Enhanced giant dielectric response in Al-substituted La1.75Sr0.25NiO4 ceramics

The structures and dielectric properties of La1.75Sr0.25Ni1−xAlxO4 (x = 0, 0.3) ceramics were presented. A single tetragonal phase was found in La1.75Sr0.25NiO4 ceramics, while minor secondary phases were presented in La1.75Sr0.25Ni0.7Al0.3O4 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 La1.75Sr0.25NiO4 ceramics. For La1.75Sr0.25Ni0.7Al0.3O4 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 La1.75Sr0.25Ni0.7Al0.3O4 ceramics.

Research highlights▶ Giant dielectric response should be attributed to small polaronic hopping process. ▶ Dielectric constant was enhanced by partially substituting nickel with aluminum ions. ▶ Enhanced dielectric response should be benefited from the strengthened GBLC effect.