Search

Microscopic retention properties have been studied in detail. Domain growth and stability of ferroelectric Pb(Zr,Ti)O 3 thin films were investigated with electrostatic force microscope to understand microscopic polarization retention loss mechanism in polycrystalline and epitaxial Pb(Zr,Ti)O 3 thin films. Growth of domains and their relaxation behaviors were investigated and compared. The larger domains were the more stable than the smaller ones. The decay behavior of domain size could be fitted to a simple exponential function. The stretched exponential decay of the averaged polarization was attributed to the superposition of relaxation processes of all domains relaxing independently with their characteristic relaxation times.

The slow dynamic behavior in Rb 1 m x (ND 4 ) x D 2 AsO 4 (DRADA) with x =0.37 mixed crystals has been studied by measuring the time decay of remant polarization. The slower relaxation is observed ...

The temperature dependence of the electro-optic coefficient of Pb 1 m x La x (Zr y ,Ti 1 m y ) 1 m y/4 O 3 ceramics with x= 0.09 and y= 0.65 was investigated in the field cooling and the zero field...

Linear birefringence and optical activity behaviours of K2ZnCl4 were studied between 100 K and 300 K. Birefringence deviation from linear thermo-optic behaviour and existence of unexpected optical gyration component were observed between 145 and 225 K, where a dielectric anomaly was also reported in the previous study. These phenomena can be ascribed to the precursor behaviour of the ferroelastic phase transition, that is, formation of ferroelastic nanodomains in the ferroelectric phase observed by previous x-ray scattering study.

The complex dielectric constants and polarization of the hydrogen-bonded mixed crystals, K1−x(NH4)xH2PO4 and Rb1−x(NH4)xH2AsO4, near the ferroelectric-proton glass phase boundary have been investigated as a function of temperature. Coexistence of both phases was discovered from a glassy dispersion at low temperature and a ferroelectric anomaly. The dielectric dispersion due to the coexisting proton glass state occurred at lower temperatures than for pure proton glass composition. The detection of polarization after field-cooling or zero field-cooling the sample showed that the ferroelectric domain and polarization were retained in the glass freezing process. These results are qualitatively consistent with the expectation of the infinite ranged random-bond random-field model in the presence of macroscopic polarization.

The complex dielectric constants and polarization of the mixed crystals of ${\mathrm{Rb}}_{1\ensuremath{-}x}({\mathrm{NH}}_{4}{)}_{x}{\mathrm{H}}_{2}{\mathrm{PO}}_{4}$ (RADP) with $x=0.15$ and 0.17 have been measured along the tetragonal a and c axes as a function of temperature. Phase coexistence of ferroelectric order and proton glass in RADP can be confirmed from a dielectric dispersion distinguished from the ferroelectric domain wall freezing at low temperature. The dielectric dispersion, which was ascribed to the proton glass state, occurred at much lower temperatures compared to pure proton glass composition. The detection of depolarization after field-cooling or zero-field cooling the sample, showed that the ferroelectric domain and polarization were retained in the glass freezing process. The result is qualitatively consistent with the expectation of the mean-field model in the presence of macroscopic polarization. The phase coexistence may be a common feature of ${\mathrm{KH}}_{2}{\mathrm{PO}}_{4}$ family mixed crystals.

The thermal conductivity of RF sputtered ${\mathrm{Z}\mathrm{n}\mathrm{S}:\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ composite film is measured in the temperature range between 50 K and 300 K using the $3\ensuremath{\omega}$ method. This composite film shows two distinct modes of behavior. One is that, at room temperature, the thermal conductivity of the composite film is lower than the conventionally estimated minimum values for disordered ZnS and ${\mathrm{SiO}}_{2}.$ The other is that the temperature dependence is weaker than for usual glasslike films. Although the Einstein model could explain values of the conductivity at room temperature, the contribution of phonons cannot be excluded at lower temperatures. The low thermal conductivity is more successfully explained by the presumed thermal boundary resistance between ZnS particles and the ${\mathrm{SiO}}_{2}$ matrix.

We have investigated domain structure and dynamics of a triglycine sulfate (TGS) single crystal with a dynamic contact mode electrostatic force microscope (DC-EFM), which is operated in contact mode. DC-EFM can overcome a problem in conventional noncontact EFM measurement. The temperature dependence of surface charge density was measured by a nulling technique. We also investigated local domain switching behaviors of TGS single crystal and PZT thin film. Complex pattern was written on a PZT thin film by the polarization reversal. A writing capability such as a writing speed and voltage dependence in PZT film has been studied by DC-EFM.

Temporal relaxation of the field-induced remanent polarization has been investigated on the deuteron glass ${\mathrm{Rb}}_{0.7}({\mathrm{ND}}_{4}{)}_{0.3}{\mathrm{D}}_{2}{\mathrm{AsO}}_{4}$ in the temperature range $10lTl30\mathrm{K}.$. The data are approximately described by Curie--von Schweidler and Kohlrausch-Williams-Watts decay laws at high $(Tg25\mathrm{K})$ and low temperatures $(Tl20\mathrm{K}),$ respectively. A nearly perfect description is, however, provided by the dynamically correlated domain model, which is based upon Chamberlin's concept of dynamical heterogeneity. On decreasing the temperature, the thermally activated dynamic behavior crosses over into nonactivated dynamics.

A dynamic contact mode operation of electrostatic-force microscopy (EFM) with an ac modulation has been developed and used to investigate the domain strucutre and dynamics of a triglycine sulfate single crystal. Well-separated topographic and domain contrast images have been obtained by detecting the force instead of the force gradient in the dynamic contact mode operation of EFM. Surface charge density and the anisotropic domain wall thickness have been measured. The evolution of domains embedded in an oppositely polarized larger domain indicates the existence of a significant interaction between domains of the same polarity.

Linear birefringence behavior of Rb 2 ZnCl 4 , K 2 ZnCl 4 , and [N(CH 3 ) 4 ] 2 ZnCl 4 were studied in the critical region of the normal-incommensurate phase transition. Exisence of linear birefringence tail above the transition temperature was observed. It was ascribed to the fluctuation effect on the linear birefringence. Results of scaling analysis imply that the exponent of LB behavior is not 1- α but 2β, contrary to the previous LB study. Contribution of the fluctuation to linear birefringence behavior is discussed comparing to XRD experiments.

Linear birefringence behavior of [NH 3 C 3 H 7 ] 2 MnCl 4 was measured near normal-incommensurate phase transitions, i.e., β-γ and δ-e transitions. Linear birefringence behaved as Δ n a b ∼| t | 0.74±0.02 in the critical region of the two phase transitions. These results imply that two normal-incommensurate phase transitions belong to the same universality class of the 3-d XY model. In addition, linear birefringence behavior in the incommensurate γ phase is also discussed while comparing it to the previous theoretical description based on classical Landau theory.

Nano-size effects on the dielectric and soft mode behaviors in the quantum paraelectric SrTiO3 were studied. Nanocrystalline SrTiO3 particles were prepared by the sol-gel method, and the particle sizes were controlled by treating temperatures. The sizes were determined to be from 12 to 44 nm using Scherrer's formula. The transition temperatures from classical paraelectric to quantum paraelectric phase were increased for the smaller sizes of the particles. Soft mode behaviors of fine particles were investigated by Raman scattering. The soft mode frequencies of the smaller sizes of the particles were higher than those of the larger ones in the low temperature. The soft mode behaviors were agreed with dielectric results through the Lyddane-Sachs-Teller relation.

Complex dielectric constants have been measured on the microcrystalline Rb1−x(NH4)xH2PO4 powder system in the concentration range, 0.15 ≤ x ≤ 0.19. Rounded peak in the real dielectric constant curve and the glassy dispersion at low temperature are observed. Dielectric behavior is largely affected by small change of ammonium concentration x near the phase boundary. More asymmetric dielectric loss behaviors are shown in the ferroelectric phase boundary region than in the pure proton glass region. The broad and asymmetric loss dispersion curves observed for x = 0.15 are believed to be related with the remaining ferroelectric clusters.

We have designed coupled diode resonators to study the effect of small perturbations due to weak symmetric coupling on chaotic dynamics. Our experiment clearly demonstrated that chaos of the diode resonators was suppressed so that chaotic motions were converted into periodic ones with small modifications to the attractor when an appropriate coupling signal perturbed the diode resonators. Many unstable periodic orbits were stabilized and they were very stable depending on the dynamical properties of the coupling signals. Our results suggest that coupling of signals belonging to the same class is effective in controlling chaos.

We have observed an interesting bifurcation sequence at very low driving voltages applied to a diode resonator. As the driving voltage increases, an ordinary period-doubling bifurcation appears. Further increase of the driving voltage results in a reverse period-doubling bifurcation and a sudden jump of an amplitude of the current oscillation of the diode. The experimental results were compared with the results of numerical simulations of the equivalent circuit of the diode resonator and they were in good agreement. This suggests that these low-voltage bifurcations are due to nonlinearity of the capacitance and current of the diode to the applied voltage. A simple one-dimensional map explaining these low-voltage bifurcations of the diode resonator is introduced and its properties are discussed.

The normal-incommensurate phase transition of K 2 ZnCl 4 and [N(CH 3 ) 4 ] 2 ZnCl 4 were studied by the linear birefringence method for the determining critical exponent, β. The critical linear birefringence behavior can well be described by standard 3-d XY model over the temperature range 10 -3

The weak coupling method is demonstrated to stabilize and track the unstable orbits in the diode resonator system. Continuous tracking of the unstable orbits could be achieved over a wide range from the periodic down to the deep chaotic regime as the control parameter is varied continuously without changing the feedback control parameter. During the tracking of unstable orbits, hysteresis as well as switching of the attractors are observed and these are supposed to be the generic properties of continuous tracking.

Nano-size effects on the dielectric properties in the quantum paraelectric SrTiO 3 were studied. Nanocrystalline SrTiO 3 powders were prepared by the sol-gel method, and the particle sizes were controlled by varying firing temperatures. The sizes were determined to be from 12 to 44 nm using Scherrer's formula. The classical paraelectric to quantum paraelectric phase transition temperatures were suggested to be increased for the smaller particle size samples. These results could be explained with the aid of transverse Ising model.

The complex diclcctric constants of (NH4)2SO4 have been measured in the temperature range from 350 K to 450 K along a, b and c axes with a frequency range from 10 kHz to 4 MHz. The frequency dependent dielectric anomaly at about 417 K with an anomaly at 408 K was observed. The heat capacity and the thermal conductivity were also measured in this temperature range using a surface heater. A peak in the heat capacity curve as well as a slight bending feature in the thermal conductivity curve was observed at 417 K.

We have developed the technique, called 3ω method, capable of measuring the dynamic specific heat of a solid in the frequency range from 0.01 Hz to 2 kHz and used this technique to measure the specific heat of KH2PO4 as a function of frequency. The specific heat becomes frequency-dependent near the Curie point.

The urea impurity effects on thiourea have been studied by measuring dielectric constant and linear birefringence of SC(NH2)2 and S0.91O0.09C(NH2)2 crystals. The impurity effects are significant near Tc and the intermediate commensurate phases of δ=1/8 and 1/9. Thermal hysteresis of S0.91O0.09C(NH2)2 is much larger than that of SC(NH2)2. The dielectric anomalies related to the phase transitions of δ=1/8 and 1/9 phases are not observable for S0.91O0.09C(NH2)2, and the linear birefringence behaviors related to the intermediate commensurate phases are also smeared out for the sample. These results clearly show that the impurities make commensurate phases unstable.

Microstructures and optical properties of ferroelectric LiNbO3 thin films on Si and sapphire substrates are investigated. For the films on Si substrates, polycrystalline films with smooth surface were obtained. Most of voids were found to be formed at the interface between the film and Si substrate. Highly (001) and (012) oriented films can be fabricated on sapphire substrates. Decrease in the gap energy as increasing the annealing temperature was discussed in conjuction with the grain growth of the films.

Birefringence and dielectric studies on urea-doped thiourea, ${\mathrm{S}}_{0.91}$${\mathrm{O}}_{0.09}$C(${\mathrm{NH}}_{2}$${)}_{2}$, have been performed under a dc electric field. For the mixed crystal, no anomalies related to the transitions to intermediate commensurate phases of \ensuremath{\delta}=1/8 and 1/9 are observed, indicating that the commensurate phases are suppressed by urea impurities. When a bias field is applied to the sample the dielectric-constant anomaly related to the ferroelectric phase transition splits into two peaks. One peak at a temperature ${\mathit{T}}_{\mathit{c}2}$\ensuremath{\approxeq}169 K shifts driving the heating process to higher temperature with ${\mathit{dT}}_{\mathit{c}2}$/dE\ensuremath{\approxeq}0.9 K/(kV/cm) while the other peak remains nearly fixed at ${\mathit{T}}_{\mathit{c}1}$\ensuremath{\approxeq}${\mathit{T}}_{\mathit{c}2}$(E=0) regardless of the electric field E. The field-induced phase between the ${\mathit{T}}_{\mathit{c}1}$ and ${\mathit{T}}_{\mathit{c}2}$ is attributable to the coexistence of ferroelectric and incommensurate phases.

Based on measurements of spontaneous linear birefringence, the phase diagram of Rb1-x(NH4)xH2AsO4 has been completed. The ferroelectric compounds (x 0.46) are strongly first-order.

Mesure de la constante dielectrique complexe de ces cristaux. Mise en evidence d'un etat de verre de proton precede de la transition de phase ferroelectrique quand la temperature diminue. La symetrie orthorhombique ferroelectrique demeure jusqu'aux basses temperatures ou est etabli l'etat vitreux

The internal vibrational modes of (Rb)1−x(NH4)xH2AsO4 mixed crystals have been investigated using infrared spectroscopy techniques. The reflectivities are measured in the frequency region of 200 - 2000 cm−1 between 100 and 300 K. Comparing the observed number of internal vibrational modes with the group analysis predictions, we found that the site symmetry of AsO4 in NH4H2AsO4 is to be S4 in the paraelectric phase and C1 in the antiferroelectric phase. It is also found that the site symmetry of AsO4 in RbH2AsO4 is to be S4 in the paraelectric phase and C2 in the ferroelectric phase. For the mixed crystals (x = 0.75, 0.70), the site symmetry of AsO4 in the low temperature phase is shown to be C1 in agreement with an earlier predictions that these samples should show antiferroelectricity.

Internal vibrational modes of CsH2PO4 are investigated by measuring the reflectance spectra in the frequency range of 200–4000 cm−1 in the 100–300 K region. From the result of Kramers-Kronig transformations and the factor group analysis, the site symmetry of PO4 is assumed to be Cs in the paraelectric phase and C1 in the ferroelectric phase. This result shows that the proton tunneling plays an important role in the phase transition of CsH2PO4.

Ce comportement est etudie en mesurant la constante dielectrique suivant les axes a et c, entre 30 et 200 K. La limite de la phase entre la phase ferroelectrique et l'etat de verre protonique est observe entre x=0,13 et 0,20. On observe une limite similaire avec la phase antiferroelectrique entre 0,44 et 0,49. Pour 0,23≤x≤0,44, les donnees dielectriques peuvent etre echelonnees en utilisant la loi de Vogel-Fuchler. Construction du diagramme de phase

Highly (0001)-oriented thin films of YMnO3 were grown directly on Si substrates by chemical solution deposition. The crystallinity of the films was investigated by using x-ray diffraction: θ–2θ scan, rocking curve, and pole figure. Analysis of the x-ray photoelectron spectroscopy data and Rutherford backscattering spectroscopy spectrum showed that the films had a single phase of stoichiometric YMnO3. The ferroelectric properties of YMnO3 were investigated by measuring the temperature dependence of the capacitance–voltage characteristics in the metal/ferroelectric/semiconductor structure. Screening of the ferroelectricity of YMnO3 thin film at room temperature was discussed in conjunction with the charge effects.

A new digital circuit for fast and stable frequency tripling was constructed. The frequency tripler covers the input frequency range from 0.1 Hz up to 5 kHz with a maximum phase shift less than 1 deg at the highest frequency. The tripler generates a stable signal synchronized to the input after just one input period. Since the circuit design is flexible, input frequency range and phase accuracy can be improved using faster integrated circuits.

Thin films of barium strontium titanate, Ba/sub 1-x/Sr/sub x/TiO/sub 3/, were deposited on Si and ITO/glass substrates with 200/spl sim/300 nm thickness by sol-gel method. The precursor solution of BST was prepared by mixing the 0.2 M precursor solutions of BaTiO/sub 3/ and SrTiO/sub 3/ with proper molar ratio. The X-ray diffraction (XRD) patterns show characteristic peaks with weak and broad features indicating that the polycrystalline BST film has poor crystallinity. The grain size and the surface morphology of the films were investigated by atomic force microscope (AFM). Especially, dependence of the film structures on the treatments of precursor solution such as hydrolysis and modification with acetic acid was investigated. The I-V (current-voltage) characteristics of the films was also dependent on the precursor structure. The C-V (capacitance-voltage) behavior of the films with MIS (metal-insulator-semiconductor) and MIM (metal-insulator-metal) structures were studied. Also, dielectric permittivity which was very strongly dependent on the crystallinity of the films was discussed in conjunction with precursor structures.

The thermal conductivity of KH2PO4 (Potassium Dihydrogen Phosphate, KDP) single crystal under dc bias fields up to 2 kV/cm was measured using a novel technique called the 3ω method. Without a bias field, a small but definite discontinuity was observed at the Curie temperature (Tc = 123 K), indicating the first-order nature of the transition. The value of the thermal conductivity was very small due to the protonic scattering of phonons. The dc bias field tended to increase the thermal conductivity of KDP only in the vicinity of Tc and round the discontinuity at the same time. These results clearly demonstrate the coupling between the heat carrying phonons and the soft mode associated with the ferroelectric transition.

Ferroelectric Bi4Ti3O12 thin films have been grown on MgO (100) and MgO(110) substrates by the pulsed laser deposition. X‐ray diffraction studies show that the films on both substrates have preferential crystallographic orientation such that most of their c axes are close to the substrate normal direction. The film on MgO(110) shows quadratic and hysteretic electro‐optic characteristics with the effective coefficient of about 3.8×10−15 m2/V2.

Physical Review Letters

Bi4Ti3O12 thin films have been grown by laser ablation on SrTiO3(100) and SrTiO3(110) substrates. Substrate surface orientation is found to be an important growth parameter which determines crystal axis orientation, grain growth behavior, and electro‐optic properties of the Bi4Ti3O12 thin films. The films grown on SrTiO3(110) shows a ferroelectric phase transition near 720 °C and a large quadratic electro‐optic effect with the effective coefficient 1.1×10−16 m2/V 2.

Highly (0001)-oriented films of YMnO3 were grown on n-type Si(100) substrates by a chemical solution deposition with a modified precursor solution. Spin-coated films were crystallized by rapid thermal annealing at 650 °C, and showed improved structural and electrical properties. Capacitance-voltage (C-V) measurements at 1 MHz showed a counterclockwise hysteresis, with a memory window of 1.9 V at 9 V, due to ferroelectric polarization, and a dielectric constant of 25. The effects of mobile ionic charge and effective interface charge in the C-V measurements were found to be small by investigating the bias sweep rate dependence and flat-band voltage shift, respectively. The interface trap density near the Si midgap was obtained to be about 1.3 × 1011 cm−2eV−1 through conductance measurements. Current-voltage characteristics showed a leakage current density of 16 nA/cm2 at 3 V. An asymmetric polarization-voltage (P-V) hysteresis curve became symmetric one with a remanent polarization value of 0.1 μ C/cm2 under He-Ne laser illumination. The depolarization field in the ferroelectric film and charge compensation by the light-generated minority carriers may be responsible for the observed P-V characteristics. The low temperature fabrication of this YMnO3 film showed good structural and electrical properties for application to nonvolatile ferroelectric memory devices.

We have demonstrated through the system of two coupled driven diode resonators that chaos of the diode resonators can be reduced by weak coupling. Stable periodic orbits emerge from the chaotic attractor when a small coupling signal perturbs the diode resonator. However, we find that the stability of the periodic orbits is strongly dependent on the coupling signals. Our results are examined with recently proposed techniques for controlling chaos.

For various materials, including liquids and disordered systems, the dielectric function in the microwave region is represented by the Debye equation. Recently, with the use of the second-moment representation for the solenoidal and irrotational losses, the generalized form of the Lyddane-Sachs-Teller (LST) relation was derived based on causality and the f-sum rule [T. W. Noh and A. J. Sievers, Phys. Rev. Lett. 63, 1800 (1989)]. However, the second-moment representation cannot be applied to the Debye equation, which does not obey the f-sum rule. A moment representation is applied to the Debye equation, and a relation equivalent to the generalized LST relation is found. In this relation, the pth moments (-1p1) should be used instead of the second moments.

A-/b- and c-axis oriented SrBi2Ta2O9 thin films were grown on the MgO(110) and MgO(100) substrates, respectively, by rf magnetron sputtering deposition method. Optical anisotropy was shown in the infrared reflectance spectra for the SrBi2Ta2O9 thin films. Quadratic electro-optic effects were observed only in the a-/b-axis oriented films. The effective quadratic electro-optic coefficient was about 3.8 ×10-17 m2/V2.

Highly (0001)-oriented YMnO3 thin films on Si(100) substrates were obtained by using a stable precursor solution and rapid thermal annealing at a low temperature of 650 °C in a chemical solution deposition process. Temperature-dependent capacitance–voltage (C–V) and current–voltage (I–V) characteristics were discussed in a metal-ferroelectric-semiconductor structure. At 300 K, the voltage-dependent increase of the memory window (ΔV) in the C–V curve and the asymmetric I–V curve were attributed to the formation of positive interfacial charges by field- and thermal-excited electron transport. On the other hand, at 220 K, the voltage-independent ΔV was attributed to ferroelectric polarization switching.