The single crystal elastic moduli of neighborite

Abstract

Abstract.The adiabatic elastic moduli of a single crystal of Neighborite (NaMgF3 perovskite) have been measured at ambient conditions using Brillouin spectroscopy. The adiabatic aggregate (Voight-Reuss-I-Iill) bulk modulus is K=75.6 GPa, and shear modulus is /~=46.7 GPa. The experimental results show the ratio of linear compressibilities/~h//~ = 0.80 for neighborite. These ratios reflect the different amounts of tilting freedom of the octahedral framework along each lattice axis of the perovskite structure. It is understood that the elastic compliance Sij of the crystal can directly sense the behavior of the octahedral tilting in the structural distortion of NaMgF 3 perovskite. The octahedral tilting angles are considered to be the order parameters of the ferroelastic phase transition in the perovskite structure. Single crystal elasticity data provide a basis for understanding the role of octahedral tilting in the ferroelasticity of perovskite. Together with high pressure compressional data, one can thus elucidate the relationship between crystal structure and physical properties of perovskite. A detailed assessment indicates that the dominant compression mechanism for NaMgF3 perovskite is shortening of the octahedral [Mg-F l bond, which is also true for orthorhombically distorted MgSiO3 perovskite.

Octahedral tilting evolution and phase transition in orthorhombic NaMgF3 perovskite under pressure

“…[10] The equation of state of NaMgF 3 could be fitted using a second-order Birch equation of state (EOS) (shown as insertion in Figure 3), keeping the pressure derivative of bulk modulus K 0 0 as 4 [Birch, 1978]. The zero pressure bulk modulus (K 0 ) is estimated as 76.0 ± 1.1 GPa, which is in good agreement with the bulk modulus value of 75.6 GPa measured from single crystal Brillouin scattering [Zhao and Weidner, 1993].…”

Perovskite solid solutions–a Monte Carlo study of the deep earth analogue (K, Na)MgF3

“…The simulated isothermal bulk modulus of NaMgF 3 is 81.5 GPa at 300 K and zero pressure, which compares very well with experiment (75.6 GPa [45] and 76.0 GPa [46]). For KMgF 3 , the calculated isothermal bulk modulus is 86.8 GPa at 300 K. This is somewhat higher than the experimental values of 75.1 GPa [47], 75.6 GPa [48], and 71.2 GPa [26], but the difference does not exceed 20%.…”

Two-phase deformation of lower mantle mineral analogs

“…A.1). For each phase, the principle stresses in the deviatoric stress tensor (σ 11 , σ 22 , and σ 33 ) can be calculated from the non-isotropic lattice strain and the elastic constants of NaMgF 3 (Zhao and Weidner, 1993) and NaCl (Liu et al, 2010); see Appendix B for details. Differential stress is defined as σ = σ 33 − σ 11 , where σ 33 is the principle stress in the direction of the loading axis, and σ 11 and σ 22 are the principal stresses perpendicular to the loading axis and are assumed to be equal.…”