Effect of Ni non-stoichiometry on the structural, thermal and conductivity properties of Nd2Ni1-xO4+δ

Neodymium nickelates Nd2Ni1-xO4+delta with Ni non-stoichiometry, varied in a wide x range of 0.0-0.08, are synthesized for the first time, and their properties are studied depending on the Ni content. The limit of Ni deficiency is found to reach 6%. According to the XRD data, the materials of the Nd2Ni1-O-x(4+delta) series are single-phase in the range of x from 0.0 to 0.06 and exhibit an orthorhombic structure with a Fmmm space group. Results of the TGA-DSC studies shows that the temperature of the Fmmm - I4/mmm phase transition changes insignif-icantly (up to similar to 5 degrees C), thus does not depend on Ni non-stoichiometry. The Raman scattering studies reveal that at low Ni deficiency the Raman spectra are typical for the Ni-stoichimetric oxidized (delta approximate to 0.2) Nd2NiO4+(delta). While at the limiting value of x equal to 0.06, the lattice disorder and [NiO6] octahedral distortions reach a maximum feasibility with Ni-O1 vibrations getting involved into Raman scattering. The highest total conductivity (101 S/ cm at the maximum) is observed for the sample with x = 0.02, which shows a more pronounced second-order overtone at 800-930 cm(-1) in Raman scattering. This material can be recommended for further studies and possible electrochemical applications as the most prospective in the series due to its superior electrical properties.