Mechanical Characterization of Anhydrous Microporous Aluminophosphate Materials: Tridimensional Incompressibility, Ductility, Isotropy and Negative Linear Compressibility

Abstract

Here, a detailed mechanical characterization of five important anhydrous microporous aluminophosphate materials (VPI-5, ALPO-8, ALPO-5, ALPO-18, and ALPO-31) is performed using first principles methods based on periodic density functional theory. These materials are characterized by the presence of large empty structural channels expanding along several different crystallographic directions. The elasticity tensors, mechanical properties, and compressibility functions of these materials are determined and analyzed. All of these materials have a common elastic behavior and share many mechanical properties. They are largely incompressible at zero pressure, the compressibilities along the three crystallographic directions being frequently smaller than 5 . Notably, the compressibilities of ALPO-5 and ALPO-31 along the three principal directions are smaller than this threshold. Likewise, the compressibilities of ALPO-18 along two directions are smaller than 5 . All of the considered materials are shear resistant and ductile due to the large bulk to shear moduli ratio. Furthermore, all of these materials have very small mechanical anisotropies. ALPO-18 exhibits the negative linear compressibility (NLC) phenomenon for external pressures in the range P = 1.21 to P = 2.70 GPa. The minimum value of the compressibility along the [1 0 0] direction, 30.9 , is encountered for P = 2.04 GPa. The NLC effect in this material can be rationalized using the empty channel structural mechanism. The effect of water molecule adsorption in the channels of ALPO-18 is assessed by studying the hydrated ALPO-18 material (ALPO-18W). ALPO-18W is much more compressible and less ductile than ALPO-18 and does not present NLC effects. Finally, the effect of aging and pressure polymorphism in the mechanical properties of VPI-5 and ALPO-5 is studied. As hydration, aging leads to significant variations in the elastic properties of VPI-5 and increases substantially its compressibility. For ALPO-5, pressure polymorphism has a small impact in its elasticity at zero pressure but a large influence at high pressure.

ZIF-75 under Pressure: Negative Linear Compressibility and Pressure-Induced Instability

“…The modifications of the crystal structures were analyzed in order to study the structural mechanism leading to the presence of the phenomenon of negative linear compressibility. The inspection of the deformation of these structures as the pressure increases led to the conclusion that the NLC phenomenon in ZIF-75 can be understood by employing the empty channel structural mechanism [81][82][83]128]. The modifications of the structure of ZIF-75 at four different pressures, P = −0.0625, 0.0, 0.0625, and 0.125 GPa, are shown in Figure 6.…”

“…The elasticity constants, that is, the elements of the elastic tensor of ZIF-75, were determined in the optimized crystal structure using the finite deformation method (FDM) [123]. This technique is highly efficient and reliable for describing the elastic response of materials and has been employed successfully in many previous works concerning uranium-containing materials [109][110][111][112][113] as well as organic crystals [102][103][104] and metal-organic compounds [81][82][83][105][106][107]124]. In particular, the elasticity of a wide variety of MOFs and microporous materials has been studied [81][82][83].…”

“…The pressure-induced amorphization in ZIF-8 has long been investigated [11,29,30,32,38,44], and the detection of pressure-induced phase transitions and amorphizations in other ZIF materials could be extremely interesting. Additional potential applications for microporous materials are possible because these materials frequently appear to exhibit the negative linear compressibility [45,[67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] and negative Poisson's ratio [81,[84][85][86][87] phenomena. These phenomena [88][89][90][91] have multiple potential applications in the development of ultrasensitive pressure-sensing devices [88,92], pressure-driven actuators [92,93], optical telecommunication cables [88], artificial muscles [94], and body armor [92,95], as well as sound attenuation [96], superconductivity modulation [97], ferroelectric enhancement [88], and transmission ...…”

“…The study of the mechanical properties of microporous compounds has been the subject of a large amount of research in recent decades [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. The first principles solid-state methodology have been satisfactorily applied for this purpose and have enhanced our knowledge of the mechanical properties of these materials since they give access to the full tensorial elasticity of these materials [34][35][36][37][67][68][69][70][81][82][83]86,87,[99][100][101][102][103][104][105][106][107][108]. The results obtained using the state-of-the-art theoretical methodology are consistently in agreement with the experiment, even for the theoretical study of complex anomalous negative mechanical phenomena [81][82][83][102][103]…”

“…The first principles solid-state methodology have been satisfactorily applied for this purpose and have enhanced our knowledge of the mechanical properties of these materials since they give access to the full tensorial elasticity of these materials [34][35][36][37][67][68][69][70][81][82][83]86,87,[99][100][101][102][103][104][105][106][107][108]. The results obtained using the state-of-the-art theoretical methodology are consistently in agreement with the experiment, even for the theoretical study of complex anomalous negative mechanical phenomena [81][82][83][102][103][104][105][106][107][108] and for crystal structure determination [109][110][111][112][113]. For example, the negative area compressibility of silver oxalate, predicted using first-principles methods [107], was recently experimentally verified [108].…”