Gradients in structure and dynamics of Y sub 2 O sub 3 nanoparticles as revealed by X-Ray and Raman scattering

• Published in: Scripta materialia 2000-08, Vol.44 (8-9), p.2127-2131
• Main Authors: Beck, C, Ehses, K H, Hempelmann, R, Bruch, C
• Format: Article
• Language: English
• ISSN: 1359-6462

Properties of nanocrystalline (nc) are more or less altered, depending upon processing and thermal history of the samples, compared to those of the conventional coarse-grained counterparts. Using X-Ray diffraction different structure parameters have been evaluated in nc-matter. It has been found, that the lattice constant increases with decreasing crystallite sizes for nc-selen but decreases for nc-MgO. Phonon confinement effects are examined for nc TiO sub 2 , carbon, silicon and Y sub 2 O sub 3 using Raman spectroscopy. To study the influence of crystallite-size effects on physical properties, the control of size and size distribution of the nc-matter is essential, and additionally one should avoid introducing a large extrinsic stress in the sample that are obstacles for revelling the intrinsic structure feature of nc-materials. Recently we have reported an improved microemulsion synthesis method, which meets these requirements. Within this contribution we present the dependence of both structural and dynamical properties on the crystallite size of nc-Y sub 2 O sub 3 . We will show that both studied phenomena, the Raman line shift to lower frequencies and the increase of the lattice constant with decreasing crystallite sizes, can be connected phenomenological, by an intrinsic structural-gradient of interatomic distances to described the revealed finite-size effect.