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.

中文翻译：

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结合实验和从头算确定La0.5Sr0.5Co0.25Fe0.75O3的热膨胀

通过第一原理声子计算结合准谐波近似（QHA）和实验方法，研究了La _0.5 Sr _0.5 Co _0.25 Fe _0.75 O ₃（LSCF55）的热膨胀。内的QHA的框架内，菱面体LSCF55的体积热膨胀系数被计算为α _V，GGA = 50.34×10 ^-6 ķ ^-1。为了进行比较，LSCF55晶粒的晶格膨胀和体积膨胀是通过原位高温X射线衍射仪（HT-XRD）测量的。菱形LSCF55的各向异性的热膨胀与α_{一个，六角}= 10.89×10^-6 ķ ^-1和α _{Ç，十六进制}= 21.18×10 ^-6 ķ ^-1被获得。的体积热膨胀系数作为α测量_V，HT-XRD = 43.17×10 ^-6 ķ ^-1。此外，多晶LSCF55棒状试样的有效各向同性膨胀系数使用的是垂直的高性能的热机械分析仪和产率α测量的_{升，棒状试样}= 17.37×10 ^-6 ķ ^-1和α _{V，棒状试样}= 52.11 ×10 ^-6 K ^-1。