Systematic study of ionic conduction in silver iodide/mesoporous alumina composites 2: effects of silver bromide doping.

In our preceding paper (Y. Fukui et al. , Phys. Chem. Chem. Phys. , 2023, 25 , 25594-25602), we reported a systematic study of the Ag + -ion conducting behaviour of silver iodide (AgI)-loaded mesoporous aluminas (MPAs) with different pore diameters and AgI-loading ratios. By optimising the control parameters, the Ag + -ion conductivity has reached 7.2 × 10 -4 S cm -1 at room temperature, which is more than three orders of magnitude higher than that of bulk AgI. In the present study, the effect of silver bromide (AgBr)-doping in the AgI/MPA composites on Ag + -ion conductivity is systematically investigated for the first time, using variable-temperature powder X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy measurements. The AgBr-doped AgI/MPA composites, AgI-AgBr/MPA, formed a homogeneous β/γ-AgI-structured solid solution (β/γ-AgI ss ) for the composites with AgBr ≤ 10 mol%, above which the composites underwent a phase separation into β/γ-AgI ss and face-centred cubic AgBr solid solutions (AgBr ss ). The onset temperature of the exothermic peaks attributed to the transition from α-AgI-structured solid-solution phase to β/γ-AgI ss or AgBr ss decreased with increasing the AgBr-doping ratio. The room-temperature ionic conductivity of the AgI-AgBr/MPA composites exhibited a volcano-type dependence on the AgBr-doping ratio with the highest value (1.6 × 10 -3 S cm -1 ) when the AgBr content was 10 mol%. This value is more than twice as high as that of the highest conducting AgI/MPA found in our previous study.