Realizing Persistent Zero Area Compressibility over a Wide Pressure Range in Cu2GeO4 by Microscopic Orthogonal‐Braiding Strategy

Abstract

AbstractZero area compressibility (ZAC) is an extremely rare mechanical response that exhibits an invariant two‐dimensional size under hydrostatic pressure. All known ZAC materials are constructed from units in two dimensions as a whole. Here, we propose another strategy to obtain the ZAC by microscopically orthogonal‐braiding one‐dimensional zero compressibility strips. Accordingly, ZAC is identified in a copper‐based compound with a planar [CuO4] unit, Cu2GeO4, that possesses an area compressibility as low as 1.58(26) TPa−1 over a wide pressure range from ≈0 GPa to 21.22 GPa. Based on our structural analysis, the subtle counterbalance between the shrinkage of [CuO4] and the expansion effect from the increase in the [CuO4]‐[CuO4] dihedral angle attributes to the ZAC response. High‐pressure Raman spectroscopy, in combination with first‐principles calculations, shows that the electron transfer from in‐plane bonding dx2‐y2 to out‐of‐plane nonbonding dz2 orbitals within copper atoms causes the counterintuitive extension of the [CuO4]‐[CuO4] dihedral angle under pressure. Our study provides an understanding on the pressure‐induced structural evolution of copper‐based oxides at an electronic level and facilitates a new avenue for the exploration of high‐dimensional anomalous mechanical materials.