases has been found to be similar, but they present a slight difference in the W/Nb ratio. (1)H and (23)Na magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectra of NaNbWO(6) and its proton-exchanged derivatives have been interpreted on the basis of the ideal TTB structure. The average structure and the morphology remain unchanged in Na(1-x)H(x)NbWO(6) derivatives. (1)H and (23)Na MAS-NMR spectroscopies have been used to monitor changes produced during exchange processes. It has been shown that the exchange of Na ions is mainly produced, but not exclusively, at tetragonal channels. However, a large amount of Na ions at the pentagonal channels do not exchange with protons, suggesting that these ions are needed to stabilize the TTB-like structure. A tentative distribution of sodium ions in the most-exchanged oxide, deduced from NMR results, approximately (Na(0.46))(p)(Na(0.08))(s)H(0.46)NbWO(6), has been proposed. NMR spectra of Na(1-x)H(x)NbWO(6) indicate that two different OH groups are formed upon exchanging. The study of samples hydrated with D(2)O allowed us to conclude that deuterons of adsorbed water exchange with protons of the two OH groups. The proton-deuteron exchange is slow at room temperature but is strongly enhanced at 90 degrees C. This observation relates to the proton conductivity displayed by exchanged products under a humid atmosphere.

16.
Chemistry ; 13(19): 5607-16, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-17415741

RESUMO

The crystal structures of several oxides of the La(2/3)Li(x)Ti(1-x)Al(x)O(3) system have been studied by selected-area electron diffraction, high-resolution transmission electron microscopy, and powder neutron diffraction, and their lithium conductivity has been by complex impedance spectroscopy. The compounds have a perovskite-related structure with a unit cell radical2 a(p)x2 a(p)x radical2 a(p) (a(p)=perovskite lattice parameter) due to the tilting of the (Ti/Al)O(6) octahedra and the ordering of lanthanum and lithium ions and vacancies along the 2 a(p) axis. The Li(+) ions present a distorted square-planar coordination and are located in interstitial positions of the structure, which could explain the very high ionic conductivity of this type of material. The lithium conductivity depends on the oxide composition and its crystal microstructure, which varies with the thermal treatment of the sample. The microstructure of these titanates is complex due to formation of domains of ordering and other defects such as strains and compositional fluctuations.


Assuntos
Óxido de Alumínio/química , Elementos da Série dos Lantanídeos/química , Compostos de Lítio/química , Titânio/química , Cristalização , Microscopia Eletrônica de Transmissão , Óxidos/química , Relação Estrutura-Atividade , Difração de Raios X
17.
Acta Crystallogr B ; 62(Pt 6): 1019-24, 2006 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-17108655

RESUMO

As in SiO2 which, at high pressures, undergoes the alpha-quartz-->stishovite transition, GaAsO4 transforms into a dirutile structure at 9 GPa and 1173 K. In 2002, a new GaAsO4 polymorph was found by quenching the compound from 6 GPa and 1273 K to ambient conditions. The powder diagram was indexed on the basis of a hexagonal cell (a=8.2033, c=4.3941 A, V=256.08 A3), but the structure did not correspond to any known structure of other AXO4 compounds. We report here the ab initio crystal structure determination of this hexagonal polymorph from powder data. The new phase is isostructural to beta-MnSb2O6 and it can be described as a lacunary derivative of NiAs with half the octahedral sites being vacant, but it also contains fragments of the rutile-like structure.


Assuntos
Arseniatos/química , Gálio/química , Cristalografia por Raios X , Modelos Moleculares , Pressão , Sensibilidade e Especificidade
18.
Rev. esp. salud pública ; 79(3): 403-414, mayo-jun. 2005. tab
Artigo em Espanhol | IBECS | ID: ibc-048259

RESUMO

Fundamento: En México el cáncer cérvicouterino (CACU) esuna de las principales causas de muerte en mujeres; sin embargo, seha encontrado una baja participación en los programas de su detecciónoportuna (DOCACU). El objetivo de este estudio fue describirlos determinantes sociales del conocimiento sobre el cáncer cérvicouterinoy la realización de la detección oportuna estableciendo lasdiferencias sociales que al respecto muestra una población de mujerestrabajadoras de una universidad pública de México.Métodos: Se realizó un estudio transversal analítico. Entre marzoy abril de 2003 se aplicó una encuesta a una muestra representativade las trabajadoras que laboraban en una universidad pública(n=228), 110 eran académicas (AC) y 118 administrativas (AD). Seeligió esta población por su elevada diferenciación socioeconómicaen función del puesto laboral (AC vs. AD), esto permitió evaluar lainfluencia de la desigualdad social sobre las conductas en salud. Laencuesta exploró tres aspectos: condiciones de vida, conocimientodel CACU y DOCACU.Resultados: Las mujeres académicas mostraron mayores nivelesde ingreso, escolaridad, conocimiento del CACU y DOCACUque las administrativas. El ingreso y la escolaridad se relacionaronpositivamente con el conocimiento sobre el cáncer cervicouterino, larealización de detección oportuna se relacionó con este último.Conclusiones: La desigualdad socioeconómica entre las mujeresestudiadas se reflejó en diferencias en el grado de conocimiento yen la práctica de la detección oportuna. Estas diferencias se asocian,sobre todo, a las diferencias en el grado de escolaridad


Background: In Mexico, cervical uterine cancer (CUC) is oneof the leading causes of death among women, however a low degreeof participation in the early detection programs has been found.This study is aimed at describing the social determinants of knowledgerelated to cervical uterine cancer and proper testing beingconducted by establishing the social differences with regard theretoamong a population of female employees at a public university inMexico.Methods: An analytical cross-sectional study was made. Duringthe March-April 2003 period, a survey was conducted of a representativesample of the female employees who were working at a publicuniversity (n=228), 110 of whom were professors (PF) and 118administrative staff (AS). This population was chosen due to themajor socioeconomic differentiation thereof in terms of their jobpositions (PF versus AS), thus affording the possibility of evaluatingthe bearing social inequality has on health-related behavior. The surveyexplored three aspects: living conditions, knowledge of CUCand of proper cervical uterine cancer detection testing.Results: The female professors showed higher levels of income,schooling and knowledge of CUC and of cervical uterine cancerdetection testing than the administrative staff. Income and schoolingwere positively related to the knowledge regarding cervical uterinecancer, cervical uterine cancer detection testing being related to thelatter.Conclusions: Socioeconomic inequality among the women studiedwas reflected in differences in the degree of knowledge and incervical uterine cancer detection testing being undergone. These differencesare associated, above all, to the differences in the level ofschooling


Assuntos
Feminino , Humanos , Neoplasias Uterinas/diagnóstico , Estudos Transversais , México/epidemiologia , Inquéritos e Questionários , Universidades , Condições Sociais , Escolaridade , Estilo de Vida
19.
Rev Esp Salud Publica ; 79: 403-414, 2005 Jun 01.
Artigo em Espanhol | MEDLINE | ID: mdl-28272388

RESUMO

OBJECTIVE: In Mexico, cervical uterine cancer (CUC) is one of the leading causes of death among women, however a low degree of participation in the early detection programs has been found. This study is aimed at describing the social determinants of knowledge related to cervical uterine cancer and proper testing being conducted by establishing the social differences with regard thereto among a population of female employees at a public university in Mexico. METHODS: An analytical cross-sectional study was made. During the March-April 2003 period, a survey was conducted of a representative sample of the female employees who were working at a public university (n=228), 110 of whom were professors (PF) and 118 administrative staff (AS). This population was chosen due to the major socioeconomic differentiation thereof in terms of their job positions (PF versus AS), thus affording the possibility of evaluating the bearing social inequality has on health-related behavior. The survey explored three aspects: living conditions, knowledge of CUC and of proper cervical uterine cancer detection testing. RESULTS: The female professors showed higher levels of income,schooling and knowledge of CUC and of cervical uterine cancer detection testing than the administrative staff. Income and schooling were positively related to the knowledge regarding cervical uterine cancer, cervical uterine cancer detection testing being related to the latter. CONCLUSIONS: Socioeconomic inequality among the women studied was reflected in differences in the degree of knowledge and in cervical uterine cancer detection testing being undergone. These differences are associated, above all, to the differences in the level of schooling.

20.
J Org Chem ; 69(6): 2084-93, 2004 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-15058956

RESUMO

Enynes connected through aromatic rings are used as substrates for metathesis reactions. The reactivity of three ruthenium carbene complexes is compared. The resulting 1,3-dienes are suitable precursors of polycyclic structures via a Diels-Alder process. Some domino RCM-Diels-Alder reactions are performed, suggesting a possible beneficial effect of the ruthenium catalyst in the cycloaddition process. Other examples require Lewis acid cocatalyst. When applied to aromatic ynamines or enamines, a new synthesis of vinylindoles is achieved. Monitorization of several metathesis reactions with NMR shows the different behavior for ruthenium catalysts. New carbenic species are detected in some reactions with an important dependence on the solvent used.


Assuntos
Fatores Biológicos/síntese química , Metano/análogos & derivados , Metano/química , Rutênio/química , Alcadienos/química , Alquinos/química , Catálise , Hidrocarbonetos , Indóis/síntese química , Indóis/química , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Solventes/química , Compostos de Vinila/química
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