Enhanced Dimerization of TiOCl under Pressure: Spin-Peierls to Peierls Transition

Abstract

We report high-pressure x-ray diffraction and magnetization measurements combined with ab-initio calculations to demonstrate that the high-pressure optical and transport transitions recently reported in TiOCl, correspond in fact to an enhanced Ti Interaction among different degrees of freedom provides a way for opening up a gap for the collective excitations, and different types of long-range order become then possible.Among the latter, a magnetoelastic coupling in S=1/2 chains results in a spin-Peierls phase transition to a low temperature nonmagnetic dimerized structure, 3,4 which is a localized counterpart of a conventional Peierls transition for itinerant electrons. 5 This effect was found in CuGeO 3 , 6 for a long time the only inorganic system with a pure spin-Peierls distortion. Recently, the possibility that TiOCl shows a low temperature spin-Peierls dimerization has been suggested, although the behavior of this material is

Two pressure-induced structural phase transitions in TiOCl

“…2,4,7 Blanco-Canosa et al 5 confirmed the occurrence of a structural phase transition, but the corresponding critical pressure was considerably lower (≈10 GPa). The high-pressure phase was specified as b-axis unique monoclinic P 2 1 /m phase with a strong dimerization of the 1D spin chain along b.…”

“…However, subsequent electrical transport measurements on powder samples did not confirm a metallization of TiOCl at high pressure and found only an anomaly in the pressureinduced decrease of the charge gap at ≈15 GPa. 4 A controversy regarding the high-pressure electronic properties of TiOCl also exists from the theoretical point of view: Ab initio calculations were carried out based on density functional theory within the LDA+U approximation 5 and using Car-Parrinello molecular dynamics. 6 While the former claims an insulating phase up to at least 30 GPa, the latter predicts the metallic character of the highpressure phases.…”

High-pressure studies with x-rays using diamond anvil cells

“…Vanadium oxides (VO2 and V2O3) display interesting metal-insulating transitions, governed by two wellknown phenomena: the strong electron correlation (Mott-Hubbard) effect mediated by a weak cation-cation interaction and the lattice dimerization (Peierls distortion) [486][487][488][489]. VO2 was first identified as a classic Peierls transition due to the formation of spin singlets associated with V-V dimers in the monoclinic phase [490].…”

Pressure-induced cation-cation bonding inV2O3

“…18,19 Indeed, the dimerization between two cations has been observed in TiOCl and MnS 2 under high pressures. 3,4,20 Vanadium sesquioxide (V 2 O 3 ) is the only transitionmetal sesquioxide that displays metallic nature at ambient condition among others (e.g., Cr 2 O 3 , Fe 2 O 3 , Ti 2 O 3 , etc), and is often referred as a typical Mott-Hubbard material, where electron-electron correlation plays an important role. 5,21,22 It crystallizes in the hexagonal corundumtype structure, with V-ions (V 3+ , 3d 2 ) occupying in facesharing octahedra along the c-axis and edge-sharing octahedra in the basal plane.…”

“…One is the strong electron-electron correlation (Mott-Hubbard) mediated by a weak cation-cation interaction, with the other being the cation-cation bonding (Peierls distortion) through strong cation interactions when these cations locate in edge-or face-sharing octahedra. [1][2][3][4] The cooperation and competition of these two effects are sensitive to conditions such as doping, temperature and pressure. [5][6][7][8][9][10][11][12][13][14][15] Understanding the roles of each condition parameter and the mechanisms governing the rich and interesting properties is of fundamental significance.…”