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High temperature thermoelectric properties of (Fe1−xVx)3Al Heusler type compounds
Journal of Alloys and Compounds 349 (2003) 37–40
L
www.elsevier.com / locate / jallcom
High temperature thermoelectric properties of (Fe 12xVx ) 3 Al Heusler type compounds Yoshiyuki Kawaharada*, Ken Kurosaki, Shinsuke Yamanaka Department of Nuclear Engineering, Graduate School of Engineering, Osaka University, 2 -1 Yamadaoka, Suita, 565 -0871 Osaka, Japan Received 28 May 2002; received in revised form 4 July 2002; accepted 4 July 2002
Abstract Heusler type compounds (Fe 12xVx ) 3 Al were made by arc melting in the concentration range 0,x,1. Their mechanical properties, high temperature electric properties, and thermal properties were measured. The thermoelectric power (TEP) showed a strong concentration dependence. The temperature and concentration dependences of the thermoelectric properties of (Fe 12xVx ) 3 Al were studied. 2002 Elsevier Science B.V. All rights reserved. Keywords: Transition metal compounds; Electrical transport; Heat conduction; Thermoelectric
1. Introduction There has been renewed interest in the field of thermoelectrics driven by the need for the reuse of exhausted heat in these days. So, in our laboratory, we have been studying semiconductor and insulator materials to develop a new thermoelectric material or to improve the thermoelectric properties [1–4]. In the present study, we studied Heusler type compounds. Heusler type compounds were first discovered by Heusler [5]. Many compounds have Heusler type structure, for instance Co 2 (V, Ti, Ta)Al [6,7], Co 2 TiSn [8], Ag 2 (Pd, Pr)In [9,10], Ni 2 Mn(Ga, Sb, Sn) [11–13]. Fig. 1 shows the crystal structure of the Heusler type compounds (Fe 12xVx ) 3 Al. It has three kinds of site named Fe I , Fe II , and Al. The Fe I and Al site have eight nearest Fe II neighbors in an octahedral configuration, and Fe 3 Al is expressed as [Fe I ][Fe II ] 2 Al. (Fe 12xVx ) 3 A1 is able to exist between x50 and x51. With increasing vanadium concentration, the crystal structure of (Fe 12xVx ) 3 Al changes from D0 3 to L2 1 [14–16]. Especially, during the change from Fe 3 Al to Fe 2 VAl, only the Fe I site is replaced by vanadium [14,16,17]. The reason for this selective replacement of vanadium is discussed elsewhere [18]. (Fe 12xVx ) 3 Al has been actively studied by its magnetic properties, residual resistivity, and Curie temperature.
Especially, Fe 2 VAl is found to be in a marginally magnetic state and to exhibit a semiconductor like behavior [17]. In these days, Heusler type compounds attract increasing attention as new thermoelectric materials because of a pseudo gap near the Fermi level and the concomitant large slope of the electron density of states around the Fermi surface. The performance of thermoelectric materials is evaluated by the so-called dimensionless figure of merit ZT. Here Z 5 a 2 s /k (a, TEP; s, electrical conductivity; k, thermal conductivity) is called a figure of merit, and the numerator in the expression for Z is called power factor. Hence it is desirable for thermoelectric materials to have low thermal conductivity, high electrical conductivity, high
*Corresponding author. Tel.: 181-6-6879-7905; fax: 181-6-68797889. E-mail address: [email protected] (Y. Kawaharada). 0925-8388 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 02 )00919-2
Fig. 1. Crystal structure of the Heusler type compounds.
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Y. Kawaharada et al. / Journal of Alloys and Compounds 349 (2003) 37–40
TEP, which is the reason why Heusler type compounds attract attention as thermoelectric materials. In the present study, the physical properties of (Fe 12xVx ) 3 Al were measured and the thermoelectric properties at high temperature were studied.
Table 1 Physical properties of Fe 2 VAl Longitudinal sound velocity Share sound velocity Debye temperature Young’s modulus Compressibility Vickers hardness
Vl Vs uD E b HV
(m / s) (m / s) (K) (GPa) (GPa 21 ) (GPa)
6380 3738 539.7 225 6.97310 23 2.02
2. Experimental Rare iron flakes (3N), vanadium chunks (3N) and aluminum chips (4N) were weighted in stoichiometric proportions, and melted in an arc furnace under argon atmosphere at 0.05 MPa. For homogeneity, the samples were turned over and melted several times. Then the samples were sealed in quartz ampoules under vacuum (,0.01 MPa) and annealed at 1073 K for 50 h to obtain homogenized samples. After homogenization, the ampoules were quenched in water. All samples were cut to various shapes for the different measurements; a disc with about 1 mm thickness and 10 mm diameter for the thermal diffusivity measurement and a bar with 12–15 mm height and 10 mm diameter for the electric and mechanical properties measurements. The X-ray diffraction (XRD) measurement was carried out and for all samples it was confirmed that they have Heusler type structure. The vanadium distribution in each sample was determined by the energy dispersion X-ray analysis (EDXA). The Vickers micro hardness was measured, with 300 g load and 30 s loading time. The sound velocity of the samples was measured by an ultrasonic pulse echo method at room temperature. The Debye temperature, compressibility and Young’s modulus were obtained from the longitudinal and the shear velocities. The heat capacity was estimated from the heat capacity of the component metals by using the Neumann–Kopp law. The thermal diffusivity was measured by a laser flash method in the temperature range 300–873 K. The thermal conductivity was calculated by using the measured sample density, the thermal diffusivity, and the estimated heat capacity. The electrical resistivity and thermoelectric power were measured by a standard four-probe d.c. analysis in the temperature range 300–873 K under helium atmosphere.
3. Results and discussions Table 1 shows the physical properties of Fe 2 VAl. For isotropic media, the shear modulus G, Young’s modulus E, and bulk modulus K can be written in terms of the longitudinal sound velocity Vl and the shear sound velocities Vs as follows [19]: G 5 rV 2
H
s3V 2l 2 4V 2s d E 5 G ]]]] sV 2l 2V 2s d
J
s3V 2l 2 4V 2s d K 5 r ]]]] 3 where r is the sample density. The Debye temperature uD for Fe 2 VAl can be estimated from the sound velocities and the lattice parameter. The Debye temperature is related to the sound velocities as follows [20]: 9N 1 2 ] 1 ]D S DS]] 4pV D S V V
h uD 5 ] k
1 ] 3
C
3 L
3 S
1 ] 3
where h is the Plank constant, k is the Boltzmann constant, N is the number of atoms in the unit cell, and VC is the volume of the unit cell, respectively. Considering that the Debye temperature of ordinary metals is in the range from 200 to 600 K, the Debye temperature of Fe 2 VAl is slightly higher than those of other metals. For various materials, the Vickers hardness is also known to be associated with Young’s modulus [21]. For some oxide and carbide ceramics, the Vickers hardness is proportional to Young’s modulus with the values HV /E50.05 [21]. For pure metals, the HV /E values have been estimated in the literature [19], and the values of 0.006 for bcc metals, 0.003 for fcc metals, and 0.004 for hcp metals have been obtained. The Vickers hardness of Fe 2 VAl is plotted in Fig. 2 as a function of Young’s modulus. As shown in Fig. 2, the mechanical properties of Fe 2 VAl show neither the character of ceramics nor that of pure metals. Fig. 3 shows the temperature dependence of the thermal conductivity. In all samples, the thermal conductivity decreases with increasing temperature at low temperatures, which reflects the phonon conduction. The thermal conductivity increases with increasing temperature at high temperatures, which reveals the phonon scattering by electrons. The thermal conductivity decreases with increasing vanadium concentration from Fe 3 Al to Fe 2.5 V0.5 Al at all temperatures but increases with increasing vanadium concentration from Fe 2.5 V0.5 Al to Fe 2 VAl. This change is probably an effect of the mass difference between iron and vanadium, and that of the transformation of the crystal structure. The thermal conductivity of (Fe 12xVx ) 3 Al is several-fold or 10-fold that of state of the art thermoelectric materials. The temperature dependence of the electrical resistivity
Y. Kawaharada et al. / Journal of Alloys and Compounds 349 (2003) 37–40
39
Fig. 4. Temperature dependence of electrical resistivity. Fig. 2. Relationship between Vickers hardness and Young’s modulus.
is shown in Fig. 4. Fe 3 Al shows metallic behavior, while the other (Fe 12xVx ) 3 Al compounds show semiconductorlike behavior. The electrical resistivity of Fe 3 Al increases with increasing temperature. The slope of the curve become smaller at around 800 K, which is caused by the presence of Curie temperature around this temperature [16]. Between x50 and x50.33, the electrical resistivity increases with increasing x as reported already in the literatures [16,22]. The electrical resistivity is 100-fold or 10-fold that of state of the art thermoelectric materials [23–25]. The temperature dependence of the thermoelectric power (TEP) is shown in Fig. 5. The values of TEP are higher than those of other metals. For actual use as thermoelectric materials, it is required to raise the value of TEP. The TEP increases with increasing vanadium concentration for x,0.33, and the sign of the TEP changes from positive to negative around x50.33. This behavior agrees with the results reported in the literature [26]. The
Fig. 3. Temperature dependence of thermal conductivity.
absolute value of TEP is maximum around x50.33 (Fe 2 VAl). So the TEP has two extreme values, positive and negative, around x50.33. The change in crystal structure, from D0 3 to L2 1 , probably affects the electronic structure of (Fe 12xVx ) 3 Al, and causes this TEP behavior, as reported for the semi-Heusler Fe 12x Ni x TiSb [27]. Fig. 6 shows the temperature dependence of the power factor, a 2 s. The power factor of (Fe 12xVx ) 3 Al comes close to that of state of the art thermoelectric materials. The temperature dependence of ZT was calculated from all the above results. Fe 2 VAl shows the largest value of ZT of all the samples. The value of ZT is lower than those of other thermoelectric materials. It is caused by the high thermal conductivity, high electrical resistivity, and slightly low TEP of (Fe 12xVx ) 3 Al, even for x50.33. The thermal conductivity, the electrical resistivity, and TEP show a fairly strong dependence on vanadium concentration as mentioned above. The TEP shows maximum value at x50.33. Our future work will deal with a study of
Fig. 5. Temperature dependence of TEP.
Y. Kawaharada et al. / Journal of Alloys and Compounds 349 (2003) 37–40
40
Fig. 6. Temperature dependence of Power factor.
(Fe 12xVx ) 3 Al around x50.33 but with smaller concentration steps. We will also address the electronic property changes with changing x, using electronic structure calculations.
4. Conclusion Heusler type compounds (Fe 12xVx ) 3 Al were made in the concentration range 0,x,1, and their thermoelectric properties were measured. All thermoelectric properties showed a strong concentration dependence. Fe 2 VAl showed the largest power factor and ZT of all the samples. For practical purposes, it is necessary to optimize the vanadium concentration for obtaining maximum values of the power factor and ZT of the (Fe 12xVx ) 3 Al compounds.
References [1] Y. Kawaharada, K. Kurosaki, M. Uno, S. Yamanaka, J. Alloys Comp. 315 (2001) 193.
[2] K. Kurosaki, A. Kosuga, M. Uno, S. Yamanaka, J. Alloys Comp. 334 (2002) 317. [3] K. Kurosaki, T. Matsuda, M. Uno, S. Kobayashi, S. Yamanaka, J. Alloys Comp. 319 (2001) 271. [4] H. Muta, K. Kurosaki, M. Uno, S. Yamanaka, J. Alloys Comp. 335 (2002) 200. [5] Fr. Heusler, Verhandlungen der Deutschen Physikalischen Gesellschaft 5 (1903) 219. [6] A.W. Carbonari, R.N. Saxena, W. Pendl Jr., J. Mestnik Filho, R.N. Attili, M. Olzon-Dionysio, S.D. de Souza, J. Magn. Magn. Mater. 163 (1996) 313. [7] P. Mohn, P. Blaha, K. Schwarz, J. Magn. Magn. Mater. 140–144 (1995) 183. [8] S. Suga, S. Imada, A. Yamasaki, S. Ueda, T. Muro, Y. Saitoh, J. Magn. Magn. Mater. 233 (2001) 60. [9] H. Mitamura, N. Takeshita, Y. Uwatoko, H. Mori, A. Yamaguchi, T. Tomita, H. Wada, N. Mori, H. Ishimoto, T. Goto, Physica B 284–288 (2000) 1341. [10] H. Mitamura, N. Takeshita, Y. Uwatoko, H. Mori, A. Yamaguchi, T. Tomita, H. Wada, N. Mori, H. Ishimoto, T. Goto, Physica B 281 / 282 (2000) 150. [11] S. Kyuji, S. Endo, T. Kanomata, F. Ono, Physica B 237 / 238 (1997) 523. [12] J.A. Caballero, A.C. Reilly, Y. Hao, J. Bass, W.P. Pratt Jr., F. Petroff, J.R. Childress, J. Magn. Magn. Mater. 198 (1999) 55. [13] J.W. Dong, J. Lu, J.Q. Xie, L.C. Chen, R.D. James, S. McKernan, C.J. Palmstrom, Physica E 10 (2001) 428. [14] D.E. Okpalugo, J.G. Booth, C.A. Faunce, J. Phys. F 15 (1985) 681. [15] P.J. Webster, K.R.A. Ziebeck, Phys. Lett. A 98 (1983) 51. [16] Y. Nishino, C. Kumada, S. Asano, Scripta Mater. 36 (1997) 461. [17] Y. Nishino, M. Kato, S. Asano, K. Soda, M. Hayasaki, U. Mizutani, Phys. Rev. Lett. 79 (10) (1997) 1909. [18] S. Ishida, J. Ishida, S. Asano, J. Yamashita, J. Phys. Soc. Jpn. 41 (1976) 1570. [19] Thermophysical Properties Handbook, Nippon Netu Bussei Gakkai, Youkendou, Tokyo, 1990. [20] H. Inaba, T. Yamamoto, Netsu Sokutei 10 (1983) 132. [21] K. Tanaka, H. Koguchi, T. Mura, Int. J. Eng. Sci. 27 (1989) 11. [22] Y. Nishino, Mater. Sci. Eng. A258 (1998) 50. [23] D.M. Rowe, CRC Handbook of Thermoelectrics, CRC Press. [24] R.S. Caputo, V.C. Truscello, in: Proceedings of IECEC, 1974, p. 637. [25] J.P. Fleurial, T. Caillat, A. Borshchevsky, in: 31st Intersoc. Convers. Eng. Conf., 1996, p. 96512. [26] Y. Hanada, R.O. Suzuki, K. Ono, J. Alloys Comp. 329 (2001) 63. [27] J. Tobola, L. Jodin, P. Pecheur, H. Scherrer, G. Venturini, B. Malaman, S. Kaprzyk, Phys. Rev. B 64 (2001) 155103.
L
www.elsevier.com / locate / jallcom
High temperature thermoelectric properties of (Fe 12xVx ) 3 Al Heusler type compounds Yoshiyuki Kawaharada*, Ken Kurosaki, Shinsuke Yamanaka Department of Nuclear Engineering, Graduate School of Engineering, Osaka University, 2 -1 Yamadaoka, Suita, 565 -0871 Osaka, Japan Received 28 May 2002; received in revised form 4 July 2002; accepted 4 July 2002
Abstract Heusler type compounds (Fe 12xVx ) 3 Al were made by arc melting in the concentration range 0,x,1. Their mechanical properties, high temperature electric properties, and thermal properties were measured. The thermoelectric power (TEP) showed a strong concentration dependence. The temperature and concentration dependences of the thermoelectric properties of (Fe 12xVx ) 3 Al were studied. 2002 Elsevier Science B.V. All rights reserved. Keywords: Transition metal compounds; Electrical transport; Heat conduction; Thermoelectric
1. Introduction There has been renewed interest in the field of thermoelectrics driven by the need for the reuse of exhausted heat in these days. So, in our laboratory, we have been studying semiconductor and insulator materials to develop a new thermoelectric material or to improve the thermoelectric properties [1–4]. In the present study, we studied Heusler type compounds. Heusler type compounds were first discovered by Heusler [5]. Many compounds have Heusler type structure, for instance Co 2 (V, Ti, Ta)Al [6,7], Co 2 TiSn [8], Ag 2 (Pd, Pr)In [9,10], Ni 2 Mn(Ga, Sb, Sn) [11–13]. Fig. 1 shows the crystal structure of the Heusler type compounds (Fe 12xVx ) 3 Al. It has three kinds of site named Fe I , Fe II , and Al. The Fe I and Al site have eight nearest Fe II neighbors in an octahedral configuration, and Fe 3 Al is expressed as [Fe I ][Fe II ] 2 Al. (Fe 12xVx ) 3 A1 is able to exist between x50 and x51. With increasing vanadium concentration, the crystal structure of (Fe 12xVx ) 3 Al changes from D0 3 to L2 1 [14–16]. Especially, during the change from Fe 3 Al to Fe 2 VAl, only the Fe I site is replaced by vanadium [14,16,17]. The reason for this selective replacement of vanadium is discussed elsewhere [18]. (Fe 12xVx ) 3 Al has been actively studied by its magnetic properties, residual resistivity, and Curie temperature.
Especially, Fe 2 VAl is found to be in a marginally magnetic state and to exhibit a semiconductor like behavior [17]. In these days, Heusler type compounds attract increasing attention as new thermoelectric materials because of a pseudo gap near the Fermi level and the concomitant large slope of the electron density of states around the Fermi surface. The performance of thermoelectric materials is evaluated by the so-called dimensionless figure of merit ZT. Here Z 5 a 2 s /k (a, TEP; s, electrical conductivity; k, thermal conductivity) is called a figure of merit, and the numerator in the expression for Z is called power factor. Hence it is desirable for thermoelectric materials to have low thermal conductivity, high electrical conductivity, high
*Corresponding author. Tel.: 181-6-6879-7905; fax: 181-6-68797889. E-mail address: [email protected] (Y. Kawaharada). 0925-8388 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 02 )00919-2
Fig. 1. Crystal structure of the Heusler type compounds.
38
Y. Kawaharada et al. / Journal of Alloys and Compounds 349 (2003) 37–40
TEP, which is the reason why Heusler type compounds attract attention as thermoelectric materials. In the present study, the physical properties of (Fe 12xVx ) 3 Al were measured and the thermoelectric properties at high temperature were studied.
Table 1 Physical properties of Fe 2 VAl Longitudinal sound velocity Share sound velocity Debye temperature Young’s modulus Compressibility Vickers hardness
Vl Vs uD E b HV
(m / s) (m / s) (K) (GPa) (GPa 21 ) (GPa)
6380 3738 539.7 225 6.97310 23 2.02
2. Experimental Rare iron flakes (3N), vanadium chunks (3N) and aluminum chips (4N) were weighted in stoichiometric proportions, and melted in an arc furnace under argon atmosphere at 0.05 MPa. For homogeneity, the samples were turned over and melted several times. Then the samples were sealed in quartz ampoules under vacuum (,0.01 MPa) and annealed at 1073 K for 50 h to obtain homogenized samples. After homogenization, the ampoules were quenched in water. All samples were cut to various shapes for the different measurements; a disc with about 1 mm thickness and 10 mm diameter for the thermal diffusivity measurement and a bar with 12–15 mm height and 10 mm diameter for the electric and mechanical properties measurements. The X-ray diffraction (XRD) measurement was carried out and for all samples it was confirmed that they have Heusler type structure. The vanadium distribution in each sample was determined by the energy dispersion X-ray analysis (EDXA). The Vickers micro hardness was measured, with 300 g load and 30 s loading time. The sound velocity of the samples was measured by an ultrasonic pulse echo method at room temperature. The Debye temperature, compressibility and Young’s modulus were obtained from the longitudinal and the shear velocities. The heat capacity was estimated from the heat capacity of the component metals by using the Neumann–Kopp law. The thermal diffusivity was measured by a laser flash method in the temperature range 300–873 K. The thermal conductivity was calculated by using the measured sample density, the thermal diffusivity, and the estimated heat capacity. The electrical resistivity and thermoelectric power were measured by a standard four-probe d.c. analysis in the temperature range 300–873 K under helium atmosphere.
3. Results and discussions Table 1 shows the physical properties of Fe 2 VAl. For isotropic media, the shear modulus G, Young’s modulus E, and bulk modulus K can be written in terms of the longitudinal sound velocity Vl and the shear sound velocities Vs as follows [19]: G 5 rV 2
H
s3V 2l 2 4V 2s d E 5 G ]]]] sV 2l 2V 2s d
J
s3V 2l 2 4V 2s d K 5 r ]]]] 3 where r is the sample density. The Debye temperature uD for Fe 2 VAl can be estimated from the sound velocities and the lattice parameter. The Debye temperature is related to the sound velocities as follows [20]: 9N 1 2 ] 1 ]D S DS]] 4pV D S V V
h uD 5 ] k
1 ] 3
C
3 L
3 S
1 ] 3
where h is the Plank constant, k is the Boltzmann constant, N is the number of atoms in the unit cell, and VC is the volume of the unit cell, respectively. Considering that the Debye temperature of ordinary metals is in the range from 200 to 600 K, the Debye temperature of Fe 2 VAl is slightly higher than those of other metals. For various materials, the Vickers hardness is also known to be associated with Young’s modulus [21]. For some oxide and carbide ceramics, the Vickers hardness is proportional to Young’s modulus with the values HV /E50.05 [21]. For pure metals, the HV /E values have been estimated in the literature [19], and the values of 0.006 for bcc metals, 0.003 for fcc metals, and 0.004 for hcp metals have been obtained. The Vickers hardness of Fe 2 VAl is plotted in Fig. 2 as a function of Young’s modulus. As shown in Fig. 2, the mechanical properties of Fe 2 VAl show neither the character of ceramics nor that of pure metals. Fig. 3 shows the temperature dependence of the thermal conductivity. In all samples, the thermal conductivity decreases with increasing temperature at low temperatures, which reflects the phonon conduction. The thermal conductivity increases with increasing temperature at high temperatures, which reveals the phonon scattering by electrons. The thermal conductivity decreases with increasing vanadium concentration from Fe 3 Al to Fe 2.5 V0.5 Al at all temperatures but increases with increasing vanadium concentration from Fe 2.5 V0.5 Al to Fe 2 VAl. This change is probably an effect of the mass difference between iron and vanadium, and that of the transformation of the crystal structure. The thermal conductivity of (Fe 12xVx ) 3 Al is several-fold or 10-fold that of state of the art thermoelectric materials. The temperature dependence of the electrical resistivity
Y. Kawaharada et al. / Journal of Alloys and Compounds 349 (2003) 37–40
39
Fig. 4. Temperature dependence of electrical resistivity. Fig. 2. Relationship between Vickers hardness and Young’s modulus.
is shown in Fig. 4. Fe 3 Al shows metallic behavior, while the other (Fe 12xVx ) 3 Al compounds show semiconductorlike behavior. The electrical resistivity of Fe 3 Al increases with increasing temperature. The slope of the curve become smaller at around 800 K, which is caused by the presence of Curie temperature around this temperature [16]. Between x50 and x50.33, the electrical resistivity increases with increasing x as reported already in the literatures [16,22]. The electrical resistivity is 100-fold or 10-fold that of state of the art thermoelectric materials [23–25]. The temperature dependence of the thermoelectric power (TEP) is shown in Fig. 5. The values of TEP are higher than those of other metals. For actual use as thermoelectric materials, it is required to raise the value of TEP. The TEP increases with increasing vanadium concentration for x,0.33, and the sign of the TEP changes from positive to negative around x50.33. This behavior agrees with the results reported in the literature [26]. The
Fig. 3. Temperature dependence of thermal conductivity.
absolute value of TEP is maximum around x50.33 (Fe 2 VAl). So the TEP has two extreme values, positive and negative, around x50.33. The change in crystal structure, from D0 3 to L2 1 , probably affects the electronic structure of (Fe 12xVx ) 3 Al, and causes this TEP behavior, as reported for the semi-Heusler Fe 12x Ni x TiSb [27]. Fig. 6 shows the temperature dependence of the power factor, a 2 s. The power factor of (Fe 12xVx ) 3 Al comes close to that of state of the art thermoelectric materials. The temperature dependence of ZT was calculated from all the above results. Fe 2 VAl shows the largest value of ZT of all the samples. The value of ZT is lower than those of other thermoelectric materials. It is caused by the high thermal conductivity, high electrical resistivity, and slightly low TEP of (Fe 12xVx ) 3 Al, even for x50.33. The thermal conductivity, the electrical resistivity, and TEP show a fairly strong dependence on vanadium concentration as mentioned above. The TEP shows maximum value at x50.33. Our future work will deal with a study of
Fig. 5. Temperature dependence of TEP.
Y. Kawaharada et al. / Journal of Alloys and Compounds 349 (2003) 37–40
40
Fig. 6. Temperature dependence of Power factor.
(Fe 12xVx ) 3 Al around x50.33 but with smaller concentration steps. We will also address the electronic property changes with changing x, using electronic structure calculations.
4. Conclusion Heusler type compounds (Fe 12xVx ) 3 Al were made in the concentration range 0,x,1, and their thermoelectric properties were measured. All thermoelectric properties showed a strong concentration dependence. Fe 2 VAl showed the largest power factor and ZT of all the samples. For practical purposes, it is necessary to optimize the vanadium concentration for obtaining maximum values of the power factor and ZT of the (Fe 12xVx ) 3 Al compounds.
References [1] Y. Kawaharada, K. Kurosaki, M. Uno, S. Yamanaka, J. Alloys Comp. 315 (2001) 193.
[2] K. Kurosaki, A. Kosuga, M. Uno, S. Yamanaka, J. Alloys Comp. 334 (2002) 317. [3] K. Kurosaki, T. Matsuda, M. Uno, S. Kobayashi, S. Yamanaka, J. Alloys Comp. 319 (2001) 271. [4] H. Muta, K. Kurosaki, M. Uno, S. Yamanaka, J. Alloys Comp. 335 (2002) 200. [5] Fr. Heusler, Verhandlungen der Deutschen Physikalischen Gesellschaft 5 (1903) 219. [6] A.W. Carbonari, R.N. Saxena, W. Pendl Jr., J. Mestnik Filho, R.N. Attili, M. Olzon-Dionysio, S.D. de Souza, J. Magn. Magn. Mater. 163 (1996) 313. [7] P. Mohn, P. Blaha, K. Schwarz, J. Magn. Magn. Mater. 140–144 (1995) 183. [8] S. Suga, S. Imada, A. Yamasaki, S. Ueda, T. Muro, Y. Saitoh, J. Magn. Magn. Mater. 233 (2001) 60. [9] H. Mitamura, N. Takeshita, Y. Uwatoko, H. Mori, A. Yamaguchi, T. Tomita, H. Wada, N. Mori, H. Ishimoto, T. Goto, Physica B 284–288 (2000) 1341. [10] H. Mitamura, N. Takeshita, Y. Uwatoko, H. Mori, A. Yamaguchi, T. Tomita, H. Wada, N. Mori, H. Ishimoto, T. Goto, Physica B 281 / 282 (2000) 150. [11] S. Kyuji, S. Endo, T. Kanomata, F. Ono, Physica B 237 / 238 (1997) 523. [12] J.A. Caballero, A.C. Reilly, Y. Hao, J. Bass, W.P. Pratt Jr., F. Petroff, J.R. Childress, J. Magn. Magn. Mater. 198 (1999) 55. [13] J.W. Dong, J. Lu, J.Q. Xie, L.C. Chen, R.D. James, S. McKernan, C.J. Palmstrom, Physica E 10 (2001) 428. [14] D.E. Okpalugo, J.G. Booth, C.A. Faunce, J. Phys. F 15 (1985) 681. [15] P.J. Webster, K.R.A. Ziebeck, Phys. Lett. A 98 (1983) 51. [16] Y. Nishino, C. Kumada, S. Asano, Scripta Mater. 36 (1997) 461. [17] Y. Nishino, M. Kato, S. Asano, K. Soda, M. Hayasaki, U. Mizutani, Phys. Rev. Lett. 79 (10) (1997) 1909. [18] S. Ishida, J. Ishida, S. Asano, J. Yamashita, J. Phys. Soc. Jpn. 41 (1976) 1570. [19] Thermophysical Properties Handbook, Nippon Netu Bussei Gakkai, Youkendou, Tokyo, 1990. [20] H. Inaba, T. Yamamoto, Netsu Sokutei 10 (1983) 132. [21] K. Tanaka, H. Koguchi, T. Mura, Int. J. Eng. Sci. 27 (1989) 11. [22] Y. Nishino, Mater. Sci. Eng. A258 (1998) 50. [23] D.M. Rowe, CRC Handbook of Thermoelectrics, CRC Press. [24] R.S. Caputo, V.C. Truscello, in: Proceedings of IECEC, 1974, p. 637. [25] J.P. Fleurial, T. Caillat, A. Borshchevsky, in: 31st Intersoc. Convers. Eng. Conf., 1996, p. 96512. [26] Y. Hanada, R.O. Suzuki, K. Ono, J. Alloys Comp. 329 (2001) 63. [27] J. Tobola, L. Jodin, P. Pecheur, H. Scherrer, G. Venturini, B. Malaman, S. Kaprzyk, Phys. Rev. B 64 (2001) 155103.