Compression and amorphization of (Mg,Fe)2SiO4 olivines: An X-ray diffraction study up to 70 GPa

Abstract

Abstract. The effect of (Mg,Fe) substitution on the compression and pressure-induced amorphization of olivines has been investigated up to more than 50 GPa in a diamond anvil cell through energy-dispersive X-ray diffraction experiments with synchrotron radiation. For the four (Mgl _~, Fex)2SiO4 olivines studied, the compressibility is the highest along the b axis and the smallest along the a axis. For compositions with x=0, 0.17, 0.66, and 1, the slope of the volume-pressure curves shows a rapid decrease at pressures of around 42, 34, 20 and 10 GPa, respectively. Assuming K; = 4, we obtained at lower pressures with a Birch-Murnaghan equation of state essentially the same room-pressure bulk modulus for all olivines, namely Ko=131_+6GPa, in agreement with previous single-crystal compression and ultrasonic measurements. At higher pressures, the compression becomes nearly isotropic and the materials very stiff. These changes could precede partial transformation of olivines to a high-pressure polymorph related to the spinel structure. Only a small fraction of olivines seems to transform actually to this phase, however, because most of the material undergoes instead pressure-induced amorphization which take place at considerably higher pressures for Mg-than for Fe-rich olivines.

Study of high-pressure and high-temperature behaviors and α-to-β phase transition of forsterite by first-principles and quasi-harmonic Debye model

“…while the GGA curve is above all of them. The average value for the coefficient of the linearly fitted V -P slope of α-phase crystal by experimental data[59,62,63,77,78] is −1.55 Å 3 /GPa, which is concordant with the LDA coefficient of −1.60 Å 3 /GPa and GGA one of −2.1 Å 3 /GPa. The agreement between the experimental and the calculated results indicates the present computational scheme is more appropriate for describing the high-pressure behavior of mineral crystals at intermediate temperature.…”

“…The linear V -P coefficients for β-phase forsterite obtained from LDA, GGA, and Hazen's experiment [55] are −2.5, −3.2, and −2. Table 3 Linearly fitted coefficients of cell volumes for α-and β-phases forsterite at different [59] −2.47 LDA −1.81 [62] −2.61 [55] −1.33 [63] −1.40 [77] −1.49 [78] −2.21 GGA −1.60 LDA Fig. 4.…”

“…The values of cell volume for α-and β-phase forsterite crystals versus pressure, from our calculations and experiments at room temperature[59,62,63,77,78]. while the GGA curve is above all of them.…”

Recent Progress in High-Pressure Brillouin Scattering: Olivine and Ice.

“…for Fe-rich olivines [10]. It is possible that the softening of the shear moduli in San Cabs olivine is the indicator of a lattice instability that ultimately leads to pressure-induced amophization [11,12].We therefor expect that the pressure over which shear elastic constants of forsterite begin to soften is higher than 16 GPa; presumably, for fayalite or more Fe-rich olivines they are even lower than in San Cabs olivine.…”

Pressure-induced structural phase transition of the iron end-member of ringwoodite ( -Fe2SiO4) investigated by X-ray diffraction and Mossbauer spectroscopy

“…Andrault et al (1995) extended the studied pressure range up to 10 GPa and obtained K 0 = 125(6) GPa with a fixed K' = 4. Speziale et al (2004) obtained elastic constants of K 0 = 136.3(2) GPa and K' = 4.9(1) for a single crystal of (Fe 0.94 Mn 0.06 ) 2 SiO 4 using Brillouin spectroscopy.…”