Synthesis and structural properties of n = 1 Ruddlesden–Popper manganites Nd1−xCa1+xMnO4

Polycrystalline samples of n = 1 Ruddlesden–Popper manganites Nd1−xCa1+xMnO4 (0.55 ≦ x ≦ 1.00) were synthesized by a solid-state reaction. X-ray diffraction (XRD) and electron diffraction (ED) measurements confirmed that the fundamental crystal structure at room temperature consists of three distorted K2NiF4-types: orthorhombic Bmab (64) phase in 0.55 ≦ x < 0.73, orthorhombic Acam (64) phase in 0.73 ≦ x < 0.85 and tetragonal I41/acd (142) phase in 0.85 ≦ x ≦ 1.00. Furthermore, in a whole range of 0.55 ≦ x ≦ 0.75, low-temperature magnetic and ED measurements revealed charge-orbital ordering (COO) states, which are accompanied by suppression of magnetization and structural modulations with q = (1 − x)a*. The COO transition temperatures are high with a maximum of ∼330 K at x = 0.67, and then higher than those in non-distorted n = 1 Ruddlesden–Popper manganites. The observations suggest that COO states are much stabilized by the distortion in the fundamental structures.