Growth of nanocrystalline PbS within a glass
- PDF / 237,333 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 117 Downloads / 189 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Growth of nanocrystalline PbS within a glass M. Mukherjee, A. Datta, and D. Chakravortya) Indian Association for the Cultivation of Science, Jadavpur, Calcutta, 700 032, India (Received 20 July 1995; accepted 12 March 1997)
Nanocrystalline PbS has been grown within a phase-separated oxide glass of composition 10 Na2 O, 15 PbO, 17 CaO, 3 Bi2 O3 , and 55 SiO2 (in mole %) by passing H2 S gas over it at temperatures varying from 773 to 943 K. The particle size ranged from 2.5 to 12.9 nm. The dc resistivity of composites of nanocrystalline PbS and the phase separated glass has been measured over the temperature range 300 to 670 K. The resistivity variation in the temperature range 550 to 670 K is characterized by the sodium ion migration in the glass with an activation energy ,1.2 eV. The resistivity in the range 300 to 500 K was controlled by conduction in PbS particles with the estimated band gap showing an increase with a decrease in the particle size.
Nanocrystalline materials are receiving increasing attention because of several novel physical properties exhibited by them.1 Glass-crystal interfaces have been utilized earlier to grow nanosized metal particles forming continuous chains within a glass ceramic.2 Recently we have reported on the synthesis of nanocrystalline semiconducting particles of PbS within a polyacrylamide medium.3 We have now been able to prepare nanosized PbS particles within a phase-separated oxide glass. From the measured electrical properties of the percolative chains of the semiconducting nanoparticles, it is evident that the effective band gap as determined from the temperature variation of resistivity is different in these materials from that of their bulk counterpart. The details are reported in this paper. The glass used in the present work had the composition 10 Na2 O, 15 PbO, 17 CaO, 3 Bi2 O3 , and 55 SiO2 (in mole %). A mixture of the weighed amounts of the different components was taken in an alumina crucible and melted in an electrically heated furnace at a temperature of 1573 K for 1 h. The glass melt was then poured onto a copper block and pressed by another block to quench it. The differential thermal analysis (DTA) of the glass sample carried out in a Shimadzu DT-40 analyzer showed a glass transition temperature of around 923 K. Glass samples of approximate dimension 10 mm 3 5 mm 3 1 mm were heat-treated at 973 K for 5 h and then quenched. H2 S gas was passed over the
heat-treated samples at temperatures varying from 773 to 943 K for periods ranging from 30 min to 1 h. X-ray diffraction studies on the heat-treated glass samples were carried out using a Phillips PW 1051 diffractometer using Cu Ka radiation to detect the presence or otherwise of any crystalline phases. The microstructures of different samples were studied by a JEM 200CX transmission electron microscope. The depth from the surface of the glass samples up to the point nanocrystalline PbS was concentrated was determined from the scanning electron micrographs taken in a
Data Loading...
