Figure 2a shows the infrared spectr

Figure 2a shows the infrared spectra of cold sintered bulk composites at different temperatures as well as the raw PEI polymer. The theoretical density of composites (5.2808 g/cm3) were calculated from the volume fractions and theoretical densities of ZnO and PEI by using mixing law22 and the relative density of the bulk ZnO/PEI composites was confirmed 95 % by the Archimedes method. The spectra analysis is verified specifically on infrared bands highlighting intensity changes with the sintering temperature. Infrared bands located at 1720 and 1780 cm-1 are assigned to stretching vibrations of C O bonding in the imide carbonyl group.26,27 The 743 and 1355 cm-1 = infrared bands are assigned to C N bending and stretching vibrations.26 ― For sintering temperatures of 220°C, we may have a carboxyl-induced PEI chain breaking mechanism (Figure 2b). This degradation mechanism was explained by Farong et al28 using mass spectroscopy, and it is here confirmed by the simultaneous and almost total disappearance of infrared bands assigned to imide carbonyl groups (1720 and 1780 cm-1) and infrared bands of the C N bonding (743 and 1355 cm-1 ― ), also illustrated in Figure 2b. According to FTIR results, the sintering temperature of 120℃ would be more appropriate for the fabrication of ZnO-based/polymer MLV device with Cu inner electrodes, without decomposing the PEI polymer that would limit the insulation performance and results of device that sintered at 220 °C can be found at supplementary data of this paper.