Negative area compressibility in oxalic acid dihydrate

Abstract

The main purpose of this communication is to show that the oxalic acid dihydrate exhibits the important phenomenon of negative area compressibility (NAC) when submitted to negative isotropic pressures. The a and c lattice parameters of the oxalic acid dihydrate increase under the effect of increasing external pressures within the ranges from −1.17 GPa to −0.12 GPa and from −1.17 GPa to −0.51 GPa, respectively. The largest magnitude of the compressibility along a direction is found at P = −0.83 GPa (ka = −166.21 TPa−1). The magnitude of the negative compressibility along the a crystallographic direction in the oxalic acid dihydrate is one the largest found up to date.