Phase stability of ternary antifluorite type compounds in the quasi-binary systems Mg2X–Mg2Y (X, Y = Si, Ge, Sn) via ab-initio calculations

Nanostructure and doping stimulated phase separation in high-ZT Mg2Si0.55Sn0.4Ge0.05 compounds

“…This result stands in good agreement with the theoretical predictions of Viennois et al [32], but contradicts a number of related publications that reported the presence of one, unique single phase. Table 2 presents an outline of these related references so far, where special emphasis was addressed to the structural characterization of Mg 2 Si 1Àx Sn x -type solid solutions as well as to the number of additional phases that were identified by certain, specific techniques.…”

“…Mg 2 Si 0.6 Sn 0.4 -based materials are situated in the boundary between the region of the formation of Mg 2 Si 1Àx Sn x solid solutions and the miscibility gap that appears in the Mg 2 Si-Mg 2 Sn phase diagram at Sn concentrations of 0.4 < x < 0.6. Thus, Mg 2 Si-Mg 2 Sn alloys currently investigated for TE applications are probably two-phase materials, as they have compositions located in the miscibility gap zone and close to the spinodal lines, as postulated by Viennois et al [32]. The aim of the present work is to make quantitative measurements of the structural constituents in various length scales of the compounds, in order to assess the effect of their microstructure in an attempt to help optimize specific length-scale effects towards further improving the figure of merit.…”

Flash spark plasma sintering of magnesium silicide stannide with improved thermoelectric properties

“…Although MSS is prone to segregation at the microscale during the heating process, the holding at 750 1C (above spinodal phase boundaries) promoted the formation of a single solid solution phase. 34 Mild phase segregation was observed in the CSPS-GC sample (Fig. 5(b)), which had experienced two cycles of heat treatments up to 750 1C without a holding time.…”

“…This is the typical reaction for MSS solid solutions with composition within the miscibility gap after heat treatment below the spinodal lines. 34 During the flash sintering process, the local Joule heating created large temperature fluctuations and gradients from the center of the grains to their surface. Part of the corner and/or shell of the grains were locally melted and squashed into the pores between the grains.…”

“…The composition around Si/Sn = 1 has a tendency to segregate into Sn-rich and Si-rich phases because of the miscibility gap in the Mg 2 Si and Mg 2 Sn pseudo-binary phase diagram. [32][33][34] This means that the microscopic composition distribution is very sensitive to local temperature fluctuations and gradients that might be created by local Joule heating in flash sintering. So MSS is an ideal candidate to study the influence of flash sintering on TE materials, including possible particle surface cleaning or oxidation layer removal effects.…”