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Vanadium dioxide (VO2) undergoes a reversible first‐order metal‐to‐insulator transition (MIT) from a high‐temperature metallic phase to a low‐temperature insulating phase at a critical temperature Tc of 68°C. The MIT is accompanied by a structural phase transition. In addition to the metallic high‐temperature rutile phase, several insulating phases may be involved depending on doping, interfacial stress, or external stimuli. Unambiguously identifying the crystal phases involved in the phase transition is of key interest from the point of view of application as well as fundamental science. We study the impact of Ti doping of VO2 thin films on (110) rutile TiO2 substrates. We conduct a careful analysis of structural properties by combining results of x‐ray diffraction, Raman spectroscopy, and transmission electron microscopy. The transition temperature Tc of the deposited thin films decreases with increasing Ti‐content. All our thin film samples undergo a structural phase transition from the monoclinic M1‐phase to the rutile R‐phase with increasing temperature without passing the intermediate monoclinic M2‐phase. A careful analysis of polarization and angle‐dependent Raman data reveals that, above Tc, the unit cell of the high‐temperature rutile TixV1‐xO2 phase is aligned with that of the rutile TiO2 substrate whereas, below Tc, 180°‐domains of the M1‐phase of TixV1‐xO2 are observed. The structural relationship between TiO2 substrate and the high respective low‐temperature phase of the TixV1‐xO2 determined by Raman spectroscopy is in excellent agreement with TEM results on these samples. Raman spectroscopy is a powerful tool for studying structural changes of VO2‐based samples in the vicinity of MIT. [ABSTRACT FROM AUTHOR]

Vanadium–oxygen materials are of interest for various applications and fields of solid‐state physics owing to the unequaled plethora of different phases. The wealth of phases and complexity of its phase diagram infer a strong sensitivity on the growth parameters for each phase. Thus, the reproducible growth of vanadium‐oxide thin‐films of defined phases by nonequilibrium techniques is challenging. Here, it is shown that ion‐beam sputter‐deposition (IBSD) is a powerful tool to reproducibly deposit defined polycrystalline vanadium oxide films by precisely controlling oxygen flux and substrate temperature in the growth process. Hence, it is demonstrated that IBSD has the potential to reliably produce binary phases (including unstable phases) from the vanadium–oxygen phase space. X‐ray diffraction (XRD) and Raman spectroscopy are used to establish a map of the different crystalline phases dependent on the growth parameters. In particular, it is proved that thin‐film V3O7 can be realized by IBSD and its Raman fingerprint is unambiguously identified. [ABSTRACT FROM AUTHOR]

Mg2Si1−xSnx solid solutions are prepared in the composition range from x = 0 to 1 by mechanical alloying using high‐energy ball milling followed by direct‐current sintering at 600–800 °C. X‐ray diffraction analysis confirms that the samples obtained are uniform solid solutions. Raman spectroscopy shows two first‐order phonon Raman bands and a distribution of Raman signals due to second‐order phonon Raman scattering. The first‐order Raman bands are assigned to the nondegenerate Raman‐forbidden F1u (LO) mode and the triply degenerate Raman‐allowed F2g mode. Both modes exhibit a linear shift of the phonon frequency with a composition showing a clear one‐mode behavior for this solid solution. The findings are discussed in the context of existing theories for the occurrence of the one‐mode or two‐mode behavior of phonons in solid solutions. [ABSTRACT FROM AUTHOR]

We demonstrate that Raman mapping provides a cheap, fast, and non-invasive way of mapping compositional fluctuations occurring in state-of-the-art thermoelectric materials. Exemplarily, we discuss Raman results obtained on an Mg 2 Si–Mg 2 Sn diffusion couple and compare resulting compositional mappings with those obtained on the same sample using electron microscopy in conjunction with energy-dispersive X-ray emission and back-scattered electrons as probes. We obtained the same level of quantitative information by the three approaches. The lateral resolution achieved in the Raman mappings can be as good as 1.4 µm and typical recording times per data point are of the order of 50 s. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The κ-Ce 2 Zr 2 O 8 phase has been synthesized starting from t -Ce 0.5 Zr 0.5 O 2 solid solution which is reduced by hydrogen at high temperatures to form the pyrochlore Ce 2 Zr 2 O 7 phase ( pyr -Ce 2 Zr 2 O 7 ) with high degree of ordering of the cationic sublattice. The final step in the synthesis of the κ-Ce 2 Zr 2 O 8 phase includes a mild re-oxidation of pyr -Ce 2 Zr 2 O 7 at around 600 °C under atmospheric conditions. Yet, the synthesis of phase-pure κ-Ce 2 Zr 2 O 8 phase (phase-pure and with highest ordering) is still not settled since most of the previous studies used reduction temperatures of 1300 °C and below. We show in this contribution that 1300 °C is not sufficient to warrant the preparation of phase-pure pyr -Ce 2 Zr 2 O 7 and κ-Ce 2 Zr 2 O 8, but that rather temperatures as high as 1500 °C are required to assure phase purity of both phases. This conclusion is drawn from extended X-ray diffraction and X-ray absorption spectroscopy analyses together with Raman spectroscopy, providing in-depth details of the structure on the level of both, the evolution of the special periodic structure and the coordination of the metal atoms. [ABSTRACT FROM AUTHOR]