Jan Fousek

Domains in Ferroic Crystals and Thin Films

A Preview of Concepts and Phenomena.- Fundamentals of Ferroic Domain Structures.- Ferroic Materials.- Methods for Observation of Domains.- Static Domain Patterns.- Domain Walls at Rest.- Switching Properties: Basic Methods and Characteristics.- Switching Phenomena and Small-Signal Response.- Ferroelectric Thin Films.

Scanning force microscopy of domain structures in Pb(Zn1/3Nb2/3)O3-8% PbTiO3 and Pb(Mg1/3Nb2/3)O3-29% PbTiO3

Domain structures of unpoled as well as poled (along [001]- and [110]-direction) Pb(Zn1/3Nb2/3)O3 (PZN)-8% PbTiO3 (PT) and Pb(Mg1/3Nb2/3)O3 (PMN)-29% PT single crystals have been investigated by scanning force microscopy (SFM) in the piezoresponse mode, at room temperature. Antiparallel domain structures have been detected mostly in unpoled crystals of both materials, with a fingerprint pattern in (001)-oriented PZN-8% PT crystal. The ferroelastic domain wall has been identified in poled (110)-oriented PZN-8% PT crystal. “Writing” of ferroelectric domains has been performed by applying a dc voltage to the SFM tip. Local re-poling has been observed for all unpoled as well as for poled (001)-oriented crystals at the voltage ±60 V. Local electrical switching was successful in poled (110)-oriented PMN-29% PT at higher voltage (±120 V) but was not successful in poled (110)-oriented PZN-8% PT crystal. Domain-engineered crystals poled in [110]-direction seem to exhibit more stable (in the sense of local re-polin...

Infrared and Raman spectroscopy of [Pb(Zn1/3Nb2/3)O3]0.92–[PbTiO3]0.08 and [Pb(Mg1/3Nb2/3)O3]0.71–[PbTiO3]0.29 single crystals

Far-infrared reflectivity spectra of [Pb(Zn1/3Nb2/3)O3]0.92–[PbTiO3]0.08 and [Pb(Mg1/3Nb2/3)O3]0.71–[PbTiO3]0.29 single crystals were investigated between 10 and 530 K, micro-Raman spectra were recorded between 300 and 800 K. No phonon softening was observed near either of the ferroelectric phase transitions. The low-frequency dielectric anomaly in the paraelectric phase is caused by contribution of dynamic polar nanoclusters with the main dispersion in the microwave range. Infrared and Raman spectra confirm the locally doubled unit cell (Zprim=2) in the paraelectric and ferroelectric phases due to the ordering in the perovskite B sites and occurrence of polar nanoclusters in the paraelectric phase. The lowest-frequency transverse optical (TO1) phonon mode active in the infrared spectra is underdamped in contrast to the recent result of inelastic neutron scattering, where no TO1 mode could be observed for the wave vectors q⩽0.2 A−1. This discrepancy was explained by different q vectors probed in infrared ...

Pressure on charged domain walls and additional imprint mechanism in ferroelectrics

Note: 1098-0121094110 Reference LC-ARTICLE-2007-020doi:10.1103/PhysRevB.75.094110View record in Web of Science Record created on 2007-10-18, modified on 2017-11-27

Patterning of dielectric nanoparticles using dielectrophoretic forces generated by ferroelectric polydomain films

A theoretical study of a dielectrophoretic force, i.e., the force acting on an electrically neutral particle in the inhomogeneous electric field, which is produced by a ferroelectric domain pattern, is presented. It has been shown by several researchers that artificially prepared domain patterns with given geometry in ferroelectric single crystals represent an easy and flexible method for patterning dielectric nanoobjects using dielectrophoretic forces. The source of the dielectrophoretic force is a strong and highly inhomogeneous (stray) electric field, which exists in the vicinity of the ferroelectric domain walls at the surface of the ferroelectric film. We analyzed dielectrophoretic forces in the model of a ferroelectric film of a given thickness with a lamellar 180° domain pattern. The analytical formula for the spatial distribution of the stray field in the ionic liquid above the top surface of the film is calculated including the effect of free charge screening. The spatial distribution of the diel...

Interpretation of the Temperature Autostabilization of a Ferroelectric Crystal

The dielectric heating of a ferroelectric crystal in an alternating electric field is discussed from the point of view of the properties of the polarization reversal process. On the basis of a simplified description of a P(E) hysteresis loop the complex permittivity of a ferroelectric crystal in strong fields is calculated as a function of the crystal temperature T and field amplitude. The amount of heat developed in the crystal is found and from the condition of thermal equilibrium of the crystal with the surroundings, T is calculated as a function of the ambient temperature Ta and the field amplitude. It is shown that the decreasing temperature dependences of the spontaneous polarization and the coercive field are responsible for the existence of states of temperature autostabilization (STA), defined by ∂T/∂Ta < 1, which were found experimentally by Glanc et al. There are three possible ways of bringing the crystal to STA which are realized at different frequencies of the applied field or at different r...

Theory of compositionally graded ferroelectrics and pyroelectricity

A thermodynamic theory of compositionally graded materials is developed, based on a term in the Landau formula for free energy of the form γPgradc, where P, c, and γ stand for the polarization, the atomic concentration, and a phenomenological coefficient, respectively. The consequence of this term is the following: (1) the original equivalence of two states with spontaneous polarization +PS and −PS is upset and the sample has the tendency to become oriented along one of the originally equivalent directions; (2) an additional polarization is induced. The consequences of the modified free energy for pyroelectricity are discussed.

Elastic aspects of domain quadruplets in ferroics

Coexistence of ferroelectric ferroelastic domains in some materials plays an important role in practical area of domain engineering. Here the problem is discussed theoretically from the point of view of elastic aspects. Domain quadruplets are considered, i.e., systems of four ferroelastic domains coinciding along one intersection line. Conditions at which the elastic energy of quadruplets is zero are specified; they would allow for the existence of permissible quadruplets. The problem has been solved for the species m3¯m-mxmy2z, m3¯m-2xymx¯ymz, m3¯m-3m, and m3¯m-4mm. It is shown that, in general, no mechanically compatible (stress-free) permissible quadruplets exist. The results make it possible to specify those conditions for spontaneous strain components which must be complied to allow for energetically acceptable quadruplets. These conditions are fulfilled in the orthorhombic phase of KNbO3. The theoretical approach offered in this paper can be used for specific discussions of the existence of multidom...

Anomalous pyroelectric effect

Anomalous pyroelectric effect has been repeatedly observed in ferroelectric films which were compositionally graded or in which strain gradient or temperature gradient was realized. The effect is represented by the shift of the hysteresis P(E) loop center due to the change of temperature. Here we propose a new interpretation of this property. It is based on the assumption that the concentration gradient induces additional polarization. This is characterized by macroscopic description based on the modified Landau-Devonshire thermodynamic potential f(P). The graphical representation of this modified potential is an asymmetric double-well. The hysteresis phenomenon is described by the motion of the “representative Brown particle” in this double-well; the shape of the latter is modulated by the time-dependent electric field. The observed anomalous pyroelectric effect is based on the coherence of the asymmetry and kinetic aspect of the phenomenon.

Stress-Free Domain Quadruplets in Ferroics

The coexistence of ferroelectric ferroelastic domains in some materials plays an important role in practical area of domain engineering. Here the problem is discussed theoretically from the point of view of elastic aspects. Domain quadruplets are considered, i.e. systems of four ferroelastic domains coinciding along one intersection line. Conditions at which the elastic energy of quadruplets is zero are specified; they would allow for the existence of permissible quadruplets. The problem has been solved for the species mm − P ϵds-mm2 representing KNbO3 crystals in which regular quadruplets have been discovered. It is concluded that such quadruplets are not permissible but can be formed when specific conditions for spontaneous strain are fulfilled. Theoretical results can be used to specify these conditions.