Most conducting materials in bulk exhibit a three dimensional (3D) isotropic electrical conductivity and electrons can flow freely along any of their crystallographic directions. How to build the highway of electrons in bulk conductors to guide them moving along a designed direction is a subject of fundamental physical interest and is important to develop advanced electronic devices.

Due to their quasi-one-dimensional (1D) metallic conductivity, the perovskite-related Sr_nNb_nO_3n+2 compounds provide people an opportunity to unveil the physical origin for the preferential pathway of electrons.

In a study published in ACS Nano, Prof. CHEN Chunlin and Prof. MA Xiuliang at Institute of Metal Research of Chinese Academy of Sciences, Prof. Johannes Georg Bednorz at Zürich Research Laboratory, Prof. Yuichi Ikuhara at The University of Tokyo and other international researchers, unambiguously determined the atomic and electronic structures of the Sr_nNb_nO_3n+2 compounds and revealed the underlying mechanism for their quasi-1D metallic conductivity.

Researchers systematically investigated the atomic and electronic structures of the Sr_nNb_nO_3n+2 compounds by combining advanced transmission electron microscopy with first-principles calculations.

It was shown that the zigzag-like slabs in perovskite-related  Sr_nNb_nO_3n+2 compounds as well as the chain-like slabs in SrNbO_3.5 are electrically insulating. This is because the NbO₆ octahedra in these slabs are significantly distorted with a large displacement of Nb from the octahedral centers and the Nb valence is Nb⁵⁺. Besides, the chain-like slabs in SrNbO_3.4 and SrNbO_3.45 are conducting since their Nb valence/electron configuration is Nb^(5-w)+/4dw with w > 0. The nearly undistorted NbO₆ octahedra lead to a metallic conductivity along the a-axis.

Researchers also found that the Sr_nNb_nO_3n+2 quasi-1D conductors can be derived by intercalating the insulating zigzag-like slabs into the 3D conducting SrNbO₃perovskite along {110} planes.

It was demonstrated that the electrical properties of the strontium niobates depend directly on the configuration of their NbO₆ octahedra, giving rise to a transition from 3D conductivity to 2D conductivity.

This study may boost the applications of 2D electrical conducting materials and devices.