Structural evolution and electronic properties of La<SUB>1+x</SUB>Sr<SUB>2−x</SUB>Mn<SUB>2</SUB>O<SUB>7</SUB>

A detailed study of the layered manganite La1+xSr2&#8722;xMn2O7 has been performed, establishing that within the composition range 0.1 &#8804; x &#8804; 0.45 the phases crystallize in the I4/mmm space group. The evolution of structural parameters with x in this composition range has been followed using a novel application of an existing program for the Rietveld analysis of powder diffraction data. The structure, a familiar intergrowth of rock-salt (La,Sr)O slabs and double perovskite (La,Sr)2Mn2O6 units, is characterized by a reluctance to deform the latter. This manifests as a "pumping" of the larger SrII ion into the 12-coordinate site of the structure as x is increased. We report these features of the structure as well as electrical transport and magnetic properties, in light of recent observations of giant, negative magnetoresistance in these systems