# Role of the V-V dimerization in insulator-metal transition and optical transmittance of pure and doped VO2 thin films

## TL;DR

This study investigates how W and Tb doping affect the insulator-metal transition, optical properties, and structural phases of VO2 thin films, revealing doping-specific impacts on transition temperature and IR switching behavior.

## Contribution

It provides new insights into how W and Tb doping modulate the IMT and optical transmittance of VO2 thin films, with implications for thermochromic applications.

## Key findings

- W doping lowers IMT temperature significantly.
- Tb doping maintains IMT temperature close to pure VO2.
- W doping reduces IR switching temperature but harms solar modulation.

## Abstract

Insulator to metal (IMT) transition (T$_t$ $\sim$ 341 K) in the VO2 accompanies transition from an infrared (IR) transparent to IR opaque phase. Tailoring of the IMT and associated IR switching behavior can offer potential thermochromic applications. Here we report on effects of the W and the Tb doping on the IMT and associated structural, electronic structure and optical properties of the VO2 thin film. Our results show that the W doping significantly lowers IMT temperature ($\sim$ 292 K to $\sim$ 247 K for 1.3\% W to 3.7\% W) by stabilizing the metallic rutile, $\it{R}$, phase while Tb doping does not alter the IMT temperature much and retains the insulating monoclinic, $\it{M1}$, phase at room temperature. It is observed that the W doping albeit significantly reduces the IR switching temperature but is detrimental to the solar modulation ability, contrary to the Tb doping effects where higher IR switching temperature and solar modulation ability is observed. The IMT behavior, electrical conductivity and IR switching behavior in the W and the Tb doped thin films are found to be directly associated with the spectral changes in the V 3$\it{d_{\|}}$ states.