Two pressure-induced structural phase transitions in TiOCl

Abstract

We studied the crystal structure of TiOCl up to pressures of p=25 GPa at room temperature by x-ray powder-diffraction measurements. Two pressure-induced structural phase transitions are observed: at pc1 ≈ 15 GPa emerges an 2a×2b×c superstructure with b -axis unique monoclinic symmetry (space group P21/m). At pc2 ≈ 22 GPa, all lattice parameters of the monoclinic phase show a pronounced anomaly. A fraction of the sample persists in the ambient orthorhombic phase (space group Pmmn) over the whole pressure range. © 2010 The American Physical Society.