Zinc oxide films with different average grain size are deposited on glass substrates by spray‐pyrolysis at 425 °C. Samples are characterized by XRD, UV–Vis transmittance, FE‐SEM, and electrical properties measurements. The increase in conductivity observed under 365 nm wavelength illumination is evaluated in terms of grain size. Films with small grains (120 nm) show higher response with respect to films with larger grains (230 and 300 nm). A model considering resistivity and grain size for the prediction of the response of films in terms of UV‐to‐dark conductivity ratio is proposed and validated with experimental results.
Resumen: Electrolitos poliméricos conductores de iones de litio, basados en alcohol de polivinilo (PVA-OH) complejado con la sal Li 2 SO 4 y diferentes relaciones de porcentaje en peso de plastificante PEG 400 fueron preparados por la técnica de solución utilizando agua desionizada como disolvente. El estudio FTIR confirma la formación del complejo polímero-sal. Las curvas de descomposición térmica obtenidas por termogravimetría (TGA) muestran que la estabilidad térmica de los electrolitos depende del porcentaje de plastificante. Un proceso de relajación es visible en el formalismo del módulo eléctrico, asociado con la dinámica de la transición vítrea, relajación-α. El máximo de cada pico se desplaza a frecuencias más altas cuando aumenta el plastificante, debido a una mejora de la movilidad dipolar en el origen de los movimientos cooperativos. La dependencia de la parte real de la conductividad eléctrica como función de la frecuencia exhibe una ley de potencias, esta variación es ajustada a la expresión Jonscher. Palabras-clave: Relajación dieléctrica, conductividad iónica, transición vítrea, baterías de ion litio.
Electrical Properties of Membranes Made with Polymer ElectrolyteComplexes PVA-OH/LI 2 SO 4 /PEG 400 Abstract: Lithium ion conducting polymer electrolytes based on polyvinyl Alcohol (PVA-OH) complexed with salt Li 2 SO 4 and different weight percent ratios of PEG 400 plasticizer have been prepared by solution cast technique using deionized water as solvent. The thermogravimetric analysis (TGA) showed that the thermal stability of the materials depended on the plasticizer content. The FTIR study confirmed the polymer-salt complex formation. The modulus spectra indicated the non-Debye nature of the material; a dominant relaxation process is visible being associated with the dynamic glass transition, relaxation-α. The maximum of each peak is shifted to higher frequencies as the plasticizer increases due to an enhancement of dipolar mobility in the origin of cooperative motions. A power law frequency dependence of the real part of the electrical conductivity is observed, which is characteristic of the effects of ion-ion and/or ion-chain correlations in ion motion. This variation is well fitted to a Jonscher′s expression.
Keywords: Electrical relaxation, ionic conductivity, glass transition, lithium ion batteries.
IntroducciónDurante muchos años la batería de níquel cadmio fue la única opción para aplicaciones portátiles como teléfonos móviles, ordenadores, aeromodelos, etc [1][2][3] . En 1990 aparecieron las baterías de níquel-metal-hidruro e ion-litio, ofreciendo mayores capacidades y menores pesos. Ambas tecnologías reclaman su superioridad sobre la otra, pero últimamente se ha hecho patente que las baterías de Ion-Litio han ganado la carrera. Por otra parte la batería de polímero de litio también conocida como lipo, se diferencia del resto de las baterías por el electrolito usado [4,5] . El diseño original data de los años 70 usando un polímero sólido como electrolito. Este electrolito se ensamblaba en...
Transparent films based on Ti, Sn and Zn oxides are of great importance in electronic devices such as sensors, solar cells and conductive films, then the characterization techniques are highly relevant. The aim of this work is to identify the advantages and disadvantages of direct methods, such as profilometry, and indirect methods such as ellipsometry and spectrophotometry used to quantify film thickness. In this work, films were deposited by spray-pyrolysis on glass substrates at 425±C. Thicknesses varied between 150 and 300 nm. Thicknesses calculated by means of spectrophotometry and ellipsometry, led to differences below 10% and 20 %, respectively, with respect to the value measuredby profilometry.
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