The calculated structure, stability and composition of the low index surfaces of La 2CuO 4 and Nd 2CuO 4

Abstract

The {100} and {001} surfaces of La 2CuO 4 and Nd 2CuO 4 are perpendicular and parallel to their (super)conducting CuO 2 planes. Surface and intergranular conductivity and weak links will be influenced by the integrity of these surfaces. This integrity will evolve during the processing of the semi-conducting precursor compounds and will be “frozen-in” when the newly formed lanthanum copper oxide is cooled below the superconducting transition temperature. Therefore, the structures and stabilities of the La 2CuO 4 surfaces and the effect of impurity segregation (Ca 2+, Sr 2+, Ba 2+, Ce 4+ and Th 4+) at these surfaces have been investigated by static lattice simulation. The greatest perturbation of the CuO 2 planes in the pure materials is predicted at the {100} surface of La 2CuO 4, the depth of which is comparable to the coherence length of the superconducting phases. Impurity segregation at {100} surface copper sites of La 2CuO 4 is also predicted, in contrast to the other surfaces.