Probing the role of thermal vibrational disorder in the SPT of VO$$_2$$ by Raman spectroscopy

Abstract

Phase competition in transition metal oxides has attracted remarkable interest for fundamental aspects and technological applications. Here, we report a concurrent study of the phase transitions in undoped and Cr-doped VO$$_2$$ 2 thin films. The structural, morphological and electrical properties of our films are examined and the microstructural effect on the metal–insulator transition (MIT) are highlighted. We further present a distinctive approach for analyzing the Raman data of undoped and Cr-doped VO$$_2$$ 2 thin films as a function of temperature, which are quantitatively correlated to the electrical measurements of VO$$_2$$ 2 films to give an insight into the coupling between the structural phase transition (SPT) and the MIT. These data are also combined with reported EXAFS measurements and a connection between the Raman intensities and the mean Debye–Waller factors $$\sigma ^2$$ σ 2 is established. We found that the temperature dependence of the $$\sigma _{R}^{2}(V-V)$$ σ R 2 ( V - V ) as calculated from the Raman intensity retraces the temperature profile of the $$\sigma _{EXAFS}^{2}(V-V)$$ σ EXAFS 2 ( V - V ) as obtained from the EXAFS data analysis. Our findings provide an evidence on the critical role of the thermal vibrational disorder in the VO$$_2$$ 2 phase transitions. Our study demonstrates that correlating Raman data with EXAFS analysis, the lattice and electronic structural dynamics can be probed.

Phase Control of Multivalent Vanadium Oxides VOx by Ion‐Beam Sputter‐Deposition

“…It is worth noting that two monoclinic VO 2 phases exist, referred to as M1 and M2. [ 67 ] The Raman‐active modes observed in Figure 4f are indicative of the M1 phase. Group theory predicts the same number of Raman‐active modes for the M2 phase changing only their character.…”

Controlling the crystalline orientation and textual morphologies of the VO2 film and the effect on insulator–metal transition properties

“…4) A remarkable feature of VO 2 SPT transition is the generation of V-V dimers; this can lead to a small lattice distortion along the c axis and a distinct band structure difference. 5,6) In the rutile phase, the near-Fermi-level t 2g band is separated as π* and d // bands by the crystal field effect, 7) and the π*d // overlapping results in metallic behavior of the rutile phase. The V-V dimers splits the d // states into bonding and antibonding bands in the monoclinic phase, and the π* band is shifted upward due to the increase of the p-d orbital overlap caused by the V-V dimer tilting.…”

Raman scattering of TixV1‐xO2 thin films on (110) rutile TiO2 in the low and high temperature phase adjacent to the metal–insulator transition

“…Furthermore, there are two modifications of the VO 2 monoclinic structure, the so-called M 1 and the M 2 -phase, which play a role in the context of the MIT of VO 2 and VO 2 -based materials. 31 As we will see in the discussion of Figures 1 and 2, we will be confronted with the M 1 -phase only and do not observe the M 2 -phase as an intermediate phase in the vicinity of the MIT. Therefore, we will focus mainly on the structural relationship between the M 1 and the R-phase of VO 2 .…”