Revista Cubana de Física

Se presentala caracterización estructural y microestructural de aleaciones de aluminio - titanio (AlxTi3-x, 0.5 ≤ x≤ 0.20) por medio de la técnica de difracción de rayos-X (DRX). El  análisis mostró la ocurrencia de una transición de fase orden – desorden en el rango de composición estudiado. La presencia de una fase minoritaria fcc en la matriz hcp de la aleación AlTi3 mostró evidencia de la presencia de defectos de apilado, cuya probabilidad de ocurrencia depende de la composición química y la distancia entre capas atómicas (parámetro de orden). El análisis microestructural usando los métodos de Warren-Averbach y Williamson-Hall mostró que unadisminución del contenido de Al, no solo disminuye la probabilidad de ocurrencia de defectos planares sino que propicia una disminución del tamaño promedio de cristalitas y aun aumento del valor medio de la microdeformación no uniforme en la aleación. Los defectos de deformación (α) predominan en este tipo de aleación.  

Lead-based piezoelectric compounds are the most widely used in a wide applications range such as sensors and transducers. However, these materials are environmentally-aggressive, so these must be replaced by using lead-free compounds. This paper presents the study on the electromechanical behavior and the main piezoelectric parameters of five piezoelectric ceramic compositions of the (B­i0.5Na0.5)1-xBaxTiO3 family, where x = 8, 10, 12, 16, 18 at%. The samples have been prepared by using the standard solid-state reaction method and then polarized under an electric field of 2 kV/mm for a temperature lower than that of the phase’s transition temperature. Results revealed d33 values higher than 120 pC/N ​​for x = 8, 10, 12 at%, better than those for lead-based compounds. There were also obtained d33, d31 and g31 values higher than those reported in the literature for a large number of lead-free systems.

The equipment LEEI-35 of Lambda Scientific for the lab practice Hall Effect in Semiconductors was evaluated. To the exercises proposed by the manufacturers were added as important goals to determine the type of semiconductor and carrier concentration present in it that are the two most important aspects when using the Hall Effect in the daily practice of semiconductors. The proposed methodology in one of the exercises suggested by the manufacturers was modified due to inaccuracies introduced in the results. The degree of accuracy achieved and the repeatability of the results reached by student teams demonstrate the quality of this assembly. This is a content of the system knowledge of Physics discipline for engineers that previously had no experimental verification and with its introduction in the lab system of the Modern Physics subject the students achieve a more complete training.

Using one experiment of the Computer Aided Physics Laboratory System HPCI-1 experimental values of the gravitational acceleration for three real pendulums with bobs of different masses in small oscillations were obtained. Elapsed times for the reduction of oscillation amplitudes in 30 and oscillation amplitude after 30 periods, both starting from initial amplitude of 50 were also measured. The results were obtained in less than 2 hours and they are the fundament of an innovative proposal for the lab practice dedicated to this physical system. Through some suggesting questions that promote the analysis of results the university students can to deep in the main characteristics of this system and overload the analysis level respect the previous educational level, they will understand which of the three pendulums differs more from the harmonic model and how this is expressed in the results for the gravitational acceleration.

Nanostructured PbS thin films were deposited on glass substrates at room temperature by radio frequency sputtering technique. XRF analysis confirm the presence of Pb and S elements. Through atomic force microscopy (AFM) it was proved that the films present a nanostructured growth, with particle size between 10 and 20 nm. The crystallite size was calculated by the Williamson-Hall method.