Oxygen non-stoichiometry and high temperature DC conductivity of SmBa2Cu3O6+x

The paper reports on coupled DC electrical conductivity measurements and ox ygen non-stoichiometry determinations on SmBa2Cu3O6+x at high temperatures (300-750 degrees C) under oxygen partial pressures from 10(-1) to 10(-5) at m. Under the lowest oxygen pressures (10(-4) and 10(-5) atm) and at the hig hest investigated temperatures (T> 700 degrees C, for the former pressure) the material shows semiconducting behavior. In the other [T, P(O-2)] field the material shows metallic conductivity. The amount of (positive) carriers is controlled by equilibrium with external oxygen coupled to oxygen point defects. A change in the mechanism of hole injection is well apparent at th e transition between the tetragonal and the orthorhombic phases. Indication s are given about the large polaron nature of the holes at high oxygen cont ent. (C) 1998 Elsevier Science B.V. All rights reserved.