Negative temperature coefficient of resistivity in bulk nanostructured Ag

The change of the temperature coefficient of resistivity (cr) with the part icle size, d(p), and the grain size, d(c), in the nanostructured Ag bulk sa mples was investigated. d(p) and d(c) were controlled by heating the nano-A g powders over the temperature range from 393 to 453 K. The electrical resi stance measurements of the nanostructured Ag bulk samples obtained by compa cting the Ag powders after heat treatments showed a change in the sign of a lpha with d(p) and d(c). When d(p) and d(c) are smaller or equal to 18 and 11 nm below room temperature or 20 and 12 nm above room temperature, respec tively, the sign of the temperature coefficient of resistivity changes from positive to negative. The negative alpha arises mainly from the high resis tivity induced by the particle interfaces with very lowly ordered or even d isordered structure, a large volume fraction of interfaces and impurities e xisting in the interfaces, and the quantum size effect appearing in the nan o-Ag grains.