Tetragonal Ferroelectrics Research Articles

Study of new rare earth family Pb 1.6K 1.2R 0.2Nb 5O 15 (R=La, Nd, Sm, Eu and Gd) of tetragonal tungsten bronze-type ferroelectrics

A new ferroelectric rare earth family Pb 1.6K 1.2R 0.2Nb 5O 15 with R=La, Nd, Sm, Eu and Gd (PKRN) of tetragonal tungsten bronze type ferroelectrics was synthesized. The ferroelectric transition with nonuniform distribution of critical temperature over a ceramic sample was found from dielectric measurements. According to X-ray diffraction measurements, the ferroelectric phase has an orthorhombic symmetry. The transition temperature was shown to decrease weakly with increasing radius of the rare earth ion R.

Theoretical Consideration on the 90° Domain Walls in Tetragonal Ferroelectrics

A theory of 90° domain walls in tetragonal ferroelectrics is proposed. It is argued that the depolarizing field discerns the stable head-to-tail wall from the unstable head-to-head wall energetically. The relation between the free energy function and the effect of the depolarizing field is discussed.

Commonalties of the influence of lower valent A-site and B-site modifications on lead zirconate titanate ferroelectrics and antiferroelectrics

Studies of the structure-property relations of lead zirconate titanate (PZT) modified with lower valent substitutions on the A- and B-sites have been performed as a function of substituent concentration. These investigations have yielded common changes induced by these substitutions on ferroelectric phases. The commonalties are the presence of fine domains and polarization pinning effects. Differences in domain morphologies were observed between the rhombohedral and tetragonal ferroelectric phases. Rhombohedral ferroelectrics were found to exhibit “wavy” domain patterns with increasing dopant concentrations, whereas a lenticular domain shape was preserved as the domain size was decreased for tetragonal ferroelectrics. These differences were explained in terms of different pinning mechanisms based on the differences in local elastic strain accommodations. Investigations of high Zr-content PZT have revealed that the ferroelectric rhombohedral phase becomes stabilized over the antiferroelectric orthorhombic with increasing concentrations of lower valent modifications. This change was explained in terms of the enhanced coupling between oxygen octahedra due to the bonding of oxygen-vacancy dipoles.

Crystallization and Conduction Mechanisms on Amorphous PbTiO3

Glass system of xPbTiO3–(100-x)B2O3 (x = 50, 70, 80) was produced by twin-roller quenching method. Glass transition temperatures were 541.3°C, 440.0°C, and 467.8°C for the x =80, 70, and 50, respectively with heating rate of 10°C/min. Crystallization temperatures(activation energies) were 517.5°C (4.10 eV), 526.5°C (3.72 eV), 547.2°C (3.79 eV), and 557.5°C (3.97 eV), for the samples of x=80, x=70, 1st crystallization of x=50, and 2nd crystallization of x=50, respectively. It was revealed that this sample crystallized two-dimensionally analyzed by modified Ozawa method. From the X-ray diffraction experiments of heat-treated samples of x=70, the PbTiO3 crystalline did not form a tetragonal phase right after crystallization temperature but a cubic phase. By further annealing the PbTiO3 crystalline became a tetragonal ferroelectrics. From the temperature- and frequency-dependence of dielectric constants, it was revealed that two conduction mechanisms are responsible for the dielectric response, and the transition frequency was thermally activated. The activation energies above and below the crystallization temperature are 1.1 and 0.7 eV, respectively.

Domain configurations due to multiple misfit relaxation mechanisms in epitaxial ferroelectric thin films. I. Theory

Possible mechanisms for strain relaxation in ferroelectric thin films are developed. The models are applicable to tetragonal thin film ferroelectrics grown epitaxially on (001) cubic single crystal substrates. We assume growth at temperatures in excess of the Curie temperature (Tc). The extent of strain accommodation by misfit dislocations is considered at the growth temperature (Tg). On cooling to Tc, further misfit dislocation generation is possible due to differences in thermal expansion behavior of the film and substrate. During the paraelectric to ferroelectric transition (PE→FE) additional strains develop in the film. The total strain for the FE phase may be relieved either by further misfit generation or by domain formation. We have developed temperature dependent stability maps that predict the stable domain structure that forms during the PE→FE transition. The stability maps incorporate the role of the following parameters: (i) substrate lattice parameter, (ii) differential thermal expansion characteristics between the film and substrate, (iii) cooling rate, and (iv) depolarizing fields and electrode geometry. Further, the role of dislocation stabilization of domain patterns is discussed.

Domain configurations due to multiple misfit relaxation mechanisms in epitaxial ferroelectric thin films. II. Experimental verification and implications

In part I, the concept of a temperature dependent domain stability map was developed for tetragonal ferroelectrics grown on cubic substrates. In this paper, a range of experimental data on domain populations in heteroepitaxial ferroelectric films is placed in the context of the stability map. Experimental data shows that differential thermal expansion, cooling rate, and applied electric fields may be effectively used to control domain structure, particularly in the system PZT, PZT/YBCO/LaAlO3, and LSCO/PLZT/LSCO/LaAlO3. It will be shown that misfit dislocations generated during growth screen the majority of the lattice mismatch with the substrate. Thus, the variety of domain patterns that develop during the Curie transition depend on processing parameters and can be successfully explained by applying the temperature dependent coherent domain stability map developed in part I.

A thermodynamic phenomenology for ferroelectric tungsten bronze Sr0.6Ba0.4Nb2O6 (SBN:60)

The tetragonal tungsten bronze ferroelectrics in the strontium barium niobate system have been extensively studied over many years. As for many of the bronzes, a crude interpretation of the experimental data has been attempted in the past using the simple Landau-Ginsburg-Devonshire expansion of the Gibbs free energy as a Taylor series in powers of the polarization, lumping all the temperature dependence into the lowest order term. In this paper new measurements are presented for the temperature dependence of dielectric polarization, permittivity, and the E-field dependence of the permittivity. It is shown that for a realistic fitting of the data, the Taylor expansion must be taken to at least the eighth power term, and that the coefficients of terms up to the sixth power must be taken as functions of temperature. Since the phenomenology describes equilibrium behavior, it is the total static polarizability that is being explored in this treatment. The nature of this temperature dependence strongly suggests that the phase transition from a macropolar to a macrononpolar state is tetracritical.

Spatial temperature and bound-charge distribution in tetragonal ferroelectrics irradiated by laser pulses

A description is given of theoretical investigations of thermal transient phenomena in a tetragonal ferroelectric crystal on which a rectangular light pulse is projected. The transient distribution of the pyroelectric element is calculated as a function of time, space variables and the k 33 k 11 ratio, and this distribution is discussed for the case of bound charge. Numerically calculated space and time distributions of temperature and volume bound charge density are given. Results obtained provide useful data for designing pyroelectric detectors and for the study of domain structure by the pyroelectric method.

Aging in Tetragonal Ferroelectric Barium Titanate

The aging phenomenon in tetragonal ferroelectric bairum titanate was investigated by optical microscopy and by electrical measurements. Transmission electron microscopy was used to observe in detail domain reactions which occurred during aging. Aging may be characterized as an exhaustion‐type process because of the increase in the apparent activation energy with time. It is concluded that aging is the relief of the residual stresses of the ferroelectric transition by the thermally activated nucleation of 90° domains.