An insight into microstructure and structure stability of Ni-doped Bi2212 ceramics

Abstract

A series of Bi2Sr2-xNixCaCu2O8+δ (x = 0.00, 0.10, 0.20 and 0.30) ceramics samples were synthesized by Pechini sol-gel method. In this work, the microstructure and structure stability of Ni-doped Bi2212 system were investigated particularly by X-ray diffraction, electron microscopy and high-pressure Raman spectroscopy. It is confirmed that the main phase of all samples is the typical Bi2212 tetragonal phase with space group I4/mmm. As Ni-doping amount x ≤ 0.20, the number of Ni atoms entering the Bi2212 lattice increases gradually with increasing x. These Ni atoms preferentially occupy Sr-sites, resulting in a gradual increase in the a and c axis lengths of Bi2212 structure. The formation of containing-Ni Bi2212 lattice is mainly derived from the insertion of sufficient Ni–O two-dimensional (2D) monomers. Contrarily, when x > 0.20, these Ni–O 2D monomers will preferentially form the NiO particle and the chance of Ni atoms entering the Bi2212 lattice is reduced, which leads to a shrinkage of Bi2212 lattice parameters. Besides, under high-pressure (0–20 GPa) condition, Raman spectrum analysis shows that the OSr peak significantly shifts to the higher wavenumber and Bi2212 phase could still maintain the tetragonal structure, suggesting that it has a relatively high structure stability.