Thermoelectric properties of La/sub 2-x/Sr/sub x/CuO/sub 4/

Abstract

La(2-x)SrxCu04 is unique among the high Tc superconductors with high values of Seebeck coefficient in the normal state for x < 0.1 , in addition to a low thermal conductivity. Seebeck coefficient and electrical conductivity were measured for samples of sintered and single crystal Lal.95Sr0.05CuO4 in order to look for the optimum concentration of Sr as related to its thermoelectric properties at room temperature. At this doping level this material is in the region of metal-insulator transition. Room temperature values of 147 pV/K and 0.01 Qcm for the Seebeck coefficient and the electrical resistivity, respectively, were obtained for a sintered sample.For a single crystal of the same composition, the Seebeck coefficient parallel to the ab planes is 143 pV/K and along the c axis it is 156 pV/K. The electrical resistivity was measured only along the ab planes, down to about 9K. The R.T. value was 0.03 Qcm. No significant change was observed after annealing , either in oxygen or in vacuum. There is a significantly different behavior of the temperature dependence of the resistivity between the sintered and single crystal samples: the sintered sample has a metallic behavior from room temperature down to 80K, and there is no superconducting transition above 10K -whereas the single crystal shows semiconducting behavior from R.T. down to the superconducting transition with an onset temperature of 17K (along the lower resistivity ab planes). Our data are compared with published data of different values of x in the system La(2-x)SrxCu04. Introduction:

In-plane thermoelectric properties of heavily underdoped high-temperature superconductor Bi2Sr2CaCu2O8+δ

“…Using the room temperature resistivity of 6 m cm from La 1.98 Sr 0.02 CuO 4 reported by Ando et al [16], we evaluate the power factor of HTSC to be 15 μW cm −1 K −2 at maximum. Using the thermal conductivity of 50 mW cm −1 K −1 found in the present study, we evaluate Z T to be 0.09 at maximum at 300 K, This evaluation is consistent with the early survey of Macklin and Moseley [7], and indeed most of the literature data do not exceed this value [8][9][10][11][12][13][14][15]. As mentioned above, the thermopower of HTSC decreases with increasing temperature at high temperatures, and therefore Z T is unlikely to exceed this value above 300 K. Even if the thermopower were constant above 300 K, Z T would be smaller than 0.27 at 900 K. In this context, we conclude that HTSC cannot be used for practical thermoelectric applications.…”

“…In addition, the block layer concepts work well in the two systems [5,6]. Macklin and Moseley [7] have already surveyed the existing literature data, and found that Z T of HTSC is 0.1 at maximum at 300 K. This survey has proved to be true; in spite of various attempts, Z T of HTSC-based materials remains small [8][9][10][11][12][13][14][15]. However, such preceding works are based on polycrystalline samples, the 1 Present address: Department of Physics, Nagoya University, Nagoya 464-8602, Japan.…”