CORRELATION FUNCTIONS OF THE TWO-STATE VERTEX MODEL ON THE CAYLEY TREE

The symmetric two-state vertex model on the Cayley tree is studied. Two types of first-order phase transitions are distinguished according to the behaviour of correlation functions in the high-temperature phase. A manifold in the model parameter space on which the correlations vanish is shown to be the same as for the honeycomb lattice.

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High Temperature Phase Transitions in BiFeO3

MRS Proceedings ◽

10.1557/proc-1199-f11-08 ◽

2009 ◽

Vol 1199 ◽

Author(s):

Donna Arnold ◽

Christopher M Kavanagh ◽

Philip Lightfoot ◽

Finlay Doogan Morrison

Keyword(s):

Phase Transition ◽

High Temperature ◽

Order Phase Transition ◽

Structure Type ◽

High Temperature Phase ◽

Temperature Phase ◽

First Order ◽

Β Phase ◽

First Order Phase Transition ◽

First Order Phase

AbstractThe high temperature phases of BiFeO3 have courted much controversy with many conflicting structural models reported, in particular for the paraelectric β-phase. High temperature powder neutron diffraction (PND) experiments indicate that the ferroelectric (R3c) α-phase transforms to the paraelectric β-phase at approximately 820 °C via a first order phase transition. We demonstrate that this phase is unambiguously orthorhombic, adopting the GdFeO3 structure-type with a space group Pbnm. On further heating BiFeO3 undergoes another first order phase transition (β-γ) at approximately 930 °C which is marked by a discontinuous decrease in cell volume consistent with an insulator-metal transition. Close inspection of the PND data show no evidence of any symmetry change, with the postulated γ-phase remaining orthorhombic Pbnm. In addition we present PND and impedance spectroscopy data for BiFeO3 which suggest that the so-called ‘Połomska’ transition observed by some authors at approximately 185 °C is not intrinsic.

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Synthesis and Lattice Distortion of Ferroelectric/Antiferroelectric Bi(III)-containing Perovskites

MRS Proceedings ◽

10.1557/proc-755-dd12.10 ◽

2002 ◽

Vol 755 ◽

Cited By ~ 3

Author(s):

Yoshiyuki Inaguma ◽

Atsushi Miyaguchi ◽

Tetsuhiro Katsumata

Keyword(s):

Phase Transition ◽

High Temperature ◽

Order Phase Transition ◽

Lattice Distortion ◽

High Temperature Phase ◽

Temperature Phase ◽

First Order ◽

First Order Phase Transition ◽

Lattice Distortions ◽

First Order Phase

ABSTRACTBi(III)-containing perovskites Bi1/2Ag1/2TiO3 and Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni) were synthesized under oxygen pressure as high as approximately 1 MPa and under a pressure as high as 6 GPa, and the lattice distortions were investigated. It was found that ferroelectric Bi1/2Ag1/2TiO3 may be rhombohedrally distorted. In constrast, Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni), the structure of which is different from GdFeO3-type compound, is monoclinically distorted. The ratio of lattice parameters of the monoclinic perovskite-subcell for Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni), am/bm is larger than that of GdFeO3-type perovskites, though the tolerance factor is close. In addition, it was found that Bi(Ni1/2Ti1/2)O3 undergoes a first-order phase transition from a GdFeO3-type phase(high-temperature phase) at around 490 K. These results indicate that the Bi3+ character in Bi(III)-containing perovskites strongly influences the structure distortion.

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In Situ Measurement of Phase Transition of Layered Perovskite BaLn2Mn2O7

Advances in Science and Technology ◽

10.4028/www.scientific.net/ast.67.113 ◽

2010 ◽

Vol 67 ◽

pp. 113-117 ◽

Cited By ~ 2

Author(s):

Hiromi Nakano ◽

Nobuo Ishizawa ◽

Hirohisa Sato ◽

Naoki Kamegashira

Keyword(s):

Phase Transition ◽

High Temperature ◽

Order Phase Transition ◽

High Temperature Phase ◽

Layered Perovskite ◽

Temperature Phase ◽

First Order ◽

First Order Phase Transition ◽

First Order Phase

The BaLn2Mn2O7 (Ln = rare earth) has a Sr3Ti2O7-type structure with double block oxygen octahedra belonging to the Ruddlesden-Popper-Type homologous series AO(ABO3)2. In-situ measurement of the phase transition for BaLn2Mn2O7 was performed using single-crystal X-ray diffraction and a high-temperature transmission electron microscope (TEM). Two types of transitions were observed in BaPr2Mn2O7: the transition from primitive tetragonal (P42/mnm) to body-centered tetragonal (I4/mmm) at around 400 K and the first-order phase transition at around 1040 K. Multiple phase transitions were also observed in BaEu2Mn2O7, with one from P42/mnm to I4/mmm at around 400 K and another, above 550 K, as a first-order phase transition. The high-temperature phase had a 1.5% lattice mismatch along the c-axis compared with the low-temperature phase. We succeeded in recording for the first time in-situ structural change in BaGd2Mn2O7 as a movie by high-temperature TEM. The high-temperature phase nucleated parallel to the (00l) plane as a layer above 550 K and grew until covering the entire inspected region at around 1023 K. The first-order phase transition was caused by the structural and/or electrical distortion of the layered perovskite structure composed of Jahn-Teller ion Mn3+.

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High temperature phase transitions and proton conductivity in some kdp-family crystals

Ferroelectrics ◽

10.1080/00150198908007907 ◽

1989 ◽

Vol 100 (1) ◽

pp. 135-141 ◽

Cited By ~ 113

Author(s):

A. I. Baranov ◽

V. P. Khiznichenko ◽

L. A. Shuvalov

Keyword(s):

Phase Transitions ◽

High Temperature ◽

Proton Conductivity ◽

High Temperature Phase ◽

Temperature Phase

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Fate of false vacua in holographic first-order phase transitions

Journal of High Energy Physics ◽

10.1007/jhep12(2020)200 ◽

2020 ◽

Vol 2020 (12) ◽

Author(s):

Francesco Bigazzi ◽

Alessio Caddeo ◽

Aldo L. Cotrone ◽

Angel Paredes

Keyword(s):

Phase Transitions ◽

Chiral Symmetry ◽

Metastable Phase ◽

Chiral Symmetry Breaking ◽

Model Parameters ◽

Temperature Phase ◽

Thin Wall ◽

Critical Temperatures ◽

First Order ◽

First Order Phase

Abstract Using the holographic correspondence as a tool, we study the dynamics of first-order phase transitions in strongly coupled gauge theories at finite temperature. Considering an evolution from the large to the small temperature phase, we compute the nucleation rate of bubbles of true vacuum in the metastable phase. For this purpose, we find the relevant configurations (bounces) interpolating between the vacua and we compute the related effective actions. We start by revisiting the compact Randall-Sundrum model at high temperature. Using holographic renormalization, we compute the derivative term in the effective bounce action, that was missing in the literature. Then, we address the full problem within the top-down Witten-Sakai-Sugimoto model. It displays both a confinement/deconfinement and a chiral symmetry breaking/restoration phase transition which, depending on the model parameters, can happen at different critical temperatures. For the confinement/deconfinement case we perform the numerical analysis of an effective description of the transition and also provide analytic expressions using thick and thin wall approximations. For the chiral symmetry transition, we implement a variational approach that allows us to address the challenging non-linear problem stemming from the Dirac-Born-Infeld action.

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