Normal-to-incommensurate phase transition in the spin-Peierls compound TiOCl: An x-ray diffraction study

Abstract

X-ray diffraction on TiOCl indicates a temperature-independent c-axis unique monoclinic distortion of the crystal lattice of ␥ = 90.023͑2͒°within the incommensurate phase between T c1 = 67 K and T c2 = 90 K. The transition at T c2 is described as a first-order phase transition driven by the formation of antiferromagnetic order on the Ti-O bilayers that is governed by the monoclinic lattice distortion. The temperature-dependent incommensurate modulation is considered to represent the growth of the number of spin-Peierls-type singlet pairs on cooling. At T c1 , too many electrons have thus been removed from the antiferromagnetic state for it to be stable, and the crystal transforms into the spin-Peierls state.

Observation of strong magnetoelastic coupling in a first-order phase transition of CrOCl

“…The difference in the center positions of the two Lorentzians provide an accurate estimate for the splitting in 2 from which the monoclinic angle ␣ can be calculated. 19 The monoclinic distortion is weakly temperature dependent and corroborates the first-order character of the phase transition ͑Fig. 8͒.…”

Phase transition, crystal structure, and magnetic order in VOCl

“…͑A detailed description of the procedure of 2 scans with narrow detector slits is given in Ref. 12.͒ Similar scans were performed on the reflections ͑4, Ϯ 2,0͒ and ͑2, Ϯ 4,0͒ at selected temperatures within the range 20 K Յ T Յ 85 K. The magnitude of the splitting appeared to depend on temperature and it was zero for T Ͼ 80 K.…”

Spin-Peierls transition in theS=12compound TiPO4featuring large intrachain coupling

“…20 Analogous arguments may apply for TiPO 4 as well. In view of the small interchain coupling the incommensurate phase between 111 K and 74 K could also be ascribed to a dynamic equilibrium between short-range-ordered dimerized segments.…”