title: High-pressure polymorphic transformation of rutile to alpha-PbO2-type TiO2 at {011}R twin boundaries.
abstract: The presence of nano-scale lamellae of the alpha-PbO2-type polymorph of TiO2 sandwiched between twinned rutile inclusions in jadeite has been confirmed by electron diffraction and high-resolution transmission electron microscopy, backed up by image simulation techniques, from ultrahigh-pressure jadeite quartzite at Shuanghe in the Dabie Mountains, China. The crystal structure is orthorhombic with lattice parameters a=4.58 A, b=5.42 A, c=5.02 A and space group Pbcn. A three-dimensional structural model has been constructed for the rutile to alpha-PbO2-type TiO2 phase transformation based on high-resolution electron microscopic images. Computer image simulation and structural model analysis reveal that rutile {011}R twin interface is a basic structural unit of alpha-PbO2-type TiO2. Nucleation of alpha-PbO2-type TiO2 lamellae 1-2 nm thick is caused by the displacement of one half of the titanium cations within the {011}R twin slab. This displacement reduces the Ti-O-Ti distance and is favored by high pressure.
authors: Faculty of Materials Science and Chemical Engineering, China University of Geosciences, Wuhan 430074, China.
authors: D W
authors: DW
authors: Meng
authors: X L
authors: XL
authors: Wu
authors: F
authors: F
authors: Sun
authors: L W
authors: LW
authors: Huang
authors: F
authors: F
authors: Liu
authors: Y J
authors: YJ
authors: Han
authors: J P
authors: JP
authors: Zheng
authors: X
authors: X
authors: Meng
authors: R
authors: R
authors: Mason