Roles of two successive phase transitions in new spin-Peierls system TiOBr

TL;DR

This study investigates the two successive phase transitions in the spin-Peierls system TiOBr, revealing the nature of incommensurate and commensurate structures and their relation to lattice distortions through diffraction analyses.

Contribution

It provides detailed insights into the roles of two phase transitions in TiOBr, highlighting the incommensurate and commensurate structures and their connection to spin-Peierls distortions.

Findings

Incommensurate superstructure exists between 27K and 47K.

A twofold superstructure is related to lattice distortion below 27K.

Structural correlations develop at high temperatures.

Abstract

In this sturdy, we determine the roles of two successive phase transitions in the new spin-Peierls system TiOBr by electron and synchrotron X-ray diffraction analyses. Results show an incommensurate superstructure along the h- and k-directions between Tc1=27K and Tc2=47K, and a twofold superstructure which is related to a spin-Peierls lattice distortion below Tc1. The diffuse scattering observed above Tc2 indicates that a structural correlation develops at a high temperature. We conclude that Tc2 is a second-order lock-in temperature, which is related to the spin-Peierls lattice distortion with the incommensurate structure, and that Tc1 is from incommensurate to commensurate phase transition temperature accompanying the first-order spin-Peierls lattice distortion.