The rhombohedral high pressure phase of MgGeO<sub>3</sub> (Ilmenite): Synthesis and single crystal structure analysis

Kirfel, A.; Hinze, Ε.; Will, G.

doi:10.1524/zkri-1978-3-411

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“…The calorimetric Clapeyron slope makes the clinopyroxene phase the low-temperature-low-pressure phase and the stable phase at ambient conditions. Interestingly, the reported experimental results of both Kirfel and Neuhaus (1974) and Ross and Navrotsky (1988) are consistent with the reported sample synthesis conditions of all other studies (Roth 1955;Ringwood and Seabrook 1962;Liebermann 1974;Sato et al 1977;Kirfel et al 1978;Ito and Matsui 1979;Ashida et al 1985;Okada et al 2008) (Figure 1b) except that of Ozima and Akimoto (1983) (Figure 1c). Ozima and Akimoto (1983) grew orthopyroxene phase and two types of clinopyroxene MgGeO3 crystals from flux at ambient pressure.…”

Section: Introductionsupporting

confidence: 88%

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Phase Diagram and Thermal Expansion of orthopyroxene-, clinopyroxene- and ilmenite-structured MgGeO3

Hunt

Santangeli

Dobson

et al. 2021

msam

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The MgGeO3 system is a low-pressure analog for the Earth-forming (Mg,Fe)SiO3 system and exhibits recoverable orthopyroxene, clinopyroxene, and ilmenite structures below 6 GPa. The pressure-temperature conditions of the clinopyroxene to ilmenite phase transition are reasonably consistent between studies, having a positive Clapeyron slope and occurring between 4 and 7 GPa in the temperature range 900–1600 K. There are, though, significant discrepancies in the Clapeyron slope of the orthopyroxene to clinopyroxene phase transition in existing works that also disagree on the stable phase at ambient conditions. The most significant factor in these differences is the method used; high-pressure experiments and thermophysical property measurements yield apparently contradicting results. Here, we perform both high pressure and temperature experiments as well as thermal expansion measurements to reconcile the measurements. High-pressure and -temperature experiments yield a Clapeyron slope of −1.0−0.7+1.0 MPa/K for the MgGeO3 orthopyroxene-clinopyroxene phase transition, consistent with previous high-pressure and -temperature experiments. The MgGeO3 orthopyroxene-clinopyroxeneilmenite triple point is determined to be at 0.98 GPa and 752 K, with the ilmenite phase stable at ambient conditions. The high-temperature (>600 K) thermal expansion of the clinopyroxene phase is greater than that of the other phases. Debye-Grüneisen relationships fitted to the volume-temperature data give Debye temperatures for the orthopyroxene, clinopyroxene, and ilmenite phases of 602(7), 693(10), and 758(13) K and V0 of 897.299(16), 433.192(10), and 289.156(6) Å3, respectively. The Clapeyron slopes calculated directly from the Debye-Grüneisen relationships are consistent with previous thermophysical property measurements. The presence of significant anharmonicity and/or formation of defects in the clinopyroxene phase at high-temperatures, which is not apparent in the other phases, accounts for the previous contradictions between studies. The inferred increased heat capacity of the clinopyroxene corresponds to an increase in entropy and an expanded phase field at high temperatures.

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Section: Introductionsupporting

confidence: 88%

“…Large symbols are data from (a) Kirfel and Neuhaus (1974) (b) Ross and Navrotsky (1988) and (c) Ozima and Akimoto (1983). Small symbols in (b) are synthesis conditions reported by Roth (1955); Ringwood and Seabrook (1962);Liebermann (1974);Sato et al (1977); Kirfel et al (1978); Ito and Matsui (1979); Ashida et al (1985); Okada et al (2008).…”

Section: Discussionmentioning

confidence: 99%

Phase Diagram and Thermal Expansion of orthopyroxene-, clinopyroxene- and ilmenite-structured MgGeO3

Hunt

Santangeli

Dobson

et al. 2021

msam

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The rhombohedral high pressure phase of MgGeO₃ (Ilmenite): Synthesis and single crystal structure analysis

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Phase Diagram and Thermal Expansion of orthopyroxene-, clinopyroxene- and ilmenite-structured MgGeO3

Phase Diagram and Thermal Expansion of orthopyroxene-, clinopyroxene- and ilmenite-structured MgGeO3

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The rhombohedral high pressure phase of MgGeO3 (Ilmenite): Synthesis and single crystal structure analysis

Cited by 1 publication

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Phase Diagram and Thermal Expansion of orthopyroxene-, clinopyroxene- and ilmenite-structured MgGeO3

Phase Diagram and Thermal Expansion of orthopyroxene-, clinopyroxene- and ilmenite-structured MgGeO3

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The rhombohedral high pressure phase of MgGeO₃ (Ilmenite): Synthesis and single crystal structure analysis