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Elasticity of phase‐X at high pressure
Author(s) -
Mookherjee Mainak,
SteinleNeumann Gerd
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl037782
Subject(s) - elasticity (physics) , pseudopotential , anhydrous , shear modulus , bulk modulus , materials science , stiffness , sodium , phase (matter) , equation of state , thermodynamics , crystallography , analytical chemistry (journal) , chemistry , condensed matter physics , physics , composite material , organic chemistry , metallurgy , chromatography
Using a plane‐wave pseudopotential method, we calculate the equation of state and elasticity of phase‐X [(K,Na) 2 Mg 2 Si 2 O 7 ] up to 30 GPa, which encompasses its experimentally observed stability field. We find that the pressure‐volume results for anhydrous phase‐X are well represented by a third order Birch‐Murnaghan formulation, with K 0 = 132 GPa, K ′ 0 = 4.4 and V 0 = 284.6 Å 3 for the potassium (K) end member and K 0 = 128 GPa, K ′ 0 = 4.0 and V 0 = 265.9 Å 3 for the sodium (Na) end member. The full elastic constant tensor reveals significantly larger stiffness along the [001] direction than in the (100) plane. We attribute such stiffness to the 180 0 angle of Si‐O‐Si units and their orientation parallel to the [001] direction. Assuming ideal behavior between Na and K phase‐X, the shear modulus softens with sodium content as G = [84 − 0.14 × Na ( wt %)] GPa.