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

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.

Crystal structure and phase transition of thermoelectric SnSe

2016 ◽  
Vol 72 (3) ◽  
pp. 310-316 ◽  
Author(s):  
Mattia Sist ◽  
Jiawei Zhang ◽  
Bo Brummerstedt Iversen
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Site Occupancy ◽  
Functional Materials ◽  
Atomic Displacement ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Lattice Constants ◽  
Temperature Phase Transition ◽  
Atomic Displacement Parameters

Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram–Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperatureCmcmphase is not pseudo-tetragonal as commonly assumed.

Phase Transitions and Distortion of [BiCl6]3– Octahedra in (C3H5NH3)3[BiCl6] – DSC and Single-Crystal X-Ray Diffraction Studies

2004 ◽  
Vol 59 (9) ◽  
pp. 1029-1034 ◽  
Author(s):  
Bartosz Zarychta ◽  
Maciej Bujak ◽  
Jacek Zaleski
Keyword(s):  
Phase Transition ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Unit Cells ◽  
Temperature Phase Transition ◽  
The Relationship ◽  
Low Temperature Phase ◽  
Disorder Type

The DSC diagram of tris(allylammonium) hexachlorobismuthate(III), (C3H5NH3)3[BiCl6], revealed three anomalies at 152, 191 and 299 K. The structure of the salt was determined at 200 and 315 K, below and above the high-temperature phase transition at 299 K. In both phases the crystals are monoclinic. At 200 K the space group is C2/c whereas at 315 K it is C2/m. The structures, at both temperatures, are composed of [BiCl6]3− octahedra and allylammonium cations. The organic and inorganic moieties are attracted to each other by a network of the N-H. . .Cl hydrogen bonds. The relationship between corresponding parameters of the unit cells has been found. The phase transition at 299 K, of the order-disorder type, is attributed to the ordering of one non-equivalent allylammonium cation in the low-temperature phase.

Preparation, Crystal Structure at 298 and 90 K and Phase Transition in (C2H5NH3)2[SbBr5] Studied by the Single Crystal X-Ray Diffraction Method

2004 ◽  
Vol 59 (3) ◽  
pp. 298-304 ◽  
Author(s):  
Maciej Bujak ◽  
Bartosz Zarychta ◽  
Aleksandra Kobel ◽  
Jacek Zaleski
Keyword(s):  
Phase Transition ◽  
Diffraction Method ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Methyl Carbon ◽  
One Dimensional ◽  
Space Groups ◽  
Molar Ratios ◽  
Low Temperature Phase ◽  
Disorder Type

The reaction of antimony(III) oxide with ethylamine, in molar ratios from 1:1 to 1:10, in concentrated hydrobromic acid leads to the formation of one product - bis(ethylammonium) pentabromoantimonate( III). The structure of (C2H5NH3)2[SbBr5] was determined at 298 and 90 K, below and above the phase transition that occurs at about 158.5 K. The orthorhombic system was found in both phases, space groups Cmca and Pbca at 298 and 90 K, respectively. At both temperatures the structure consists of [SbBr6]3− octahedra connected via cis bromine atoms forming one-dimensional zig-zag [{SbBr5}2−]n chains. The ethylammonium cations fill the space between polyanionic chains. The organic and inorganic substructures are held together by a system of N(-H)···Br interactions. Their influence on the deformation of [SbBr6]3− octahedra is well reflected in differences in the corresponding Sb-Br bond lengths and Br-Sb-Br angles in both phases. The phase transition is of the first order and the order-disorder type. It is related to changes in the molecular dynamics of the ethylammonium cations. In the low-temperature phase the organic cations are ordered, while at 298 K both crystallographically independent cations are disordered. The type of disorder is realized by the presence of two positions of the methyl carbon atoms

scholarly journals Thermal expansion effects on the one-dimensional liquid-solid phase transition in high temperature phase change materials

AIP Advances ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 025125 ◽  
Author(s):  
Rubén Darío Santiago Acosta ◽  
José Antonio Otero ◽  
Ernesto Manuel Hernández Cooper ◽  
Rolando Pérez-Álvarez
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
High Temperature ◽  
Phase Change Materials ◽  
Solid Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
One Dimensional ◽  
Solid Phase Transition ◽  
The One

scholarly journals High-temperature phase transition of SrRuO3and SrHfO5: X-ray diffraction and PAC spectroscopy

1996 ◽  
Vol 52 (a1) ◽  
pp. C364-C364
Author(s):  
J. A. Guevara ◽  
S. L. Cuffini ◽  
Y. P. Mascarenhas ◽  
P. de la Presa ◽  
A. Ayala ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Pac Spectroscopy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Phase Transition

scholarly journals Ionic Conductivity and Phase Transition Behaviour in 4AgI-(1-)-2CuI System

2008 ◽  
Vol 2008 ◽  
pp. 1-4 ◽  
Author(s):  
Mohammed Hassan ◽  
Rfi Rafiuddin
Keyword(s):  
Phase Transition ◽  
Ionic Conductivity ◽  
Binary System ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Conductivity Measurements ◽  
Temperature Dependent ◽  
X Ray ◽  
Dsc Curves ◽  
Transition Behaviour

Samples of general formula 4AgI-(1-)-2CuI, , have been prepared and investigated by XRD, DSC, and temperature-dependent conductivity studies. X-ray diffractograms showed the presence of binary system consisting of AgI and in the sample . Cu-substituted samples showed very similar diffractograms to that of the pure compound which indicates that no effect for the substitution on the nature of the binary system. DSC curves showed the presence of phase transition whose temperature increased with ratio in the system. Ionic conductivity measurements confirmed the occurrence of the phase transition and showed that the high temperature phase is superionic conducting, whose conductivity increases with the increasing amount in the system.

Parameterization of the coupling between strain and order parameter for LuF[SeO3]

2014 ◽  
Vol 47 (2) ◽  
pp. 701-711 ◽  
Author(s):  
Oxana V. Magdysyuk ◽  
Melanie Müller ◽  
Robert E. Dinnebier ◽  
Christian Lipp ◽  
Thomas Schleid
Keyword(s):  
Phase Transition ◽  
Order Parameter ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Time Resolved ◽  
Synchrotron Powder Diffraction ◽  
First Order Phase Transition ◽  
Temperature Phase Transition ◽  
First Order Phase

The high-temperature phase transition of LuF[SeO3] has been characterized by time-resolved high-resolution synchrotron powder diffraction. On heating, a second-order structural phase transition was found at 393 K, while on cooling the same phase transition occurs at 371 K, showing a large hysteresis typical for a first-order phase transition. Detailed analysis using sequential and parametric whole powder pattern fitting revealed that the coupling between the strain and the displacive order parameter determines the behaviour of the material during the phase transition. Different possible coupling mechanisms have been evaluated and the most probable rationalized.

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