Anatase, one of the TiO2 polymorphs, is known to show different phase transition paths depending on its crystalline and shape. Particle size of 15∼25 nm anatase has been subjected to highpressure Raman spectroscopy and X-ray diffraction studies using a diamond anvil cell. We observe that the starting sample transforms to an amorphous phase above approx. 20 GPa, which is retained upon pressure release to ambient condition. This is in contrast to previously established transition to baddeleyite

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... ase and we suspect difference in the particle distribution state trigger phase instability of nanoparticles and hence amorphization.