Melting and crystal structure of iron at high pressures and temperatures

Shen, Guoyin; Mao, Ho Kwang; Hemley, Russell J.; Duffy, Thomas S.; Rivers, Mark L.

doi:10.1029/97gl03776

Cited by 389 publications

(265 citation statements)

References 19 publications

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“…Other experimentalists, however, have failed to detect such a post-hcp phase (e.g. Shen et al, 1998;Nguyen and Holmes, 2004), and have suggested that the previous observations were due either to minor impurities or to metastable strain-induced behaviour. Figure 1 also shows that there is also considerable disagreement between different theoretical studies.…”

Section: Introductionmentioning

confidence: 92%

The stability of bcc-Fe at high pressures and temperatures with respect to tetragonal strain

Vočadlo

Wood

Gillan

et al. 2008

Physics of the Earth and Planetary Interiors

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe phase that iron adopts at the conditions of the Earth's inner core is still unknown. The two primary candidates are the hexagonal-close-packed (hcp) structure and the bodycentred-cubic (bcc) structure polymorphs. Until recently, the former was favoured, but it now seems possible that bcc iron could be present. A remaining uncertainty regarding the latter phase is whether or not bcc iron is stable with respect to tetragonal strain under core conditions. In this paper, therefore, we present the results of high precision ab initio free energy calculations at core pressures and temperatures performed on bcc iron as a function of tetragonal strain. Within the uncertainties of the calculations, direct comparison of free energy values suggests that bcc may be unstable with respect to tetragonal strain at 5500 K; this is confirmed when the associated stresses are taken into account. However, at 6000 K, the results indicate that the bcc phase becomes more stable, although it is unclear as to whether complete stability has been achieved. Nevertheless, it remains distinctly possible that the addition of light elements could stabilise this structure convincingly. Therefore, bcc-Fe cannot be ruled out as a candidate inner core phase.

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Section: Introductionmentioning

confidence: 92%

The stability of bcc-Fe at high pressures and temperatures with respect to tetragonal strain

Vočadlo

Wood

Gillan

et al. 2008

Physics of the Earth and Planetary Interiors

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“…Moreover, we know from other experiments on iron [14] that when iron is quenched from the stability field of the fcc phase, the XRD pattern of the quenched sample shows lines belonging to hcp and double hcp phases. Therefore, it is not necessary that the fcc peaks in XRD patterns of quenched samples are due to the stabilization of the fcc phase at high temperature.…”

mentioning

confidence: 93%

“…This EAM has been proved to perform very well. For example, it allows one to reproduce the structure of liquid iron [14]- [16] as well as its viscosity [7,17]. It also allows one to explain a number of features of IC [9,10].…”

mentioning

confidence: 99%

Quenching of bcc-Fe from high to room temperature at high-pressure conditions: a molecular dynamics simulation

et al. 2009

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“…3). This melting criterion has been applied in many previous investigations to determine melting in a wide variety of substances [20][21][22] and it has been directly correlated with the appearance of liquid S(Q) during in situ x-ray diffraction experiments in the LH-DAC [14,20].…”

Section: B Thermal Signal Processingmentioning

confidence: 99%

High-pressure melting behavior of tin up to 105 GPa

et al. 2017

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The melting curve of Sn initially rises steeply as a function of pressure but exhibits a decrease in slope (dT m /dP ) above 40 GPa to become nearly flat above 50 GPa. Previous studies have argued that a body-centered tetragonal (bct) to cubic (bcc) phase transition occurs in this range at room temperature. However, our investigations have shown that the phase behavior is more complex in this region with orthorhombic (bco) splitting of reflections occurring in the x-ray diffraction pattern above 32 GPa and coexisting diffraction signatures of bco and bcc structures are observed between 40 and 70 GPa. Here we have documented the simultaneous presence of bco and bcc reflections up to the melting point, negating the possibility that their coexistence might indicate a kinetically hindered first-order phase transformation. In this paper we have extended the observation of Sn melting relations into the megabar (P > 100 GPa) range using the appearance of liquid diffuse scattering in x-ray diffraction patterns and discontinuities during thermal signal processing to diagnose the occurrence of melting. Both techniques yield consistent results that indicate the melting line maintains the same low slope up to the highest pressure examined and does not flatten. The results below approximately 40 GPa agree well with the melting relations produced recently using a multiphase equation of state fitted to available or assumed data. Above this pressure the experimental melting points lie increasingly below the predicted crystal-liquid phase boundary, but above the flat melting from past studies, indicating that the thermodynamic properties of the body-centered "γ "-Sn structure remain to be clarified.

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Melting and crystal structure of iron at high pressures and temperatures

Cited by 389 publications

References 19 publications

The stability of bcc-Fe at high pressures and temperatures with respect to tetragonal strain

The stability of bcc-Fe at high pressures and temperatures with respect to tetragonal strain

Quenching of bcc-Fe from high to room temperature at high-pressure conditions: a molecular dynamics simulation

High-pressure melting behavior of tin up to 105 GPa

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