Influence of A-site deficiency on structural evolution of Pr2-xNiO4+δ with temperature

We report on the structural evolution with temperature of layered A-site deficient Pr2-xNiO4+δ (x = 0–0.2) with the K2NiF4 structure. Data of neutron diffraction and thermogravimetric analysis reveals that Pr deficiency causes generation of lattice oxygen vacancies on equatorial and apical sites but does not influence the concentration of interstitial oxygen. High-temperature X-ray diffraction shows for all materials a reversible orthorhombic-to-tetragonal phase transition with negligible hysteresis in the range ~400–450 °C, reducing tilting and twisting of the NiO6 octahedra. The phase transition temperature is found to decrease slightly with increasing A-site deficiency. Thermal decomposition to Pr4-zNi3O10-y and Pr6O11 is found to occur in the temperature range 580–800 °C with apparent activation energy 166–221 kJ/mol.