Modulated charge ordering process in Sm0.5Ca0.5Mn1–xCrxO3 manganites
Abstract
The oxides Sm0.5Ca0.5Mn1–xCrxO3 , with 0≤x≤0.07, have been studied by electron diffraction and electron microscopy versustemperature from 90 K to 300 K, in connection with their magnetic and transport properties. An incommensurate charge ordering appears atTCO=275 K for the undoped compound, then a progressive transition from an incommensurate to a commensurate modulated structure is observed as Tdecreases from 275 K to 170 K. But the most important point is that chromium doping enhances the incommensurability of the structure: theq vector of the low temperature form decreases and TCO decreases abruptly as the chromium content x increases, so that the charge ordering process is weakened and finally disappears for x=0.05. The structure of the low temperature form of these manganites is characterized by a double supercell, 2ap √2×2ap ×ap √2, similar to that observed for other Ln0.5Ca0.5MnO3 manganites with Ln=La, Pr, Nd, Tb. However, in these series, one observes similar space groups (P2mmorPmmm) for Ln=Nd, Sm, different from those observed for Ln=La, Tb.