Crystal structure of Nd2NiO4.08

A neodymium nickel oxide of Nd2NiO4.08 has a very small orthorhombic strain at room temperature, 2(b − a) / (b + a) = 0.0014. An orthorhombic Pccn structure model of Nd2NiO4.08 is proposed for explaining the reason for the existence of the very small orthorhombic strain of Nd2NiO4.08. The orthorhombic Pccn structure model is drawn from the Fmmm structure model and the tetragonal P42/ncm structure model. Results of the Rietveld analyses using the Fmmm, the P42/ncm, and the Pccn structure models are compared. The Fmmm structure model can explain the reason for the existence of orthorhombic strain but cannot explain the presence of the forbidden reflections of the face-centered lattice in the X-ray powder diffraction pattern. On the contrary, the P42/ncm structure model can explain the presence of the forbidden reflections of the face-centered lattice in the diffraction pattern but cannot explain the presence of orthorhombic strain. The Pccn structure model can explain both the presence of the forbidden reflections of the face-centered lattice in the diffraction pattern and the presence of orthorhombic strain.