ISSN 0020-1685, Inorganic Materials, 2013, Vol. 49, No. 12, pp. 1213–1219. © Pleiades Publishing, Ltd., 2013 Original Russian Text © L.P. Lyashenko, L.G. Shcherbakova, E.S. Kulik, R.D. Svetogorov, Ya.V. Zubavichus, 2013, published in Neorganicheskie Materialy, 2013, Vol. 49, No. 12, pp. 1316–1323. 1213 INTRODUCTION The formation of nanostructured materials was first observed in microstructural studies of fluorite-like R 2 MO 5 (R = lanthanide, Y, Sc; M = Ti, Zr, Hf) phases with a high density of structural defects [1–4]. Nano- structured materials were also obtained by doping a number of fluorite phases with rare-earth elements: M 1– x R x F 2+ x , where M = Ca, Sr, or Ba [5]. A charac- teristic feature of melted crystals of these compounds is that, having an inhomogeneous structure, they behave as single crystals when studied by X-ray diffrac- tion [3, 5]. Structural features of nanostructured fluorite-like R 2 TiO 5 and solid solutions based on these compounds are essentially unexplored. As determined by the diffu- sion layer method, solid solutions in the TiO 2 –Er 2 O 3 system exist in the composition range 50–60 mol % Er 2 O 3 , with Er 2 TiO 5 and Er 3 TiO 6.5 as end-members [6]. According to scanning electron microscopic examination and X-ray diffraction characterization with monochromatized CuK α radiation, these solid solutions have an inhomogeneous structure, which consists of a fluorite-like disordered phase and a nanoscale ( 40–1000 nm) pyrochlore-like ordered phase coherent with the matrix [7]. In this paper, we report a detailed structural study of high-temperature nanostructured Er 2 O 3 –TiO 2 ≃ (50–60 mol % Er 2 O 3 ) solid solutions by synchrotron X-ray diffraction with the aim of gaining additional information about these materials. EXPERIMENTAL хEr 2 O 3 ⋅ (1 – х)TiO 2 (x = 0.5, 0.55, 0.57, 0.6) sam- ples for this investigation were prepared by a ceramic processing technique, using appropriate mechanical mixtures of TiO 2 (extrapure grade) and Er 2 O 3 (Er-0-2). In the synthesis of the samples by the ceramic pro- cessing technique, appropriate ratios of the starting oxides were mixed by grinding in a jasper mortar with ethanol. The mixtures were pressed into disks 0.7 cm in diameter and 0.5–1 cm in thickness at a pressure of 15 MPa, which were then fired in an electric furnace with a platinum–rhodium heater at a temperature of 1600°C for 13 h in air. In our studies, we also used sin- gle-crystal samples prepared through induction skull melting. Monochromatic synchrotron X-ray diffraction measurements (λ = 0.68886 Å, Si monochromator) were performed at the Station for X-ray Crystallogra- phy and Materials Science (Kurchatov Center for Synchrotron Radiation and Nanotechnology) in transmission geometry using a Fujifilm image plate detector. X-ray diffraction intensity data were col- lected at 20°C in integral mode. The use of a high- intensity monochromatic synchrotron radiation Synchrotron X-ray Diffraction Study of Nanostructured Er 2 O 3 –TiO 2 (50–60 mol % Er 2 O 3 ) Solid Solutions L. P. Lyashenko a , L. G. Shcherbakova b , E. S. Kulik c , R. D. Svetogorov c , and Ya. V. Zubavichus c a Institute of Problems of Chemical Physics, Russian Academy of Sciences, pr. Akademika Semenova 1, Chernogolovka, Moscow oblast, 142432 Russia b Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia c National Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia e-mail: lyash@icp.ac.ru Received June 10, 2013 Abstract—Monochromatic synchrotron X-ray diffraction data demonstrate that single-crystal and polycrys- talline xEr 2 O 3 ⋅ (1 – x)TiO 2 (x = 0.5–0.6) solid solutions consist of a fluorite-like disordered (Fm3m) phase and a nanoscale ( 40–1000 nm) pyrochlore-like ordered phase (Fd3m) of the same composition in the range 0.5 ≤ x ≤ 0.57, coherent with the disordered phase. Reducing the density of structural defects in the unit cell of Er 3 TiO 6.5 (x = 0.6) leads to a structural transformation of the pyrochlore-like phase into a Ta 2 O 3 -type ordered phase (Ia3), derived from the fluorite phase. In the composition range of the solid solutions (0.5 < x < 0.6), the lattice parameter of the fluorite-like phase follows Vegard’s law. The formation of nanodomains with different degrees of order is shown to be caused by the internal strain due to the high density of structural defects in their unit cells. DOI: 10.1134/S0020168513120108 ≃