The effect of the nanodiamonds additive on ionic conductivity of silver iodide

Composite solid electrolytes AgI-C_ND (C_ND is nanodiamonds powder) were prepared and their properties were investigated by methods of X-ray diffraction, differential scanning calorimetry (DSC) and impedance spectroscopy. It was found that the addition of C_ND results in a strong increase in the ionic conductivity of AgI at temperatures below phase transition to the α-AgI phase. According to the results of DSC, no strong changes in thermodynamic properties of the salt in the composites occur. Therefore, in contrast to the AgI-oxide composites, the most probable reason of the conductivity increase in AgI-C_ND composites is formation of stable network of intergrains and anti-phase domain boundaries acting as conductivity pathways in the composites. Due to the particle-reinforcement effect on nanodiamond particles the AgI matrix in the composites may undergo strong local stresses leading to the stabilization of the polytypes. The peaks of such phases are detected in X-ray diffractograms of the composites. The maximum conductivity of AgI-C_ND composites, 5.6·10^-4 S/cm at 31 °C observed in the composites containing 80 mol % C_ND, is comparable to the best values obtained for oxide-based composites with silver iodide. Thus, nanodiamonds is the first non-oxide additive which caused a strong enhancement of the ionic conductivity of AgI low temperatures.