Initially, vanadium dioxide seems to be an ideal first-order phase transition case study due to its deceptively simple structure and composition, but upon closer inspection there are nuances to the driving mechanism of the metal-insulator transition (MIT) that are still unexplained. In this study, a local structure analysis across a bulk powder tungsten-substitution series is utilized to tease out the nuances of this first-order phase transition. A comparison of the average structure to the local structure using synchrotron x-ray diffraction and total scattering pair-distribution function methods, respectively, is discussed as well as comparison to bright field transmission electron microscopy imaging through a similar temperature-series as the local structure characterization. Extended x-ray absorption fine structure fitting of thin film data across the substitution-series is also presented and compared to bulk. Machine learning technique, non-negative matrix factorization, is applied to analyze the total scattering data. The bulk MIT is probed through magnetic susceptibility as well as differential scanning calorimetry. The findings indicate the local transition temperature (
Straining the vanadium dimers along the rutile
- Award ID(s):
- 1719875
- NSF-PAR ID:
- 10452324
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- Volume:
- 8
- Issue:
- 9
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract ) is less than the average$$T_c$$ supporting the Peierls-Mott MIT mechanism, and demonstrate that in bulk powder and thin-films, increasing tungsten-substitution instigates local V-oxidation through the phase pathway VO$$T_c$$ V$$_2\, \rightarrow$$ O$$_6$$ V$$_{13} \, \rightarrow$$ O$$_2$$ .$$_5$$ -
null (Ed.)Epitaxial films of vanadium dioxide (VO 2 ) on rutile TiO 2 substrates provide a means of strain-engineering the transition pathways and stabilizing of the intermediate phases between monoclinic (insulating) M1 and rutile (metal) R end phases. In this work, we investigate structural behavior of epitaxial VO 2 thin films deposited on isostructural MgF 2 (001) and (110) substrates via temperature-dependent Raman microscopy analysis. The choice of MgF 2 substrate clearly reveals how elongation of V–V dimers accompanied by the shortening of V–O bonds triggers the intermediate M2 phase in the temperature range between 70–80 °C upon the heating–cooling cycles. Consistent with earlier claims of strain-induced electron correlation enhancement destabilizing the M2 phase our temperature-dependent Raman study supports a small temperature window for this phase. The similarity of the hysteretic behavior of structural and electronic transitions suggests that the structural transitions play key roles in the switching properties of epitaxial VO 2 thin films.more » « less
-
Abstract Mott insulator VO2exhibits an ultrafast and reversible semiconductor‐to‐metal transition (SMT) near 340 K (67 °C). In order to fulfill the multifunctional device applications, effective transition temperature (
Tc ) tuning as well as integrated functionality in VO2is desired. In this study, multifunctionalities including tailorable SMT characteristics, ferromagnetic (FM) integration, and magneto‐optical (MO) coupling, have been demonstrated via metal/VO2nanocomposite designs with controlled morphology, i.e., a two‐phase Ni/VO2pillar‐in‐matrix geometry and a three‐phase Au/Ni/VO2particle‐in‐matrix geometry. EvidentTc reduction of 20.4 to 54.9 K has been achieved by morphology engineering. Interestingly, the Au/Ni/VO2film achieves a record‐lowTc of 295.2 K (22.2 °C), slightly below room temperature (25 °C). The change in film morphology is also correlated with unique property tuning. Highly anisotropic magnetic and optical properties have been demonstrated in Ni/VO2film, whereas Au/Ni/VO2film exhibits isotropic properties because of the uniform distribution of Au/Ni nanoparticles. Furthermore, a strong MO coupling with enhanced magnetic coercivity and anisotropy is demonstrated for both films, indicating great potential for optically active property tuning. This demonstration opens exciting opportunities for the VO2‐based device implementation towards smart windows, next‐generation optical‐coupled switches, and spintronic devices. -
Abstract Vanadium dioxide (VO2) is a well‐studied Mott‐insulator because of the very abrupt physical property switching during its semiconductor‐to‐metal transition (SMT) around 341 K (68 °C). In this work, through novel oxide‐metal nanocomposite designs (i.e., Au:VO2and Pt:VO2), a very broad range of SMT temperature tuning from
≈ 323.5 to≈ 366.7 K has been achieved by varying the metallic secondary phase in the nanocomposites (i.e., Au:VO2and Pt:VO2thin films, respectively). More surprisingly, the SMTT ccan be further lowered to≈ 301.8 K (near room temperature) by reducing the Au particle size from 11.7 to 1.7 nm. All the VO2nanocomposite thin films maintain superior phase transition performance, i.e., large transition amplitude, very sharp transition, and narrow width of thermal hysteresis. Correspondingly, a twofold variation of the complex dielectric function has been demonstrated in these metal‐VO2nanocomposites. The wide range physical property tuning is attributed to the band structure reconstruction at the metal‐VO2phase boundaries. This demonstration paved a novel approach for tuning the phase transition property of Mott‐insulating materials to near room temperature transition, which is important for sensors, electrical switches, smart windows, and actuators. -
Abstract Distinct properties of multiple phases of vanadium oxide (VO
x ) render this material family attractive for advanced electronic devices, catalysis, and energy storage. In this work, phase boundaries of VOx are crossed and distinct electronic properties are obtained by electrochemically tuning the oxygen content of VOx thin films under a wide range of temperatures. Reversible phase transitions between two adjacent VOx phases, VO2and V2O5, are obtained. Cathodic biases trigger the phase transition from V2O5to VO2, accompanied by disappearance of the wide band gap. The transformed phase is stable upon removal of the bias while reversible upon reversal of the electrochemical bias. The kinetics of the phase transition is monitored by tracking the time‐dependent response of the X‐ray absorption peaks upon the application of a sinusoidal electrical bias. The electrochemically controllable phase transition between VO2and V2O5demonstrates the ability to induce major changes in the electronic properties of VOx by spanning multiple structural phases. This concept is transferable to other multiphase oxides for electronic, magnetic, or electrochemical applications.