The experimental study herein presented was conducted aiming to evaluate the influence of nanosilica (nS) addition on properties of ultra-high performance concrete (UHPC). Thermo gravimetric analysis results indicated that nS consumes much more Ca(OH) 2 as compared to silica fume, specifically at the early ages. Mercury intrusion porosimetry measurements proved that the addition of nS particles leads to reduction of capillary pores. Scanning electron microscope observation revealed that the inclusion of nS can also efficiently improve the interfacial transition zone between the aggregates and the binding paste. The addition of nS also resulted in an enhancement in compressive strength as well as in transport properties of UHPC. The optimum amount of cement replacement by nS in cement paste to achieve the best performance was 3 wt.%. However, the improper dispersion of nS was found as a deterrent factor to introduce higher percentage of nS into the cement paste.

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Metal oxides are widely used in many applications such as thermoelectric, solar cells, sensors, transistors, and optoelectronic devices due to their outstanding mechanical, chemical, electrical, and optical properties. For instance, their high Seebeck coefficient, high thermal stability, and earth abundancy make them suitable for thermoelectric power generation, particularly at a high-temperature regime. In this article, we review the recent advances of developing high electrical properties of metal oxides and their applications in thermoelectric, solar cells, sensors, and other optoelectronic devices. The materials examined include both narrow-band-gap (e.g., Na x CoO 2 , Ca 3 Co 4 O 9 , BiCuSeO, CaMnO 3 , SrTiO 3 ) and wide-band-gap materials (e.g., ZnO-based, SnO 2 -based, In 2 O 3 -based). Unlike previous review articles, the focus of this study is on identifying an effective doping mechanism of different metal oxides to reach a high power factor. Effective dopants and doping strategies to achieve high carrier concentration and high electrical conductivities are highlighted in this review to enable the advanced applications of metal oxides in thermoelectric power generation and beyond.

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