Silver Oxalate: Mechanical Properties and Extreme Negative Mechanical Phenomena

Abstract

The crystal structure and mechanical properties of silver oxalate, Ag 2 C 2 O 4 , are determined using first-principles solid-state methods. The set of calculated mechanical properties include the bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson's Ratio and the ductility, hardness, and anisotropy indices. Silver oxalate is a highly anisotropic brittle material possessing a small bulk modulus of 9.6 GPa. It displays the negative Poisson's ratio (NPR) phenomenon, the value of the lowest NPR having a very large magnitude, −1.27. Besides, it exhibits the most extreme form of the negative linear compressibility (NLC) phenomenon found to date. Silver oxalate displays anisotropic NLC for external pressures in the range −0.1 to −2.4 GPa directed along the [010] crystallographic direction and isotropic NLC for isotropic pressures in the range −0.51 to 13.4 GPa. The lowest value of the negative compressibility, −831.9 ± 10 TPa −1 , is found for an isotropic pressure of −0.16 GPa. 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.

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.…”