Synthesis and oxidation stability of monosized and monocrystalline Pr nanoparticles
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Frank Einar Kruis Institute for Technology of Nanostructures, University of Duisburg-Essen, 47057 Duisburg, Germany
Vidya Nand Singh Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India (Received 27 August 2008; accepted 27 October 2008)
This study reports the synthesis of monosized Pr nanoparticles with a controllable size ranging from 5 to 20 nm. Pr agglomerates generated by a spark generator, first sizeselected by a differential mobility analyzer and subsequently sintered in-flight at different temperatures result in spherical and monocrystalline Pr nanoparticles. The dependence of size and size distribution of Pr nanoparticles has been studied as a function of deposition parameters related to spark generator, differential mobility analyzer, and sintering. Transmission electron microscopy, energy-dispersive x-ray analysis, glancing angle x-ray diffraction, and x-ray photoelectron spectroscopy studies confirm that initial Pr agglomerates and the resulting nanoparticles are metallic with d-hexagonal structure and remain stable in air during post-deposition exposure. Incomplete or partially sintered nanoparticles were found to be oxidized, resulting in the formation of amorphous oxide phase due to enhanced oxidation at grain boundaries.
I. INTRODUCTION
The distinctive nature of the unpaired 4f and 5d orbital electrons causes rare-earth (RE) metals to possess wideranging physical and chemical properties, such as, large magnetic moments, high electrical conductivities, and high chemical reactivities. These properties enable the RE materials in the form of metals, compounds, and alloys to have applications in various fields, such as, permanent magnets, magnetic refrigeration, high-temperature superconductors, nickel-RE hydride batteries, chemical and temperature sensors, additives, and colorants.1–8 These materials are possible candidates for hydrogen storage batteries (RE-Ni hydrides), which is a promising energy source for the near future. RE metals and their oxides are observed to improve the corrosion and fatigue resistance of steel.9,10 The tendency of these materials to get oxidized in ambient conditions due to their high reduction potential has been a nagging hindrance for their use in the abovementioned applications. Bulk RE metals are normally kept under an inert atmosphere or in mineral oil, and suitable techniques have been used for their safe handling. Experimental investigations of RE materials are normally a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0281
2276
http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 7, Jul 2009 Downloaded: 14 Mar 2015
performed under high vacuum or in inert conditions.11–13 Thin films of RE metals are found to readily react with hydrogen, water, and oxygen.14 Hence, different properties of RE thin films are generally investigated by depositing a protective overlayer of Pd, graphite, or Au.7,15–17 Some efforts have also been made towards synthesizi
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