The negative temperature coefficient resistivities of Ag2SAg 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 °C, they converted to stable Ag2SAg core-shell structures. The mechanism for the formation of the Ag2SAg 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 Ag2SAg 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 Ag2SAg films display an exponentially decreased resistivity with increasing temperature from 25 to 170 °C. The negative temperature coefficient resistivity of Ag2SAg 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.