Homogeneity of Zone-melted n-type Bi1.96Sb0.04Te2.70Se0.30 Thermoelectric Material

doi:10.15541/jim20250045

Abstract

Abstract:

Zone melting technique is an important method for commercial preparation of Bi₂Te₃-based thermoelectric materials. The zone melting purification process is affected by segregation of materials. However, so far, the effect of zone melting process on the segregation mechanism of Bi₂Te₃-based materials has not yet formed unified understanding. In particular, increase of material components significantly affects the segregation process and uniformity. In this study, n-type Bi_1.96Sb_0.04Te_2.694Se_0.3Br_0.006 material was used as the research object, and the melting-zone melting-annealing process was used to systematically explore the influence of zone melting temperature on the composition and uniformity of thermoelectric performance. It was found that the zone melting temperature had a great influence on uniformity of the ingot, and the axial composition segregation was an important factor affecting its uniformity. At high zone melting temperature (≥988 K), the segregation of Bi₂Te₃-rich phase appeared at the top of the ingot, which made the poor uniformity of thermoelectric properties of the material. The maximum difference of ZT at room temperature in different regions (center top, edge top (ET), center bottom, edge bottom) of samples with zone melting temperatures of 988 and 1003 K reached 31.5% and 28.6%, respectively. Reducing the zone melting temperature to 958 K significantly inhibited the segregation of Bi₂Te₃-enriched phase, and a cylindrical ingot (inner diameter of 16 mm, height of 55 mm) with excellent thermoelectric properties and uniformity was prepared. The maximum difference of ZT at room temperature in different regions was only 14%, and the maximum ZT of 958 K-ET sample was 1.05 at 350 K. This study reveals the regulation mechanism of zone melting temperature on the composition and thermoelectric performance uniformity of multi-component n-type (Bi, Sb)₂(Te, Se)₃-based materials, which provides important guidance for the preparation of high-performance thermoelectric materials with excellent uniformity.

Key words: n-type bismuth telluride, zone melting process, homogeneity, thermoelectric property

CLC Number:

TQ174

WU Mingxuan, LI Junjie, CHEN Shuo, YAN Yonggao, SU Xianli, ZHANG Qingjie, TANG Xinfeng. Homogeneity of Zone-melted n-type Bi_1.96Sb_0.04Te_2.70Se_0.30 Thermoelectric Material[J]. Journal of Inorganic Materials, 2025, 40(11): 1252-1260.

Figures/Tables 9

Fig. 1 Schematic diagram of positions of the test samples in the zone melting bar

Fig. 2 σ, S and PF of different regions in Bi1.96Sb0.04Te2.694Se0.3Br0.006 with zone melting temperatures of (a) 958, (b) 973, (c) 988, and (d) 1003 K

Fig.3 (a, d) Thermal conductivities κ, (b, e) κL+κb and (c, f) ZT of Bi1.96Sb0.04Te2.694Se0.3Br0.006 samples

Fig. 4 XRD patterns of Bi1.96Sb0.04Te2.694Se0.3Br0.006 samples (a) 2θ=10°-70°; (b) 2θ=27.5°-28.5°

Fig. 5 Variation trends of Bi/Sb and Te/Se of different regions in Bi1.96Sb0.04Te2.694Se0.3Br0.006 samples prepared under different zone melting temperatures Colorful figures are available on website

Fig. 6 ne and μ of different regions in Bi1.96Sb0.04Te2.694Se0.3Br0.006 samples prepared under different zone melting temperatures

Fig. S1 Cross-sectional FESEM images of the free fracture cross sections of (a) 1003 K-CB and (b) 1003 K-CT samples

Fig. S2 BSE images of polished surface and surface distributions of Bi, Sb, Se, Te and Br elements in the corresponding regions for (a) 958 K-Bottom and (b) 988 K-Top

Table S1 σ, S, κ and ZT of Bi1.96Sb0.04Te2.694Se0.3Br0.006 samples at room temperature

Sample	σ/(×10⁴, S·m⁻¹)	S/(μV·K^-1)	κ/(W·m^-1·K^-1)	ZT
958 K-CB	11.1	-186	1.37	0.86
958 K-CT	10.9	-195	1.43	0.89
958 K-EB	10.4	-195	1.38	0.88
958 K-ET	11.4	-199	1.42	0.98
973 K-CB	11.2	-197	1.50	0.89
973 K-CT	9.86	-201	1.48	0.82
973 K-EB	9.45	-196	1.50	0.74
973 K -ET	9.88	-204	1.48	0.85
988 K-CB	11.1	-205	1.47	0.96
988 K-CT	8.54	-202	1.44	0.73
988 K-EB	9.98	-200	1.48	0.76
988 K-ET	9.05	-201	1.43	0.86
1003 K-CB	9.00	-206	1.47	0.80
1003 K-CT	7.27	-216	1.39	0.74
1003 K-EB	7.34	-202	1.47	0.63
1003 K-ET	7.51	-214	1.39	0.76

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