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Site-Specific Structural Measurements Using X-Ray Standing Waves: The Electronic and Geometric Structure of the Perovskite La1/2Sr3/2MnO4

Published

Author(s)

E J. Nelson, Joseph C. Woicik, Z Hasan, Z -. Shen, D Heskett, L E. Berman

Abstract

In the vicinity of an x-ray Bragg reflection, the incident and reflected x-rays coherently superpose to form an x-ray standing wave, with a periodicity equal to the diffracting plane spacing. The phase relationship between the two x-rays can be tuned by changing either the photon energy or the angle of the incident x-ray. Thistuning results in a shift of the maxima of the x-ray standing wave field intensity relative to the diffracting planes. Unlike conventional x-ray diffraction, where diffracted intensities are measured and the phase relationship between the incident and scattered waves and hence the phase of the crystal structure factor are lost, the interferometric x-ray standing wave (XSW) technique directly determines the amplitude and phase of the structure factor of absorbing atoms. By examining the atomic absorption as the standing wave is swept though the unit cell, site-specific structural data are measured. By using both valence band and core-levelphotoelectron yields to monitor the absorption, both the site-specific electronic structure of the valence band and the element-specific geometric structure of the crystal may be determined.To demonstrate the applicability of this technique to materials of technological interest, we present our results on the perovskite material La1/2Sr3/2MnO4. The perovskite structure is common to colossal magnetoresistive (manganite) and high-Tc superconducting (cuprate) materials. These effects originate in the Mn-O (or Cu-O) planes in the layered planar tetragonal structure of the perovskites, and charge ordering and orbital ordering of valence electrons in the Mn-O plane have been observed.The position-tunable electric field is the basis of a unique technique to directly probe the photoemission partial densities of states of crystalline materials. For La1/2Sr3/2MnO4, we find that Mn valence-state emission is enhanced at the top and bottom parts of the valence band, while the middle part is higher in La, Sr, and O valence-state density. These results are consistent with theoretical partial densities of states for the related perovskite compound La0.7Sr0.3MnO3.In addition to retaining phase information, the x-ray standing waves technique using core-level photoemission yields also has an advantage over conventional x-ray diffraction in that it is element-specific. The atomic position distribution of each of the four elements in La1/2Sr3/2MnO4 was separated, and each was found tobe consistent with the model structure verified by x-ray diffraction. The identical lineshapes of the La and Sr core-level yields directly verify that La substitutes in the Sr sites.
Citation
Site-Specific Structural Measurements Using X-Ray Standing Waves: The Electronic and Geometric Structure of the Perovskite La1/2Sr3/2MnO4

Keywords

interferometric x-ray standing wave, perovskite, perovskite La1/2Sr3/2MnO4, site-specific structural data, x-ray Bragg reflection

Citation

Nelson, E. , Woicik, J. , Hasan, Z. , Shen, Z. , Heskett, D. and Berman, L. (2001), Site-Specific Structural Measurements Using X-Ray Standing Waves: The Electronic and Geometric Structure of the Perovskite La1/2Sr3/2MnO4, Site-Specific Structural Measurements Using X-Ray Standing Waves: The Electronic and Geometric Structure of the Perovskite La1/2Sr3/2MnO4 (Accessed April 12, 2024)
Created January 1, 2001, Updated February 19, 2017