Energetics of the oxygen vacancy order-disorder transition in Ba2In2O5

The heat capacity and the enthalpy associated with the reported oxygen vacancy order-disorder transition in Ba2In2O5 were measured by high temperature step scanning calorimetry. The transition temperature is 1205 ± 2 K. The transition appears first order or nearly so. The enthalpy and entropy of transition are 1.3 kJ/mol and 1.1 J/mol K, respectively. The latter is only 4.8% of the configurational entropy, arising from mixing one vacancy and five oxygens per formula unit, 22.5 J/mol K. This suggests that the transition involves only a small fraction of the oxygen vacancies and implies extensive short-range order, SRO, in the high temperature phase.

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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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The order–disorder transition in Cu2Se and medium-range ordering in the high-temperature phase

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials ◽

10.1107/s2052520620002164 ◽

2020 ◽

Vol 76 (2) ◽

pp. 201-207

Author(s):

Ping Lu ◽

Wujie Qiu ◽

Yuyu Wei ◽

Chenxi Zhu ◽

Xun Shi ◽

...

Keyword(s):

High Temperature ◽

Structural Changes ◽

Structural Evolution ◽

High Temperature Phase ◽

Temperature Phase ◽

Face Centered Cubic ◽

Thermally Induced ◽

Disorder Transition ◽

Medium Range ◽

Face Centered

The high thermoelectric performance of cuprous selenide (Cu2Se) arises from its specific structures consisting of two independent sublattices, i.e. the rigid face-centered cubic (f.c.c.) Se sublattice and the flexible Cu sublattice showing a variety of ordered configurations at numerous interstitial sites. Upon increasing the temperature, the Cu sublattice undergoes an order-to-disorder transition but the details of the structural evolution have not been fully elucidated. Here, in situ transmission electron microscopy (TEM) is used to investigate the thermally induced structural changes of Cu2Se in both real and reciprocal spaces. Order–disorder transition was found to proceed in nanoblocks accompanied by the structural fluctuations between low-temperature and high-temperature phases. Electron diffraction revealed the emergence of medium-range ordering of Cu atoms in the high-temperature f.c.c. phase. By referring to the Coulomb interaction evaluations, the superstructures for the medium-range ordering were constructed. Such medium-range atomic ordering was sustained over a wide temperature range (from the phase transition temperature to over 800 K in the TEM) but gradually changed to short-range ordering as indicated by the appearance of diffuse scattering rings.

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Evidence for the presence of a first order Raman spectrum in the high temperature phase of SrTiO3

Solid State Communications ◽

10.1016/0038-1098(67)90781-8 ◽

1967 ◽

Vol 5 (5) ◽

pp. 387-390 ◽

Cited By ~ 16

Author(s):

L. Rimai ◽

J.L. Parsons

Keyword(s):

Raman Spectrum ◽

High Temperature ◽

High Temperature Phase ◽

Temperature Phase ◽

First Order

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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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Rigid-Body Disorder Models for the High-Temperature Phase of Ferrocene

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768197005132 ◽

1997 ◽

Vol 53 (6) ◽

pp. 928-938 ◽

Cited By ~ 45

Author(s):

C. P. Brock ◽

Y. Fu

Keyword(s):

High Temperature ◽

Low Temperature ◽

Rigid Body ◽

High Temperature Phase ◽

Body Motion ◽

Temperature Phase ◽

Acta Cryst ◽

Disorder Transition ◽

Simple Order ◽

Low Temperature Phase

Ferrocene, [Fe(C5H5)2], which crystallizes at room temperature in space group P21/a with Z = 2, is described in many textbooks as having D 5d symmetry. Previous work has shown, however, that the librational amplitude associated with motion about the fivefold axis does not decrease with temperature and that the crystals are probably disordered. Ferrocene molecules in triclinic crystals grown below 169 K have approximate D 5 symmetry and an almost eclipsed conformation; the low- and high-temperature phases may be related by an order–disorder transition, during which the number of independent atoms changes by a factor of 4. The structure of the high-temperature phase has been reinvestigated with rigid-body refinements of the neutron diffraction data collected at 173 and 298 K by Takusagawa & Koetzle [Acta Cryst. (1979), B35, 1074–1081]. The C5H5 ring was treated as a rigid group of C 5 symmetry; C—C and C—H distances were allowed to vary, as was the displacement of the H atoms from the C5 plane. The rigid-body motion of the C5H5 ligand was described by the TLS model. All the rigid-body disorder models fit better than conventional independent-atom models. A disorder model that includes three sites for each C5H5 ring is the best of the models that were investigated, which indicates that the structure of the high-temperature phase cannot be described by the superposition of the two independent ferrocene molecules in the low-temperature phase. The phase transition between the high- and low-temperature phases is not a simple order–disorder transition.

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Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr2B2O5 pyroborate and crystal structures of β and α phases

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials ◽

10.1107/s2052520617012689 ◽

2017 ◽

Vol 73 (6) ◽

pp. 1056-1067 ◽

Cited By ~ 2

Author(s):

Sergey Volkov ◽

Michal Dušek ◽

Rimma Bubnova ◽

Maria Krzhizhanovskaya ◽

Valery Ugolkov ◽

...

Keyword(s):

Phase Transitions ◽

High Temperature ◽

Crystal Structures ◽

Intermediate Phase ◽

Orientational Order ◽

High Temperature Phase ◽

Basic Unit ◽

Temperature Phase ◽

Scanning Calorimetry ◽

X Ray

Crystal structures of γ-, β- and α-Sr2B2O5 polymorphs resulting from the γ ↔ (at 565 K) β ↔ (at 637 K) α′ ↔ (at 651 K) α sequence of reversible first-order phase transitions are studied by high-temperature single-crystal X-ray diffraction, high-temperature X-ray powder diffraction, differential scanning calorimetry and impedance spectroscopy. Out of these phases, the structure of γ-Sr2B2O5 was already known whereas the structures of β- and α-Sr2B2O5 were determined for the first time. The sequence of phase transitions is associated with an unusual change of symmetry, with triclinic intermediate β-Sr2B2O5 phase and monoclinic low-temperature γ-Sr2B2O5 as well as high-temperature α-Sr2B2O5 phase. Taking the α-Sr2B2O5 phase with space group P21/c as a parent structure, the γ-Sr2B2O5 phase was refined as a twofold superstructure with symmetry P21/c, whereas the β-Sr2B2O5 phase was a sixfold superstructure with symmetry P{\overline 1}. To construct a unified structure model for all Sr2B2O5 modifications, phases of γ- and β-Sr2B2O5 were also refined as commensurately modulated structures using the basic unit cell of the parent α-Sr2B2O5. The phase transitions are related to the orientational order–disorder arrangement of B2O5 pyroborate groups, where the degree of disorder grows towards the high-temperature phase. Thermal expansion is strongly anisotropic and dictated by preferable orientations of BO3 triangles in the structure. The intermediate phase α′-Sr2B2O5, stable over a narrow temperature range (637–651 K), features the largest anisotropy of expansion for the known borates: α11 = 205, α22 = 57, α33 = −81 × 10−6 K−1.

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

International Journal of Modern Physics B ◽

10.1142/s0217979292001523 ◽

1992 ◽

Vol 06 (21) ◽

pp. 3469-3477 ◽

Cited By ~ 2

Author(s):

M. KOLESÍK

Keyword(s):

Phase Transitions ◽

High Temperature ◽

Correlation Functions ◽

Cayley Tree ◽

High Temperature Phase ◽

Honeycomb Lattice ◽

Temperature Phase ◽

Vertex Model ◽

First Order ◽

First Order Phase

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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