Nowadays, concentrating solar power systems have been considered using heat generated by concentrating solar radiation on a small surface. According to previous researches in this field and the obligation and necessity of using materials with higher melting points to increase the operational temperature of these solar systems, the aim of this study was to create cost-effective, high melting point ceramic nanocomposites with appropriate mechanical and optical properties. In this regard, pure Al2O3 (alumina) and TiO2 (titania) ceramic powders were used. According to the alumina-titania phase diagram, three distinct molar ratios (Al2O3 / TiO2) were considered as 1/3, 1 and 3 and then mechanically milled for two hours in an argon atmosphere. So, the average particle size of the complex has decreased to 170 nm, succeesfully. Then, after determining the approximate synthesis temperature using differential scanning calorimetry, the samples were subjected to spark plasma sintering (SPS) process at three different temperatures of 1300, 1400 and 1500 ° C and two sintering times (10 and 15 minutes). The microstructure of the sintered specimens were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) test and MAUD software. The results showed that higher sintering times and temperatures will lead to more tialite phase percentage in such the way that in sample synthesized at 1500 °C for 15 minutes, the weight fraction of the tialite phase increased up to 90%. In order to eva‎luate the optical properties of the sintered ceramic composites, UV-Vis test was employed. The findings indicated that by increase in tialite content, the absorption of the specimens increased up to 95%. On the other hand, non-synthesized samples showed high reflectances of 60-100% in 400-2200 nm wavelength range. Analysis of the absorbance spectrums using Kubelka-Monk theory showed a high reduction in the band gap energy of the specimens after the SPS process and the formation of tialite phase has a great effect on the deep level defects, led to further reduction in forbidden energy gap of the specimens. The main reason of decrease in band gap energy of the composites was due to the effect of spark plasma sintering process on the formation of a large volume of oxygen vacancies that was proved by X-ray photoelectron spectroscopy (XPS). In addition, photoluminescence (PL) tests confirmed the results showing some index peaks at different wavelengths after the sintering process. Finally, examining of the specimens using electrochemical impedance spectroscopy showed that the amount of charge carriers increased with increase in tialite content and decrease in specimens’ density. The results of this study demonstrated an excellent optical performance of nanocomposites sintered by spark plasma sintering method by absorbing sunlight in all infrared, visible and ultraviolet wavelength reagon by reducing band gap energies.

مرتضي شمعانيان، فخرالدين اشرفي‌زاده

عباس بهجت، رحمت اله عمادي، احمد كرمانپور