Phase Transition In BaTiO3 Research Articles

Electron microscopic studies of ferroelectric crystals

It is shown that a surprising variety of microstructural phenomena in ferroelectric materials are accessible by high-resolution electron microscopic techniques. Recent observations are reviewed concerning (i) domain wall widths and surface roughness in LiTaO3, KNbO3 and barium sodium niobate (BNN); (ii) microdomain textures and fluctuations at the cubic/tetragonal phase transition of BaTiO3; (iii) the commensurate superlattice structure of BNN and (iv) the hierarchy of chaotic states coexisting within the incommensurate superstructure phase of strontium barium niobate (SBN) at room temperature.

Interface motion in ferroelectrics

The phase plane method is used for solution of the time-dependent Ginzburg-Landau equation. It is shown that the obtained kink solution is a moving interface. The stability of the kink solution under small perturbations is proved. The estimate of the interface velocity at ferroelectric phase transitions in BaTiO 3 and PbTiO 3 crystals shows a satisfactory agreement with experiments.

Isotope Effect in BaTiO3 Phase Transition

The isotope effect of Ti on the ferroelectric curie temperature has studied when the (48Ti) in BaTiO3 is replaced with the light isotope (46Ti). Curie temperature of Ba46TiO3 is found to be 131–133°C whereas that of Ba48TiO3 is 121–122°C. the result is surprising because the Curie temperature of light-isotope-rich sample is usually lower than that of heavyisotope rich one in contrast to our result in BaTiO3.

Study of structural phase transitions by the hyper-Raman scattering

It is discussed that the hyper-Raman and Rayleigh scattering serves to study the structural phase transitions in solids including the case where the pseudo-spins in addition to or coupled to the phonons are involved, since both modes are usually hyper-Raman active in the prototype phase above Tc. Experimentally, rather anomalous aspects of the hyper-Raman spectra and their temperature dependences in cubic BaTiO3 are shown, and the overall results are compared with the ones in the incipient ferroelectric state of SrTiO3 showing rather simpler behaviour. As a result, a rather microscopic model that the phase transition of BaTiO3 is caused by the pseudospins coupled bilinearly with the lowest-frequency TO phonon is proposed for interpreting well the present results. This model is also shown to lead to the Curie-Weiss law of the dielectric constant.An enhancement of the intensity of a quasi-elastic hyper-Rayleigh component as T approaches Tc is also discussed.

Nonlinear phenomena in kinetics of phase transitions

The kink-type solution of the time-dependent Ginzburg-Landau equation is obtained. It represents the moving interface at first-order phase transitions. The estimate of the velocity of the interface at the ferroelctric phase transition in BaTiO 3 shows a satisfactory agreement with the experiment.

A note on tunneling in the presence of a superintense laser field

The influence of a superintense laser field on the transmission probability of a charged particle through a potential barrier is discussed. It is shown that the effect of the intense laser field is to weaken the potential barrier in such a way that its height decreases exponentially with the laser field. The implications to the ferro — to para - electric phase transition in BaTiO 3 under an intense CO 2 - laser field is also discussed.

Why does devonshire's theory work so well

Abstract The great success of Devonshire's1 phenomenological theory in explaining a wide variety of data connected with ferroelectric phase transitions in BaTiO3, has led to a belief that in this system, fluctuation effects are unimportant and can be neglected. However, as has been shown by Vaks,2 there are a number of anomalous features associated with such a mean field description of the phase transition. Recently the authors3 have presented a calculation for the free energy of a compressible ising system taking fluctuation effects into account. In this paper we show that the success of the Devonshire theory can be attributed to the fact, that the form of the free energy functional that is postulated closely mimics the true free energy taking fluctuation effects into account. This also provides a very satisfactory explanation for all the anomalous features encountered.

Behavior of the A1symmetry phonon-polariton at the tetragonal-cubic phase transition in BaTiO3

Abstract The temperature dependence of the A1 modes at the tetragonal-cubic phase transition in BaTiO3 has been studied by Raman measurements in the forward scattering geometry. The unshifted broad structure at around 270 cm−1 in polariton spectra as well as its presence in the cubic phase is explained. The “disorder” model of Comes, Lambert and Guinier is used to explain the phonon behavior at the phase transition. A comparative analysis with recent infrared studies and previous Raman works is also made.

Influence of magnetic field on the paraelectric to ferroelectric phase transition in BaTiO3

Abstract Ferroelectricity in perovskites is closely related to the strong and nonlinear polarizability of the oxygen ion 1-3. This unusual behaviour of the O– ion is due to a dynamically enhanced dϵ/pπ hybridization between unfilled transition metal d orbitals and O 2p orbitals. A direct possibility of studying the polarizability of the oxygen ion in bulk materials is provided by a strong magnetic field which directly couples to the orbital wave functions and thereby causes a change in dϵ/pπ hybridization. This effect can be observed directly via a shift in the paraelectric to ferroelectric phase transition temperature 4. For BaTiO3 we obtained for a field of 20 Tesla a shift of δTc ≈ 0.35 K. A second feature of the magnetic field experiments is the slight- almost zero- increase in slope in the 1/ϵ versus T curves with increasing magnetic field. From this result we can directly conclude that the nonlinear part of the core-shell force constant of the oxygen ion changes not or only very slightly with magnet...

Symmetry problems on raman scattering by pure and doped BaTiO3in the cubic phase

Abstract In the last years, a controversy has developed as to whether the ferroelectric phase transition in BaTiO3 is of displacive or order-disorder type. Central to the resolution of this question is the interpretation of the A1(TO) phonon spectrum of the tetragonal phase which seems to remain in the cubic.

Influence of magnetic field on the paraelectric to ferroelectric phase transition in BaTiO 3

The first experimental results on the effect of a strong magnetic field on the stability of the ferroelectric phase in perovskites are presented. In BaTiO 3 a magnetic field of 20 T increases the paraelectric to ferroelectric phase transition temperature by about 0.3 K for E ‖ B and by about 0.2 K for E ⊥ B.

Exoelectron emission at phase transitions in BaTiO3

Unipolar electron emission in monodomain single crystal BaTiO3 is observed in a temperature range corresponding to three well-known phase transitions. Electron energy spectra from, and photoelectron work function of the crystal face perpendicular to the polar axis were measured. The mechanism of electron emission and the nature of the phenomenon are discussed.

First-order phase transition stimulated by an external electromagnetic field

The mechanism of the influence of an external electromagnetic field upon the temperature of the first-order phase transition in BaTiO 3 is discussed in the framework of the vibronic theory of ferroelectricity. The irradiation is shown to decrease the phase transition temperature. The results are in good agreement with the experimental findings.

The dynamic light scattering in the region of the ferroelectric phase transition in BaTiO3

The observation of a new effect, the photoinduced Rayleigh light scattering, (the PIRLS) was found in BaTiO3. This scattering has the two following features: it exists simultaneously with a bulk photovoltaic effect in BaTiO3 and it is an example of dynamic (but noncritical) scattering process. The main purpose of this letter is to describe the possible micromechanism responsible for the observed dynamic scattering close to the ferroelectric-paraelectric phase transition in BaTiO3.

The chain structure and phase transition of BaTiO 3 and KNbO 3

The correlation of the atomic displacements in KNbO 3 and BaTiO 3 explains the small entropy change between the ferroelectric tetragonal and the paraelectric cubic phase. It also accounts for the high Curie constant found for this transition.