Revealing Rutherfordine Mineral as an Auxetic Material

Abstract

The mechanical behavior of the uranyl carbonate mineral, rutherfordine, UO2CO3, was studied by means of theoretical solid-state methods based in Density Functional Theory using plane waves and pseudopotentials. The results of the computations reported in this work show that this mineral exhibits the important negative Poisson ratio (NPR) phenomenon. In order to show that this feature is not an artifact associated to the theoretical treatment employed, additional calculations were carried out using very large calculation parameters. These calculations improved the mechanical description of this mineral and confirmed its auxeticity, i.e., it shows NPR values. Rutherfordine is a highly anisotropic material showing a maximum value of the NPR of the order of −0.3 ± 0.1 for applied stresses directed along the X axis, the transverse direction being the Y axis perpendicular to the structural sheets in rutherfordine structure. The underlying reason for this observation is that under the effect of applied positive pressures, the interlayer space between the sheets of rutherfordine vary in the opposite way to the expected behavior; that is, it decreases instead of increasing.

Silver Oxalate: Mechanical Properties and Extreme Negative Mechanical Phenomena

“…Therefore, the dependence of the mechanical properties of Ag 2 C 2 O 4 as functions of the direction of the applied strain was computed. As may be noticed in Figure 3E and Table S6 The results obtained in previous works [1][2][3][4][5][6] show that the presence of large negative Poisson's ratios is frequently accompanied by the presence of the important negative linear compressibility phenomenon. As may be noticed in Figure 3E and Table S6 The results obtained in previous works [1][2][3][4][5][6] show that the presence of large negative Poisson's ratios is frequently accompanied by the presence of the important negative linear compressibility phenomenon.…”

“…[19] Synthetic and design approaches have been devised to obtain materials displaying specific mechanical properties. The main motivation of this study and the previous ones, [1][2][3][4][5][6] was to investigate the presence of negative mechanical phenomena in organic materials because these effects have rarely been studied in this kind of compounds, revealing a significant gap in their study. For this reason, the search for NLC materials has lost to some extent its initial impetus in recent years.…”

“…[77] The calculated elasticity matrix, C i j , is reported in Table S5, Supporting Information. As in previous studies, [1,2,5,6,[83][84][85][86] the Reuss approximation was chosen as the best approach in the case of silver oxalate because it provided the best comparison of the results for the calculated bulk modulus, B = 9.64 ± 2.51 GPa, with that determined from the EOS. For monoclinic crystals, the generic necessary and sufficient Born criterion is that all eigenvalues of the C matrix be positive.…”

“…The compressibility is a mechanical property which measures the relative volume change of a material as a response to a pressure change. Negative linear compressibility (NLC) is not related to unstable materials and may refer [1][2][3][4][5][6]19] to: a) Anisotropic negative linear compressibility (ANLC): the positive variation of the volume when the material is submitted to a uniform compression directed along a given direction; and b) Isotropic negative linear compressibility (INLC): the increase of one or two single directions of the unit cell of a material under the application of an isotropic pressure. [1,11,19,93,94] Counterexamples to the general statement of positivity of the compressibility have been found for constrained systems.…”

“…The absolute value of the computed lowest NLC is extremely large, about three times larger than the absolute value of the lowest NLC found so far. The NLC pressure range is also very wide, its width being more than two times the largest range found to date.The mechanical properties of some small organic acids and metal-organic materials in the solid-state were obtained in previous works [1][2][3][4][5][6] using theoretical solid-state methods based in Density Functional Theory (DFT) using plane waves and pseudopotentials. High-quality computational setups, comprising large plane wave basis sets and dense k-point meshes, were employed in order to obtain realistic descriptions of their mechanical behavior.…”