Relation between tolerance factor and Tc in Aurivillius compounds

2001 ◽  
Vol 16 (11) ◽  
pp. 3139-3149 ◽  
Author(s):  
Donají Y. Suárez ◽  
Ian M. Reaney ◽  
William E. Lee
Keyword(s):  
Room Temperature ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
Tolerance Factor ◽  
Structural Phase Transitions ◽  
Aurivillius Phases ◽  
Ferroelectric Phase Transition Temperature ◽  
Transmission Electron ◽  
Octahedral Tilting ◽  
Permittivity Measurements

The structures and microstructures of a range of Aurivillius phases were investigated by transmission electron microscopy. Systematic rows of superlattice reflections arising from tilting of octahedra around the c axis were identified, and their intensities at room temperature were shown to diminish as the tolerance factor (t) of the perovskite blocks increased. For compounds with t's approaching 1, no superlattice reflections were observed. the paraelectric-to-ferroelectric phase transition temperature (Tc) was monitored through permittivity measurements as a function of temperature, and Tc was also shown to decrease as t increased. Consequently, the onset of octahedral tilting and Tc appeared to be strongly related Aurivillius phases. Planar defects arising from the structural phase transitions and from stacking irregularities were also discussed.

Origin of Ferroelectricity in Aurivillius Compounds

2000 ◽  
Vol 658 ◽  
Author(s):  
Donají Y. ◽  
Suárez Ian M. Reaney ◽  
William E. Lee
Keyword(s):  
Electron Microscopy ◽  
Ferroelectric Phase Transition ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
Tolerance Factor ◽  
Aurivillius Phases ◽  
Ferroelectric Phase Transition Temperature ◽  
Transmission Electron ◽  
Octahedral Tilting ◽  
Permittivity Measurements

ABSTRACTThe structures and microstructures of a range of Aurivillius phases have been investigated using transmission electron microscopy. Superlattice reflections arising from rotations of octahedra around the c-axis have been identified and their intensity at room temperature has been shown to diminish as the tolerance factor of the perovskite blocks increases. The paraelectric to ferroelectric phase transition temperature (Tc) has been monitored using permittivity measurements as a function of temperature and Tc has also been shown to decrease as tolerance factor increases. It is proposed that the onset of octahedral tilting and Tc are related in Aurivillius phases.

scholarly journals Влияние наноконфайнмента на кинетику фазовых переходов в органическом сегнетоэлектрике DIPAI

2020 ◽  
Vol 62 (7) ◽  
pp. 1059
Author(s):  
А.Ю. Милинский ◽  
С.В. Барышников ◽  
Е.В. Чарная ◽  
И.В. Егорова ◽  
Н.И. Ускова
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
Porous Alumina ◽  
Structural Phase ◽  
Polar Phase ◽  
Temperature Hysteresis ◽  
Structural Phase Transitions ◽  
Alumina Films ◽  
Heating And Cooling

The results of studying the linear and nonlinear dielectric properties of a new organic ferroelectric diisopropylammonium iodide (DIPAI), embedded in porous alumina films, in comparison with bulk DIPAI, are presented. It was found, for DIPAI in pores 300 and 60 nm in diameter the ferroelectric phase is formed in the heating and cooling modes in the temperature interval between two structural phase transitions above room temperature. No noticeable temperature hysteresis was observed for both phase transitions. It was shown that the boundaries of the intermediate polar phase for nanostructured DIPAI shift to low temperatures with decreasing pore size. For bulk DIPAI, two structural transitions were revealed during heating with the formation of an intermediate polar phase and only one transition during cooling, below which ferroelectricity occurred. The temperature of this transition was much lower than the corresponding temperature during heating. It is assumed that the observed differences in phase transitions for DIPAI in pores and bulk DIPAI are associated with acceleration of the phase transitions kinetics under conditions of nanoconfinement.

scholarly journals The origin of the lattice thermal conductivity enhancement at the ferroelectric phase transition in GeTe

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Đorđe Dangić ◽  
Olle Hellman ◽  
Stephen Fahy ◽  
Ivana Savić
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Phase Transitions ◽  
Thermoelectric Materials ◽  
Ferroelectric Phase Transition ◽  
Lattice Thermal Conductivity ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
High Symmetry ◽  
Structural Phase Transitions

AbstractThe proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ. However, the κ of GeTe increases at the ferroelectric phase transition near 700 K. Using first-principles calculations with the temperature dependent effective potential method, we show that this rise in κ is the consequence of negative thermal expansion in the rhombohedral phase and increase in the phonon lifetimes in the high-symmetry phase. Strong anharmonicity near the phase transition induces non-Lorentzian shapes of the phonon power spectra. To account for these effects, we implement a method of calculating κ based on the Green-Kubo approach and find that the Boltzmann transport equation underestimates κ near the phase transition. Our findings elucidate the influence of structural phase transitions on κ and provide guidance for design of better thermoelectric materials.

Temperature-induced structural phase transitions in RERhSn (RE = Y, Gd-Tm, Lu)

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Simon Engelbert ◽  
Rolf-Dieter Hoffmann ◽  
Jutta Kösters ◽  
Steffen Klenner ◽  
Rainer Pöttgen
Keyword(s):  
Rare Earth ◽  
Phase Transitions ◽  
Driving Force ◽  
Room Temperature ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray

Abstract The structures of the equiatomic stannides RERhSn with the smaller rare earth elements Y, Gd-Tm and Lu were reinvestigated on the basis of temperature-dependent single crystal X-ray diffraction data. GdRhSn crystallizes with the aristotype ZrNiAl at 293 and 90 K. For RE = Y, Tb, Ho and Er the HP-CeRuSn type (approximant with space group R3m) is already formed at room temperature, while DyRhSn adopts the HP-CeRuSn type below 280 K. TmRhSn and LuRhSn show incommensurate modulated variants with superspace groups P31m(1/3; 1/3; γ) 000 (No. 157.1.23.1) (γ = 3/8 for TmRhSn and γ = 2/5 for LuRhSn). The driving force for superstructure formation (modulation) is a strengthening of Rh–Sn bonding. The modulation is expressed in a 119Sn Mössbauer spectrum of DyRhSn at 78 K through line broadening.

Release of Tetrahydrofuran, Structural Phase Transitions and Dynamic Relaxation Processes in Ca (BH4)2

2012 ◽  
Vol 184 ◽  
pp. 24-32 ◽  
Author(s):  
Annalisa Paolone ◽  
O. Palumbo ◽  
P. Rispoli ◽  
Rosario Cantelli ◽  
E. Rönnebro ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Structural Phase ◽  
Young Modulus ◽  
Relaxation Processes ◽  
Structural Phase Transitions ◽  
Exponential Factor ◽  
Β Phase ◽  
Α Phase ◽  
Calcium Borohydride

Various calcium borohydride samples were investigated by means of combined measurements of thermogravimetry and mass spectrometry, and anelastic spectroscopy. On heating, the release of 2-5% tetrahydrofuran (THF) is detected in all the samples at temperatures below ~480 K, even in those which were previously thermally treated, according to procedures known from the literature, in order to remove the solvent. Dehydrogenation takes place above 480 K. Above room temperature the temperature dependence of the Young modulus of Ca (BH4)2clearly monitors the release of THF and two irreversible structural phase transitions: from the α to the α’ phase around 460 K and from the α’ to the β phase, nearly completely evolved around 590 K. Moreover, the coefficient of elastic energy dissipation presents two dynamic processes below room temperature; a peak around 120 K characterized by an activation energy of 0.20 eV and a pre-exponential factor typical of atom-cluster relaxations, that we attributed to the dynamics of THF molecules retained in the borohydride lattice, and a peak around 200 K, possibly due to the relaxation of H vacancies.

FORMATION OF INTERFACES AND TEMPLATES IN THE Si(111)-Cr SYSTEM

1995 ◽  
Vol 02 (04) ◽  
pp. 439-449 ◽  
Author(s):  
N.I. PLUSNIN ◽  
N.G. GALKIN ◽  
V.G. LIFSHITS ◽  
S.A. LOBACHEV
Keyword(s):  
Room Temperature ◽  
Structural Phase ◽  
High Mobility ◽  
Epitaxial Films ◽  
Semiconductor Film ◽  
Structural Phase Transitions ◽  
Surface Phase ◽  
Surface Phases ◽  
Formation Conditions ◽  
Cr System

The literature data and new data on investigation of the Si(111)-Cr system were systematized to the diagram of structural phase transitions. The ranges on this diagram give the formation conditions of various phases and reflect the mechanism of the Cr/Si (111) and CrSi 2/ Si (111) interface formation during room-temperature Cr deposition following annealing. The proofs of the multilayer surface phase formation and the data about transitions between the multilayer surface phases and bulk silicides during formation of the Cr/Si (111) and CrSi 2/ Si (111) interfaces were presented. The investigation of A- and B-type CrSi 2 templates formation was carried out. It was discovered that nucleation conditions and, in particular, the type of surface phases determine the azimuthal orientation of the epitaxial CrSi 2 islands relative to Si (111) under their nucleation. The A- and B-type CrSi 2 epitaxial films were grown by means of the template technique. The A-type CrSi 2 semiconductor film with low concentration and high mobility of holes was obtained.

Phase and Structural Behaviour in the NdAlO3-EuAlO3 System

2013 ◽  
Vol 200 ◽  
pp. 93-99 ◽  
Author(s):  
Natalia Ohon ◽  
Leonid Vasylechko ◽  
Yurii Prots ◽  
Marcus Schmidt ◽  
Caroline Curfs
Keyword(s):  
Phase Diagram ◽  
Phase Transitions ◽  
Binary System ◽  
Solid Solutions ◽  
Room Temperature ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Structural Behaviour ◽  
First Order

Phase and structural behaviour in the NdAlO3–EuAlO3 system has been studied in the whole concentration range. Depending on x two kinds of solid solutions Nd1‑xEuxAlO3 exist at room temperature: one with rhombohedral (x < 0.15) and one with orthorhombic (x≈ 0.15–0.20, where the co-existence of both phases was observed. First-order structural phase transitions Pbnm↔Rc has been detected in Nd1-xEuxAlO3 with x = 0.3, 0.4, 0.6 at 520 K, 627 K and 988 K, respectively. Based on the experimental and literature data, the phase diagram of the pseudo-binary system NdAlO3–EuAlO3 has been constructed.

Sign in / Sign up

Export Citation Format

Share Document