Phase Relations in CaSiO3 System up to 100 GPa and 2500 K

Phase relations in one of the key petrological systems, CaSiO 3 , have been comprehensively investigated for the first time in the pressure range 0–100 GPa and temperatures 0–2500 K within the density functional theory using the method of lattice dynamics in the quasi-harmonic approximation. The res...

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Bibliographic Details
Published in:Geochemistry international 2021-08, Vol.59 (8), p.791-800
Main Authors: Sagatova, D. N., Shatskiy, A. F., Sagatov, N. E., Litasov, K. D.
Format: Article
Language:English
Subjects:
Approximation
Density functional theory
Dicalcium silicate
Earth and Environmental Science
Earth Sciences
Geochemistry
High temperature
Low temperature
Mathematical analysis
Perovskite structure
Perovskites
Phase equilibria
Phase transitions
Pressure
Pseudowollastonite
Temperature
Titanite
Transition temperature
Transition temperatures
Wollastonite
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Summary:Phase relations in one of the key petrological systems, CaSiO 3 , have been comprehensively investigated for the first time in the pressure range 0–100 GPa and temperatures 0–2500 K within the density functional theory using the method of lattice dynamics in the quasi-harmonic approximation. The results showed that at atmospheric pressure and 0 K CaSiO 3 is stable in the wollastonite structure, which above 1250 K transforms to the high-temperature pseudowollastonite modification. Above a pressure of 4 GPa, CaSiO 3 is stable in the breyite structure. The phase equilibrium curve has a negative slope of dP/dT = –0.6 MPa/K. At 8 GPa, CaSiO 3 decomposes into an assemblage of Ca 2 SiO 4 -larnite and titanite-structured CaSi 2 O 5 . The phase equilibrium curve has a positive slope of dP/dT = 1.35 MPa/K. At a pressure of 13 GPa, Ca 2 SiO 4 -larnite reacts with CaSi 2 O 5 , forming a phase with a perovskite-like structure – CaSiO 3 -perovskite. The pressure of this phase transition is practically independent of temperature. In the low-temperature region, Ca-perovskite is stable in the tetragonal modification CaSiO 3 - I 4/ mcm . Above 340 K at 13 GPa, Ca-perovskite is stable in the cubic modification CaSiO 3 - The phase transition temperature increases to 755 K with pressure increase to 100 GPa. The thermodynamic parameters were also calculated for the first time for wollastonite, pseudowollastonite, and titanite-structured CaSi 2 O 5 .
ISSN:0016-7029
1556-1968
DOI:10.1134/S0016702921080073