Critical X-ray Scattering Studies of Jahn-Teller Phase Transitions in TbV$_{1-x}$As$_{x}$O$_{4}$

TL;DR

This study investigates the critical behavior of Jahn-Teller phase transitions in TbV$_{1-x}$As$_{x}$O$_{4}$ crystals using high-resolution x-ray scattering, revealing mean field strain behavior and fluctuation effects near the transition.

Contribution

It provides detailed experimental insights into the critical phenomena and twinning behavior in Jahn-Teller transitions with varying disorder levels in TbV$_{1-x}$As$_{x}$O$_{4}$.

Findings

Orthorhombic strain exhibits mean field behavior near T_C.

Fluctuation effects cause divergence in Bragg scattering width with a specific power law.

Disordered samples show stable twin domains at low temperatures.

Abstract

The critical behaviour associated with cooperative Jahn-Teller phase transitions in TbV$_{1-x}$As$_{x}$O$_{4}$ (where \textit{x} = 0, 0.17, 1) single crystals have been studied using high resolution x-ray scattering. These materials undergo continuous tetragonal $\to$ orthorhombic structural phase transitions driven by Jahn-Teller physics at T$_C$ = 33.26(2) K, 30.32(2) K and 27.30(2) K for \textit{x} = 0, 0.17 and 1 respectively. The orthorhombic strain was measured close to the phase transition and is shown to display mean field behavior in all three samples. Pronounced fluctuation effects are manifest in the longitudinal width of the Bragg scattering, which diverges as a power law, with an exponent given by $x=0.45 \pm 0.04$, on approaching the transition from either above or below. All samples exhibited twinning; however the disordered x = 0.17 sample showed a broad distribution of twins which were stable to relatively low temperatures, well below T$_C$. This indicates that while the orthorhombic strain continues to develop in a conventional mean field manner in the presence of disorder, twin domains are easily pinned by the quenched impurities and their associated random strains.