Postsynthetic Route for Modifying the Metal—Insulator Transition of VO₂ by Interstitial Dopant Incorporation

Abstract

The thermally driven orders-of-magnitude modulation of resistance and optical transmittance observed in VO2 makes it an archetypal first-order phase transition material and underpins functional applications in logic and memory circuitry, electromagnetic cloaking, ballistic modulation, and thermochromic glazing to provide just a few representative examples. VO2 can be reversibly switched from an insulating to a metallic state at an equilibrium transition temperature of 67 °C. Tuning the phase diagram of VO2 to bring the transition temperature closer to room temperature has been a longstanding objective and one that has tremendous practical relevance. Substitutional incorporation of dopants has been the most common strategy for modulating the metalinsulator transition temperature but requires that the dopants be incorporated during synthesis. Here we demonstrate a novel postsynthetic diffusive annealing approach for incorporating interstitial B dopants within VO2. The postsynthetic method allows for the transition temperature to be programmed after synthesis and furthermore represents an entirely distinctive mode of modulating the phase diagram of VO2. Local structure studies in conjunction with density functional theory calculations point to the strong preference of B atoms for tetrahedral coordination within interstitial sites of VO2; these tetrahedrally coordinated dopant atoms hinder the rutile → monoclinic transition by impeding the dimerization of V–V chains and decreasing the covalency of the lattice. The results suggest that interstitial dopant incorporation is a powerful method for modulating the transition temperature and electronic instabilities of VO2 and provides a facile approach for postsynthetic dopant incorporation to reach a switching temperature required for a specific application.

Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO2 upon Iridium Doping

“…For instance, the introduction of Al and Cr on the vanadium sublattice of VO 2 stabilizes the M 2 polymorph, whereas substitutional W‐ and Mo‐doping on the vanadium sublattice preferentially stabilizes the R polymorph over the M 1 polymorph even rendering the former metallic phase accessible at room temperature . Interstitial B‐doping of VO 2 similarly stabilizes the R polymorph over the M 1 polymorph, thereby strongly depressing the characteristic MIT temperature, whereas in contrast, interstitial H incorporation stabilizes two distinct orthorhombic phases, O 1 and O 2 . In this work, we demonstrate the stabilization of a metastable orthorhombic VO 2 (P) phase with rectangular tunnels upon substitutional Ir doping on the cation sublattice of VO 2 .…”

Insertion of Mono- vs. Bi- vs. Trivalent Atoms in Prospective Active Electrode Materials for Electrochemical Batteries: An ab Initio Perspective

“…The rutile phase is however predicted by DFT to be the most stable phase; more importantly, it is stabilized by Li insertion which makes it more stable than the semiconductor phase [34]. Stabilization of rutile VO 2 was also reported in experimental studies on hydrogen and boron doping in VO 2 nanowires [133,134]. Moreover, the X-ray diffraction (XRD) measurements identified the presence of VO 2 (R) phase during Li-ion battery cycling, consistent with our calculations [124].…”

Reversible and repeatable phase transition at a negative temperature regime for doped and co-doped spin coated mixed valence vanadium oxide thin films

“…This claim is amply supported by the fact that (T t ) around only 0 C is reported for VO thin lms with and without W-F and B doping and/or codoping. 19,29 The transition temperature hysteresis plots exhibit the difference between the transition temperatures observed during the heating and corresponding cooling cycles. These data are plotted in Fig.…”

“…techniques. However, only a few 19,29 have succeeded. For instance, Bukhardt et al 19 obtained the T t of 0 C for the (W and F) co-doped VO 2 thin lms.…”

“…Recently, B doping has been utilized for signicant reduction of T t (e.g., 4 C) in VO 2 thin lms. 29 In view of the importance of nature and amount (i.e., at%) of doping, resulting phase structure recorded by XRD at room temperature, processing technique and the corresponding (T t ), a typical survey of literature data [18][19][20][30][31][32][33][34][35][36][37] is presented in Table 1. A wide variety of processing techniques are employed.…”