Crossover between variable range hopping and small polaron hopping mechanisms in Pr2NiTiO6

The crossover between two conduction mechanisms for polycrystalline Pr2NiTiO6 (PNT) is probed using a combination of conductivity and impedance spectroscopic techniques. X-ray diffraction (XRD) in conjunction with Raman spectroscopic investigations establish a distorted monoclinic P21/n symmetry for PNT. The splitting of the vibrational modes authenticates the distortions present in the octahedral environment around the B-site. The Ag mode manifests itself as a breathing vibration of the TiO6 octahedra. The scanning electron micrograph (SEM) establishes a high density in the sample. The conductivity spectra highlight the contribution of electrodes, grain-boundaries, and grains to the conduction mechanism. With the decrease in temperature, the dc resistivity observations point towards a transition from small polaron hopping (SPH) to Mott s variable range hopping (VRH) around 490 K, showing that the hopping range below 490 K is larger than the distance between neighboring equivalent sites owing to the lower activation energy. The impedance spectra modeled by the constant phase element (CPE) formalism complement the findings of the conductivity investigations. The dielectric relaxation mechanism indicates a deviation from the ideal Debye model.