Extreme negative mechanical phenomena in the zinc and cadmium anhydrous metal oxalates and lead oxalate dihydrate

Abstract

The crystal structures and elastic properties of the anhydrous zinc and cadmium oxalates and lead oxalate dihydrate are determined using rigorous first-principles solid-state methods. The three materials are shown to display negative Poisson's ratios (NPR) and to exhibit the negative linear compressibility (NLC) phenomenon. Anhydrous zinc and cadmium oxalates display NLC for a very wide range of external pressures applied in the direction of minimum compressibility in the ranges −1.3 to 5.5 GPa and −1.2 to 2.7 GPa, respectively. The increase of volume in both materials is substantial for pressures larger than 3.6 and 1.8 GPa and the compressibilities become −70.1 and −67.0 TPa −1 for pressures of 5.2 and 2.6 GPa, respectively. The increase of volume is so drastic that these materials become unstable for pressures larger than 5.5 and 2.7 GPa. Lead oxalate dihydrate also displays NLC along the direction of minimum Poisson's ratio for negative pressures in the range −0.05 to −0.08 GPa and undergoes a pressure induced phase transition for relatively low external pressures of the order of 0.1 GPa. The presence of NPR and NLC phenomena in these three materials together with the previous finding of these phenomena for silver oxalate, strongly suggest that other metal oxalate materials could also exhibit an extremely anomalous mechanical behavior.

Organic acids under pressure: elastic properties, negative mechanical phenomena and pressure induced phase transitions in the lactic, maleic, succinic and citric acids

“…The mechanical properties of polycrystalline aggregates of L-(+)-lactic were determined in terms of the elasticity matrix using the Voigt, 261 Reuss 262 and Hill 263 approximations. As in many previous works, 70,71,74,76,77,264 the best agreement between the calculated bulk modulus with the single crystal bulk modulus computed from the 4th Birch-Murnaghan equation of state (BM-EOS, see Appendix A in the ESI †) was obtained with the Reuss scheme. The computed mechanical properties in the Reuss approximation together with the bulk modulus and its first two derivatives with respect to pressure extracted from the BM-EOS are reported in Table 3.…”

“…Theoretical methods of different degree of complexity, ranging from empirical force field approaches to fully featured quantum theory based methods as those used in this work have been employed in the study of the mechanical properties of solid materials. 5,8,28,[70][71][72][73][74][75][76][77][78] The first works concerning the computer modelling of materials displaying negative Poisson's rations (known as auxetic 46 ) were the pioneering papers of Wojciechowski. 204 The utilization of large-scale calculations employing state of the art first principles computational modelling techniques for the description of solid-state materials has produced very reliable results and, therefore, this methodology is sufficiently advanced today to predict their mechanical properties in good agreement with experimental measurements.…”

“…The isotropic negative linear compressibility (INLC) 52, 62,70,72,76 phenomenon is an important elastic anomaly in which one dimension of a given material increases upon hydrostatic compression. The anisotropic linear compressibility phenomenon (ANLC), 70,71,[75][76][77][78] however, involves the increase of the dimensions of a given material under the effect of a compressive stress applied along a certain direction. The INLC effect is quantified by means of compressibility associated to a given dimension c, k c = 1/cÁ(qc/qP) P , where P is the external pressure.…”

Structural, mechanical, spectroscopic and thermodynamic characterization of the copper-uranyl tetrahydroxide mineral vandenbrandeite

“…The Voigt, 187 Reuss, 188 and Hill 189 approaches were used to calculate the mechanical properties of polycrystalline aggregates of vandenbrandeite. As it has been encountered in many preceding works, 113,[115][116][117]123,141,165,166,168,169 the Reuss approach provided the best agreement between the calculated bulk modulus with the value of the single crystal bulk modulus obtained from the Birch-Murnahan equation of state (see next Section). The results obtained for the calculated elastic properties in the Reuss approximation are reported in Table 3.…”

“…This method, which appears to be more efficient for this purpose than density functional perturbation theory and the energy based methods, 163 has been effectively applied for the computation of the elastic response of many solid materials. 113,[115][116][117][118]120,122,141,142,144,[165][166][167][168][169] The derivatives of the bulk modulus with respect to pressure were determined by tting the lattice volumes and associated pressures to a 4 th order Birch-Murnahan equation of state. 170 The unit cell volumes in the neighborhood of the optimized structure were obtained by optimizing the vandenbrandeite crystal structure under sixteen different external pressures with values in the range À1.0 to 9.0 GPa.…”