STRUCTURAL CHARACTERIZATION OF NANOCRYSTALLINE SNO2 BY X-RAY AND RAMAN-SPECTROSCOPY

Tin dioxide nanocrystalline powders were prepared by precipitation of alpha-stannic acid followed by various thermal and chemical treatments , An original preparation via a colloidal solution step led to particl es having a particular two-dimensional microstructure, The size of the crystallites was found to increase from 2 nm for as-prepared samples to 30 nm for samples annealed for 3.5 hr at 920 degrees C, The compoun ds were characterized by X-ray diffraction, scanning electron microsco py (SEM), and infrared and micro-Raman spectroscopy, As reported in th e literature, the Raman spectral signature was found to change drastic ally with the size of the particles, A new spectral feature centered a t about 500 cm(-1) was found for compounds prepared via the colloidal step and having typical sizes smaller than 4.5 nm, The powder Raman sp ectra are interpreted in terms of volume modes and surface modes, Thei r frequency evolution with crystallite size is discussed in terms of t ensile surface stresses, (C) 1998 Academic Press.