Giant dielectric constant in Nd2NiO4+δ ceramics obtained by spark plasma sintering

The crystal structure and dielectric properties of Nd2NiO4+δ ceramics prepared by spark plasma sintering (SPS) process were characterized. The crystal structure belonged to orthorhombic system with a space group of F mmm, and the excess oxygen content, δ, was about 0.192. Temperature-stable giant dielectric constants (ɛ′ ∼ 105) up to high frequency (5 MHz) over a wide temperature range (200–500 K) were observed in the present ceramics. After comparing the activation energies of dielectric relaxation and electrical conduction, we found the giant dielectric response should be mainly attributed to the adiabatic small polaronic hopping process, while the polaronic hopping process was closely related to the charge ordering in the present ceramics.