Lead titanate (PbTiO3), a ferroelectric material with perovskite structure, has received a great deal of attention owing to a unique combination of its piezoelectric, pyroelectric, dielectric, electo- and acousto-optic properties [1–3]. PbTiO3 is a very attractive material for the use in a wide variety of fields, including ultrasonic sensors, infrared detectors, electro-optic modulators, and ferroelectric random access memories. To harness the intrinsic properties of PbTiO3 for device applications, however, high-quality epitaxial films are required. PbTiO3 thin films have been prepared by various methods such as chemical vapor deposition, rf magnetron sputtering, pulsed laser deposition, hydrothermal method, and sol-gel technique. Surprisingly, molecular beam epitaxy (MBE), with its precise control over composition, has not been widely applied, except of a few reports on MBE growth with the use of ozone as an oxidizing agent [4]. In the present work, high-quality single-crystal PbTiO3 layers were grown on (001) SrTiO3 substrates by MBE with the use of hydrogen peroxide as an oxidant [5]. Phase composition as well as structural and optical properties of the films were examined as a function of growth parameters by high-resolution x-ray diffractometry, spectroscopic ellipsometry, and photoluminescence. It was found that single-phase PbTiO3 films grew epitaxially at substrate temperatures above 600°C, whereas layers grown at lower temperature contained lead oxide inclusions. All the PbTiO3 layers were c-axis oriented with the epitaxial relationship PbTiO3(100)//SrTiO3(100) and PbTiO3[001]//SrTiO3[001]. No evidence of a-domains was found. Full width at half maximum of (001) rocking curves for 50–60 nm thick PbTiO3 layers are as low as 6–8 arcmin, indicating their good crystal quality. Pseudodielectric function of PbTiO3 was measured using variable angle spectroscopic ellipsometry at room temperature. Refractive index was found to be 2.605 at 633 nm (1.96 eV), which is consistent with the literature data. With the help of the standard critical point (SCP) lineshape analysis the band gap energy was calculated to be (3.778±0.005) eV.

Single phase multifunctional materials such as Pb(Fe0.5 Nb0.5)O3 (PFN), where ferroelectric and magnetic order coexist, are very promising and have great interest from the academic and technological points of view. PFN ceramics have been prepared from different kinds of FeNbO4 precursors with either monoclinic or orthorhombic structures. Crystallographic, compositional and surface morphological studies and the temperature-frequency response carried out and reported in previous works are summarized. Ferroelectric hysteretic, magnetic and magnetoelectric behaviors were measured. The remanent polarization (Pr) and coercive field (EC) as functions of temperature and external electric fields (Eext) were determined. Measurements of magnetic susceptibility (χm) exhibited antiferromagnetic order and, above the Núel point near 122 °K, Curie–Weis behavior; whereas a weak ferromagnetic observed from electron paramagnetic resonance (EPR) is discussed. However, magnetoelectric effects were not observed. Ferroelectric and magnetic behaviors, as functions of the kind of precursor used in the preparation, are discussed and correlated with the previous dielectric characterization where microstructural and equivalent circuit models were established using the impedance spectroscopy technique.

Investigations on microwave magneto-electric (ME) interactions at 1-10 GHz have been carried out on yttrium iron garnet (YIG)-lead zirconate titanate (PZT) and YIG-lead magnesium niobate lead titanate (PMN-PT) bilayers. Ferromagnetic resonance is a powerful tool for such studies. An electric field E applied to the composite produces a mechanical deformation in PZT or PMN-PT, resulting in a shift in the resonance field for YIG. Information on the nature of high frequency ME coupling has been obtained from data on resonance field shift vs E. A cavity resonator or stripline structure was used. The measured ME interactions are in the range 1-5 Oe cm/kV. The coupling strength has been found to be dependent on magnetic field orientation. The strongest interaction is measured in YIG-PZT systems. The design and characterization of ferromagnetic resonance based, electric field tunable ME resonators and filters are discussed.

Relaxors (PZN, in particular) is an important class of self-assembled nanostructure composite ferroelectric oxides (or perovskite) materials. The interesting features associated with the nanoregions/nanodomains required to describe these relaxors give rise to the most relevant device related characteristics and peculiar physical properties in these materials. In addition, they possess astronomical property coefficients by themselves or when modified with lead titanate (PT) forming solid solution. In the past, we conducted temperature dependent Raman scattering studies on solid solution (1−x)PZN−xPT relaxors single crystals with varying composition; x = 0.02, 0.085, and 0.11. These studies were performed to obtain relevant information about lattice/phonon dynamics for matching the application criteria such as electromechanical actuators. We showed that the sharp structural phase transition occurs at or near 460 K which is a first-order transition by fitting two spectroscopic variables in Raman spectra for one of the representative bands occurring at 277 cm−1. Besides structural phase transition, polarization mechanism for the unpoled (x = 0.02) and poled (x = 0.05) specimens is also investigated to understand the polarization mechanism in relaxors using Raman spectroscopy. The difference in the case of poled specimen is accounted for by the influence of residual electric field. Poling also suggested an enhanced local ordering and the increase in the volume of the polar nano-regions. In the present report, we attempted to determine the nanopolar region size and distribution using the above mentioned temperature dependent Raman spectra. We discuss the most suitable mathematical form of nanodomain size distribution for such inhomogeneous material is log-normal and it is bimodal depending upon the temperature regime in addition to composition. These studies helped to determine the size distribution of nanoscopic embodiments in relaxor ferroelectrics using Raman spectroscopy as a function of temperature which is a dynamical phenomenon.

YMnO3, which is one of hexagonal RMnO3 compounds, has antiferromagnetic and ferroelectric properties, simultaneously. Recently, it has been reported that cross-correlation in the magnetic dielectric properties on hexagonal YMnO3 single crystals. However, the cross-correlation in the magnetic-ferroelectric properties has not been understood yet. In this study, we investigated the cross correlation between magnetism and ferroelectricity on YMnO3 epitaxial films with excellent crystallinity. YMnO3 epitaxial films were deposited pulsed laser deposition. The YMnO3 epitaxial films show the dielectric anomalies at around Néel point of the films. It was suggested that the ferroelectric domain switching was suppressed by the magnetic ordering. The relationship between the magnetic structure and the ferroelectric properties are discussed in terms of the temperature dependences of magnetization and dielectric permittivity. Moreover, the ablation plume of YMnO3 was investigated by optical emission spectroscopy. The effect of the ablation conditions on the thin film growth and electrical properties was discussed.

An examination of the low temperature (20 K) dielectric permittivity revealed dispersion between the MHz and THz frequencies in both disordered and ordered Pb(Sc1/2Ta1/2)O3 (PST) thin films. The difference between the lattice contribution in the THz regime and that measured in the MHz regime at extremely low temperatures points to the peculiar contribution of polar regions which maintain their mobility on cooling. Experiments measuring the permittivity upon cooling under an electric bias field revealed an additional peculiar feature of polar regions in disordered PST thin films: the application of a DC field of 30kV/cm failed to induce a phase transition to a long range polar state.

Poled ferroelectric lead zirconate titanate (PZT) films comprising a (111) texture on (100)Si/SiO2/(111)Pt substrates were investigated by piezoresponse force microscopy (PFM). Depending on the film thickness, the crystallite orientation varies from purely (111) (related to the Pt bottom electrode orientation) to a more random texture. By PFM, 90° domains with a width of 50 nm were obtained in an individual grain Pb(Pb0.10Zr0.21Ti0.69)O3 − PPZT (10/21/69). It was shown that the virgin (unpoled) films possess large piezoelectric activity comparable to that after local poling (self-polarization effect). This corresponds to a clear predominance of the domains with a polarization oriented from the bottom electrode to the free surface of the film.

Electronic structure in multiferroic compound RFe2O4. is studied theoretically. We suggest that orbital degree of freedom in a Fe2+ ion is active. The effective Hamiltonian for spin, charge and orbital degrees of freedom is derived. Numerical analyses with the multi-canonical Monte-Carlo simulation show that the electric polarization is attributed to the charge order with momentum (1/3, 1/3). A magnitude of the polarization is enhanced around the magnetic ordering temperature due to the coupling between spin and charge. Conventional orbital order is not expected from the numerical calculation. We discuss possible orbital state at low temperatures.

The dielectric response of La- and Dy- doped BiFeO3 thin films to electric- and magnetic fields was measured at microwave frequencies (up to 12GHz) in a temperature range from 25 °C to 300 °C. Interesting phenomena were observed. Significant oscillations in the C(f) characteristic which were unaffected by the electric field or by elevated temperature but which were dampened by a magnetic field. We also observed ‘N’-type I-V characteristics. A possible explanation for this mesoscopic response is the presence of structural features that cause resonance (e.g. grains, grain-boundaries, domains, domain walls etc), with a contribution strong enough to be averaged by the system. The exact origin of these features is unknown at present.

To investigate the long-term retention characteristics of a ferroelectric-data-storage system, 80-nm-thick congruent LiTaO3 plates with inverted-domain dot arrays composed of 100-nm-φpdots were baked at 220, 250, 280 and 300°C. After heat treatment over a range of different time intervals, the dots shrank. From the change in the dot radius data, the activation energy (Ea) and frequency factor (α), parameters of the Arrhenius equation, were determined to be = 0.76 eV, = 2.21×105. From these parameter we can predict competitive retention characteristics compared with general memory devices. The phenomenon of dot shrinking can be explained from the energy transition of the system based on wall energy.

We have investigated the dielectric properties of the Cr2O3 films using ferromagnetic electrode; (La0.66, Sr0.33)MnO3. The relationships between those properties and their crystallinity also have been investigated. The well crystallized sample was exhibited low leakage current density. Although all samples show capacitance decreasing by applying voltages, the decreasing ratio was the largest on the sample with lowest leakage current density. Since the Cr2O3 film with same leakage current density as that sample using non-magnetic electrode didn't show any capacitance changes by applying voltages, it is suggested that the dielectric properties of Cr2O3 film might be affected by the ferromagnetic film.

To explore the nature of ferroelectric behavior induced by Pr ion in the SrTiO3 ceramic, we brought together a combination of Synchrotron x-ray powder diffraction and thermal analysis. Rietveld analysis shows a clear peak splitting strongly suggesting a cubic-tetragonal structural transition when 15 % Pr substitutes the Sr site. To determine the temperature of the structural instability differential thermal analysis at high temperatures (30-900 °C) and specific heat at low temperatures (2-300 K) were performed. The difference in the heat capacity for Pr doped and undoped samples are very small. A plateau in Cp/T vs T at 110 K is a clear evidence of the competing effect of two kinds of order parameters, one represented by the polarization and the other by the rotation of the oxygen octahedral in the perovskite structure. Upon heating, DTA analysis shows an unexpected single endothermal broad anomaly at about 118 °C. The occurrence of this thermal anomaly could be related to displacive structural contributions providing unambiguous evidence of diffuse phase transition.

Hydrothermal lead zirconate titanate (Pb(Zr,Ti)O3: PZT) films with a thick of about 10 μm on both a Ti foil and a Ti layer sputtered stainless steel (SS) foil were obtained. Both PZT films showed same morphology and crystalinity. After repeating the hydrothermal process, the films were formed to cantilever shape. A tip displacement measurement of the cantilevers was carried out in order to estimate transverse piezoelectric constant (d31). The obtained d31 value of the PZT films on Ti sputtered SS foils is -29 pm/V, which is larger than that on Ti foil (-24 pm/V). Amorphous layer consist of Pb and Ti was observed at the interfaces between the both PZT film and the Ti metals. The thickness of the layer for PZT film on Ti foil (350 nm) is thicker than that for PZT film on SS foil (200 nm). The relative permittivity of the layer is estimated to be small compared with that of PZT. Accordingly, the effective electric field for PZT layer is decreased. The deference of d31 values between the obtained PZT films is thought to be attributed to the thickness of amorphous layer.

Piezoelectric materials have been investigated as vibration energy converters to power wireless devices or MEMS devices due to recent low power requirement of such devices and the development of miniaturization technology. It has shown the potential that piezoelectric power generator can be an alternative to the traditional power source-battery because of facile vibration sources in our environment and the potential elimination of maintenance required for large volume batteries. To date, PZT (Lead Zirconium Titanate) has been commonly exploited as a piezoelectric material for energy conversion since it can generate higher power density even at low-g (< 1 g) vibration environment. Its high fragility, however, can limit its applicability at high-g conditions. Therefore, other types of piezoelectric materials such as polymer and composite are necessary to investigate the applicability at severe vibration conditions. In this study, piezoelectric power generators based on cantilever beam structure were designed, optimized, and fabricated by considering matching the resonant frequency with environmental vibration, achieving maximum output power, and reaching maximum g-value without device failure. As piezoelectric materials, ceramic PZT, polymer PVDF (Polyvinylidene fluoride) and composite MFC (Macro Fiber Composite) were utilized. The energy conversion of all three types of generator devices was systematically evaluated. All three devices were measured to generate enough power density for providing electric energy to wireless sensor or MEMS device. The PZT device shows the highest output energy density and PVDF device has the highest durability to operate at high-g vibration condition.

The VO2 phase of vanadium oxide is known to exhibit large changes in the electrical and optical properties in the vicinity of the structural phase transition at 68C. Here, we report on the fabrication and study of thin film vanadium oxide (VO2) devices deposited on R-plane sapphire. Thin films prepared by electron beam evaporation have been processed by photolithography into two-terminal strips for electrical measurements. Measurements on such specimens exhibit reproducibility across a chip, in addition to hysteretic transport, and a one-to-two orders of magnitude change in the resistance in the vicinity of the structural transition. In sum, these experiments show that e-beam evaporation of VO2 constitutes a simple and useful approach to realizing devices from this technologically important material.

Dielectric and ferroelectric properties were studied in Sr0.85−yPr0.15VyBi2Ti2O9 polycrystalline samples where cation vacancies were induced. DRX characterization shows that the Aurivillius structure can accept 10% of induced vacancies without precipitation of second phases. Thermoelectric analysis and ferroelectric hysteresis measurements show that the vacancies modify the transition temperature Tc and slightly the polarization values. From the ε-T curves it was observed that the polarization magnitude and Tc are affected as a consequence of the induced vacancies. A broad peak at Tc, typical of the diffuse phase transition behavior of this material was also observed. Furthermore, the induced vacancies in praseodymium-modified SBT produce an increased on Tc from ∼180 to ∼240 °C, these facts show that induced vacancies in the structure are a tuning mechanism for the dielectric and ferroelectric properties.

PbZr0.53Ti0.4703 doped with 0.6% at. of Gd2O3 has been produced following the traditional solid state reaction technique. The ferro-paraelectric transition temperature is reduced from 386 °C to 352 °C. Remnant polarization and coercive field measurements were made from the hysteresis loops obtained at 23 °C and at different applied electric fields up to a maximum of 17 kV/cm. Piezoelectric performance was studied in the 4 Hz to 4 MHz frequency range at 25 °C and the radial electromechanical coupling factor was determined. A detailed electrical conductivity study in the 30-450 °C temperature range is performed in a wide frequency interval. The different participating transport mechanisms are elucidated and the corresponding activation energies were determined by fitting the experimental data. In particular, in the 30 to 300 °C temperature interval, the ac conductivity follows Jonscher universal relaxation law.

The effect of CuO on the microstructure and microwave dielectric properties of the CaTiO3-Ca(Zn1/3Nb2/3)O3 ceramics prepared by the conventional solid-method has been investigated. Doped with the 0.5∼1.25wt% CuO powder, the system of which the sintering temperatures were lowered exhibited the orthorhombic perovskite. It can effectively promote the microwave dielectric properties of the 0.3CaTiO3-0.7Ca(Zn1/3Nb2/3)O3 system at lower sintering temperature at the level of 1.0wt% CuO additive. The quality factor increases from 10860 to 13900GHz and not any significant change was observed in the TCF value with fixed CuO additive at different sintering temperature.

A new type of ferroelectric gate field-effect transistor (FET) using ferroelectric-insulator interface conduction has been proposed. Drain current flows along the interface between the ferroelectric and insulator layers and requires no semiconductor. This FET is fabricated by forming of source and drain electrodes on a SiON/Si substrate, dpositing SrBi2Ta2O9(SBT) film, forming topgate electrode, and forming bottom electrode. Drain current versus topgate voltage characteristics show a clockwise hysteresis loop similarly to the conventional metal-ferroelectric-insulator-semiconductor-FET(MFIS-FET). This FET shows that the On/Off ratio of the drain current is 104 to 105 and the Off state current of about 10−9 A.

Among various possible candidates of high-k gate dielectrics, SrTiO3 plays an important role because it has high dielectric constant and it can be epitaxially grown on silicon substrate. The fabrication process and properties of SrTiO3 gate dielectrics are reported. The effect of the addition of SiO2 on the microstructure and electrical properties of SrTiO3 gate dielectric is also presented. The minimization of the effect of interfacial layer between SrTiO3 and Si is the most important issue for obtaining high quality high-k gate dielectrics. The possible methods to improve the interfacial properties and the measurement techniques to characterize the interfacial layer are discussed.