Zero compression is a rare mechanical phenomenon that can exhibit stability in one or more axial dimensions under hydrostatic pressure. Compared with one-dimensional zero compression materials, two-dimensional zero compression (i.e. zero plane compression) materials not only have higher dimensional mechanical stability, but can also be applied in signal transmission dependent on flux area.
The microstructure model of zero plane compressed materials is very complex, and the coupling torsion of structural elements in the lattice under pressure is directly projected onto a plane. The zero compressibility in two directions is usually entangled with each other, making it extremely difficult to control. Inspired by the fact that the bidirectional cross ripple (BDCC) structure of the orthogonal braiding model in composites can achieve high mechanical strength, the research team of the Institute of Physical and Chemical Technology of the Chinese Academy of Sciences proposed to achieve zero plane compressibility by constructing an atomic scale BDCC structure. Researchers first construct corrugated structures to achieve zero compressibility in one dimension, and then arrange these banded corrugated structures in a bi-directional cross (i.e. orthogonal weaving) arrangement. Through separate control of mechanical properties in both directions, zero plane compressibility is ultimately achieved. This study utilized this structural control design strategy to conduct large-scale structural searches in crystal databases, and discovered the unique BDCC structure of the zero plane compressed copper based compound Cu2GeO4 through high-pressure synchrotron radiation experiments. The zero plane compressibility of Cu2GeO4 is as low as 1.58 (26) TPa-1, and it has excellent compressive strength, with the widest pressure range among the discovered zero plane compression materials. High pressure Raman testing combined with first principles calculations reveals that the zero plane compressibility of Cu2GeO4 comes from a clever balance between the normal contraction effect of the [CuO4] group in the [CuO2] ∞ band under pressure and the anomalous expansion effect of the opening of the [CuO4] - [CuO4] dihedral angle. In Cu2+ions, under pressure, electrons transfer from dx2-y2 bonded orbitals to non bonded dz2 orbitals, enhancing the repulsive force between adjacent [CuO4] groups and driving the anomalous expansion effect of [CuO4] - [CuO4] dihedral angle opening.
The structural design strategy proposed in this work, which utilizes the BDCC structure to regulate the one-dimensional direction separately before multi-dimensional composite, provides a new and convenient approach for the structural design of anomalous mechanical responsive materials and the exploration of new materials. The research found that Cu2GeO4 is a rare zero plane compression material, which is expected to provide a basic functional material for precision information transmission, signal detection stability, and sensitivity improvement in extreme and complex environments such as deep sea and deep earth.
The relevant research results were published in the Journal of Applied Chemistry in Germany, titled Realizing Persistent Zero Area Compressibility over a Wide Pressure Range in Cu2GeO4 by Microscopic Orthodox Drawing Strategy. The research work is supported by the National Natural Science Foundation of China.
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