Local structure of Fe in Fe-doped misfit-layered calcium cobaltite: An X-ray absorption spectroscopy study

Local structure determination of substitutional elements in Ca3Co4−xMxO9(M = Fe, Cr, Ga) using X-ray absorption spectroscopy

“…To relax the [Ca 2 CoO 3 ] 4 [CoO 2 ] 6 structure, the density functional theory (DFT) calculation was performed by using the Vienna ab initio Simulation Package (VASP) . The details of the structure optimization process can be found in our earlier publication .…”

“…However, for polycrystalline materials, the ZT of Ca 3 Co 4 O 9 is relatively lower and there are many attempts to improve ZT . One of the approaches to enhance thermoelectric efficiency is by doping other elements into the system at the Co‐site . However, there are two different Co sites since the Ca 3 Co 4 O 9 is the simplification of the formula [Ca 2 CoO 3 ][CoO 2 ] 1.61 .…”

Effects of Eu and Fe co-doping on thermoelectric properties of misfit-layered Ca3Co4O9+δ

“…and Fe 3? , its average valance state is lower than that of cobalt [9]. Therefore, the substitution of Co with Fe is hole-doping, which results in an increase of the carrier concentration and decrease the electrical resistivity.…”

“…In this family, the misfit-layered Ca 3 Co 4 O 9?d (CCO) has received a considerable attention because of its relatively large ZT and chemical stabilities at high temperature in air [7][8][9]. In practically, Shikano and Funahashi [4] reported that ZT of CCO in a single crystal form is 0.83 at 973 K. Such good thermoelectric performance may be attributed to its unique layer structure which is comprised of alternating stacks of the distorted NaCltype [Ca 2 CoO 3 ] layer and the CdI 2 -type [CoO 2 ] layer along the c-axis [10].…”

“…can enhance the thermopoower, but also increase the resistivity [11][12][13][14][15][16]. In contrast, doping in Co-site is more complicated due to the intrinsic feature of multiple oxidation states of the transition metals as dopants as well as the presence of two nonequivalent Co sites in the [Ca 2 CoO 3 ] and [CoO 2 ] subsystems [7,9,[17][18][19]. The second approach focuses on advanced processing techniques, including spark plasma sintering (SPS), hot-pressing, multisheet corfiring (MSC), and sol-gel based electrospinning, which induce desired textures and nanocrystalline structures in the thermoelectric oxides [20][21][22][23][24][25].…”