Abstract In this work, the electrochemical anodization process was carried out on titanium grade 2, using an electrolytic solution of 3 M and 0.15 M HCl with voltages of 11 V, 12 V and 15 V, as well as time variations in the experimental process and later an annealing process at 750 °C. According to the results obtained, the TiO2 coatings presented different morphologies on their surface, which consisted of nanopores, nanowires and clusters of oxide grains, as well as a combination of anatase and rutile crystalline phases. Band Gap variations were found to be non-significant despite changes in the morphology of the coatings at different anodization conditions, with an average value of 2.91 eV. It was observed that the anodized samples treated by the annealing process at 750 °C, thickness values up to 16 μm were obtained.

Abstract Copper aluminate (CuAlO2) is a p-type semiconducting thermoelectric material that crystalize in delafosite phase at a temperature of 1100 °C. In this work, two samples were synthesized by Pechini method and calcined using two different procedures in order to determine the effect of thermal history on the phase formation and the thermoelectric properties. Sample M1 was calcined at 1100 °C after a termal treatment at 550 °C and the sample M2 was calcined at 1100 °C without previous treatment. Crystalline structure of obtained materials was analyzed by X-ray diffraction and bandgap energy obtained from Kubelka-Munk method applied to UV-Vis diffuse reflectance spectra. In sample M1 a mixture of spinel and delafossite phases was obtained and in sample M2 a mixture of Al2O3 and delafossite. Electrical conductivity, carrier density and Seebeck effect were measured from 100 °C to 800 °C, confirming that both samples are p-type semiconductors and their conductivity occurs from small polarons. It is shown that temperature ramp and pre-treatment affect the formation of secondary phases, which has a direct effect on thermoelectric properties of the material.

Resumen El aluminato de cobre (CuAlO2) es un material termoeléctrico semiconductor tipo-p, que cristaliza en fase delafosita a temperatura de 1100 °C. En este trabajo se sintetizaron dos muestras por el método Pechini y se calcinaron por dos procedimientos diferentes para determinar el efecto de la historia térmica en la formación de las fases y en las propiedades termoeléctricas. La muestra M1 se calcinó a 1100 °C después de un tratamiento térmico a 550 °C y la muestra M2 se calcinó a 1100 °C sin tratamiento térmico previo. La estructura cristalina de los materiales obtenidos se analizó por difracción de rayos X y el ancho de banda prohibida se obtuvo por el método de Kubelka-Munk a partir de los espectros de reflectancia difusa en el ultravioleta-visible. En la muestra M1 se tiene una mezcla de fases, espinela y delafosita y en la M2 se observa una mezcla de Al2O3 y delafosita. Se midió la conductividad eléctrica, la densidad de portadores y la movilidad de la muestra M2 por efecto Hall a temperatura ambiente, así como la conductividad eléctrica y el coeficiente Seebeck en un intervalo de temperaturas de 100 °C a 800 °C, confirmándose que las dos muestras son semiconductores tipo-p y que la conductividad ocurre por polarones pequeños. Se demuestra que las rampas de temperatura y pre tratamiento térmico tienen un efecto en la formación de fases secundarias, lo que afecta directamente las propiedades termoeléctricas del material.

Metallic zinc nano structures have been grown by the thermal evaporation and condensation technique using a mixture of zinc and manganese oxide powders and nitrogen as carrier gas. 650 °C and 1 atm were used as processing temperature and pressure, respectively. It was found that the shape of zinc structures is dependent on the source materials. When a mixture of Zn/MnO2 powders is used as raw material micro-particles with oblate spherical shape and micro-columns are obtained. On the other hand, when only zinc powder is used as source material, spherical stones without facets are deposited. It is assumed that evaporation from the source is inhibited when a mixture of Zn and MnO2 is used. Therefore, supersaturation downstream from the source changes and as a consequence the morphology of the structures is modified. Synthesized material is make-up of zinc atoms and no other impurities or catalytic particles were detected according to elemental analysis. Vapor-solid is though as mechanism for growing those zinc structures.