Copper selenides are attractive materials for high-temperature thermoelectric applications. They exhibit remarkably enhanced thermoelectric properties originating from their superionic liquid character. In this work, the synthesis of Cu-Se compounds is investigated using mechanical alloying, aiming to obtain the Cu2Se phase and modify the crystal structure by annealing at high temperatures and quenching. In the first part, Cu-Se powders are prepared at various milling times. They are characterized regarding their structure, morphology and composition by X-ray diffraction analysisand scanning electron microscopy. After 2.5 h of synthesis,α-Cu2Se andβ-Cu2Se was attained in the powder, with the former having the highest percentage contribution. The crystallite size of these phases was calculated to be in the range of 17.0-19.6nm. The synthesized powder consisted of grains with dimensions from nanometers to micrometers and their aggregates. A trace of a possibly surficial layer of copper oxide was also detected on the sample. In the second part of this study, the optimum synthesized powder wassubjected to 2 hof annealing at 650 °C, followed by quenching. According to X-ray diffraction analysis,the percentage contribution of the thermoelectrically inferiorα-Cu2Se phase increased being the vast majority of the material and almost eliminated β-Cu2Se. The crystallite size was calculated to be in the range of 31.2-34.5nm. Overall, the desired Cu2Se compound can be obtained by the mechanical alloying technique asα- and β-phase, and the crystal structure can be modified by annealing under appropriate conditions.

Thermoelectricity is a green method of energy production by converting waste heat into electricity. Silicides and selenides are candidate materials for thermoelectric applications due to their high performance in their operating temperature range. Additionally, they are composedof abundant and negligibly toxic elements. The current study focuses on the fabrication of alternative thermoelectric materials, aiming todevelop compounds with advanced thermoelectric properties. Pure Mg2Si andAl-doped Mg2Si samples are synthesized by Pack Cementation (PC), and Ag2Se powder is produced via Ball Milling (BM). The chosen synthesis methods are suggested as environmentally friendly, fast and economic. The samples were structurally characterized by X-ray diffraction (XRD), while the morphology and the chemical composition were studied by X-ray photoelectron spectroscopy (XPS)and scanning electron microscopy (SEM). In the case of magnesium silicide, the thermoelectric phase was formed without residual traces of the initial elemental powders. The Al addition diffused in the material homogeneously and no secondary phases were developed. Regarding the Ag2Se powder, α-phase (low temperature) was obtained after 2.5 h of mechanical alloying (BM) the elements.SEM and XPS analysis detected traces of unreacted Ag and Se, indicating that the ball milling process should last longer to achieve a complete reaction between the elements.