Enhanced giant dielectric response in Al-substituted La 1.75Sr 0.25NiO 4 ceramics

Abstract

The structures and dielectric properties of La 1.75Sr 0.25Ni 1− x Al x O 4 ( x = 0, 0.3) ceramics were presented. A single tetragonal phase was found in La 1.75Sr 0.25NiO 4 ceramics, while minor secondary phases were presented in La 1.75Sr 0.25Ni 0.7Al 0.3O 4 ceramics. Giant dielectric response was found in these ceramics. The dielectric constant was enhanced while the dielectric loss was suppressed by partially substituting nickel with aluminum ions. After comparing the activation energies of dielectric relaxation and electrical resistivity, we concluded that the overlapped low frequency dielectric relaxation was attributed to grain boundaries, while the normal low-temperature relaxation was mainly attributed to the bulk factor, that was, thermally activated small polaronic hopping in La 1.75Sr 0.25NiO 4 ceramics. For La 1.75Sr 0.25Ni 0.7Al 0.3O 4 ceramics, the low-temperature dielectric relaxation was also mainly attributed to the bulk factor. The enhanced dielectric response should be benefited from the strengthened grain boundary layer capacitor effect in La 1.75Sr 0.25Ni 0.7Al 0.3O 4 ceramics.