Properties of thermoelectric Zn–Sb type material directly synthesized by spark plasma sintering

In Situ TEM Studies of Nanostructured Thermoelectric Materials: An Application to Mg‐Doped Zn4Sb3 Alloy

“…Indexing the ring pattern using the CrysTBox package (Supporting Information, S1, S2) [47] shows another single phase with at rigonal/hexagonal unit cell (a = 1.235 nm, b = 0.775 nm, c = 1.251 nm), which is close to that of the Zn 6 Sb 5 phase. [37,53] This reveals the formation of at wo-phase structure (primary rhombohedral Zn 5.54 Sb 5 phase and secondary trigonal Zn 6 Sb 5 phase) during heating. Further to structural determination using SAD, the crystal structure of the primary ands econdary phases are also clarifiedb yu sing convergent-beam electron diffraction (CBED);t he resultsa re represented in Figure 3d-f.…”

“…The dark-contrast of the secondary nanoprecipitationp hase (Figure 5b,c) indicates al ower average atomic number of the nanoprecipitation than that in the matrix in terms of Z-contrast principle in STEM-HAADFi mage, [46] whereas uniform bright contrast (Figure 5a)i nt he sample at room temperature shows ac ompositional single-phase. [20,36,37] This process also causes damage to the TEM specimen and prohibits further characterization of the decomposeds ample. Figure 6i llustrates STEM-EDXe lemental maps and elemental line distribution of the Mg-doped Zn 4 Sb 3 sample after heating to 573 Ka nd holding at that temperature for 15 minutes.D is- (Figure 6b,d).…”

“…[38,48] Our observations indicate that no decomposition process occurred at temperatures below 673 K, as suggested in an umber of previous studies. [20,36,37] The origin of the movement and self-diffusion is the high mobility of Zn atoms, whichh as been knownasahigh superionic conductor. [49] High-resolution transmission electron microscopy (HRTEM) (Figure 4) allows us to understand in more depth the crystalline nature of the primary and secondary phasesi nw hich the secondary Zn 6 Sb 5 phase is visible as nanoprecipitations on the matrix of the primary Zn 5.54 Sb 5 phase.…”

“…[1] Nanocomposites with enhanced zT have been found in the various TE material families, including Bi 2 Te 3 -based nanocomposites, [5][6][7][8] PbTe-based nanostructured materials, [9][10][11] SiGe-based nanocomposites, [12][13][14][15] and ZnSb alloys, [16][17][18][19][20] etc. [17,[28][29][30][31][32][33][34][35][36] TheZ n 4 Sb 3 was also proposed to decompose into ZnSb and Zn, [21,[36][37][38] but this hypothesisw as only supported by indirect experimental work, for example, TE characterization in different conditions and high-temperature powder X-ray diffraction, [17,23] which could only give very limited understanding of the processes at atomic scales. In addition, Zn 4 Sb 3 consists of low-costa nd abundant elements; hence,i th as been considered as one of the best p-type candidates for making al ow-cost and high-conversion-efficiency thermoelectric powerg enerators (TEG).…”

“…Such nanostructures strongly enhances phonon scattering, resulting in ad ecreasei nt he thermal conductivity leading to a zT value of 1.4 at 718 K. of Zn 4 Sb 3 have proposed migration of high dynamic Zn into Zn interstitial (hcp)s ites at elevated temperature as the main mechanism of Zn 4 Sb 3 degradation. [17,[28][29][30][31][32][33][34][35][36] TheZ n 4 Sb 3 was also proposed to decompose into ZnSb and Zn, [21,[36][37][38] but this hypothesisw as only supported by indirect experimental work, for example, TE characterization in different conditions and high-temperature powder X-ray diffraction, [17,23] which could only give very limited understanding of the processes at atomic scales. There remained an umber of limitations:i )the explanation relied on experimental resultsc ollected from different typeso fs tudied sample;t hat is, powder materialsf or XRD and pressed pellet for TE characterization;i i) the test conditions of Zn 4 Sb 3 materials was not equivalent to the TE conditions (i.e.…”