Low-temperature route to nanoscale P 3 N 5 hollow spheres
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Yitai Qiana) Structure Research Laboratory and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China (Received 12 May 2003; accepted 7 July 2003)
Nanoscale hollow spheres of amorphous phosphorus nitride (P3N5) were synthesized by reacting PCl3 with NaN3 at 150–250 °C. Transmission electron microscope images show that the hollow spheres have a diameter of 150–350 nm, and the thickness of the shell is 20 nm. A very small amount of curly films were also found in the sample prepared at 150 °C. The infrared spectrum indicates a high degree of purity. X-ray photoelectron spectroscopy indicates the presence of P and N, with a molar ratio of 1:1.62 for P:N. Ultraviolet-visible absorption spectroscopy shows an absorption band at 265–315 nm. Under photoluminescent excitation at 230 nm, the P3N5 emits ultraviolet light at 305 nm. With a band gap of 4.28 eV, the products may be a wide gap semiconductor. A possible mechanism and the influence of temperature on the formation of the hollow spheres are also discussed. I. INTRODUCTION
The discoveries of fullerene and carbon nanotubes as new forms of matter in the nanoscale range have opened a challenging new field in solid-state physics, chemistry, and materials science.1,2 Since then, much attention has been paid to the development of new methods for the preparation and fullerenelike structures of other materials.3,4 Besides crystalline nanotubes and fullerenelike structures, amorphous microtubes of molybdenum polysulfide have been recently reported, which undoubtedly indicate that amorphous materials can also aggregate into tube- and spherelike morphologies.5 As an inorganic polymer, phosphorus nitride (P3N5) has three different stable forms: ␣–, –, and ␥–P3N5.6,7 It has the potential for various ceramic applications (e.g., ionic conductors,8 sintering additives,9 pigments,10 or microporous materials).11 Crystalline P3N5 is built up by a three-dimensional network structure of corner sharing PN4 tetrahedra with two-fifths of the nitrogen atoms bonded to three P atoms and three-fifths of the nitrogen atoms bonded to two P atoms.7 Recently, amorphous phosphorus nitride (P3N5) with flakelike morphology has been synthesized by a solvent-free reaction between PCl5 (0.005 mol) and NaN3 (0.025 mol) in an autoclave at 190–250 °C.12 Herein, we report the synthesis of amorphous nanoscale P3N5 hollow spheres by the reaction of excess PCl3, also used as solvent, with NaN3 in the a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 10, Oct 2003
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temperature range from 150 to 250 °C. In this experiment, not only were different morphologies—large-scale hollow spheres and some curly films—observed in the as-prepared P3N5 product; but also peculiar optical properties—a band gap of 4.28 eV and an emission peak at 305 nm, which are characteristics of wide gap semiconductors—were first found in the amorphous P 3 N 5 material. II.
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