Effect of Ti-doping on the dimer transition in Lithium Ruthenate

TL;DR

This study investigates how Ti-doping affects the structural phase transition in lithium ruthenate, revealing persistent Ru-Ru dimerization and a non-monotonic change in transition temperature, with implications for local dimer cluster formation.

Contribution

It provides a comprehensive structural analysis showing Ti-doping's complex impact on phase transition and local dimer correlations in lithium ruthenate.

Findings

Ti-doping causes non-monotonic changes in transition temperature.

Persistent Ru-Ru dimerization observed despite doping.

Dimer correlation length remains around 10 Å regardless of doping.

Abstract

We carried out a comprehensive crystal structure characterization of Ti-doped lithium ruthenate (Li$_2$Ti$_x$Ru$_{1-x}$O$_3$), to investigate the effect of Ti-doping on the structural phase transition. Experimental tools sensitive to the average structure (X-ray diffraction), as well as those sensitive to local structure (Extended X-ray Absorption Fine Structure, EXAFS; pair distribution function, PDF) are used. We observed non-monotonic dependence of the structural transition temperature on the Ti-doping level. At low doping, the transition temperature slightly increases with doping, while at high doping, the temperature decreases significantly with doping. We note two important observations from our studies. First, Ti K-edge EXAFS data shows persistent Ti-Ru dimerization even with substantial Ti doping. Second, we were able to use the PDF data to estimate the dimer correlation length above the transition temperature, which would correspond to the size of the proposed local `dimer clusters' formed by Ru-Ru and Ti-Ru neighbours. The dimer correlation length is found to be around 10~\AA, which remains robust regardless of doping. Our study therefore suggests that Ti$^{4+}$ with its $d^0$ electronic configuration is a special type of dopant when replacing Ru.