Crystal structure refinement of the layered copper-titanium perovskites Ln2Ba2Cu2Ti2O11 (Ln = La, Nd) from neutron powder diffraction data

摘要

Neutron powder diffraction data of the oxides Ln2Ba2Cu2Ti2O11 (Ln = La, Nd) are presented and analyzed by means of Rietveld profile refinements. These data confirm the existence, in both cases, of a tetragonal superstructure based on a quadruple perovskite (ap x ap x 4ap). Whereas the Nd derivative presents complete long range order of Cu/Ti, Ln/Ba, and oxygen vacancies, in the lanthanum derivative this order is only partial.