Colossal Pressure-Induced Softening in Scandium Fluoride

Abstract

The counterintuitive phenomenon of pressure-induced softening in materials is likely to be caused by the same dynamical behavior that produces negative thermal expansion. Through a combination of molecular dynamics simulation on an idealized model and neutron diffraction at variable temperature and pressure, we show the existence of extraordinary and unprecedented pressure-induced softening in the negative thermal expansion material scandium fluoride ScF 3. The pressure derivative of the bulk modulus B, B 0 ¼ ð∂B=∂PÞ P¼0 , reaches values as low as −220 AE 30 at 50 K, and is constant at −50 between 150 and 250 K.

Quantitative understanding of negative thermal expansion in scandium trifluoride from neutron total scattering measurements

“…VI, in the Supplemental Material [39], and in the parallel Ref. [11]. The Supplemental Material also includes a citation of Ref.…”

“…The model introduced briefly in the previous section, and in our parallel paper on pressure-induced softening in ScF 3 [11], is described in more detail in the Supplemental Material [39]. The model has been designed and analyzed to see the effect of various independent parameters on the NTE.…”

“…This phenomenon of negative thermal expansion (NTE) [1][2][3][4] is of fundamental interest from a structural and thermodynamic point of view, and also commercially important [5][6][7], for instance in preparing substrates resistant to thermal shock. It is among the most widely studied of the anomalous negative thermodynamic properties, others including auxetics with negative Poisson's ratio [8] and materials which soften under pressure (negative derivative of the bulk modulus with pressure) [9][10][11].…”

Negative and Near-Zero Thermal Expansion in A2M3O12 and Related Ceramic Families: A Review

“…Pressure-induced softening can be seen to arise from simple models of chains of atoms which exhibit the tension effect (Fang et al, 2014a), suggesting that the softening is a consequence of thermomiotic materials' tendency to undergo buckling of floppy linkages upon the application of both pressure and temperature. The pressure-induced softening reaches values of up to (zK/zp) T −220 in ScF 3 (Wei et al, 2020), much larger in magnitude than the value of (zK/zp) T ≈ 4 seen in many conventional materials (Hofmeister, 1991). Thermal expansion is also directly connected to the temperature derivatives of the elastic constants, as these depend on the anharmonicity of the interatomic force constants (Rao, 1974).…”

“…Other connections between NTE and elasticity exist outside of the Grüneisen theory, including the tendency of thermomiotic materials to undergo pressure-induced softening (Fang et al, 2013a;Fang and Dove, 2013b;Fang et al, 2014b;Hester et al, 2016;Wei et al, 2020). For simple solids, the pressure derivative of the bulk modulus can be expressed as follows:…”