First-principles study on the phase transition temperature of X-doped (X = Li, Na or K) VO₂

Abstract

Vanadium dioxide (VO 2 ) is one of the most interesting thermochromic materials with a phase transition temperature of 340 K. Our first-principles calculation indicates that Li, Na or K dopants with a doping level of 1 atomic percentage could reduce the phase transition temperature of VO 2 by 43K, 49K, 94 K, respectively. In addition, the V-V chains feature the dimerization characteristics in the Li, Na or K doped VO 2 (R).The calculated electronic structures and optical properties indicate that K is as an appropriate doping element for VO 2 , since it can effectively lower the phase transition temperature as well as enhance the near-infrared absorption.10 and the K-doped VO 2 (M) for the near infrared light. Fig. 5(a) shows a weak absorption for the pure VO 2 (M), indicating that infrared light could easily penetrate the VO 2 (M), in good agreement with the experimental observations. When the systems are doped with K, the VO 2 (M) exhibits a larger absorption coefficient for the light with energy less than 1.6 eV in Fig. 3(b), suggesting the introduction of K increases the absorption of the infrared light in VO 2 (M). The optical properties of the K-doped VO 2 (M) can be explained through its electronic structures. As displayed in Figure 3(h), there is a 0.562 eV band-gap near the bottom of conduction band of K-doped VO 2 (M). The infrared light would lead to electronic transitions from the occupied state to the unoccupied states, which just corresponds to the strong absorption for the light with energy less than 1.6 eV. Concluding remarksIn summary, by using first-principles calculation, we investigated the behavior of Li, Na or K-doping and its influence on the transition temperature (T c ) of VO 2 . The Li atom is easily located at the tetrahedral interstitial site in VO 2 , whereas the Na or K atom is easily located at the octahedral interstitial site, which can be ascribe to different atomic sizes of the dopants. The phase transition temperature of VO 2 can be reduced by 43 K, 49 K or 94 K with 1% of Li, Na or K doping, respectively. The atomic structures show that the V-V chains feature the dimerization characteristics in the Li, Na or K doped VO 2 (R). The K can be selected as an appropriate doping alkali for VO 2 , since it can lower the phase transition temperature and enhance the near-infrared absorption.

The Effect of Alkali Metal (Na, K) Doping on Thermochromic Properties of VO2 Films

“…The first dopant, sodium decreased the Tc to 57 C. Compared to Na doping, K dopant was found to be the most efficient one, as it offered a higher Tc reduction to 47 °C. These values are still higher than as reported by Cui et al26 who reported first-principle calculations on the basis of sodium and potassium doped VO2 films, can reduce the Tc by 49 K and 94 K per 1 at % dopant. Similarly, potassium resulted in a higher degree of reduction in the Tc, with 15 °C per 1.5 % dopant.…”

“…Li, Na and K dopants were also investigated by calculation and K found to effectively decrease the Tc as well as improve the transmittance modulation in near infra-red region. Level of 1 at % could reduce the phase transition temperature of VO2 by 43 K, 49 K, 94 K, respectively 26 . To the best of our knowledge, these dopants have not been not reported in any experimental work yet.…”

Graphene‐Based Nanocomposites for Energy Storage

“…Similarly, graphene/LiMn 2 O 4 , graphene/LiMnPO 4 , graphene/Li 3 V 2 (PO 4 ) 3 , graphene/Li 3 T 2 (PO4) 3 , graphene/Li 2 FeSiO 4 , graphene/Li 2 MnSiO 4 , graphene/V 2 O 5 , graphene/FePO 4 , graphene/FeF 3 , and graphene/LiNi 1/3 Co 1/3 Mn 1/3 O 2 have been explored as possible cathodes for rechargeable Li‐ion batteries. For instance, FeF 3 /graphene composites delivered a charge capacity of 155, 113, and 73 mAh g −1 at 104, 502, and 1040 mA g −1 current density, with stable cyclability for over 100 cycles, which was attributed to the buffering effect and lowered resistance from the graphene…”

First‐Principles Calculations on the Group‐IIIA Elements X‐Doped (X = Ga, In, Tl) VO2

“…Like other works in ref. , our current calculations are performed without using the spin‐polarization.…”

“…For example, N‐doped VO 2 can effectively reduce the energy gap and lower the T c . Cui et al found that the K element can enhance the near‐infrared absorption of VO 2 and decrease the T c when they had studied the alkali metal‐doped VO 2 . The fourth main group elements of Si, Ge, Sn, and Pb‐doped VO 2 have also been investigated .…”