Solving unknown complex oxide structures by precession electron diffraction: AgCoO 2 , PbMnO 2.75 and LiTi 1.5 Ni 0.5 O
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1184-GG01-06
Solving unknown complex oxide structures by precession electron diffraction: AgCoO2, PbMnO2.75 and LiTi1.5Ni0.5O4 H. Klein1, M. Gemmi1,2, A. Rageau1 1 Institut Néel, Université Joseph Fourier and CNRS, 25 av. des Martyrs, BP 166, 38042 Grenoble Cedex 9 2 Dipartimento di Scienze della Terra 'Ardito Desio', Sezione di Mineralogia, Via Botticelli 23, I20133 Milano, Italy ABSTRACT Oxides synthesized in high temperature / high pressure conditions often show complex structures and contain several phases which makes a structure solution by X-ray crystallography very difficult or even impossible. Electron crystallography can then be a powerful alternative. We show here the structure solution of 3 oxides by precession electron diffraction. The phases include a simple hexagonal structure (AgCoO2), a complex monoclinic structure (PbMnO2.75) with a quasi 2-dimensional unit cell and a complex trigonal structure (LiTi1.5Ni0.5O4). In the last case even the positions for the light element Li were determined. INTRODUCTION Oxides are a vast class of materials presenting various properties used in different technological applications. You can find these materials in batteries, fuel cells, high Tc superconductors, multiferroics, etc. Many of the new phases in this field are synthesized at high temperature (HT) and under high pressure (HP). Single crystals suitable for X-ray diffraction are therefore rarely available and powder X-ray diffraction suffers from severe peak overlap. Even in the rare cases where the powders contain only one phase this hinders cell parameter determination and inhibits structure solution. Electron crystallography has proven to be a powerful tool for structure solution in cases where X-rays fail due to the above mentioned problems. Many examples have been shown in which electron crystallography has been able to solve even complex structures correctly (for recent examples see [1-3]. Recently, the availability of the precession technique for electron diffraction has permitted to collect data suitable for use in standard crystallographic software for structure determination. However, compared to X-ray crystallography it remains a delicate and time consuming method. Therefore it finds its real application in cases where X-rays are not sufficient to solve the structures. Prominent examples are multi-phase powders constituted of nanometer sized grains. In this contribution we give an overview over different structures we have solved by precession electron diffraction (PED). The phases include a simple hexagonal structure (AgCoO2) synthesized for potential thermoelectric properties, a complex monoclinic structure (PbMnO2.75) produced at HT/HP in search of new multiferroic materials and a trigonal structure (LiTi1.5Ni0.5O4) fabricated in order to enhance the performance of Li batteries. Each of these phases presents a difficulty for X-ray powder diffraction (XRPD) structure determination. The particles of the AgCoO2 powder showed a particular morphology inducing
preferential orientation of the particles
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