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Instruments / Technical Area	Publication Details	Published
I07-Surface & interface diffraction	Temperature effect on surface structure of single crystal SrLaAlO4(001) P. Mousley , C. Nicklin , S. S. Pramana , C. Van Den Bosch , M. P. Ryan , S. J. Skinner Apl Materials 11 DOI: 10.1063/5.0167091 Diamond Proposal Number(s): [11597] Open Access Show Abstract ▼ Abstract: Development of next-generation electrochemical devices, such as solid oxide cells, requires control of the charge transfer processes across key interfaces. Structural strain at electrolyte:electrode interfaces could potentially alter the devices’ charge transport properties, therefore understanding the structural behavior of electrode surfaces under operating conditions is important. The functional oxide single crystal substrate SrLaAlO4 has been well-characterized with bulk structure studies; however, there are very few studies of SrLaAlO4 surface structures. Here, we present an investigation of the surface structure of SrLaAlO4 (001) substrates using surface x-ray diffraction under UHV conditions (10−10 Torr) with the substrate held at either room temperature or 650 °C. Best-fit models using a 1:1 ratio of Sr:La showed significant distortions to the surface AlO6 octahedra.	Nov 2023
I07-Surface & interface diffraction	Understanding surface structure and chemistry of single crystal lanthanum aluminate Stevin S. Pramana , Andrea Cavallaro , Jiahui Qi , Chris L. Nicklin , Mary P. Ryan , Stephen J. Skinner Scientific Reports 7 DOI: 10.1038/srep43721 Diamond Proposal Number(s): [11597] Open Access Show Abstract ▼ Abstract: The surface crystallography and chemistry of a LaAlO3 single crystal, a material mainly used as a substrate to deposit technologically important thin films (e.g. for superconducting and magnetic devices), was analysed using surface X-ray diffraction and low energy ion scattering spectroscopy. The surface was determined to be terminated by Al-O species, and was significantly different from the idealised bulk structure. Termination reversal was not observed at higher temperature (600 °C) and chamber pressure of 10−10 Torr, but rather an increased Al-O occupancy occurred, which was accompanied by a larger outwards relaxation of Al from the bulk positions. Changing the oxygen pressure to 10−6 Torr enriched the Al site occupancy fraction at the outermost surface from 0.245(10) to 0.325(9). In contrast the LaO, which is located at the next sub-surface atomic layer, showed no chemical enrichment and the structural relaxation was lower than for the top AlO2 layer. Knowledge of the surface structure will aid the understanding of how and which type of interface will be formed when LaAlO3 is used as a substrate as a function of temperature and pressure, and so lead to improved design of device structures.	Mar 2017
I11-High Resolution Powder Diffraction	Correlation of local structure and diffusion pathways in the modulated anisotropic oxide ion conductor CeNbO4.25 Stevin S. Pramana , Thomas Baikie , Tao An , Matthew G. Tucker , Ji Wu , Martin K. Schreyer , Fengxia Wei , Ryan D. Bayliss , Christian L. Kloc , Timothy J. White , Andrew P. Horsfield , Stephen J. Skinner Journal Of The American Chemical Society 138 (4), pp 1273–1279 DOI: 10.1021/jacs.5b11373 PMID: 26771687 Show Abstract ▼ Abstract: CeNbO4.25 is reported to exhibit fast oxygen ion diffusion at moderate temperatures, making this the prototype of a new class of ion conductor with applications in a range of energy generation and storage devices. To date, the mechanism by which this ion transport is achieved has remained obscure, in part due to the long-range commensurately modulated structural motif. Here we show that CeNbO4.25 forms with a unit cell ∼12 times larger than the stoichiometric tetragonal parent phase of CeNbO4 as a result of the helical ordering of Ce3+ and Ce4+ ions along z. Interstitial oxygen ion incorporation leads to a cooperative displacement of the surrounding oxygen species, creating interlayer “NbO6” connectivity by extending the oxygen coordination number to 7 and 8. Molecular dynamic simulations suggest that fast ion migration occurs predominantly within the xz plane. It is concluded that the oxide ion diffuses anisotropically, with the major migration mechanism being intralayer; however, when obstructed, oxygen can readily move to an adjacent layer along y via alternate lower energy barrier pathways.	Jan 2016

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