High-resolution High Energy X-ray Diffraction Studies of Charge Ordering in Cmr Manganites and Nickelates

High-resolution, high-energy, X-ray diffraction results are presented for the study of weak charge ordering phenomenon. By utilizing X-rays in the 100 keV region the dramatic increase in the penetration depth allows for both bulk-sensitive and highresolution measurements to be made. The strontium doped La2NiO4 system is a prototypical system in the understanding of strong electron-phonon coupling, and the resultant effects on material properties. At doping levels of 1/3 and 1⁄2 commensurate charge modulations are observed indicating real-space charge stripes. We have measured the correlation lengths of these charge stripes using both 100 keV X-rays and 8.3 keV X-rays. In comparing our results we have observed that the charge stripes appear to be well correlated in the near-surface region with correlation lengths ξ≈ 2400Å. However, our bulk sensitive measurements show that the charge stripes appear in a possible stripe glass phase with a correlation length of only ξ ≈ 300Å. Our measurements on the 3D charge order manganite system Nd0.5Sr0.5MnO3 show that the charge ordering appears to be well correlated in the bulk of the sample in contrast to our nickelate results.