Preparation and size evaluation of nanometer gadolinium powder
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Preparation and size evaluation of nanometer gadolinium powder Y. Z. Shao Department of Physics, Zhongshan University, Guangzhou 510275, People’s Republic of China
C. H. Shek and J. K. L. Lai Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (Received 11 December 1995; accepted 25 May 1998)
Nanometer-size gadolinium powders (nm-Gd) have been prepared by means of evaporation condensation of Gd atoms within inert gas atmosphere. Microscopic analyses, based on measurements of small angle x-ray scattering (SAXS), x-ray diffraction (XRD), Raman scattering spectrum (RSS), and observation with transmission electron microscope (TEM), have been carried out in order to evaluate the size and size distribution of the as-prepared nm-Gd powder. It turns out that the size distribution function of nm-Gd powder agrees very well with the distribution function of Rayleigh instead of logarithmic distribution. The mean size d of nm-Gd powders bears a linear relationship with the logarithm of the pressure p of the inert gas atmosphere as follows: d a 1 b ? ln p. A discussion concerning the influence of particle size of nm-Gd powder on nanostructured material parameters such as the size distribution, specific surface area, and the percentage of interface atoms have been given in detail.
I. INTRODUCTION
Nanostructured materials are characterized by their remarkable novel properties owing to their small particle or grain sizes which give rise to quantum size effects and tunneling effects and have attracted extensive attention of scientific researchers in recent years.1,2 The rare-earth element gadolinium, Gd, possesses a Curie point at around 290 K and the most obvious magnetocaloric effect (MCE) at room temperature. These features make Gd one of the most eligible materials for investigation of the influences of nanostructures on magnetic critical phenomena near room temperature such as Curie temperature, magnetic entropy, and MCE. Bennet et al.,3 McMichael et al.,4 and Chen et al.5 have made outstanding achievements in these aspects since 1992. On the basis of superparamagnetism, they conducted a series of theoretical calculations on the magnetic entropy change of nanostructured superparamagnet and deduced that nanosized superparamagnetic materials possess enhanced MCE and higher magnetic entropy, which were proved experimentally by Shull6 in nanocomposite GGIG (Gd3 Ga3.25 Fe1.75 O12 ). Since both particle size and its distribution of a nanosized material affect material behaviors evidently, it is worthwhile to evaluate particle size and its distribution precisely. Based upon our recent experimental results from small-angle x-ray scattering (SAXS), x-ray diffraction (XRD), Raman scattering spectrum (RSS), and transmission electron microscope (TEM), we analyzed the particle size and its distribution as well as other structural parameters of nm-Gd powders in this paper. J. Mater. Res., Vol. 13, No. 10, Oct 1998
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