Combined experimental and ab initio based determination of the thermal expansion of La0.5Sr0.5Co0.25Fe0.75O3

The thermal expansion of La_0.5Sr_0.5Co_0.25Fe_0.75O₃ (LSCF55) is investigated both by first principles phonon calculations combined with the quasi‐harmonic approximation (QHA) and by experimental approaches. Within the framework of the QHA, the volumetric thermal expansion coefficient of rhombohedral LSCF55 is calculated as α_V,GGA = 50.34 × 10^?6 K^?1. For comparison, the lattice expansion and the volume expansion of LSCF55 grain are measured by in situ high‐temperature X‐ray diffractometer (HT‐XRD). An anisotropic thermal expansion of rhombohedral LSCF55 with α_a,hex = 10.89 × 10^?6 K^?1 and α_c,hex = 21.18 × 10^?6 K^?1 is obtained. The volumetric thermal expansion coefficient is measured as α_V,HT‐XRD = 43.17 × 10^?6 K^?1. In addition, the effectively isotropic expansion coefficients of a polycrystalline LSCF55 bar specimen are measured using a vertical high‐performance thermo‐mechanical analyzer and yield α_{l,bar specimen} = 17.37 × 10^?6 K^?1 and α_{V,bar specimen} = 52.11 × 10^?6 K^?1.