Antiferroelectric Transition Research Articles

Thermal desorption measurement of ultrathin epitaxial organic films by optical spectroscopy

Thermal desorption of epitaxial films of vanadyl phthalocyanine (VOPc:C 32N 8H 16VO) and squaric acid (SQ:C 4O 4H 2) was measured by using temperature programmed optical absorption spectroscopy. The activation energies for the desorption and pre-exponential factors were determined by measuring the amount of the molecules remaining in the film. Change in the molecular arrangement of VOPc during the desorption was detected from the spectra. The effects of hydrogen bonding and antiferroelectric transition of SQ are discussed.

Lattice instabilities, anharmonicity and phase transitions in PbZrO3 from first principles

An effective Hamiltonian for the antiferroelectric transition in PbZrO3 is constructed from first-principles density-functional-theory total-energy and linear-response calculations through the use of a localized, symmetrized basis set of “lattice Wannier functions''. The effective Hamiltonian consists of three-component vector degrees of freedom at the Pb sites and two-component vector degrees of freedom at the oxygen sites. This effective Hamiltonian allows us to analyze the structural energetics and identify the role of various physical contributions. We find that there exists a strong competition between sets of coupled unstable modes in producing low energy states. Two such groups of instabilities found from the effective Hamiltonian are seen to be relevant to the experimental ground and intermediate states.

Effect on Electrical Properties of Barium and Strontium Additions in the Lead Lanthanum Zirconate Stannate Titanate System

The effect of barium (Ba) and strontium (Sr) additions on the electrical properties of lead lanthanum zirconate stannate titanate (PLZST) ceramics and their electrically induced phase change behavior was examined. Sr additions decreased both the ferroelectric (FE) ↔ antiferroelectric (AFE) transition temperature (TAFE‐FE) and the temperature of the maximum dielectric constant (TMAX). This indicates that Sr additions stabilize the AFE phase. Along with B‐site modifications Sr additions can be used to decrease the switching field and hysteresis. Ba additions caused the temperature range of the AFE phase to narrow by increasing TAFE‐FE and decreasing TMAX. This behavior indicates an ability to lower the switching field and suppress hysteresis. Using a combination of both A‐site and B‐site modifications it is possible to tailor the properties (for example, switching field, hysteresis, and operating temperature range) of this group of phase change materials to meet the requirements of specific applications.

Structural Phase Transition in La-Substituted Pb[(Yb 1/2Nb 1/2) 0.88Ti 0.12]O 3 Relaxor System

We have investigated the effect of substitution of La2O3 + Yb2O3 to the perovskite solid solution near the composition (PbYb1/2Nb1/2O3)0.88–(PbTiO3)0.12 in the chemical formula (1-x)[(PbYb1/2Nb1/2O3)0.88 (PbTiO3)0.12]–xLaYbO3. When x = 0.0 and x =0.01, these solid solution have partially disordered pseudocubic structure and behave as a ferroelectric relaxor. For x ≥0.02, the character of phase transition changes from a ferroelectric relaxor type to an antiferroelectric one and the transition temperature surprisingly increases with LaYbO3 addition. In this composition range, the solid solution displays a sharp antiferroelectric transition. The effect on the tendency toward antiferroelecticity with increasing LaYbO3 content is displayed in restoring of the superlattice reflections due to antiferroelectric order. From the structural study of ceramic specimen having various PbTiO3 and LaYbO3 concentration, we have constructed a portion of phase diagram of pseudoternary PbYb1/2Nb1/2O3–PbTiO3–LaYbO3 system.

Dimensionality crossover and the nonlinear dielectric response in betaine phosphate/arsenate mixed crystals

Dielectric properties of quasi-one-dimensional hydrogen-bonded chains are studied for mixed crystals of antiferroelectric betaine phosphate and ferroelectric betaine arsenate at three different mixing concentrations, x = 0.1, 0.3, and 0.4 (x being the concentration of arsenate). For mixed crystals with x = 0.3 and 0.4 dielectric study revealed dimensionality crossover at around 82 K, where the quasi-one-dimensional nature was turned into three-dimensional Curie - Weiss behaviour on lowering the temperature, well above the antiferroelectric transition point. For x = 0.1 mixed crystal, on the other hand, the crossover point was almost coincident with the antiferroelectric transition point, showing still too-weak interchain coupling and strong one-dimensionality, almost to the point of antiferroelectric transition. For this system, the electric bias field effect revealed temperature-dependent nonlinearity of the dielectric constant, which may be ascribed to a development of competition between antiferroelectric and ferroelectric interchain couplings, the latter growing with increasing bias field and lowering temperature.

Phase coexistence in proton glass

Proton glasses are crystals of composition M{sub 1{minus}x}(NW{sub 4}){sub x}W{sub 2}AO{sub 4}, where M = K,Rb, W = H,D, A = P,As. For x = 0 there is a ferroelectric (FE) transition, while for x = 1 there is an antiferroelectric (AFE) transition. In both cases, the transition is from a paraelectric (PE) state of tetragonal structure with dynamically disordered hydrogen bonds to an ordered state of orthorhombic structure. For an intermediate x range there is no transition, but the hydrogen rearrangements slow down, and eventually display nonergodic behavior characteristic of glasses. The authors and other have shown from spontaneous polarization, dielectric permittivity, nuclear magnetic resonance, and neutron diffraction experiments that for smaller x there is coexistence of ferroelectric and paraelectric phases, and for larger x there is coexistence of antiferroelectric and paraelectric phases. The authors present a method for analytically describing this coexistence, and the degree to which this coexistence is spatial or temporal.

Ferroelectric and antiferroelectric modes in a new chiral thiobenzoate liquid crystal

Abstract This work concerns the dielectric relaxation study of a new compound containing a thiobenzoate group with a fluoro substituent, which presents a sequence of antiferro-, ferri-, ferroelectric and SCα phases. The polar character of these phases was confirmed by optical hysteresis loops. Three modes with a nearly monodispersive behaviour were identified: the soft mode, the Goldstone mode and a non-collective azimuthal mode. The soft mode softens above the SA - SCα transition and triggers another mode within the SCα phase. Moreover, a collective anti-phase azimuthal mode appears and may be the origin of the onset of the antiferroelectric SCA phase. A strong influence of surface interactions on the thermal hysteresis and on the dielectric constant was evident in this work.

Phase behaviour and quasi-one dimensionality of betaine arsenate/phosphate mixed crystals

The temperature dependence (24 K < T < 300 K) of the complex permittivity in a ferroelectric mixed crystal has been studied. In order to tune the intermolecular dipolar interactions and to study the stability and kinetics of the different phases of the crystal under investigation, we performed measurements under application of hydrostatic pressures (p < 350 MPa), biasing fields , and different measurement frequencies . These experiments allowed us to depict the corresponding pressure - temperature and electric field - temperature anomaly diagrams of the crystal investigated. Furthermore, in order to analyse the changes in the dipolar system accompanying the dielectric anomalies, we performed dielectric hysteresis measurements. These measurements finally enabled us to identify the character of the phase transitions and the corresponding changes in the dipole system accompanying the dielectric anomalies. A high-temperature transition into an antiferroelectrically ordered phase followed by a re-entrant glassy phase has been found. The high-temperature antiferroelectric transition is discussed in the framework of the quasi-one-dimensional Ising model and compared to the corresponding transitions of the pure compounds, ferroelectric betaine arsenate (BA) and antiferroelectric betaine phosphate (BP), respectively. The low-temperature transition into the re-entrant glassy phase is treated according to the frequency-dependent shift of its indicating anomaly by means of an Arrhenius versus Vogel - Fulcher analysis.

Dielectric Properties and Phase Transition of Polydiacetylene-bis (p-Toluene Sulphonate)

Dielectric constants are measured for the crystals of a polydiacetylene (PTS); dielectric anomalies are observed in the directions parallel and perpendicular to the chain axis of PTS in a temperature range including a phase transition around 195 K. The crystals of PTS show an antiferroelectric transition. We derive a Landau free energy on the basis of group theoretical analysis of both the high and low temperature phases. The anomalous dielectric behavior is discussed with the free energy.

Raman spectroscopic investigation on the phase transitions in Rb 3H(SeO 4) 2 and Rb 3D(SeO 4) 2 single crystals

A temperature dependent Raman spectroscopic investigation of Rb 3H(SeO 4) 2 and Rb 3D(SeO 4) 2 single crystals is carried out from liquid nitrogen temperature up to 620 K. The observed spectra show that the phase transitions are due to restructuring of the system of hydrogen bonds. The ferroelastic phase transition observed in the protonated compound at 451 K is of second order, which corresponds to a rise of symmetry from the room temperature monoclinic to the trigonal phase. The higher wavenumber for the ν(SeO) band at the onset of the transition indicates a positional disorder of protons. In the high temperature phase, the protons are in a highly disordered state followed by fast tunneling. The absence of a frequency shift in the low temperature spectra of the deuterated compound and the invariance of the symmetry during the transition show that the antiferroelectric transition at 95 K is second order and of the order-disorder type.

Raman investigation of undoped, niobium-doped, and lanthanum-doped lead zirconate-titanate ceramics

In a previous article, we proved and characterized a phase transition of an order-disorder type, below room temperature, in the Pb1−3X/2LaX⧠X/2(Zr0.95Ti0.05)O3 (X=0.5–4 wt % La) ceramics. In the present article, the analysis of this order-disorder transition is continued on the basis of the comparative study of Raman scattering, as a function of the Nb or La dopant. The parallel analysis and the interpretation of the Raman spectra of the nondoped, Nb-doped, and La-doped Pb(Zr0.95Ti0.05)O3 ceramics lead to new information concerning the identification of the vibrational modes involved. In addition, the correlation between the phase transitions and the nature of the dopants is established. New information concerning the cell doubling, during the ferroelectric low temperature to ferroelectric high temperature phase transition, is obtained as well. The Raman study of the lead-lanthanum zirconate-titanate ceramics allowed us to identify for the first time the so-called ‘‘antiferroelectric mode’’ and ‘‘ferroelectric mode’’ which had been theoretically predicted.

Localized basis for effective lattice Hamiltonians: Lattice Wannier functions.

A systematic method is presented for constructing effective Hamiltonians for general phonon-related structural transitions. The key feature is the application of group theoretical methods to identify the subspace in which the effective Hamiltonian acts and construct for it localized basis vectors, which are the analogue of electronic Wannier functions. The results of the symmetry analysis for the perovskite, rocksalt, fluorite and A15 structures and the forms of effective Hamiltonians for the ferroelectric transition in $PbTiO_3$ and $BaTiO_3$, the oxygen-octahedron rotation transition in $SrTiO_3$, the Jahn-Teller instability in $La_{1-x}(Ca,Sr,Ba)_xMnO_3$ and the antiferroelectric transition in $PbZrO_3$ are discussed. For the oxygen- octahedron rotation transition in $SrTiO_3$, this method provides an alternative to the rotational variable approach which is well behaved throughout the Brillouin zone. The parameters appearing in the Wannier basis vectors and in the effective Hamiltonian, given by the corresponding invariant energy expansion, can be obtained for individual materials using first- principles density-functional-theory total energy and linear response techniques, or any technique that can reliably calculate force constants and distortion energies. A practical approach to the determination of these parameters is presented and the application to ferroelectric $PbTiO_3$ discussed.

Electro-Optic Effect and Third-Order Nonlinear Dielectric Response in Antiferroelectric Liquid Crystals

We have theoretically studied the electro-optic effect and third-order nonlinear dielectric response in antiferroelectric liquid crystals on the basis of phenomenological equations of motion. It has been found that the antiferroelectric soft and Goldstone modes can be excited by an electric field, though they respond to the square of the field but not to the field itself, and they modulate the dielectric constant both for the visible light and low frequencies, contributing to the electro-optic effect and the third-order nonlinear dielectric response, respectively. The transmitted intensity and the third-order dielectric constant were theoretically derived, and the former was compared with experimental results.

X-Ray and Dielectric Studies of the Phase Transitions in Pb(Yb 1/2Nb 1/2)O 3-PbTiO 3 Ceramics

Phase analysis and dielectric measurement have been conducted for a comprehensive study of the phase transition in the whole composition range of (1-x)Pb(Yb1/2Nb1/2)O3-xPbTiO3 (PYN-PT) ceramic system. For all compositions, a continuous series of complete solid solutions of the antiferroelectric (AFE) and the ferroelectric (FE) compounds was found. With increasing PT concentration x, the phase transition in this system can be categorized as three distinct classes in connection with the degree of the structural ordering. The PYN-rich solutions showed a relatively sharp first-order paraelectric (PE)–AFE transition behavior and the transition temperature decreases rapidly with increasing x. For 0.10 < x < 0.25, the phase transition is broadened and frequency-dependent. Beyond x = 0.25, the normal PE–FE phase transition was observed and the transition temperature increases rapidly with increasing x. In the FE side, it was also revealed that the morphotropic phase boundary between pseudocubic and tetragonal structure lies in the vicinity of x = 0.5. Moreover, the resultant phase diagram with temperature and PT concentration is presented.

Organic hydrogen-bonded dielectrics: Quantum paraelectricity based on tautomerization of 9-hydroxyphenalenone derivatives

Dielectric properties based on tautomerization in 9-hydroxyphenalenone derivatives were examined. While the 5-methyl derivative 2 exhibits an antiferroelectric transition at 41 K, such a phase transition was not observed in 5-bromo derivative 3 down to 4.2 K. Suppression of the phase transition in the latter may be interpreted in terms of quantum paraelectricity based on proton-tunneling along the hydrogen bond. The reason for the appearance of antiferroelectric ordering coupled with the phase transition in 2 may be ascribed to reduction of the tunneling frequency due to symmetry breaking caused by the methyl group. The present system can be regarded as zero-dimensional hydrogen-bonded system and is interesting in reference to inorganic hydrogen-bonded dielectrics.

Antiferroelectric superstructures of Pb2MgWO6

Abstract The antiferroelectrk superstructures of Pb2MgWO6 were investigated by x-ray diffraction and transmission electron microscopy at various temperatures. The analysis of electron diffraction patterns revealed the existence of an intermediate phase in a narrow temperature range just below the well-known antiferroelectric transition temperature T c =39 °C. The superstructure of the low temperature phase is found to be modulated with superimposition of two independent modulation modes {110} p and {1/2 1/2 0} p . We will also discuss this lattice modulation in conjunction with well-known antiferroelectric structure of PbZrO3.

互変異性過程を内包する水素結合系結晶の結晶内ダイナミックス

9-Hydroxyphenalenones exhibit a dynamical disorder due to a tautomeric process or a reorientational motion in the solid state depending on the crystal environment. Both 5-methyl and 5-bromo derivatives undergo a rapid tautomerization in crystals along the symmetrical double-well potential of the hydrogen bond. While the tautomerization of 5-methyl derivative was quenched at 41K due to the antiferroelectric phase transition, 5-bromo derivative does not show any transition down to 4K, because the antiferroelectric transition is suppressed due to the “quantum fluctuation” caused by the tunnelling effect on the proton transfer along the hydrogen bond. On the other hand, the unique dielectric behavior of 9-hydroxyphenalenone in phase II was interpreted in terms of the motion of the domain walls between left-and right-directed molecules based on the reorientational motion in crystals.

Pseudopotential periodic hartree-fock investigation of potassium dihydrogen phosphate

Periodic Hartree-Frock calculations have been performed in order to investigate the electronic structure and the proton transfer mechanism in the solid phase of potassium dihydrogen phosphate (KDP). The calculated structure is in good agreement with experiment. The proton transfer potential energy curve has been simulated by a collective anti-ferroelectric mode which yields a symmetric double well, with a rather low barrier of 162 cm-1 for the optimized O—O distance. It is shown that the barrier height is very sensitive to this soft coordinate. Proton dynamics is investigated by collocation techniques.

Molecular statistical model for ferroelectric - antiferroelectric transition in chiral smectic liqitid crystals

Abstract We discuss ferroelectric-antiferroelectric transition in chiral smectic liquid crystmais with molecular theorp. The pair interaction between model molecules consist's of repulsive hard core potential aid short range attractive force. We take a distinction of the head and tail of the molecule into consideration as an asymmery of the short range attractive part of the pair interaction. Using this model, we show that the head-tail asymmetry contributes to the stability of the ferrielectric phase.

Fluctuation forces and the devil's staircase of ferro/antiferroelectric smectic C*'S

Abstract We propose a mechanism for the long range interaction needed to explain the occurance of a “Devil's staircase” in smectic C* materials at the ferroelectric antiferroelectric transition point.