Complete order parameter condensate of low-symmetry phases upon structural phase transitions

1989 ◽  
Vol 152 (2) ◽  
pp. 431-446 ◽  
Author(s):  
G. M. Chechin ◽  
T. I. Ivanova ◽  
V. P. Sakhnenko
Keyword(s):  
Phase Transitions ◽  
Order Parameter ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Complete Order ◽  
Low Symmetry

scholarly journals Computer simulation of the structural phase transitions in thin ferroelectric films

2017 ◽  
Vol 07 (01) ◽  
pp. 1750004 ◽  
Author(s):  
O. G. Maksimova ◽  
A. V. Maksimov ◽  
O. S. Baruzdina
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Boundary Conditions ◽  
Order Parameter ◽  
Mixed Boundary ◽  
Structural Phase ◽  
Film Surface ◽  
Mixed Boundary Conditions ◽  
Structural Phase Transitions ◽  
Ferroelectric Films

The influence of free surface and depolarizing field on structural phase transitions in thin ferroelectric films from an ordered state to a disordered one is investigated. The dependences of the order parameter on the distance from the free film surface are calculated. It is shown that with the presence of the depolarizing field and in its absence, the effective thickness of the surface layer depends on the temperature. Nearby the phase transition point, the thickness increases indefinitely. Calculations considering depolarizing field showed that the phase transition points for the bulk ferroelectrics and the film under given boundary conditions coincide. Also shown that in the absence of depolarizing field with mixed boundary conditions, the film thickness does not affect the order parameter, and in presence of the field, this influence is observed.

Evidence for precursor clusters associated with structural phase transitions in antifluorite crystals

1982 ◽  
Vol 60 (4) ◽  
pp. 397-398 ◽  
Author(s):  
Robin L. Armstrong ◽  
Marie D'Iorio ◽  
Maximo E. Ramia
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Structural Phase ◽  
Indirect Evidence ◽  
Cubic Phase ◽  
Structural Phase Transitions ◽  
Type Phase ◽  
Symmetry Phase ◽  
Nuclear Quadrupole ◽  
Low Symmetry

Measurements of the temperature dependence of the intensities of the halogen nuclear quadrupole resonances in K2PtBr6 and K2ReCl6, in the cubic phase are reported. These results provide indirect evidence for the formation of dynamic clusters of the low symmetry phase as a precursor to the occurrence of rotative type phase transitions to tetragonal structures in these crystals.

Structural phase transitions of HfV2 at low temperatures

2000 ◽  
Vol 56 (4) ◽  
pp. 601-606 ◽  
Author(s):  
Yusheng Zhao ◽  
Fuming Chu ◽  
Robert B. Von Dreele ◽  
Qing Zhu
Keyword(s):  
Phase Transitions ◽  
Low Temperatures ◽  
Structural Phase ◽  
Orthorhombic Phase ◽  
Unit Cell ◽  
The Body ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Structural Phase Transitions ◽  
Low Symmetry

We report a high-resolution synchrotron X-ray powder diffraction study on HfV2, hafnium divanadium, at low temperatures. In this work we show, for the first time, a complete sequence of structural phase transitions of HfV2 from cubic (Fd3m) to tetragonal (I41/amd) to orthorhombic (Imma) in succession as temperature decreases. Peak splitting and extra diffraction peaks owing to lattice distortion can be clearly distinguished for the low-symmetry phases. The atomic positions and lattice parameters were obtained by Rietveld refinement. The bond lengths and angles of the HfV2 crystal structure at the low-symmetry phases were correctly determined from the structure refinement. The face-centered cubic (Fd3m) unit cell (Z = 24) transforms to a body-centered tetragonal (I41/amd) phase with a 45° rotation relative to the cubic cell and with a reduced number of atoms (Z = 12) in the unit cell at a temperature of T = 112 K. The orthorhombic phase occurs at T = 102 K and it keeps the body-centered symmetry (Imma) and Z = 12 in the unit cell. The refinement results indicate that there may be a small amount of untransformed cubic phase left over in the lower symmetry phases. The abnormal thermal contraction of both tetragonal phase and orthorhombic phase marks the significance of structural change in HfV2.

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