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

In order to elucidate the relationship between the electrical properties and composition ( d and x ) of La 1− x Sr x MnO 3+ d , precise measurements were made on the conductivity, σ , and Seebeck coefficient, Q , for the oxide with 0≤ x ≤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 models reported by the present authors. It was shown that σ and Q in the oxygen excess La 1− x Sr x MnO 3+ d ( d >0) are fixed to the value at those of the stoichiometric oxygen content, d =0. In the oxygen deficient La 1− x Sr x MnO 3+ d , they are essentially determined by the mean Mn valence and temperature. The predominant electrical conduction was found to take place by the electron hopping on the e g ↑ level of Mn. In La 1− x Sr x MnO 3+ d ( d ≤0) under the condition of z = x +2 d ≤1/3, σ is given by: σ=(2.8×10 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 ≥1/3, it is given by: σ=(2.8×10 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 ↑ level. The major carrier conduction is p-type and the minor carrier is n-type for z ≤0.5 and vice versa for z ≥0.5.