Intermediate Phase IV in Structural Phase Transitions of TlCoCl$_3$

TL;DR

This study investigates the structural phase transition of TlCoCl$_3$ around phase IV using neutron diffraction, revealing a stable intermediate phase with specific Bragg peaks and proposing a transition sequence.

Contribution

The paper provides detailed neutron diffraction analysis of phase IV in TlCoCl$_3$, identifying a stable intermediate phase and its unique structural features not previously characterized.

Findings

Identification of a Bragg peak at (1/6 1/6 2) in phase IV

Detection of coexistence of (1/4 1/4 2) peak indicating precursor phenomena

Confirmation of a stable, nontransient phase with specific unit cell dimensions

Abstract

The structural changes of TlCoCl$_3$ around phase IV (68 K $<T<$ 75 K) were studied by single-crystal neutron diffraction measurement. The present investigation revealed that a small but definite Bragg peak at (${1/6} {1/6} 2$) appeared only in phase IV. A precursor phenomenon of the phase V ($T<$ 68 K) structure in the phase IV temperatures was also identified as the coexistence of a slightly broadened (${1/4} {1/4} 2$) Bragg peak. We confirmed that intermediate phase IV is a stable, nontransient, single phase with $2\sqrt{3}a\times 2\sqrt{3}a\times c$ unit cells. A possible sequence of structural phase transitions was proposed.