High-pressure in-situ X-ray diffraction and Raman spectroscopy of Ca2AlFeO5 brownmillerite

ABSTRACTThe behavior of Ca2AlFeO5 brownmillerite was studied by in situ synchrotron X-ray diffraction and Raman spectroscopy at 300 K with pressures up to 26.5 and 32.1 GPa, respectively. A reversible structural phase transition was observed. The P–V data were fitted by a third-order Birch–Murnaghan equation of state, and the isothermal bulk modulus was obtained as K0 = 181.9(76) GPa with K0′ = 4.4(17). If K0′ was fixed to 4, K0 was obtained as 183.8(20) GPa. Ca2AlFeO5 brownmillerite shows an axial elastic anisotropy since the b-axis is more compressible than a- and c-axis. Combined with previous results, the isothermal bulk modulus and axial compressibility of Ca2AlFeO5 brownmillerite increase with more Al incorporated in the structure. The Raman spectra of Ca2AlFeO5 brownmillerite were analyzed and the pressure coefficients vary from 2.23 to 4.90 cm−1/GPa. The isothermal mode Gruneisen parameters range from 0.83 to 1.77 and the thermal Gruneisen parameter is determined as 1.08(11).