Space group determination and first-principles structure optimization of the A-site ordered perovskite-type manganite NdBaMn2O6

Space groups and crystal structures of A-site ordered NdBaMn2O6 perovskite have been investigated by a combination of selected-area electron diffraction (SAED), convergent-beam electron diffraction (CBED), and first-principles methods at high-temperature (HT approximate to 450 K), room-temperature (RT approximate to 293 K), and low-temperature (LT approximate to 95 K) phases. By symmetry analysis of the CBED patterns, space groups of NdBaMn2O6 at HT, RT, and LT phases have been determined to be P4/mmm (No. 123), C2mm (No. 38), and P2(1)am (No. 26), respectively. The space groups and the optimized structures using first-principle calculations at the HT and RT phases allow a single crystallographic site for Mn atoms, indicating no charge ordering state. At the LT phase, the observed SAED and CBED patterns revealed the existence of fourfold periodicity along the c axis compared with the pseudocubic unit cell. The optimized structure of the LT phase suggested four inequivalent Mn sites classified into two crystallographically different MnO2 layers. Moreover, the structure showed that the four distinct MnO6 octahedra are similarly compressed in the apical direction.

Automated summary

The space groups and crystal structures of A-site ordered NdBaMn2O6 perovskite were investigated at different temperatures, revealing different space groups and crystal structures. The low-temperature phase exhibited a fourfold periodicity.