Electronic conductivity, Seebeck coefficient, defect and electronic structure of nonstoichiometric La1-xSrxMnO3

In order to elucidate the relationship between the electrical properties an d composition (d and x) of La1-xSrxMnO3+d, precise measurements were made o n the conductivity, sigma and Seebeck coefficient, Q, for the oxide with 0 less than or equal to x less than or equal to 0.7 as a function of T and P( O-2) up to 1273 K. Analysis was made for the high-temperature paramagnetic state using the nonstoichiometry data and defect and electronic structure m odels reported by the present authors. It was shown that sigma and Q in the oxygen excess La1-xSrxMnO3+d (d > 0) are fixed to the value at those of th e stoichiometric oxygen content, d = 0. In the oxygen deficient La1-xSrxMnO 3+d, they are essentially determined by the mean Mn valence and temperature . The predominant electrical conduction was found to take place by the elec tron hopping on the e(g)up arrow level of Mn. In La1-xSrxMnO3+d (d less tha n or equal to 0) under the condition of z = x + 2d less than or equal to 1/ 3, sigma is given by: sigma = (2.8 x 10(6)/T){2 (-z(2) - z + 6)(6 - 18z)/(17 - z)(2) + (-z(2) - z + 6) (z(2) + 18z + 5)/(17 - z)(2)} exp{(-Ea/(kT)} where the activation energy Ea = - 0.59(3 + z) + 2.00 eV. For z greater tha n or equal to 1/3, it is given by: sigma = (2.8 x 10(6)/T) z(1 - z) exp{(-Ea/(kT)} where Ea = -0.036(3 + z) + 0.16 eV. Q is also described essentially by this model. However, the effect of minority carrier conduction is clearly found in Q in addition to the major conduction on e(g)up arrow level. The major carrier conduction is p-type and the minor carrier is n-type for z less tha n or equal to 0.5 and vice versa for z greater than or equal to 0.5. (C) 20 00 Elsevier Science B.V. All rights reserved.