Phase transition at ambient pressure in complex oxide Sr3ScCoO6+δ. Morphotropic row Sr3ScMO7-δ (M = Ni–Cr)

Highlights: • It was found that Sr₃ScMO_7-δ (M=Ni–Cr) is a morphotropic series. • The only compound Sr₃ScCoO_6+δ exists in two modifications. • The unique 1D.→2D phase transition at 1296–1433 (K) was detected in Sr₃ScCoO_7-δ at ambient pressure. • The 2D-structure of Sr₃ScCoO_6+δ has a significantly larger magnetization compared to 1D-one. • Stability criteria for 1D and 2D structures in the Sr₃ScMO_6+δ (M=Ni–Cr) series were established. A phase transition from a quasi-one-dimensional hexagonal structure (1D) to a two-dimensional layered structure (2D) of the second homolog of the Ruddlesden-Popper series was detected in the Sr₃ScCoO_6+δ complex oxide. The transition is unique since it occurs when the temperature increases without the use of high pressures and changes in the oxygen partial pressure. Using high-temperature X-ray diffraction and differential scanning calorimetry in situ, a transition temperature range 1296K–1433K was established. It is shown that in the quasi-one-dimensional phase the scandium and cobalt cations are ordered by prismatic and octahedral positions, while in the two-dimensional perovskite-like oxide they are statistically distributed by octahedral positions. Sr₃ScCoO_6+δ is the only compound in the Sr₃ScMO_7-δ (M=Ni - Cr) morphotropic series, which exists in two structural types. The 1D → 2D transformation is associated with the ability of cobalt to be in various combinations of oxidation states and spin states. The temperature dependence of the magnetic susceptibility of oxides of both types of structure in the Sr₃ScMO_7-δ (M=Ni - Cr) series is paramagnetic due to magnetic dilution with Sc ion. The tetragonal modification of Sr₃ScCoO_6+δ has a significantly larger magnetic moment compared to the hexagonal one.