Crystal chemistry of layered manganites Ln(1.4)Sr(1.6)Mn(2)O(7) (Ln = La, Pr, Nd, Sm, Eu, and Gd)

The powder X-ray diffraction patterns of a series of layered manganite comp ounds, Ln(1.4)Sr(1.6)Mn(2)O(7) (Ln = La, Pr, Nd, Sm, Eu, Gd), were refined with the Rietveld method. The Ln occupancy in the rock: salt site increases on moving from La through Gd. The variations of the lattice parameters and the bond distances correlate and can be accounted for with the distributio n of Ln and Sr in the perovskite and rock salt sites. The structural analys is implies that the physical properties of these compounds have to vary mon otonically from La through Sm and then more or less the same from Sm throug h Gd, which is not the case. Therefore, in order to understand the various physical properties of these compounds depending on Ln another factors such as the magnetic properties of Ln need to be considered.