Thermopower analysis of metal-insulator transition temperature modulations in vanadium dioxide thin films with lattice distortion

TL;DR

This study uses thermopower measurements to analyze how lattice distortion influences the metal-insulator transition temperature in VO2 thin films, revealing differences in transition detection methods and providing insights into the transition process.

Contribution

It demonstrates that thermopower measurements can effectively detect early metallic domains and offers a new approach to studying the MI transition in VO2 thin films with controlled lattice distortions.

Findings

Seebeck coefficient decreases significantly during transition

Transition temperatures decrease with lattice shrinkage

Thermopower detects metallic domains earlier than resistivity

Abstract

Insulator-to-metal (MI) phase transition in vanadium dioxide (VO2) thin films with controlled lattice distortion was investigated by thermopower measurements. VO2 epitaxial films with different crystallographic orientations, grown on (0001) alpha-Al2O3, (11-20) alpha-Al2O3, and (001) TiO2 substrates, showed significant decrease of absolute value of Seebeck coefficient (S) from ~200 to 23 microV K-1, along with a sharp drop in electrical resistivity (rho), due to the transition from an insulator to a metal. The MI transition temperatures observed both in rho (Trho) and S (TS) for the VO2 films systematically decrease with lattice shrinkage in the pseudo-rutile structure along c-axis, accompanying a broadening of the MI transition temperature width. Moreover, the onset TS, where the insulating phase starts to become metallic, is much lower than onset Trho. This difference is attributed to the sensitivity of S for the detection of hidden metallic domains in the majority insulating phase, which cannot be detected in rho-measurements. Consequently, S-measurements provide a straightforward and excellent approach for a deeper understanding of the MI transition process in VO2.