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- Boras, Dominik, et al.
(författare)
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Determining internal porosity in Prussian blue analogue cathode materials using positron annihilation lifetime spectroscopy
- 2023
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Ingår i: Journal of Materials Science. - : Springer Nature. - 0022-2461 .- 1573-4803. ; 58:42, s. 16344-16356
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Tidskriftsartikel (refereegranskat)abstract
- Prussian blue analogues (PBAs), AxM[M’(CN)6]1–y·zH2O, are a highly functional class of materials with use in a broad range of applications, such as energy storage, due to their porous structure and tunable composition. The porosity is particularly important for the properties and is deeply coupled to the cation, water, and [M’(CN)6]n– vacancy content. Determining internal porosity is especially challenging because the three compositional parameters are dependent on each other. In this work, we apply a new method, positron annihilation lifetime spectroscopy (PALS), which can be employed for the characterization of defects and structural changes in crystalline materials. Four samples were prepared to evaluate the method’s ability to detect changes in internal porosity as a function of the cation, water, and [M’(CN)6]n– vacancy content. Three of the samples have identical [M’(CN)6]n– vacancy content and gradually decreasing sodium and water content, while one sample has no sodium and 25% [M’(CN)6]n– vacancies. The samples were thoroughly characterized using inductively coupled plasma-optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Mössbauer spectroscopy as well as applying the PALS method. Mössbauer spectroscopy, XRD, and TGA analysis revealed the sample compositions Na1.8(2)Fe2+0.64(6)Fe2.6+0.36(10)[Fe2+(CN)6]·2.09(2)H2O, Na1.1(2)Fe2+0.24(6)Fe2.8+0.76(6)[Fe2.3+(CN)6]·1.57(1)H2O, Fe[Fe(CN)6]·0.807(9)H2O, and Fe[Fe(CN)6]0.75·1.5H2O, confirming the absence of vacancies in the three main samples. It was shown that the final composition of PBAs could only be unambiguously confirmed through the combination of ICP, XRD, TGA, and Mössbauer spectroscopy. Two positron lifetimes of 205 and 405 ps were observed with the 205 ps lifetime being independent of the sodium, water, and/or [Fe(CN)6]n– vacancy content, while the lifetime around 405 ps changes with varying sodium and water content. However, the origin and nature of the 405 ps lifetime yet remains unclear. The method shows promise for characterizing changes in the internal porosity in PBAs as a function of the composition and further development work needs to be carried out to ensure the applicability to PBAs generally.
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| 2. |
- Nielsen, Ida, 1996-
(författare)
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New strategies for characterizing Prussian blue analogues
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Prussian blue analogues (PBAs), AxM[M’(CN)6]1–y·zH2O, are used in many different applications, such as energy storage, due to their tunable composition and structural diversity. To understand the material properties, it is important to accurately determine the composition and atomic structure of these materials. Determining the composition of iron-based PBAs is challenging due to the interdependent relationship between the three compositional parameters namely the sodium (Ax), water (z), and [Fe(CN)6]n– (y) vacancy content. In addition, the atomic structure depends on the composition leading to a rich structural landscape, which further influences the material properties. This thesis presents a comprehensive strategy for characterizing the composition and atomic structure of iron-based PBAs by applying different characterization techniques. Firstly, it was shown that to accurately determine the composition of iron-based PBAs, it is crucial to combine multiple characterization techniques in combination. In particular, Mössbauer spectroscopy proved to be a key technique for accurately determining the vacancy content in iron-based PBAs, where both metal sites (M and M’) are occupied by iron. Furthermore, positron annihilation lifetime spectroscopy was explored as a potential method for determining the internal porosity in PBAs. A correlation between the average positron lifetime and varying PBA compositions was found and is compared to other standard characterization techniques. Secondly, the impact of the synthesis method of Na2Fe[Fe(CN)6]·zH2O was studied using X-ray and neutron diffraction. Independent of the synthesis method, it was found that a P21/n phase exists at room temperature, which transitions to an R-3 phase upon heating to 40 °C. The two structures were differentiated in terms of the octahedral tilting system and sodium-ion displacements. These results were compared to the structure of the dehydrated material. In addition, it was found that there is a significant difference in the rate and magnitude of thermal expansion of the hydrated relative to the dehydrated material.
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