Post-perovskite

CaIrO3

second-order Birch-Murnaghan · Original · 2007

V₀

226.632

Å³

Unit cell

K₀

180.200

GPa

Isothermal

K′

—

dimensionless

Volume (V₀)

Value	Unit	Basis	Z
226.632	Å³	Unit cell	—

Reported value and unit are preserved as extracted. Z (formula units per cell) is not stored yet, so molar ↔ Å³/f.u. conversion is not applied automatically.

Composition

CaIrO3

Conditions & method

T_ref: 300 K
P_ref: 0.000 GPa
Structure: post-perovskite (CaIrO3-type, Cmcm)
Method: experiment (XRD / DAC / multianvil compression)
monochromatic X-ray powder diffraction in diamond anvil cell (1-ID-C and 13-ID-D, APS); 4:1 methanol:ethanol medium to 7.6(1) GPa (ruby fluorescence pressure) and NaCl medium with laser annealing to 29(1) GPa (Decker NaCl scale)
Sample: CaIrO3 synthesized in multi-anvil press from Ca2IrO4 + IrO2 at 6.2(2) GPa and 1223(50) K; Table 1B volume fit

Source

Paper: Compression, thermal expansion, structure, and instability of CaIrO3, the struc…
Authors: C. David Martin; Karena W. Chapman; Peter J. Chupas; V. Prakapenka; P. L. Lee; S. D. Shastri; John B. Parise
DOI: 10.2138/am.2007.2473
Year: 2007
Journal: American Mineralogist
Origin: Original (measured or fitted in the source paper)

Evidence from the paper

Analysis of pressure-temperature dependent monochromatic X-ray powder diffraction data yield the bulk modulus [KT = 180.2(28) GPa] ... of CaIrO3, the structure model for post-perovskite MgSiO3. TABLE 1B. Bulk modulus constants were obtained using a 2nd-order Birch-Murnaghan equation of state: V | V0 (Å3) 226.632(45) | KT (GPa) 180.2(28). Equation of state constants describing compressibility were obtained by fitting data to a 2nd-order Birch-Murnaghan equation of state.

Additional notes

note on Kp

K′ not reported numerically; a 2nd-order Birch-Murnaghan EOS was used, which implicitly fixes K′ = 4 (not stated explicitly in text)

axial comparative bulk moduli Table 1B

{
  "a": {
    "L0_A": "3.14685(36)",
    "KT_GPa": "222.9(49)"
  },
  "b": {
    "L0_A": "9.8662(21)",
    "KT_GPa": "116.7(32)"
  },
  "c": {
    "L0_A": "7.29947(60)",
    "KT_GPa": "267.1(48)"
  },
  "note": "The cube of each unit-cell length, i.e., a3, has been fit to obtain a comparative bulk modulus"
}

ambient unit cell 1bar 300K

a = 3.14147(5) Å, b = 9.87515(19), c = 7.29711(11), V = 226.3754(78) Å3 at 1 bar and 300 K (best-fit unit-cell parameters)

thermal expansion

{
  "V0_A3": "226.3754(78)",
  "alpha0": "2.841(34) × 10^-5 K^-1",
  "alpha1": "3.37(48) × 10^-9 K^-2",
  "reference_temperature": "300 K"
}

relevance

CaIrO3 is the structure model (analog) for MgSiO3 post-perovskite, discussed in context of Earth's lower mantle and D'' layer

max pressure

29(1) GPa (NaCl medium, laser annealed); alcohol medium data to 7.6(1) GPa