Synchrotron based x-ray absorption spectroscopy investigation and temperature dependent ferroelectric properties of Ni doped BaTiO3 nanostructures

Abstract

In this report, the local structure geometry of BaTi1-xNixO3 (0.0 ≤ x ≤ 0.06) ceramics has been studied through synchrotron based x-ray-absorption spectroscopy, measured at the Ti K, Ba L3 and Ni K-edges at room temperature. The x-ray absorption near edge spectroscopy (XANES) at Ti K-edge confirms the TiO6 octahedron geometry of Ti atom due hybridization between Ti(3d)-O(2p) orbitals and signifies the non-centrosymmetric nature of BaTiO3 samples. However, Ti–O off-center displacement (non-centrosymmetric) is disturbed under the effect of Ni doping as a result of oxygen vacancies formation. More interestingly, XANES studies at Ni K-edge ensure successful substitution of Ni in BaTiO3 as Ni2+ ions. Extended x-ray absorption fine structure (EXAFS) data at Ni K-edge have been fitted to estimate pertinent local structural parameters of the Ni–O, Ni–Ba, Ni–Ti and Ni–Ni shells (viz. bond lengths and disorder parameters) and it also reveal that the structural disorders around the Ti sites in the doped BaTiO3 expand with Ni doping. The mixed-valence states of titanium ion, i.e., Ti4+ and Ti3+ in the doped samples were established with the x-ray photoelectron spectroscopy (XPS). Moreover, XPS divulges the creation of oxygen vacancies due to Ni doping in BaTiO3 matrix. The complementary information about the lattice vibration is analyzed through Raman studies that approve the softening of the transverse optical (TO) mode present at 515 cm−1. The temperature dependent ferroelectric studies affirm that the ferroelectricity vanishes in the doped samples due to the decrement in the off-center displacement between the Ti4+ and O2− ions in the TiO6 octahedral geometry. Differential thermal analysis (DTA) exhibits a ferroelectric tetragonal to para-electric cubic phase transition in the pristine as well as Ni doped BaTiO3 samples.