Phase transition-induced superstructures of β-Sn films with atomic-scale thickness

AbstractThe detailed structure of nanocrystalline BaTiO3 powder during ball milling has been studied using XRD & TEM. The study illustrates important advances in understanding atomic scale properties of this material. Ferroelectric BaTiO3 powder undergoes phase transformation along the sequence Cubic(Pm3m)-tetragonal(P4mm)-orthohombic (Amm2)-rhombohedral(R3m) structure when pressureless sintered samples are cooled from high temperature to low temperature. The high to low symmetry phases are not related to group subgroup symmetry as transformation is discontinuous and first order in nature and the twin relationship in the low symmetry is forbidden by Landau theory. In case of ball milled BaTiO3 powder a continuous and diffusionless phase transition occur via second order to and from a metastable intermediate phase. In this pathway crystallites in the aggregation are twinned and the twin structure is related to crystal point group m3m which in the present case is illustrated as having 6mm symmetry formed under low driving force. The unit cell evolution due to phase transition and the crystallographic relationship are established. The phase transformation, coalescence and twin structure of thermally annealed BaTiO3 nanocrystals under high vacuum has been investigated using in situ high temperature XRD. The structure analysis is performed with the use of the method of computer modelling of disorder structure and simulation of corresponding diffraction pattern.

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Atomic Scale Study of Surface Structures and Phase Transitions with Reflection High-Energy Positron Diffraction

Materials Science Forum ◽

10.4028/www.scientific.net/msf.607.94 ◽

2008 ◽

Vol 607 ◽

pp. 94-98

Author(s):

Atsuo Kawasuso ◽

Yuki Fukaya ◽

M. Hashimoto ◽

Ayahiko Ichimiya ◽

H. Narita ◽

...

Keyword(s):

Phase Transition ◽

Atomic Displacement ◽

High Energy ◽

Chain Structure ◽

High Temperature Phase ◽

Atomic Scale ◽

Zigzag Chain ◽

Temperature Phase ◽

One Dimensional ◽

Disorder Type

In this work, we studied a few surfaces, of which the structures have not yet been revealed, using reflection high-energy positron diffraction (RHEPD). We studied the Ge(111)/Pb and Ge(111)/Sn surfaces that exhibit the phase transition from 3×3 to √3×√3 periodicities at around 200K. We found that in both phases the equilibrium positions of Pb and Sn adatoms are conserved. That is, in the unit-cell, one of three adatoms is located upper position and two of them are located lower positions (one-up-two-down). The phase transition is interpreted in terms of an order-disorder type. We furthermore studied the quasi-one dimensional Si(111)/In surface which exhibits the metal-insulator transition at around 120K. The high temperature phase is well explained as the zigzag chain structure. We found that a dynamic atomic displacement which leads to the formation of hexagon structure occur below 120 K. We confirmed the appearance of the band gap using the surface structure determined from the RHEPD rocking curves.

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Direct Atomic-Scale Imaging of Multistep Phase Transition during the Lithiation of Nanowires by In-Situ (S)TEM

Microscopy and Microanalysis ◽

10.1017/s1431927614003869 ◽

2014 ◽

Vol 20 (S3) ◽

pp. 428-429

Author(s):

Anmin Nie ◽

Robert F. Klie ◽

Sreeram Vaddiraju ◽

Reza Shahbazian -Yassar

Keyword(s):

Phase Transition ◽

Atomic Scale

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Crystal structure of the high-P polymorph of Ca2B6O6(OH)10·2(H2O) (meyerhofferite)

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials ◽

10.1107/s2052520621009768 ◽

2021 ◽

Vol 77 (6) ◽

Author(s):

Davide Comboni ◽

Tomasz Poreba ◽

Francesco Pagliaro ◽

Tommaso Battiston ◽

Paolo Lotti ◽

...

Keyword(s):

Crystal Structure ◽

Phase Transition ◽

High Pressure ◽

Large Volume ◽

Atomic Scale ◽

Deformation Mechanisms ◽

X Ray Diffraction ◽

X Ray ◽

First Order ◽

Structural Differences

The crystal structure of the high-pressure polymorph of meyerhofferite, ideally Ca2B6O6(OH)10·2(H2O), has been determined by means of single-crystal synchrotron X-ray diffraction data. Meyerhofferite undergoes a first-order isosymmetric phase transition to meyerhofferite-II, bracketed between 3.15 and 3.75 GPa, with a large volume discontinuity. The phase transition is marked by an increase in the coordination number of the boron B1 site, from III to IV, leading to a more interconnected and less compressible structure. The main structural differences between the two polymorphs and the P-induced deformation mechanisms at the atomic scale are discussed.

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