Jun Hatano

Domain structure and polarization reversal in ferroelectrics studied by atomic force microscopy

The ferroelectric domain structure and its dynamics under applied electric field have been studied with nanoscale resolution by atomic force microscopy (AFM). Two mechanisms responsible for the contrast between opposite domains are proposed: large built‐in domains are delineated in friction mode due to the tip–sample electrostatic interaction, and small domains created by an external field are imaged in topography mode due to piezoelectric deformation of the crystal. The ability of effective control of ferroelectric domains by applying a voltage between the AFM tip and the bottom electrode is demonstrated. It is experimentally confirmed that the sidewise growth of domain proceeds through the nucleation process on the domain wall.

Scanning Force Microscopy Studies of Domain Structure in BaTiO3 Single Crystals.

Domain structure of barium titanate single crystals has been studied by scanning force microscopy (SFM). In the SFM topography mode, a–c-domain contrast was observed due to surface deformation as a result of lattice distortion on the domain wall separating a- and c-domains. The variety of configurations in which a- and c-domains are arranged results in complex topography of the crystal surface. Antiparallel c-domains of submicron size were produced by applying a voltage bias to the SFM tip and subsequently imaged in the SFM piezoresponse mode with a resolution of less than 20 nm.

Scanning force microscopy as a tool for nanoscale study of ferroelectric domains

Abstract Scanning force microscopy (SFM) has been used for studying surface morphology of solids for almost ten years. Recently the possibility of ferroelectric domain imaging by SFM was reported. In the present study we exploit SFM for visualization and control of domain structure in ferroelectrics at the nanometer scale. An advanced technique for domain imaging based on the detection of piezoelectric vibration of the ferroelectric sample is presented. The study involves the use of thin films of lead titanate, lead zircon ate titanate and single crystals of barium titanate and lithium niobate. A conductive SFM tip was used to write and image ferroelectric domain patterns with an average resolvable spacing down to 30 nm.

Refraction and Reflection of Light at Ferroelastic Domain Walls in Rochelle Salt Crystal

When a laser beam transmits through an a -cut plate of Rochelle salt in the ferroelectric (simultaneously ferroelastic) phase, two types of weak intensity beams deflected from the direct beam direction are observed. The relation between the angle of incidence and the angle of deflection, and polarizing directions of light are satisfactorily explained by refraction and reflection at a domain wall, on both sides of which refractive indicatrices are mutually inclined a few degrees. The refraction and reflection occur at equal angles, and the respective polarizing directions are symmetrical with respect to the wall. There exists a critical angle of incidence, above which one type of deflection beams appears. Diffraction effects due to multi-walls do not account for the experimental results.

Deflection of Light by Ferroelastic Domains in Gd2(MoO4)3 and Bi4Ti3O12 Crystals

The relation between angles of incidence and deflection caused by the refraction and reflection of light beam at the ferroelastic domain walls in Gd 2 (MoO 4 ) 3 , Bi 4 Ti 3 O 12 and Rochelle salt crystals has been treated on the basis of crystal optics. Numerical analysis of the relation has been carried out for incident angles from 0° to 90°. At the incident angle of 0°, the deflection angles obtained by the analysis are 2.25° for the c plate of Gd 2 (MoO 4 ) 3 , 14.6° for the b plate of Bi 4 Ti 3 O 12 and 4.43° for the a plate of Rochelle salt. The experimental results with a He-Ne laser for these crystals are in satisfactory agreement with the calculated ones. The intensity ratio of the deflected beam to the direct beam is in the order of 10 -2 for Gd 2 (MoO 4 ) 3 and 10 -3 for Rochelle salt.

Orientation of the Ferroelectric Domain Wall in Triglycine Sulfate Crystals

The domain wall energy as a function of wall orientation in triglycine sulfate (TGS) crystals has been calculated on the basis of the Zhirnov-type continuum theory. Contrary to the Fouseks misleading conclusion [Japan. J. appl. Phys. 6 (1967) 950.], the isotropic treatment of the correlation-energy coefficient κ gives an inadequate result to explain the observed wall orientation which is nearly perpendicular to the crystallographic c axis. An anisotropy of κ has been reasonably introduced; a wall orientation consistent with the observations has been successfully brought about. The. anisotropies of the dielectric, elastic and electrostrictive constants of TGS rather ineffectively contribute to the orientation of the domain walls.

Field-Induced Phase Transitions in Antiferroelectric Liquid Crystal

Cell thickness dependence and field impression rate dependence of field-induced phase transition in an antiferroelectric liquid crystal (MHPOBC) have been investigated by observing the optical transmittance hysteresis loop and texture of the cells. In thin cells, pseudo-triple hysteresis loops due to coexistence of ferroelectric and antiferroelectric domains have been observed. In thick cells, an antiferroelectric phase is stabilized near the zero-field region of a ferrielectric phase of a field-temperature phase diagram. A possible model for molecular orientational structure of the phases and field-induced transitions among them is discussed on the basis of these experimental results.

Domain-Wall Orientations and Wall Energies in Ferroelectric Triglycine Selenate Crystals

Detailed observations of domain structure in triglycine selenate crystals have been made in special respect to the orientations of the 180° domain-walls by an improved powder-deposition technique. Two kinds of flat wall can be seen; one is parallel to the crystallographic (001) planes and another is to the (\bar201) planes. The angular dependence of the wall-energy density has been numerically calculated on the basis of the Zhirnov-type continuum theory. Two minima in the energy are obtained, each of which corresponds to the wall orientations observed experimentally. The numerical values of elastic stiffness, electrostrictive, dielectric constants and correlation-energy coefficients required for the calculation have been also determined experimentally. The theoretical and experimental results of wall orientations are discussed in comparison with those of triglycine sulfate crystals.

Spiral patterns on GASH

Abstract On the center region of cleavage surface of GASH (guanidinium aluminum sulfate hexahydrate) crystals grown at high temperatures, peculiar spiral domains have been observed by a powder deposition technique. Triangular etch pits found at the center of the spirals are direct evidence for the screw dislocation mechanism of crystal growth. Dislocations of high density are associated with the defects at the sites of crystallization water introduced during crystal growth at high temperatures. The formation model of the spiral domains are discussed on the basis of the spiral growth theory of crystal.

Compensation for Ferroelectric Hysteresis Loop Distortion and Its Application to Phase Transition Studies

A compensation for ferroelectric hysteresis loop distortion has been developed and applied to some ferroelectric or antiferroelectric phase transitions. The distortion of loop has been numerically synthesized on the basis of an equivalent circuit and subtracted from the measured signal; in the calculation, nonlinearity of the circuit can be taken into account as necessary. Successful results were obtained in ferroelectrics near the second-order phase transition and in antiferroelectrics which show nonlinear conductivity or a nonlinear dielectric constant.