The negative temperature coefficient resistivities of Ag2S-Ag core shell structures

In this paper, the conductivity of silver nanoparticle films protected by 3-mercaptopropionic acid (Ag/MPA) has been investigated. When the nanoparticles were annealed in air at 200 degrees C, they converted to stable Ag2S-Ag core-shell structures. The mechanism for the formation of the Ag2S-Ag core-shell structures along with the compositional changes and the microstructural evolution of the Ag/MPA nanoparticles during the annealing process are discussed. It is proposed that the Ag2S-Ag core-shell structure was formed through a solid-state reduction reaction, in which the Ag+ ions coming from Ag2S were reduced by sulfonate species and sulfur ions. The final Ag2S-Ag films display an exponentially decreased resistivity with increasing temperature from 25 to 170 degrees C. The negative temperature coefficient resistivity of Ag2S-Ag films can be adjusted by changing the S/Ag molar ratio used for the synthesis of the Ag/MPA nanoparticles, paving the way for the preparation of negative temperature-coefficient thermistors via printing technology for use in the electronics. (C) 2013 Elsevier B.V. All rights reserved.