The negative temperature coefficient resistivities of Ag2Ssingle bondAg 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 Ag2Ssingle bondAg core–shell structures. The mechanism for the formation of the Ag2Ssingle bondAg 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 Ag2Ssingle bondAg 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 Ag2Ssingle bondAg films display an exponentially decreased resistivity with increasing temperature from 25 to 170 °C. The negative temperature coefficient resistivity of Ag2Ssingle bondAg 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.