Concentration or Modulation Layering of Perfect Single Crystals Bi2Sr2-xLaxCuO6+δ and Bi2-yPbySr2-xLaxCuO6

Precision structural studies of layering of perfect crystals Bi2Sr2-xLaxCuO6+delta (BSLCO) similar to 10 mu m thick, grown by free growth within crystallized melt cavities, detect a macrolayer structure with each layer up to 0.1 mu m thick. In the lanthanum concentration range x = 0.6-0.8, only modulation layering is observed. In the concentration range x = 0.3-0.5, either layers with two different lanthanum concentrations, but with the same modulated superlattice type, or layers with the same lanthanum concentration, but with two different modulated superlattice types are observed. At low lanthanum concentrations (0 < x < 0.26), layering into two or even three layer types with different lanthanum concentrations are almost always observed. Modulation suppression when lead is added to a mixture leads to the same layered structure of samples, but with appreciable variations in lattice parameters in the ab plane of individual layers and a and b axis rotation by several degrees with respect to each other in these layers. Thus, the superlattice in BSLCO single crystals stabilizes their composition in the ab plane, and inevitable variations in growth conditions lead to the layered structure of such crystals.