Zeolites are microporous crystalline materials that find wide application in industry, for example, as catalysts and gas separators, and in our daily life, for example, as adsorbents or as ion exchangers in laundry detergents 1 . The tetrahedrally coordinated silicon and aluminium atoms in the zeolite unit cell occupy the so-called crystallographic T-sites. Besides their pore size, the occupation of specific T-sites by the aluminium atoms determines the performance of the zeolites 2 . Despite its importance, the distribution of aluminium over the crystallographic T-sites remains one of the most challenging, unresolved issues in zeolite science. Here, we report how to determine unambiguously and directly the distribution of aluminium in zeolites by means of the X-ray standing wave technique 3 using brilliant, focused X-rays from a thirdgeneration synchrotron source. We report in detail the analysis of the aluminium distribution in scolecite, which demonstrates how the aluminium occupancy in zeolites can systematically be determined.Zeolites are widely used materials with a very wide range of applications. They are used in households in laundry detergents and in industry as catalysts for petrochemical refining and they have become increasingly important in fine-chemical production and in environmental applications; they are used as air and water purifiers and in heating and refrigerating, and they are used in agriculture as selective absorbents. With natural zeolites being discovered more than 200 years ago, intensive research is nowadays aimed at developing new, synthetic zeolites with tailored properties for specific tasks. The functionality of a zeolite is determined basically by just a few parameters: the size and connectivity of the pores and cages, the Si/Al ratio and the placement of the trivalent aluminium atoms at specific crystallographic T-sites. Among them, the placement of aluminium is still unknown for many zeolites because no generally applicable experimental method has been reported to solve this problem. This seriously hampers the understanding of the function of some technologically important zeolites and hinders the development of new zeolites with novel functionalities.In a zeolite, the replacement of a tetravalent silicon atom by a trivalent aluminium atom on a T-site places a negative charge on the framework, which is compensated by non-framework cations. These charge-compensating cations are loosely held in the pores and cages of a zeolite and can be exchanged by other cations. This property makes zeolites good cation exchangers, which are useful in water softening and in the removal of nuclear waste. When the charge-compensating species are protons or elements that are involved in oxidation or reduction reactions, zeolites become catalytically active in Brønsted and redox reactions, respectively. The Si/Al ratio and the aluminium distribution over the framework T-sites thus determine the species and the positions of the chargecompensating cations in a zeolite, which strongly affect its cata...

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We present a detailed study of the electronic structure and band alignment in LaAlO 3 /SrTiO 3 oxide heterostructures by hard x-ray photoelectron spectroscopy. Our spectroscopic measurements find no evidence for the strong potential gradient within the polar LaAlO 3 film predicted by band theory. Due to the high interface sensitivity of the method, we are further able to determine the valence band offset between the LaAlO 3 film and the SrTiO 3 substrate, which is found to be independent of the number of LAO overlayers. Finally, we discuss several explanations for the apparent absence of the built-in field in ex situ prepared LaAlO 3 /SrTiO 3 heterostructures.

Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO3(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO3/Pt junctions with a sub-μm Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of ∼30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO3/Pt (Cr/BaTiO3) interface +0.42(−0.03) eV following downward to upward polarization reversal.