Atomic displacements at and order of all phase transitions in multiferroic YMnO3 and BaTiO3

2009 ◽  
Vol 65 (4) ◽  
pp. 450-457 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Landau Theory ◽  
Unit Cell ◽  
Paramagnetic Phase ◽  
First Order ◽  
Atomic Displacements ◽  
Magnetic Symmetry

Coordinate analysis of the multiple phase transitions in hexagonal YMnO3 leads to the prediction of a previously unknown aristotype phase, with the resulting phase-transition sequence: P63′cm′(e.g.) ↔ P63 cm ↔ P63/mcm ↔ P63/mmc ↔ P6/mmm. Below the Néel temperature T N ≃ 75 K, the structure is antiferromagnetic with the magnetic symmetry not yet determined. Above T N the P63 cm phase is ferroelectric with Curie temperature T C ≃ 1105 K. The nonpolar paramagnetic phase stable between T C and ∼ 1360 K transforms to a second nonpolar paramagnetic phase stable to ∼ 1600 K, with unit-cell volume one-third that below 1360 K. The predicted aristotype phase at the highest temperature is nonpolar and paramagnetic, with unit-cell volume reduced by a further factor of 2. Coordinate analysis of the three well known phase transitions undergone by tetragonal BaTiO3, with space-group sequence R3m ↔ Amm2 ↔ P4mm ↔ Pm\overline 3m, provides a basis for deriving the aristotype phase in YMnO3. Landau theory allows the I ↔ II, III ↔ IV and IV ↔ V phase transitions in YMnO3, and also the I ↔ II phase transition in BaTiO3, to be continuous; all four, however, unambiguously exhibit first-order characteristics. The origin of phase transitions, permitted by theory to be second order, that are first order instead have not yet been thoroughly investigated; several possibilities are briefly considered.

The Ion Conducting Properties of Perovskite-Type Solid Solutions (La0.5Li0.5) [Ti1-x(M0.5Nb0.5)x]O3 (M = Al, Ga)

2006 ◽  
Vol 514-516 ◽  
pp. 407-411 ◽  
Author(s):  
Elena A. Fortalnova ◽  
Alexander V. Mosunov ◽  
Marina G. Safronenko ◽  
Nikolay U. Venskovskii ◽  
Ekaterina D. Politova
Keyword(s):  
Phase Transitions ◽  
Low Temperature ◽  
Cell Volume ◽  
Solid Solutions ◽  
Unit Cell Volume ◽  
Relaxation Effect ◽  
Unit Cell ◽  
Temperature Dependences ◽  
Ion Conducting ◽  
Perovskite Type

The influence of B-site substitution on electroconducting properties of perovskite-type solid solutions (La0.5Li0.5)[Ti1-x(M0.5Nb0.5)x]O3 with M = Al, Ga, have been studied. A decrease in the conductivity due to the unit cell contraction with increasing x in case of M = Al has been revealed. In case of Ga and Nb substitutions for Ti the unit cell volume has been found to increase with increasing x while the conductivity decreases due to the impurity phases presence. The high and low temperature anomalies on the temperature dependences of dielectric characteristic related to both the relaxation effect and phase transitions have been revealed.

scholarly journals Low-temperature phase transition and highpressure phase stability of 1H-pyrazole-1carboxamidine nitrate

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Piotr Rejnhardt ◽  
Marek Drozd ◽  
Marek Daszkiewicz
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase I ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Negative Thermal Expansion ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Scanning Calorimetry

The phase transition observed in a temperature-dependent experiment at 174 K is unachievable under high-pressure conditions. Negative thermal expansion for phase (II) and negative compressibility for phase (I) were observed. A new salt of 1H-pyrazole-1-carboxamidine, (HPyCA)NO3, for guanylation reaction was obtained in a crystalline form. The compound crystallizes in monoclinic space group P21/c and a phase transition at 174 K to triclinic modification P 1 was found. An unusual increase of the unit-cell volume was observed just after transition. Although the volume decreases upon cooling, it remains higher down to 160 K in comparison to the unit-cell volume of phase (I). The mechanism of the phase transition is connected with a minor movement of the nitrate anions. The triclinic phase was unreachable at room-temperature high-pressure conditions up to 1.27 GPa. On further compression, delamination of the crystal was observed. Phase (I) exhibits negative linear compressibility, whereas abnormal behaviour of the b unit-cell parameter upon cooling was observed, indicating negative thermal linear expansion. The unusual nature of the compound is associated with the two-dimensional hydrogen-bonding network, which is less susceptible to deformation than stacking interactions connecting the layers of hydrogen bonds. Infrared spectroscopy and differential scanning calorimetry measurements were used to investigate the changes of intermolecular interactions during the phase transition.

Enantiotropic phase transition in a binuclear tin complex with anO,N,O′-tridentate ligand

2013 ◽  
Vol 69 (11) ◽  
pp. 1336-1339 ◽  
Author(s):  
Anke Schwarzer ◽  
Lydia E. H. Paul ◽  
Uwe Böhme
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Tridentate Ligand ◽  
Asymmetric Unit ◽  
Disorder Transition ◽  
Vinyl Group

The crystal structure of chlorido{μ-2-[(2-oxidobenzylidene)amino]ethanolato-κ4O,N,O′:O′}{2-[(2-oxidobenzylidene)amino]ethanolato-κ3O,N,O′}trivinylditin(IV), [Sn2(C2H3)3(C9H9NO2)2Cl], is disordered above 178 K. A doubling of the unit-cell volume is observed on cooling. The asymmetric unit at 93 K contains two ordered molecules. The phase transition corresponds to an order–disorder transition of one vinyl group bound to the SnIVatom.

scholarly journals Geometric considerations of the monoclinic–rutile structural transition in VO2

2019 ◽  
Vol 48 (25) ◽  
pp. 9260-9265
Author(s):  
Shian Guan ◽  
Aline Rougier ◽  
Matthew R. Suchomel ◽  
Nicolas Penin ◽  
Kadiali Bodiang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Structural Transition ◽  
Unit Cell

Geometrical and experimental examinations of VO2 show how hysteretic phase transition phenomena across the MIT can be driven by positive crystal energy effects of increasing unit cell volume.

MULTIPLE PHASE TRANSITIONS IN PEROVSKITE STRUCTURE CERAMICS: STRUCTURAL TRANSITIONS

1999 ◽  
Vol 13 (22n23) ◽  
pp. 791-799
Author(s):  
C. H. EAB ◽  
B. WIWATANAPATAPHEE ◽  
I. M. TANG
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Structural Phase Transition ◽  
Perovskite Structure ◽  
Landau Theory ◽  
Structural Phase ◽  
Free Energies ◽  
Ginzburg Landau ◽  
First Order ◽  
Multiple Phase

A Ginzburg–Landau theory for the multiple structural phase transition observed in the cuprate perovskite structure ceramics is developed. The order parameters Λi for each phase are defined in terms of the deformations which occur in each phase. In terms of the deformation, the expansion of the free energies is to the twelfth order. The theory can account for a second-order tetragonal to orthorhombic-I transition at high temperatures and a first-order orthorhombic-I to orthorhombic-II transition at lower temperatures. The criterion for the existence of a tricritical line is established.

Characterization of the pressure-induced second-order phase transition in the mixed-valence vanadate BaV6O11

2009 ◽  
Vol 65 (3) ◽  
pp. 326-333 ◽  
Author(s):  
Karen Friese ◽  
Yasushi Kanke ◽  
Andrzej Grzechnik
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Ambient Pressure ◽  
Mixed Valence ◽  
Volume Effect ◽  
Unit Cell ◽  
Additional Degree ◽  
Diamond Anvil

The pressure dependence of the structure of the mixed-valence vanadate BaV6O11 was studied with single-crystal X-ray diffraction in a diamond–anvil cell. The compressibility data could be fitted with a Murnaghan equation of state with the zero-pressure bulk modulus B 0 = 161 (7) GPa and the unit-cell volume at ambient pressure = 387.1 (3) Å^3 (B′ = 4.00). A phase transition involving a symmetry reduction from P63/mmc to P63 mc can be reliably detected in the high-pressure data. The estimated transition pressure lies in the range 1.18 < P c < 3.09 GPa. The transition leads to a breaking of the regular Kagomé net formed by part of the V ions. While in the ambient pressure structure all V—V distances in the Kagomé net are equal, they split into inter-trimer and intra-trimer distances in the high-pressure phase. In general, these changes are comparable to those observed in the corresponding low-temperature transition. However, the pressure-induced transition takes place at a lower unit-cell volume compared with the temperature-induced transition. Furthermore, overall trends for inter-trimer and intra-trimer V—V distances as a function of the unit-cell volume are clearly different for datapoints obtained by variation of pressure and temperature. The behavior of BaV6O11 is compared with that of NaV6O11. While in the latter compound the transition can be explained as a pure volume effect, in BaV6O11 an additional degree of freedom related to the valence distribution among the symmetrically independent vanadium sites has to be taken into account.

scholarly journals Electric properties of olive oil under pressure

2021 ◽  
Author(s):  
L. T. Pawlicki ◽  
R. M. Siegoczyński ◽  
S. Ptasznik ◽  
K. Marszałek
Keyword(s):  
Molecular Structure ◽  
Phase Transition ◽  
Phase Diagram ◽  
Phase Transitions ◽  
Olive Oil ◽  
Material Parameters ◽  
First Order ◽  
Long Time ◽  
Capacitive Reactance ◽  
First Order Phase

AbstractThe main purpose of the experiment was a thermodynamic research with use of the electric methods chosen. The substance examined was olive oil. The paper presents the resistance, capacitive reactance, relative permittivity and resistivity of olive. Compression was applied with two mean velocities up to 450 MPa. The results were shown as functions of pressure and time and depicted on the impedance phase diagram. The three first order phase transitions have been detected. All the changes in material parameters were observed during phase transitions. The material parameters measured turned out to be the much more sensitive long-time phase transition factors than temperature. The values of material parameters and their dependence on pressure and time were compared with the molecular structure, arrangement of molecules and interactions between them. Knowledge about olive oil parameters change with pressure and its phase transitions is very important for olive oil production and conservation.

scholarly journals Allanite at high temperature: effect of REE on the thermal behaviour of epidote-group minerals

2021 ◽  
Vol 48 (9) ◽  
Author(s):  
G. Diego Gatta ◽  
Francesco Pagliaro ◽  
Paolo Lotti ◽  
Alessandro Guastoni ◽  
Laura Cañadillas-Delgado ◽  
...  
Keyword(s):  
Cell Volume ◽  
Thermal Behaviour ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Atomic Scale ◽  
Elastic Behaviour ◽  
Positive Trend ◽  
Cell Parameters ◽  
Thermal Anisotropy ◽  
Different Temperatures

AbstractThe thermal behaviour of a natural allanite-(Ce) has been investigated up to 1073 K (at room pressure) by means of in situ synchrotron powder X-ray diffraction and single-crystal neutron diffraction. Allanite preserves its crystallinity up to 1073 K. However, up to 700 K, the thermal behaviour along the three principal crystallographic axes, of the monoclinic β angle and of the unit-cell volume follow monotonically increasing trends, which are almost linear. At T > 700–800 K, a drastic change takes place: an inversion of the trend is observed along the a and b axes (more pronounced along b) and for the monoclinic β angle; in contrast, an anomalous increase of the expansion is observed along the c axis, which controls the positive trend experienced by the unit-cell volume at T > 700–800 K. Data collected back to room T, after the HT experiments, show unit-cell parameters significantly different with respect to those previously measured at 293 K: allanite responds with an ideal elastic behaviour up to 700 K, and at T > 700–800 K its behaviour deviates from the elasticity field. The thermo-elastic behaviour up to 700 K was modelled with a modified Holland–Powell EoS; for the unit-cell volume, we obtained the following parameters: VT0 = 467.33(6) Å3 and αT0(V) = 2.8(3) × 10–5 K−1. The thermal anisotropy, derived on the basis of the axial expansion along the three main crystallographic directions, is the following: αT0(a):αT0(b):αT0(c) = 1.08:1:1.36. The T-induced mechanisms, at the atomic scale, are described on the basis of the neutron structure refinements at different temperatures. Evidence of dehydroxylation effect at T ≥ 848 K are reported. A comparison between the thermal behaviour of allanite, epidote and clinozoisite is carried out.

scholarly journals Study of Structural, Magnetic, and Mossbauer Properties of Dy2Fe16Ga1−xNbx (0.0 ≤ x ≤ 1.0) Prepared via Arc Melting Process

2021 ◽  
Vol 7 (3) ◽  
pp. 42
Author(s):  
Jiba N. Dahal ◽  
Kalangala Sikkanther Syed Ali ◽  
Sanjay R. Mishra
Keyword(s):  
Isomer Shift ◽  
Cell Volume ◽  
Intermetallic Compounds ◽  
Unit Cell Volume ◽  
Rietveld Analysis ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Arc Melting ◽  
Nb Content

Intermetallic compounds of Dy2Fe16Ga1−xNbx (x = 0.0 to 1.00) were synthesized by arc melting. Samples were investigated for structural, magnetic, and hyperfine properties using X-ray diffraction, vibration sample magnetometer, and Mossbauer spectrometer, respectively. The Rietveld analysis of room temperature X-ray diffraction data shows that all the samples were crystallized in Th2Fe17 structure. The unit cell volume of alloys increased linearly with an increase in Nb content. The maximum Curie temperature Tc ~523 K for x = 0.6 sample is higher than Tc = 153 K of Dy2Fe17. The saturation magnetization decreased linearly with increasing Nb content from 61.57 emu/g for x = 0.0 to 42.46 emu/g for x = 1.0. The Mössbauer spectra and Rietveld analysis showed a small amount of DyFe3 and NbFe2 secondary phases at x = 1.0. The hyperfine field of Dy2Fe16Ga1−xNbx decreased while the isomer shift values increased with the Nb content. The observed increase in isomer shift may have resulted from the decrease in s electron density due to the unit cell volume expansion. The substantial increase in Tc of thus prepared intermetallic compounds is expected to have implications in magnets used for high-temperature applications.

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