A polycrystalline Pb(ZrTi)O3 (PZT) film with Pb excess is considered as a heterophase medium that consists of PZT grains and semiconductor PbO phase. The latter is segregated on PZT grain boundaries during the PZT formation and forms conducting channels between the electrodes. In such medium, uncompensated polarization charge of PZT grains generates an electric field both inside PZT grains and PbO phase. This electric field affects on ferroelectric polarization itself and stimulates carrier transport through the PbO channels. A theory is developed, where the reciprocal effect of the electric field on the polarization is taken into account. The polarization is found due to this effect to be increased up to ∼30% near the interfaces, which differs from reduction of the polarization near the interfaces in homogeneous PZT films. Using the theory, the electric field, electrostatic potential and carriers transport in PbO channels are calculated. A comparison is made with the results calculated for the approach of the polarization constancy.

Symmetric and asymmetric superlattices (SLs) composed of ferromagnetic La0.6Sr0.4MnO3 (LSMO) and ferroelectric 0.7Pb(Mg1/3Nb2/3)O3 – 0.3PbTiO3 (PMN-PT) with different periodicities have been fabricated on LaNiO3 (LNO) coated LaAlO3 (100) (LAO) substrates by pulsed laser ablation deposition. Structural, ferromagnetic and ferroelectric properties have been studied for all the SLs. All the heterostructures exhibited good ferromagnetic response over a wide range of temperatures (10K – 300K), whereas only the asymmetric SLs exhibited reasonably good ferroelectric behaviour. Ferromagnetic and ferroelectric hysteresis loops observed in the asymmetric SLs confirmed their biferroic nature. Studies were conducted towards understanding the influence of LSMO layers on the electrical responses of the heterostructures. Absence of ferroelectricity in the symmetric SL structures has been attributed to their high leakage characteristics. Strong influence of an applied magnetic field of 1.2T was observed on the ferroelectric properties of the asymmetric SLs. The effect of magnetic field on the ferroelectric properties of the SLs indicated possibility of strong interfacial effect.

Low temperature magnetic properties and Raman spectrum of highly (111)-oriented rhombohedral BiFeO3 (BFO) thin films epitaxially grown on (111) SrTiO3 substrates by pulsed laser deposition have been studied. Zero field cooled (ZFC) and field cooled (FC) magnetization curves display divergence at characteristic temperature Tirr (H), which are magnetic field dependent, suggesting a spin-glass like behavior of the film. The change in magnetic ordering results in anomalous phonon behavior such as the extraordinary enhancement and appearance of new Raman modes due to Brillouin zone folding below ∼200 K.

Lead iron tantalate Pb(Fe1/2Ta1/2)O3 (PFT) is a compound derived of general formula Pb(BIxBII1-x)O3 wherein x=1/2. In this work synthesis, sintering processes, dielectric, electrical, magnetic measurement, and Raman spectroscopy properties of PFT ceramics are described. The dielectric properties of PFT showed typical relaxor behaviors. We saw that ferroelectric and magnetic orders coexist in PFT at room temperature.

We provide a comparative study of the piezoresponse in thin Pb(ZrxTi1−x)O3 (PZT) films deposited onto GaN/sapphire and Pt/Ti/SiO2/Si substrates using the sol-gel process. The effective piezoelectric coefficient was measured by Piezoresponse Force Microscopy. The resulting effective piezoelectric coefficient obtained for PZT(∼180 nm)/GaN/sapphire structure is 16.7 ± 3.4 pm/V and for PZT(∼180 nm)/Pt/Ti/SiO2/Si structure is 7.8 ± 0.8 pm/V. We also discuss the substrate clamping effect of both structures and explain the relatively stronger piezoresponse of PZT on GaN by different orientation of films formed on the two types of substrates. In this investigation, the PZT thin films crystallized with preferred (100) and (110) orientations on platinum and GaN, respectively. The phase mode of the Piezoresponse Force Microscopy was used to demonstrate remanent polarization in PZT/GaN/sapphire structure.

Development of electronic devices with higher performance and smaller size requires the passive components to be embedded within a printed wire board (PWB). The “film-on-foil” approach is the most viable method to fabricate suitable passive components. We have deposited high-permittivity thin films of ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) on base metal foils by chemical solution deposition. These capacitors could be embedded into PWBs. However, formation of a parasitic low-permittivity interfacial layer of nickel oxide during thermal processing of the PLZT films considerably reduces the capacitance density. Two approaches were taken to overcome the problem. In the first, a conductive buffer layer of lanthanum nickel oxide (LNO) was inserted between the PLZT film and the nickel foil to hinder the formation of deleterious interfacial oxide. In the second, high temperature processing was done under low oxygen partial pressure such that no interfacial oxide was formed. By these approaches, we have grown high-quality ferroelectric PLZT films on nickel and copper foils. With samples of PLZT grown on LNO-buffered Ni, we measured a dielectric constant of 1300 (at 25°C) and 1800 (at 150°C), leakage current density of 6.6 × 10−9 A/cm2 (at 25°C) and 1.4 × 10−8 A/cm2 (at 150°C), and breakdown field strength >1.2 MV/cm. With samples of PLZT on Cu, we obtained encouraging initial results of dielectric constant >450 and dielectric loss tan(δ) ≈0.04.

Dynamical nonlinearities in piezoelectric materials have been investigated over different time and frequency scales using four different methods; measurements of displacement and electric polarization of bulk material, measurements of nanometer scale surface structure of the material by an atomic force microscope (AFM), and numerical modelling of ferroelectric materials with quenched randomness. Laser vibrometer measurements of the deformations of piezoelectric materials, d31 type PZT and PMN-PT sheets, have been done under sinusoidal voltage loading with different frequencies. This yields information about the dynamical hysteresis behavior, such as the area of the hysteresis loops as a function of the applied frequency f and voltage amplitude. Similarly the hysteresis loops have been measured for the electric polarization of the same samples. Relaxation behaviors of the same materials have been measured by an AFM. Topography of the piezo sheets was measured after applied DC voltage, indicating slow collective changes in the polarization close and at the sample surface. To investigate the time-dependent hysteresis, we have studied numerically a Ginzburg-Landau-Devonshire (GLD) model for ferroelectric materials including dilution type quenched randomness. Quantities studied include the area of the hysteresis loop, of the polarization in the material, and the coercive electric field Ec as a function of the frequency f, both as a function of the disorder strength.

Spinel ferrite oxides doping non-magnetic ions show the photo-induced magnetization (PIM) effect at high temperature [1-3]. Such a magnetization enhancement by light irradiation is a unique property in this material. In order effectively to use the PIM effect and precisely to control the magnetism, direct light-emission from light-emitting element substrates would be a useful technique. In this study, spinel ferrite Al0.2Ru0.8Fe2O4 (ARFO) thin films, with the high temperature PIM effect, were prepared on GaAs(001) substrates by a pulsed laser deposition technique to aim integration with light-emitting devices based on GaAs lattice-matched materials in the future. Results showed that (001)-oriented ARFO thin films were successfully grown by using MgO buffer layers. The magnetic properties were approximately the same as ARFO films using other substrates such as Al2O3(0001) or MgO(001).

The Cr2O3 thin films were grown on Al2O3(1102)(r-cut sapphire), Al2O3(1120)(a-cut sapphire), and Al2O3(0001)(c-cut sapphire) substrates to apply magnetoelectric oxides to oxides electronics. The Cr2O3 is a representative magnetoelectric material with antiferromagnetic insulator with the Néel temperature of 308 K. From the results of X-ray diffraction and the reflection high energy electron diffraction, epitaxial Cr2O3 thin films were obtained on all cut sapphire substrates using off-axis DC-RF magnetron sputtering method. The epitaxial relationship was Cr2O3[1120]//Al2O3[1120] and Cr2O3(1102)//Al2O3(1102) on r-cut, and Cr2O3[1100]//Al2O3[1100] and Cr2O3(1120)//Al2O3(1120) on a-cut, and Cr2O3[1120]//Al2O3[1120] and Cr2O3(0001)//Al2O3(0001) on c-cut. Optimized Cr2O3 film was obtained grown at 600°C on c-cut sapphire substrate. The surface roughness (Ra) of the film was 0.28 nm, and full width at half maximum of rocking curve for Cr2O3(0006) Bragg reflection was 0.23°. Growth difference is expected to be caused by the stacking order of atoms normal to the substrate surface and arrangement of atoms of the substrate surface.

Epitaxial BiFeO3 (BFO) thick films were fabricated on SrTiO3 (STO) substrates by a simple liquid-phase epitaxy (LPE) growth technique. To avoid the evaporation of Bi, in this process, we used the lid substrate. As starting materials, we used calcined powder or amorphous films deposited by pulsed laser ablation. The fabricated films were found to have a single perovskite phase and be (100)-oriented. Cube-on-cube epitaxial growth of film on the STO substrate was also confirmed by ϕ-scan measurements. The films grown on the substrate display a multigrain structure with a maximum in-plane size of approximately 100μm, and the film thickness was about 3-35 μm. The interface structure between the film and the substrate was relatively smooth. These results indicate that the proposed simple LPE technique is highly suitable for the fabrication of BFO thick films.

Thin film ferroelectric capacitors have been integrated with resistors and active functions such as ESD protection into small miniaturized modules, which enable a board space saving of up to 80%. With the optimum materials and processes, integrated capacitors with capacitance densities of up to 100 nF/mm2 and breakdown voltages of up to 90 V have been achieved. The integration of these high density capacitors with extremely high breakdown voltage is a revolution in the world of integrated passive components and has not yet been achieved in any other passive integration technology.

The high frequency operation of BST capacitors necessitates the development of low series resistance electrodes. As an alternative to platinum, DC magnetron sputtered IrO2/Aluminum top electrode metallization for BST capacitors has been proposed. The capacitance voltage characteristics of BST capacitors did not change significantly due to the deposition of aluminum on iridium oxide. Post annealing in nitrogen environment shows that IrO2/Al metallization does not degrade annealing temperature up to 450 oC.

Ceramic/polymer composite made of nanosize Ba0.5Sr0.5TiO3 (BST) powders and P(VDF-CTFE) copolymers as matrix. The concentration of the composites with BST from 0% to 50% in volume was investigated. The dielectric properties and structure as well as the morphology of the composites were characterized over a broad temperature range. It is found that the wetability between the polymer and ceramic powder is not good. The approach to improve the uniformity of composites was investigated. Due to the dielectric-constant-maximum temperature of the BST is different from that of copolymer, a weak dependence of the dielectric constant on temperature was observed over temperature from 10 °C to 100 °C.

We have investigated the effect of Bi-excess surface layers of stoichiometric BiFeO3 thin films prepared by chemical solution deposition. A stoichiometric BiFeO3 thin film with both the Bi-excess top and bottom surface layers shows improved crystallinity with the remanent polarization of 65 μC/cm2 at 80 K, which is larger than BiFeO3 film prepared by the same process using stoichiometric solution. These results are attributed to the reduction of the imperfect crystal at the interface between BiFeO3 film and electrode. Stoichiometric BiFeO3 thin film with Bi-excess top and bottom surface layers also reserves the magnetic property of stoichiometric film. Stoichiometric BiFeO3 thin films with Bi-excess surface layers are an effective way to obtain good multiferroic properties.

A new multiferroic compound Bi2NiMnO6 was synthesized in both bulk and thin-film forms. Bulk samples were prepared under a high pressure condition at 6 GPa, and thin-film samples were epitaxially grown on single-crystal SrTiO3 substrates by a pulsed-laser deposition method. The crystal structure of the material is a double perovskite, in which Ni2+ and Mn4+ ions are ordered in a rock-salt configuration. Bi3+ ions at the A-site cause a noncentrosymmetric (C2) structural distortion which allows a spontaneous ferroelectric polarization at room temperature. Ni2+–O–Mn4+ magnetic paths lead to ferromagnetism through the superexchange interaction according to the Kanamori-Goodenough rule. A coupling between the ferromagnetic and ferroelectric interactions appears to exist, but it is quite small.