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

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 ($1/61/62$) 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 ($1/41/42$) 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.

4 pages, 3 figures