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Lithium niobate and tantalate are among the most important and widely used materials of acoustooptics and acoustoelectronics. They have high piezoelectric constants enabling their use as actuators. Their use is however restricted by the thermal instability of lithium niobate crystals and the low Curie temperature TC of lithium tantalate crystals. Overcoming these drawbacks typical of some compounds is possible by growing LiNb1-xTaxO3 single crystals. Good quality LiNb1-xTaxO3 single crystals have been grown using the Czochralsky technique. High-temperature poling process of LiNb1-xTaxO3 single crystals has been studied. The main differences between the process modes required for poling of congruent LiNb1-xTaxO3 single crystals and congruent LiNbO3 single crystals have been demonstrated. Parameters of high-temperature electric diffusion processing of LiNb1-xTaxO3 single crystals that provide for singledomain crystals for further study of physical properties have been reported.

We investigate the generation of optical third-harmonic frequency in quadratic crystals with a nonlinear domain lattice optimized with the aid of a random number generator. In the developed Monte Carlo algorithm and numerical experiments, we consider domain thicknesses to be taking either the values d1 or d2, with d1 and d2 being the coherence lengths for the cascaded parametric interactions 2ω=ω+ω and 3ω=2ω+ω, respectively. We focus on the cases with single segments formed by equal and/or different domains, showing that frequency tripling can be achieved with high conversion efficiency from an arbitrary input wavelength. The presented approach allows one to accurately determine the optimized random alternation of domain thicknesses d1 and d2 along the propagation length.

International audience; A complex study of the electron transport and magnetic characteristics of epitaxial manganite films La0.7Ba0.3MnO3 (LBMO) was carried out under conditions of the crystal structure tension caused by a mismatch between the parameters of the LBMO crystal and the substrate. The epitaxial thin films with the thickness 40-100 nm were grown by pulsed laser deposition at T = 700-800 °C in pure oxygen pressure 0.3-1 mbar. The substrates (110) NGO, (001) STO, (001) LAO, and (001) LSAT were used. By comparison of the lattice parameter of LBMO targets with substrate's one, the lattice mismatches were derived. We used substrates in which the lattice parameter was less than for the LBMO crystal one. It is shown that the temperature dependence of the film resistance in the low-temperature region does not depend on the film stress and is in good agreement with the calculation that takes into account the interaction of carriers with magnetic excitations in the presence of strongly correlated electron states. A nonmonotonic temperature dependence of the resistance of an LBMO film deposited on ferroelectric crystals PMN-PT that was observed. This feature is typical for manganites, and indicating the presence of ferromagnetism in the system was observed. Rare earth manganite with perovskite structure Re1-xAxMnO3 (Re-rare earth elements such as La or Nd and A-alkaline earth metals such as Sr, Ca, Ba) exhibits a wide range of unusual electrical and magnetic properties (see, for review [1]). The parameters of epitaxial films of these materials very often differ significantly from the properties of single crystals. As it has been shown in several studies [1, 2], the tension of the films due to mismatch with the substrate is the reason for the change in the electric and magnetic parameters of the films. It was shown that the three-dimensional compression of the crystal lattice increases the hopping probability amplitude in the double exchange model, which leads to an increase in the Curie temperature (TC), while the biaxial distortions of the Jahn-Teller type cause an increase in the localization of the electrons and decrease TС [3, 4]. Manganite films, for which TС is close to room temperature, are particularly attractive for practical applications. The ferromagnetic phase transition for a La0.7Ba0.3MnO3 (LBMO) crystal occurs at TC = 345 K [5]. In the LBMO crystal, a fairly large magnetostriction (up to 4 × 10 −4) was observed at a temperature equal to the Curie temperature [6]. The magnetic and resistive properties of LSMO films have been studied in a number of works [2, 5,6,7,8,9,10,11,12,13,14,15,16]. Usually, substrates from SrTiO3 (STO) [9, 13,14,15] were used. The film tension was changed either by changing the thickness of the LBMO film, or by changing the ratio of La and Ba. It was shown that in addition to the substrate-induced strain, oxygen content plays a very important role in determining the transport and magnetic properties of La1−xBaxMnO3 thin films [9]. For correct comparison of the effect of the stress on the film properties either film deposited on the different substrate under the same conditions [2], or piezo substrate are used [17, 18]. In LBMO films, when the film tension changes in piezo substrate, multiple resistive states arise. They are modulated by the magnetic field in a wide

Multicaloric materials show thermal changes that can be driven simultaneously or sequentially by more than one type of external field, and the resulting multicaloric effects can be large in multiferroic materials. The use of more than one driving field can permit access to larger thermal changes, with smaller field magnitudes, over wider ranges of operating temperature, while manipulating hysteresis. The thermodynamics behind multicaloric effects is well established, but only a small number of multicaloric effects have been experimentally studied to date. Here we describe the fundamentals of multicaloric effects, and discuss the performance of representative multicaloric materials. Exploiting multicaloric effects could aid the future development of cooling devices, where key challenges include energy efficiency and operating temperature span.

The remote controlling of ferroic properties with light is nowadays a hot and highly appealing topic in materials science. Here, we shed light on some of the unresolved issues surrounding light–matter coupling in ferroelectrics. Our findings show that the capacitance and, consequently, its related intrinsic material property, i.e., the dielectric constant, can be reversibly adjusted through the light power control. High photodielectric performance is exhibited across a wide range of the visible light wavelength because of the wavelength-independence of the phenomenon. We have verified that this counterintuitive behavior can be strongly ascribed to the existence of “locally free charges” at domain wall.

The features of the crystal structures and spontaneous polarization (Ps) under an electric field (E) have been reviewed for (1 − x)(Bi0.5Na0.5)TiO3–xBaTiO3 (BNT–BT). In-situ measurements of high-resolution synchrotron radiation X-ray diffraction (SR-XRD) under electric fields show that single crystals with x = 0 (BNT) and 5% have a monoclinic distortion in space group Cc at 25 °C. The SR-XRD study combined with density functional theory (DFT) calculations demonstrates that BNT–5%BT exhibits a rotation of Ps in the monoclinic a–c plane by 2° under an E of 70 kV/cm along the pseudo-cubic direction, which is much larger than BNT.

We simulate the fracture processes of ferroelectric polycrystals in three dimensions using a phase-field model. In this model, the grain boundaries, cracks and ferroelectric domain walls are represented in a diffuse way by three phase-fields. We thereby avoid the difficulty of tracking the interfaces in three dimensions. The resulting model can capture complex interactions between the crack and the polycrystalline and ferroelectric domain microstructures. The simulation results show the effect of the microstructures on the fracture response of the material. Crack deflection, crack bridging, crack branching and ferroelastic domain switching are observed to act as the main fracture toughening mechanisms in ferroelectric polycrystals. Our fully 3-D simulations illustrate how the combination of these mechanisms enhances the fracture toughness of the material, and pave the way for further systematic studies, including fracture homogenization.

Domain engineering in ferroelectric crystals is an increasingly important technique for applications in different areas including photonics and integrated optics, liquid manipulation, particles trapping and recently these crystals are emerging also for biotechnology applications. Among those, periodically poled lithium niobate (PPLN) continues to attract interest, and most efforts have been devoted to one-dimensional and two-dimensional PPLN crystals. These are ferroelectric materials broadly used in nonlinear optics frequency conversion processes by quasi-phase-matched (QPM). Fabrication of periodically reversed ferroelectric domains is usually achieved by an electric field poling (EFP) process. The period of the ferroelectric domain patterns usually range from hundreds of µm down to nm, depending on the specific applications. The fabrication of submicron periodic domain structures in ferroelectric crystals allows different types of optical components, such as electrically controlled Bragg reflectors, beam-steering devices, and narrow band filters. A variety of methods have recently been investigated to improve the pattern fidelity of the reversed domains. Technique of domain patterning in PPLN uses a lithographically patterned insulating layer and lithium chloride liquid electrodes contained in a chuck, sandwiching the sample between two O-ring gaskets. Upon application of an external electric field exceeding the coercive field of the material, domains first nucleate along the edges of the electrodes, due to the increase in field strength caused by the fringing field, and then spread laterally underneath the adjacent insulating layer. Usually, the external electric field is applied through appropriate waveforms or pulses that critically depend on many parameters depending on the material. However one main difficulty in achieving multi-periodicity in inverted ferroelectric domains is that when there are photoresist masks with different sizes patterns: it is very difficult to calibrate and modulate the electric field in order to avoid overpoling of shorter pitches without incurring in under-poling of larger structures. Thus, fabricating multi-periods PPLN is very arduous by a standard EP process that uses photoresist masks. The only way to have the chance to create the poled with freely patterns is by point-wise scanning techniques such as e-beam, electric tip AFM. Nonetheless, even if such scanning probe techniques allow getting patterns with whatever geometry they are very time-consuming in respect to the flexibility offered by single-shot classical EP process. In order to evaluate the poling process several attempts have been performed and new tools have been explored. In this work was adopted the interferometric approaches based on digital holography (DH) in microscopy configuration that allows at same time non-destructive inspection, full-field analysis and quantitative evaluation for assessing the quality of the poling process. This work presents the TEFP process as a tool for fabricating multi-scale PPLN samples avoiding cross drawbacks between over-poling and under-poling. The two EFP steps were applied with two different photoresist gratings. Since the pitch of the two gratings have periods with different scales, the final result is intriguing as it allows one to fabricate a sort of satellite structures.

En col·laboració amb la Universitat Autònoma de Barcelona (UAB), la Universitat de Barcelona (UB) i l’Institut de Ciències Fotòniques (ICFO) Ferroelectric photovoltaic has been intensively studied during the last years due to possible high efficient charge separation by presence of an internal electric field. Ferroelectric materials show permanent electrical polarization. Ideally, electric contacts would screen the polarization, but if screening is not perfect, it results in the generation of depolarization field. In this report, we study the photoelectric response of LuMnO3 that shows a small bandgap compared to archetypical ferroelectric materials and a sizeable internal polarization. We have studied its photoresponse dependence on polarization state.

The origins of high piezoelectric properties in the lead-free (K,Na)NbO3-based tetragonal composition (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 (KNL-NTS) is investigated by quantifying the intrinsic and extrinsic contributions from high energy X-ray diffraction measurements. The applied methodology, which allows discerning between the intrinsic contribution, related to the field induced lattice distortion, and the extrinsic contributions, related to non-180° domain wall motion, is widely described in this work. The non-180° domain reorientation of the KNL-NTS piezoceramic is quantify from the integrated intensities of the 002 and 200 reflections obtained from line profile, while the shifts in peak position versus the applied electric field is used to obtain the lattice strain contribution. Large non-180° domain wall contribution to the electric field induced macroscopic strain (80% of the macroscopic strain) is verified in KNL-NTS.

The Preisach model is a classical method for describing nonlinear behavior in hysteretic systems. According to this model, a hysteretic system contains a collection of simple bistable units which are characterized by an internal field and a coercive field. This set of bistable units exhibits a statistical distribution that depends on these fields as parameters. Thus, nonlinear response depends on the specific distribution function associated with the material. This model is satisfactorily used in this work to describe the temperature-dependent ferroelectric response in PZT- and KNN-based piezoceramics. A distribution function expanded in Maclaurin series considering only the first terms in the internal field and the coercive field is proposed. Changes in coefficient relations of a single distribution function allow us to explain the complex temperature dependence of hard piezoceramic behavior. A similar analysis based on the same form of the distribution function shows that the KNL–NTS properties soften around its orthorhombic to tetragonal phase transition.

Copyright 2015 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. We demonstrate infrared femtosecond laser-induced inversion of ferroelectric domains. This process can be realised solely by using tightly focused laser pulses without application of any electric field prior to, in conjunction with, or subsequent to the laser irradiation. As most ferroelectric crystals like LiNbO3, LiTaO3, and KTiOPO4 are transparent in the infrared, this optical poling method allows one to form ferroelectric domain patterns much deeper inside a ferroelectric crystal than by using ultraviolet light and hence can be used to fabricate practical devices. We also propose in situ diagnostics of the ferroelectric domain inversion process by monitoring the Cerenkov second harmonic signal, which is sensitive to the appearance of ferroelectric domain walls.

This thesis is concerned with the study of two families of materials which contain magnetically frustrated triangular lattices. Each material is concerned with a different use; the first, analogues of YMnO₃, is from a family of materials called multiferroics, the second, A₂MCu₃F₁₂ (where A = Rb¹⁺, Cs¹⁺, M = Zr⁴⁺, Sn⁴⁺, Ti⁴⁺, Hf⁴⁺), are materials which are of interest due to their potentially unusual magnetic properties deriving from a highly frustrated Cu²⁺-based kagome lattice. YFeO₃, YbFeO₃ and InFeO₃ have been synthesised as their hexagonal polymorphs. YFeO₃ and YbFeO₃ have been studied in depth by neutron powder diffraction, A.C. impedance spectroscopy, Mössbauer spectroscopy and magnetometry. It was found that YFeO₃ and YbFeO₃ are structurally similar to hexagonal YMnO₃ but there is evidence for a subtle phase separation in each case. Low temperature magnetic properties are also reported, and subtle correlations between the structural, electrical and magnetic properties of these materials have been found. InFeO₃ was found to adopt a higher symmetry and is structurally similar to the high temperature phase of YMnO₃. TbInO₃ and DyInO₃ have also been synthesised and studied at various temperatures. The phase behaviour of TbInO₃ was analysed in detail using neutron powder diffraction and internal structural changes versus temperature were mapped out – there is also evidence for a subtle isosymmetric phase transition. Neither DyInO₃ nor TbInO₃ show long-range magnetic order between 2 and 300 K, or any signs of ferroelectricity at room temperature. The new compounds Cs₂TiCu₃F₁₂ and Rb₂TiCu₃F₁₂ have both been synthesised and shown to be novel kagome lattice based materials. The former shows a transition from rhombohedral to monoclinic symmetry in the powder form and from rhombohedral to a larger rhombohedral unit cell in the single crystal – a particle size based transition pathway is suggested. For Rb₂TiCu₃F₁₂ a complex triclinic unit cell is found, which distorts with lowering temperature. Both materials show magnetic transitions with lowering temperature. The solid solution Cs₂₋ₓRbₓSnCu₃F₁₂ (x = 0, 0.5, 1.0, 1.5, 2.0) was synthesised and investigated crystallographically, demonstrating a range of behaviours. Rb₂SnCu₃F₁₂ displays a rare re-entrant structural phase transition. In contrast, Cs₀.₅Rb₁.₅SnCu₃F₁₂ shows only the first transition found in the Rb⁺ end member. CsRbSnCu₃F₁₂ adopts a lower symmetry at both room temperature and below. Cs₁.₅Rb₀.₅SnCu₃F₁₂ and Cs₂SnCu₃F₁₂ show a rhombohedral - monoclinic transition, which is similar to that found in Cs₂TiCu₃F₁₂.

Nonlinear optics studies the class of phenomena occurring when an intense light field, typically from a laser source, modifies the optical properties of a transparent material in a nonlinear way. The polarization \(\vec{P}(\vec{x},t)\) of the material can be written as a power series in the field strength \(\vec {E}(\vec{x},t)\) : $$\vec{P}=\chi^{(1)}\vec{E}+\chi^{(2)}\vec{E}^{2}+\chi^{(3)}\vec{E}^{3}+\cdots $$ where χ (i) is the i-order optical susceptibility of the material. Nonlinear phenomena arise from the nonzero value of the χ (2) susceptibility in noncentrosymmetric crystals. A large class of nonlinear materials (among them LN, KTP, BBO, and LBO) has been studied and used since 1960’s for up/down-conversion of the existing laser sources to wavelength regions which are not directly accessible otherwise. Some of these materials also belong to ferroelectrics, and this feature can be exploited to engineer the orientation of their nonlinear susceptibility. One of the earliest and most commonly used material is LiNbO3 (LN), because of its high nonlinear coefficient (d 33≈27 pm/V) and its wide transparency range from the UV to the mid IR (0.3÷5 μm). A technique giving access to d 33 in LN for optimizing nonlinear conversion processes, named quasi-phase-matching (QPM), was thought even before the first fabrication of this material. About 20 years later, the first experimental demonstration of this idea was obtained, and nowadays periodic poling of ferroelectrics crystals is a widely spread technology making these devices world-wide used and commercially available.

International audience; The thermodynamic description of a ferroelectric material is generally done using the approach of Landau. This latter is based on the development of the free energy around the para/ferro-electric transition temperature. Following the formulation of Devonshire (1949), many authors have tried to improve the description level. In this context, the free energy due to the elastic behavior of the material has been included in models. Despite this progress, the development of the free energy in successive power of the polarization still depends on parameters that must be set in an ad hoc manner. We propose here a formulation of the free energy for displacive ferroelectrics which takes direct account of the polarization but also of the coupling with temperature and of the electrostrictive coupling. We apply this formalism to the case of BaTiO3 single crystal. A comparison with experiment and with previous works is performed. The proposed approach allows for example to properly account for the evolution of the spontaneous polarization and lattice parameters as a function of temperature in all polar phases.

Agradecimentos: The authors wish to thank FAPESP (Proc. 2008/04025-0 and 2010/11187-6) and CNPq for the financial support and to Francisco J. Picon and Natalia A. Zanardi for technical assistance Abstract: Presented here are the results of magnetic data that reveal that both Pb-based perovskites samples, Pb(Fe1/2Nb1/2)O-3 (lead iron niobate - PFN) and Pb(Fe2/3W1/3)O-3 (lead iron tungstate - PFW), exhibit a change in magnetic ordering from paramagnetic (PM) to weak ferromagnetic state at high temperature: a weak ferromagnetic order occurs in the samples around 530K. The experimental results suggest a possible involvement of the Pb ions into the superexchange of antiferromagnetic (AFM) phase FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

We study theoretically the Čerenkov-type second-harmonic generation by a Gaussian beam in quadratic nonlinear media with periodically reverted ferroelectric domains. In particular, we consider the role of fundamental beam width on the harmonic emission process. We show that varying the beam width of the fundamental wave not only affects the strength of the emitted Čerenkov harmonic signal but also changes the sensitivity of the emission process to wavelength tuning.

Agradecimentos: The authors wish to thank FAPESP (Proc. 2008/04025-0 and 2010/11187-6) and CNPq for the financial support and to Mr. Francisco J. Picon and Mrs. Natalia A. Zanardi for the technical assistance Abstract: Dielectric and magnetic properties were investigated in Pb(Fe2/3W1/3)(0.83)Ti0.17O3 ceramics. The dielectric constant in these samples exhibits colossal changes at the magnetic ordering temperature under the presence of bias external electric fields, which presents a close connection with magnetoelectrics effects (ME), confirming the possibility to control magnetic proprieties with electric fields. The ferroelectromagnetoelastic coefficient was determined from the dielectric response as a function of the electric field. The analysis of magnetic and dielectric susceptibilities based on the Landau-Devonshire thermodynamic formalisms indicates that the ME effects is a contribution of intrinsic ME coupling and a field dependent term FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Metal, semiconductor crystals and their alloy XPS are measuring in the world. However, the ferroelectric electronic structure, form bands and their changes were not investigated. The aim of dissertation is to interpret and theoretically calculate the experimentally measured SbSI, SbSeI, BiSI, TlInSe2, Sn2P2S6 crystals XPS. The same crystals of different phases and even very different crystal forms of the XPS bands similarity shows their basic nature. Therefore, XPS analysis, their approximation and analysis have principled theoretical value explaining what from these crystals valence bands depends on, how phase transition changes electronic structure of crystal and what bands changes determine surface crystal properties and temperature. Explanation of physical phenomena is based not only on quantitative assessments of changes in the experimental XPS but theoretical ab initio calculations of the molecular models. For the first time XPS forms were investigated in a wide temperature range and completely new results were received. This commenced a unique scientific direction - Ferroelectrics XPS forms and their dependence on electronic structure studies, thus we have managed to avoid the surface ionization problems and look at the crystal volume.

Metal, semiconductor crystals and their alloy XPS are measuring in the world. However, the ferroelectric electronic structure, form bands and their changes were not investigated. The aim of dissertation is to interpret and theoretically calculate the experimentally measured SbSI, SbSeI, BiSI, TlInSe2, Sn2P2S6 crystals XPS. The same crystals of different phases and even very different crystal forms of the XPS bands similarity shows their basic nature. Therefore, XPS analysis, their approximation and analysis have principled theoretical value explaining what from these crystals valence bands depends on, how phase transition changes electronic structure of crystal and what bands changes determine surface crystal properties and temperature. Explanation of physical phenomena is based not only on quantitative assessments of changes in the experimental XPS but theoretical ab initio calculations of the molecular models. For the first time XPS forms were investigated in a wide temperature range and completely new results were received. This commenced a unique scientific direction - Ferroelectrics XPS forms and their dependence on electronic structure studies, thus we have managed to avoid the surface ionization problems and look at the crystal volume.

The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the core levels (CL) of uniaxial ferroelectric Sn2P2S6 single crystals from different crystallographic planes in both paraelectric and ferroelectric phases. The XPS were measured with monochromatized Al Kα radiation in the energy range 0-1400 eV. The VB consists of five bands with the maxima between 3.3 eV and 14.5 eV below the Fermi level. Experimental energies of the VB and core levels are compared with the results of theoretical ab initio calculations of the molecular model of the Sn2P2S6 crystal. The electronic structure of the VB is revealed. Ferroelectric phase transition changes the atom's charge and strength of the bonds, electronic structure of VB, width of CL lines and chemical shifts for the Sn, P and S states which are crystallographic plane-dependent.

The structure and ferroelectric properties of PbZr0.53Ti0.47O3 thin films were investigated in detail by using the x-ray diffraction technique. The surface morphology of the film was studied by using the atomic force microscopy technique, showing a film with a dense morphology and a smooth surface. Based on recent results reported by Pandey et al (2008 Acta Crystallogr. A 64 192), Rietveld refinements of the structure were conducted considering different models proposed in the literature. Results suggested the monoclinic and tetragonal (M + T) phase coexistence, with P4mm and Cm space groups, respectively. The monoclinic phase (68 mol%) is dominant over the tetragonal phase (32 mol%) for this PZT film composition FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

We demonstrate a dual interferometric technique for simultaneous and independent measurements of the temperature dependence of the thermo-optic and thermal expansion coefficients in ferroelectric crystals. The crystal temperature can be changed from room temperature up to about 200°C by an actively stabilized heater (stability < 0.1°C). The thermal expansion coefficient is determined using a moire interferometer and monitoring the period of a grating written on the z-face of the crystal sample as a function of the temperature of the crystal. The thermo-optic coefficients of both ordinary and extraordinary axes are estimated by measuring the optical path variation measured by a Mach-Zehnder interferometer with one arm passing through the crystal perpendicularly to the crystal z-axis. This method can be applied to a wide variety of optical materials, when an accurate knowledge of the temperature dependence of the refractive index and thermal expansion is needed.

The fundamental optical absorption edge and dielectric permeability and its temperature and pressure dependence in the vicinity of phase transitions in (Sn0.95Zn0.05)2P2S6 ferroelectric crystals is measured . Based on these data, the p,T-phase diagram of (Sn0.95Zn0.05)2P2S6 crystals is built., На основе исследований температурной и барической зависимости энергетического положения края фундаментального поглощения света и температурных зависимостей диэлектрической проницаемости в окрестности фазовых переходов сегнетоэлектрических кристаллов (Sn0.95Zn0.05)2P2S6 впервые построена их фазовая p,T-диаграмма., На основі досліджень температурної та баричної залежності енергетичного положення краю фундаментального поглинання світла та температурних залежностей діелектричної проникності в околі фазових переходів сегнетоелектричних кристалів (Sn0.95Zn0.05)2P2S6 вперше побудована їх фазова p,T-діаграма.

A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM, respectively) has been used to map the out-of-plane and in-plane polarization distribution, respectively, of (111)-oriented Pb(Zr,Ti)O-3-based (PZT) ferroelectric patterned and reactively-ion-etched capacitors. While VPFM and LPFM have previously been used to determine the orientation of the polarization vector in ferroelectric crystals and thin films, this is the first time the technique has been applied to determine the three-dimensional polarization distribution in thin-film capacitors and, as such, is of importance to the implementation of nonvolatile ferroelectric random access memory. Sequential VPFM and LPFM imaging have been performed in poled 1x1.5 mum(2) PZT capacitors. Subsequent quantitative analysis of the obtained piezoresponse images allowed the three-dimensional reconstruction of the domain arrangement in the PZT layers of the capacitors. It has been found that the poled capacitors, which appear as uniformly polarized in VPFM, are in fact in a polydomain state as is detected by LPFM and contain 90degrees domain walls. Despite the polycrystallinity of the PZT layer, regions larger than the average PZT grain size are found to have the same polarization orientation. This technique has potential for clarifying the switching behavior and imprint mechanism in micro- and nanoscale ferroelectric capacitors. National Science Foundation Fujitsu Limited Author has checked copyright AD 14/01/2014

We investigate the domain structure obtained on overpoled both sides polished z-cut Lithium Niobate crystal sample by applying an electric field on periodic liquid electrodes. Lithium Niobate sample was spatially patterned with photoresist by use of interference photolithographic process. The sample was then etched in a mixture of hydrofluoric and nitric acid to reveal the reversed domains. The different etch rate of the two opposite z faces of the crystal domains allowed to measure the surface profile of the sample by using a profilometer. Overpoling the crystal caused the appearance of high density and submicrometer spacing single dot domains vertically aligned along the direction of the interference fringes in the patterned region. ( Summary only available )

Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) is an important ferroelectric material that has outstanding room temperature dielectric constant and electro-mechanical coefficient. Unlike most other ferroelectric materials, PMN-PT is difficult to prepare because of the formation of unwanted pyrochlore phase. Many methods of PMN-PT preparation have been developed to overcome this problem over the past decades. The remaining major problems for these methods are the high sintering temperature of 1200°C and the complex processing steps. In this thesis, a new coating method is introduced for PMN-PT processing. This method involves coating Mg(OH)2 on the surface of Nb2O5 particles to increase the mixing of chemical components and enhance the complete transformation from pyrochlore phase to perovskite phase. With this method, the processing is simplified to only one-step calcination for PMN-PT powder preparation and one-step sintering for PMN-PT dense part preparation. At the same time, the sintering temperature is decreased to 1000°C. To gain fundamental understanding on the colloidal coating process, a modified SAK simulation model was developed. In powder processing, it was shown that smaller particle size and better powder configurations were the reasons for eliminating pyrochlore phase. On the other hand, smaller particle size and reactive sintering are responsible for the lower temperature sintering. Finally, processing optimization study showed that 0-2 at.% PbO excess is the ideal composition for high quality PMN-PT preparation.

Ferroelectric crystals are commonly used in nonlinear optics for frequency conversion of laser radiation. The quasi-phase matching (QPM) approach uses a periodically modulated nonlinearity that can be achieved by periodically inverting domains in ferroelectric crystals and allows versatile and efficient frequency conversion in the whole transparency region of the material.