Academia.eduAcademia.edu

Figure 5 – uploaded by Yulia Eka Putri

See full PDFdownloadDownload figure
with increasing doping levels, which further contributes to the increase in Seebeck coefficient, as shown in Fig. 6. This is different from our previous study, in which the alkaline earth metal doping ((BiS); 2(Tio.9sMgo.05S2)2, (Bio9Cao18)1.2(TiS2). and (Bio.9Sro.1S)1.2(TiS2)2) decreased the effective mass. It is believed that pure (BiS); 2(TiS2)2 has a non-parabolic band structure, so the decrease in carrier concentration can reduce the effective mass [22,23]. In the case of chromium doping, however, the effective mass increases as the decreasing of the carrier concentration, which may be due to the formation of additional states near Fermi level. Further investigation is needed to prove this assumption.

Figure 6 with increasing doping levels, which further contributes to the increase in Seebeck coefficient, as shown in Fig. 6. This is different from our previous study, in which the alkaline earth metal doping ((BiS); 2(Tio.9sMgo.05S2)2, (Bio9Cao18)1.2(TiS2). and (Bio.9Sro.1S)1.2(TiS2)2) decreased the effective mass. It is believed that pure (BiS); 2(TiS2)2 has a non-parabolic band structure, so the decrease in carrier concentration can reduce the effective mass [22,23]. In the case of chromium doping, however, the effective mass increases as the decreasing of the carrier concentration, which may be due to the formation of additional states near Fermi level. Further investigation is needed to prove this assumption.

Related Figures (8)

Fig. | The natural superlattice structure of (BiS), 2(TiS2)2 misfit layer sulfide.
Fig. | The natural superlattice structure of (BiS), 2(TiS2)2 misfit layer sulfide.
Figure 1 shows that pure (BiS), (TiS). has a natural superlattice structure, in which double TiS, layers and one BiS layer stack alternatively in the c-axis direction. Cr** (0.63 A) was intended as a substitute at the Ti” (0.68 A) site, rather than the Bi*’ (0.96 A) site. XRD patterns of the pellets were observed in the direction perpendicular to the applied pressure during the sintering process and are shown in Fig. 2(a). Several
Figure 1 shows that pure (BiS), (TiS). has a natural superlattice structure, in which double TiS, layers and one BiS layer stack alternatively in the c-axis direction. Cr** (0.63 A) was intended as a substitute at the Ti” (0.68 A) site, rather than the Bi*’ (0.96 A) site. XRD patterns of the pellets were observed in the direction perpendicular to the applied pressure during the sintering process and are shown in Fig. 2(a). Several
Figure 3 shows that chromium doping into titantum sites in TiS» layers significantly reduces the electrical conductivity in the whole temperature range studied. The decrease in electrical conductivity is in agreement with the increase in chromium doping levels. Furthermore, all compounds depicting this kind of change in electrical conductivity are metallic conductors [14-16]. The electrical conductivity of a
Figure 3 shows that chromium doping into titantum sites in TiS» layers significantly reduces the electrical conductivity in the whole temperature range studied. The decrease in electrical conductivity is in agreement with the increase in chromium doping levels. Furthermore, all compounds depicting this kind of change in electrical conductivity are metallic conductors [14-16]. The electrical conductivity of a
Fig. 4 Hall mobility of (BiS).(Ti;.Cr,S2)2 (« = 0, 0.025, 0.05 and 0.1). Figure 4 shows the temperature dependence of Hall mobility. The mobility for x = 0 has a temperature dependence proportional to T ee indicating the dominance of electron scattering by acoustic phonons [17-19]. However, increasing the chromium doping amount leads to a decrease in the dependence of Hall mobility on temperature. This implies that, in addition to acoustic phonon scattering, ionized impurity scattering or alloy scattering also takes place [20,21]. scattering or alloy scattering also takes place [20,21].
Fig. 4 Hall mobility of (BiS).(Ti;.Cr,S2)2 (« = 0, 0.025, 0.05 and 0.1). Figure 4 shows the temperature dependence of Hall mobility. The mobility for x = 0 has a temperature dependence proportional to T ee indicating the dominance of electron scattering by acoustic phonons [17-19]. However, increasing the chromium doping amount leads to a decrease in the dependence of Hall mobility on temperature. This implies that, in addition to acoustic phonon scattering, ionized impurity scattering or alloy scattering also takes place [20,21]. scattering or alloy scattering also takes place [20,21].
Fig. 6 The change in effective mass as a function of carrier concentration. The total thermal conductivity («) can be expressed
Fig. 6 The change in effective mass as a function of carrier concentration. The total thermal conductivity («) can be expressed
Table 1 Density, Vi, Vy, and Vy, of (BiS),.(Ti,-. Cr,S2)2 samples
Table 1 Density, Vi, Vy, and Vy, of (BiS),.(Ti,-. Cr,S2)2 samples
Fig. 8 The dimensionless figure of merit Z7 for (BiS))2(Tij_xCr,S2)2 (x = 0, 0.025, 0.05 and 0.1). Figure 8 shows the ZT value calculated from the measured electrical conductivity, Seebeck coefficient and thermal conductivity. All chromium-doped samples exhibit an increase in ZT of 0.24—0.3 at a temperature of 750K. Although the chromium substitution did not result in higher power factor, its low total thermal conductivity contributed to an increase in Z7.
Fig. 8 The dimensionless figure of merit Z7 for (BiS))2(Tij_xCr,S2)2 (x = 0, 0.025, 0.05 and 0.1). Figure 8 shows the ZT value calculated from the measured electrical conductivity, Seebeck coefficient and thermal conductivity. All chromium-doped samples exhibit an increase in ZT of 0.24—0.3 at a temperature of 750K. Although the chromium substitution did not result in higher power factor, its low total thermal conductivity contributed to an increase in Z7.
Related topics:
Advanced Ceramics
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved