Thermoelectric properties of n- and p-type polycrystalline Pr1-xSrxMnO3 (0.1≦x≦0.9)
Masaki Kubota, Yosuke Watanabe, Hiroshi Nakatsugawa
Yokohama National University
Graduate School of Engineering, Yokohama National University,
79-5 Tokiwadai, Hodogaya-ku, Yokohama-shi, Kanagawa 240-8501, Japan
TEL: +81-45-339-3854 E-mail: naka@ynu.ac.jp
Introduction Thermoelectric energy conversion is a technology that attracts renewed interest as a
new energy resource. There is a finite coupling between the electrical and entropy currents, which isknown as the thermoelectric phenomena, i.e., the Seebeck or the Peltier effects because electrons orholes in solid carry the electricity together with the entropy. The thermoelectric energy conversion
generates energy from the temperature gradient and the heat flow. Thus the thermoelectric energy
conversion efficiency is defined by the ratio between the output electrical power with the thermal
entropy flux. By optimizing the efficiency with respect to a load resistance, the maximum efficiency
max is obtained as a monotonically increasing function of the dimensionless figure of merit of thethermoelectric material ZT . A higher temperature with a larger temperature difference gives alarger max . Therefore, oxides are quite attractive in this respect because of the chemical stability in
air at high temperature. After the discovery of the thermoelectric oxide NaxCoO2,1) oxide
thermoelectrics using 3d transition-metal oxides have been extensively investigated.
3d transition-metal oxides Compared with other thermoelectric materials, 3d transition-metaloxides are quite unique in the sense that (i) the electron correlation is strong enough to make theHeikes formula2): S   k B  ln g  86  V K  ln  g 3 x  , where the ratio g3 is determined by thege Ng 1 x
4

4Hund’s rule coupling, x is the carrier concentration of quadribalent ions, and S is the Seebeckcoefficient, (ii) the resistivity is barely metallic in which the mean free path is of the order of theunit cell length, and (iii) the spin fluctuation significantly affects the thermoelectric properties.
Results and Discussion By using such oxides, we have fabricated polycrystalline Pr1-xSrxMnO3(0.1≦x≦0.9) using a solid-state reaction method. Figure 1 shows the temperature dependence ofthe power factor of Pr1-xSrxMnO3 (0.1≦x≦0.9). The positive S values of x=0.1 and 0.2 confirm
that the dominat electrical carriers are holes.On the other hand, the negative S values of 0.3≦x≦
0.9 confirm that the dominant electrical carriers are electrons. The figure of merit Z wascalculated from the following formula Z  S 2 /   Cd  , where  , C , d are the thermal diffusivity，
specific heat capacity, and density, respectively. Figure 2 shows the temperature dependence of ZTof Pr1-xSrxMnO3 (0.1≦x≦0.9). In particular, ZT shows maximum value of 0.06 for x=0.7 sample.
0.08
Pr1−xSrxMnO 3

2x=0.500x=0.1200400600
T (K)

800

ZT

2

x=0.6

x=0.6

0.04
0.02

x=0.4
x=0.9
x=0.3
1000 x=0.2

Fig.1 Temperature dependence of the power
factor S2/ρ(×10-6W/mK2).

x=0.7

0.06

x=0.7

S / (W/mK )100

Pr1−xSrxMnO 300x=0.1

200400600T (K)

800

1000

Fig.2 Temperature dependence
dimensionless figure of merit ZT .

References
1) I.Terasaki, Y.Sasago, and K.Uchinokura, Phys. Rev. B56, R12685 (1997).
2) W.Koshibae, K.Tsutsui, and S.Maekawa, Phys. Rev. B62, 6869 (2000).

x=0.5
x=0.4
x=0.9
x=0.3
x=0.2ofthe