Design and synthesis of three-dimensional hybrid Ruddlesden-Popper nickelate single crystals

Advancement of technologies relies on discovery of new materials with emerging physical properties that are determined by their crystal structures.2][3][4][5][6] In R-P phases, intergrowth is well-known in the short range; 7-9 however, no existing compounds have been reported to have different n mixed in bulk single crystals.Here we design a hybrid R-P nickelate La2NiO4•La3Ni2O7 by alternatively stacking bilayers, which is the active structural motif in the newly discovery high-Tc superconductor La3Ni2O7 and single layers of the antiferromagnetic insulator La2NiO4.We report the successful synthesis of La2NiO4•La3Ni2O7 single crystals, and X-ray diffraction and real-space imaging vis STEM show that the crystal structure consists of single layers and bilayers of NiO6 octahedral stacking alternatively perpendicular to the ab plane, characterized by the orthorhombic Immm (No.71) space group.Resistivity measurements indicate a peculiar insulator-to-metal transition around 140 K on cooling.Correlated density functional theory (DFT+U) calculations corroborate this finding, and reveal that the single layer becomes paramagnetic metallic due to charge transfer via LaO layers.The discovery of La2NiO4•La3Ni2O7 opens a door to access a completely new family of 3D hybrid R-P phases with the formula of An+1BnX3n+1•A'm+1B'mX'3m+1 (n≠m), which potentially host a plethora of emerging physical properties