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57 Fe transmission Mössbauer spectroscopy (TMS) and back scattered conversion electron Mössbauer spectroscopy (CEMS) measurements were carried out on Fe-filled multiwalled carbon nanotubes (Fe-MWCNTs) grown by chemical vapor deposition with ferrocene as precursor. Samples of Fe-MWCNTs material deposited on the inner wall of the quartz tube reactor and samples of aligned Fe-MWCNTs grown perpendicularly to the oxidized Si substrate were characterised by the TMS method. The data show that Fe phases encapsulated within the carbon nanotubes comprise ␣-Fe, ␥-Fe, and Fe 3 C in different percentage ratio depending on the sample preparation. These results are in a good accordance with the previously measured magnetic characteristics and with the structural data found by x-ray diffraction as well by selected area electron diffraction methods and allow a new complementary characterization of the Fe(Fe-alloy)-MWCNT systems. The CEMS method applied for the characterization of metal containing MWCNTs reveals that close to the top surface of the aligned Fe-MWCNTs samples only the ␥-Fe phase is found. This technique shows an additional potential for further investigation of the spatial distribution of the crystalline phases in the depth of aligned Fe-MWCNT samples.

We have performed morphological analysis of samples of Fe nanowires encapsulated into aligned multiwalled carbon nanotubes (Fe-MWCNTs) via Fe57 Mössbauer spectroscopy. The aligned Fe-MWCNTs were obtained by pyrolysis of ferrocene onto an oxidized Si substrate. Transmission Mössbauer spectroscopy (TMS) and backscattered conversion electron Mössbauer spectroscopy (CEMS) were applied in order to distinguish different Fe phases and their spatial distribution within the whole sample and along the tubes’ height. A characterization (on a large spatial scale) of the aligned CNT samples was performed by obtaining TMS spectra for selected spots positioned at different locations of the sample. While the total Fe content changes considerably from one location to another, the γ-Fe∕α-Fe phase ratio is constant onto a relatively large area. Using TMS and CEMS for all aligned Fe-MWCNT samples it is also shown that along the CNT axes, going to the top of the nanotube the relative content of the γ-Fe phase increases. Going to the opposite direction, i.e., towards the silicon substrate, the relative content of the Fe3C phase increases, which is in agreement with our previous works. The results of an additional Mössbauer spectroscopy experiment in TMS and CEMS modes performed on a nonaligned sample support the conclusion that in our case the iron phases in the channels of carbon nanotubes are spatially separated as individual nanoparticles. The relative intensity ratio of the α-Fe phase Mössbauer sextets shows good magnetic texture along the nanotubes’ axis for one of the aligned samples and the lack of such orientation for the others.

Ba 2 MSbO 6-δ (M = Fe, Co) double perovskites have been prepared in polycrystalline form by the solid-state reaction in air and characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD), magnetic measurements and Möss-bauer spectroscopy (for M = Fe). At room temperature, the crystal structure of both compounds can be defined as a 6-layered (6H) hexagonal perovskite structure (space group P6 3 /mmc), with a = 5.7875(1) Å and c = 14.2104(2) Å for M = Fe and a = 5.7548(2) Å and c = 14.1439(7) Å for M = Co. M and Sb cations are randomly distributed over 4f and 2a Wickoff positions. The crystal structure is constituted by dimer units of (M,Sb) 4f O 6 octahedra sharing a face along the c axis; the dimers, which sharing corners, are connected by a single layer of (M,Sb) 2a O 6 octahedra. A severe degree of antisite disordering was detected in the Fe compound, which indicates the presence of 52.8 % Fe:47.2 % Sb at the (Fe,Sb) 2a positions, whereas for Co, 64.0 % Sb is present at the (Co,Sb) 2a sites. Mössbauer spectroscopic data for Ba 2 FeSbO 6