Introducing a ZnO–PTFE (Polymer) Nanocomposite Varistor via the Cold Sintering Process

A ZnO–PTFE nanocomposite is formed from a cold sintering process with volume fractions of PTFE up to 40 vol%. The polymer is distributed along grain boundaries and used to limit current from across adjacent grains, enabling this varistor response, with α ≈ 7 being observed. The nanocomposite structure is verified to have polymer intergranular phase in a thickness range from 2 to 5 nm. The electrical characteristics are made to show nonlinear I–V behavior; the barrier-layer effective permittivity is established through an impedance spectroscopy analysis. The activation energies controlling resistance at the grain boundary is determined to range between 0.2 and 0.76 eV with volume fractions between 0 and 40 vol% PTFE. Under high fields and across a broad temperature ranges, the authors quantified of the non-linear conductions with a variety of voltages, the low field higher temperatures are consistent with a Schottky thermionic emission controlled conduction, and Fowler–Nordheim plots shows the current is transitioned to tunneling controlled. The authors also discuss the possibility of designing new types of nanocomposites with the process indicated here, and also having the possibility of taking advantage of interfacial size effects with thin polymer films between ceramic grains.