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Charge manipulation and fabrication of stable domain patterns in ferroelectric materials by scanning probe microscopy open up broad avenues for the development of tunable electronics. Harnessing the polarization energy and electrostatic forces with specific geometry of the system enables producing the nanoscale domains by-design. Along with that, domain engineering requires mastery of underlying physical mechanisms that govern the domain formation. Here, we present a theoretical description of the domain formation by a scanning probe microscopy tip in a ferroelectric film with strong in-plane anisotropy of polarization. We demonstrate that local charge injection produces wedge-shaped domains that propagate along the anisotropy axis, whereas the tip-written lines of charge generate a comb-like domain structure. The results of our calculations agree with earlier experimental observations and allow for the optimization of the targeted domain structures. [ABSTRACT FROM AUTHOR]

Using the multicomponent Landau-Devonshire functional we study the field-induced polarization switching inc-oriented ferroelectric phase of epitaxial perovskite film and found that two different regimes are possible: (i) longitudinal switching with change of the polarization modulus and (ii) transversal switching with virtual admixing of thea-component of polarization. The results are specified for the case of barium titanate oxide BaTiO3where the crossover line between two types of switching is found at strain-temperature phase diagram. [ABSTRACT FROM PUBLISHER]

Using the tight-binding approximation we calculated the diamagnetic susceptibility of graphene quantum dots (GQDs) of different geometrical shapes and characteristic sizes of 2–10 nm, when the magnetic properties are governed by the electron edge states. Two types of edge states can be discerned: the zero-energy states (ZESs), located exactly at the zero-energy Dirac point, and the dispersed edge states (DESs), with the energy close but not exactly equal to zero. DESs are responsible for a temperature-independent diamagnetic response, while ZESs provide a temperature-dependent spin paramagnetism. Hexagonal, circular, and randomly shaped GQDs contain mainly DESs, and, as a result, they are diamagnetic. The edge states of the triangular GQDs are of ZES type. These dots reveal the crossover between spin paramagnetism, dominating for small dots and at low temperatures, and orbital diamagnetism, dominating for large dots and at high temperatures. [ABSTRACT FROM AUTHOR]

Bounded charges induced by the polarization gradient in finite-size ferroelectrics are known to produce the unfavorable depolarization electric field that suppresses the uniform ferroelectric state. To reduce the depolarization energy the non-uniform vortex (toroidal) state is formed inside ferroelectric nano-particles, nano-disks, and nano-rods. Based on self-consistent solution of Ginzburg-Landau equations coupled with electrostatic equations, we study the multivortex toroidal states appearing in the nanometric easy-plane ferroelectric cylinder. The geometrical textures, critical temperatures and stability regions for these states are calculated. [ABSTRACT FROM AUTHOR]

Abstract: We have developed the set of numerical (finite-element) and analytical tools that are based on the self-consistent solution of the electrostatic equations coupled with material Ginzburg–Landau equations with an objective to model the profile of domain textures in the entire temperature region. We calculated the evolution of principal parameters of domain texture: modulation vector, distribution of polarization, renormalization of critical temperature etc. In contrast to the Kittel approximation we conclude that the profile of polarization across domains in nanometric ferroelectric thin films is highly nonuniform. [Copyright &y& Elsevier]

We investigate the ferroelectric phase transition and the domain formation in a periodic multilayer structure consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. The principle result of this study is that the polarization domains formed in the different FE layers interact with each other through the PE layers via an inhomogeneous depolarizing electric field emerging from the domains of the neighboring FE layers. We call this a proximity effect. Based on electrostatic equations coupled with those obtained by the minimization of the Ginzburg-Landau functional for a ferroelectric, we calculated the renormalization of T c as a function of the FE/PE superlattice modulation period. We can describe quantitatively the recent experiments on the thickness dependence of the ferroelectric transition in KNbO 3 -KTaO 3 strained-layer superlattices. [ABSTRACT FROM AUTHOR]

The problem of the effective conductivity and the distributions of a field and currents is analyzed in a regular two-component system composed of regular triangles. An efficient solution method is developed that admits a generalization to multicomponent systems. [ABSTRACT FROM AUTHOR]

A pressing quest for overcoming Boltzmann tyranny in low-power nanoscale electronics ignited an extensive search for the devices possessing the negative circuit constants. The emergent concept of the ferroelectric-based negative capacitance triggered then the explosive activity in the field. However, most of the research addressed transient negative capacitance, leaving the basic question of the existence of the steady-state negative capacitance unresolved. Here, we show that the ferroelectric nanodot capacitor hosts a stable two-domain state realizing the static reversible negative capacitance device thus opening routes for the extensive use of the negative capacitance in domain wall-based nanoelectronics. Negative capacitance describes a phenomenon where the increase in the charge of the capacitor results in decreasing its voltage. The authors put forth a ferroelectric nanodot harboring two polarization domains which stabilize static reversible negative capacitance. [ABSTRACT FROM AUTHOR]

We present the results of 13C nuclear magnetic resonance (NMR) measurements on potassium and rubidium doped Buckminster fullerene C60 at room temperature. By using high-resolution magic angle spinning NMR spectroscopy we were able to identify and characterize the different, thermodynamically stable phases. Based on an analysis of the different NMR spectra, we discuss the effects of the intercalation on the molecular dynamics as well as on the electronic properties in these compounds. [ABSTRACT FROM AUTHOR]

Ferroelectric domain walls, across which there is a divergence in polarization, usually have enhanced electrical conductivity relative to bulk. However, in lead germanate, head-to-head and tail-to-tail walls are electrically insulating. Recent studies have shown that this is because, when oppositely oriented domains meet, polar divergence is obviated by a combination of domain bifurcation and suspected local dipolar rotation. To explore the uniqueness, or otherwise, of this microstructure, we have used tomographic piezoresponse force microscopy to map three-dimensional domain morphologies in another uniaxial ferroelectric system: triglycine sulfate. This mapping reveals an abundance of domain wall saddle points, which are characteristic of interlocking bifurcated domains. Conducting atomic force microscopy, performed close to the saddle points, showed no evidence for highly localized conducting domain wall sections, across which a divergence in polarization might be implied; this supports the notion that localized dipolar rotation occurs to minimize any potential polar discontinuity. Overall, our study, therefore, confirms that mutual domain bifurcation and suspected local dipolar rotation are not unique to lead germanate and instead may be widely present in other uniaxial ferroelectrics. [ABSTRACT FROM AUTHOR]

We present an overview of our recent results on quantum magnetic oscillations in new functional materials. We begin with the Lifshitz and Kosevich approach for quasi-2D layered materials and obtain general formulas for the oscillatory parts of the grand thermodynamic potential and magnetization. Then we consider the oscillations of the Nernst-Ettingshausen coefficient which consists of thermal and magnetization parts. The difference between normal and Dirac carriers is also discussed. To conclude we consider a model for multilayer grapheme which allows to calculate exactly the Berry phase which remains undetermined in the Lifshitz-Kosevich approach. The magnetic oscillations of the density of states and capacitance for different number of the carbon layers are described. [ABSTRACT FROM AUTHOR]

Abstract: In microscale and nanoscale ferroelectric samples, the formation and growth of domains are the usual stages of the polarization switching mechanism. By assuming weak polarization anisotropy and by solving the Ginzburg–Landau–Khalatnikov equation we have explored an alternative mechanism which consists in ferroelectric switching induced by vortex formation. We have studied the polarization dynamics inside a ferroelectric circular capacitor where switching leads to the formation of a metastable vortex state with a rotational motion of the polarization. Our results are consistent with recent first-principle simulations [I.I. Naumov, H.X. Fu, Phys. Rev. Lett. 98, 077603 (2007)] and with experiments on PbZr0.2Ti0.8O3 [A. Gruverman, D. Wu, H.J. Fan, I. Vrejoiu, M. Alexe, R.J. Harrison, J.F. Scott, J. Phys. Condens. Matter 20 342201(2008)] and demonstrate that vortex-induced polarization switching can be an effective mechanism for circular nanocapacitors. [Copyright &y& Elsevier]

Abstract: We study the influence of the surface of the ferroelectric films on the properties of the intrinsic ferroelectric polarization state in frame of statistical Transverse Ising Model (TIM). The quality of the surface is modelled by the dilution parameter that reflects the relative weight of the paraelectric impurities vs. ferroelectric ions. Using the effective field approach the variation of the average value of spontaneous polarization as function of temperature for different film thicknesses has been investigated as function of dilution parameter . The phase diagram of the system and crossover from the ferroelectric to the paraelectric phase is discussed. [Copyright &y& Elsevier]

Chirality, an intrinsic handedness, is one of the most intriguing fundamental phenomena in nature. Materials composed of chiral molecules find broad applications in areas ranging from nonlinear optics and spintronics to biology and pharmaceuticals. However, chirality is usually an invariable inherent property of a given material that cannot be easily changed at will. Here, we demonstrate that ferroelectric nanodots support skyrmions the chirality of which can be controlled and switched. We devise protocols for realizing control and efficient manipulations of the different types of skyrmions. Our findings open the route for controlled chirality with potential applications in ferroelectric-based information technologies. [ABSTRACT FROM AUTHOR]

Over the past decades, there has been significant interest in new cooling technology based on the large electrocaloric effect observed in polymeric and inorganic ferroelectric materials. We report a dramatic impact of annealing on the electrocaloric effect observed by direct measurements in Pb 0.88 La 0.12 (Zr 0.65 Ti 0.35) 0.97 O 3 bulk ceramics (12/65/35 PLZT). In addition, the EC response was measured deep in a relaxor part of the PLZT composition phase diagram. After additional one-hour sample annealing at 600 °C, the EC response increased by about six times. Electrocaloric results confirm the existence of the significant electrocaloric response with the EC temperature change (Δ T EC) of 4.5 K at 360 K and 90 kV/cm in an annealed sample. This value exceeds previously obtained maximum Δ T EC values at the same field in perovskite relaxor ferroelectrics such as Pb(Mg1/3Nb2/3)O 3 -PbTiO 3 (PMN-PT) and 8/65/35 PLZT ceramics. The electrocaloric responsivity Δ T /Δ E = 5.09 × 10−7 Km/V determined at 360 K is among the highest observed in bulk perovskite ferroelectrics at a relatively high electric field of 90 kV/cm. • Relaxor ferroelectrics exhibit mostly an electrocaloric effect (ECE) of about 3 K. • The stress field makes the ferroelectric state more supercritical with smaller ECE. • The annealing enhances the ECE in 12/65/35 PLZT ceramics by about six times. • ECE of 4.5 K exceeds previously obtained values in bulk relaxor ferroelectrics. • The ECE responsivity is the highest observed at a relatively high electric field. [ABSTRACT FROM AUTHOR]

The first-order semiconductor-metal Mott transition in single nano-crystal of VO has been observed using scanning tunneling spectroscopy. The variation of the band gap E with an external thermal stimulus on a single VO nano-crystal in the temperature range of 293.5-361.0 K is reported for the first time. The corresponding tuneable I- V characteristics versus temperature could be applied in thermally or optically tunable electronic nano-gating in the femtosecond regime in view of the ultrafast dynamic in VO. [ABSTRACT FROM AUTHOR]

We have studied the resistive switching (RS) phenomenon in series of BiFeO3thin films of thickness of 40 – 154 nm deposited by PLD technique on conducting Nb-doped substrate of SrTiO3and with Pt top electrodes. It was found that 154 nm film demonstrates the interface-provided I–V characteristic of Schottky diode when the applied voltage does not exceed the threshold value Vd= 1.3 V. The RS phenomenon appears as the current hysteresis loop during the 0 → Vm→ 0 → −Vm→ 0 voltage sweep cycle, provided that the maximal stop-voltage Vmis larger than Vd. For thinner films neither diode-like I–V behavior nor substantial RS effect were observed. The results are interpreted in terms of the filamentary model of the mobile oxygen vacancies. [ABSTRACT FROM PUBLISHER]

New compositions of Tetragonal Tungsten Bronze (TTB) ferroelectrics Pb1-xK2xNb5O15(PKN) with x = 0.1, 0.2, 0.25 and 0.3 were synthesized using the solid state reaction method. Structural and electrical properties were examined as a function of the ratio Pb/K using X-ray diffraction, Raman spectroscopy and dielectric measurements. The dielectric permittivity and the loss tangent of each composition have been measured in a frequency range 10 Hz–1 MH and in a temperatures range 25–600°C. It was shown that the Pb substitution induces the diffuse phase transition. [ABSTRACT FROM PUBLISHER]

Abstract: Ferroelectric ceramics Pb2−x K1+x Li x Nb5O15 (PKLN), with , having the tetragonal tungsten bronze (TTB) structure, were synthesized using a solid-state reaction and characterized by X-ray diffraction. The temperature dependence of dielectric permittivity was measured from 35 to 550 °C in the frequency range from 20 Hz to 1 MHz. These measurements permit us to present the phase diagram of this family and the evolution of the transition temperature as function of the chemical composition. [Copyright &y& Elsevier]

Powders and thin films of ferroelectric Bi3.25La0.75Ti3O12 (BLT) have been prepared from a sol-gel precursor heated at various temperatures, up to 600°C. The BLT precursor and the BLT powders have been characterized by thermal analyses, X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). Then, the precursor has been used to deposit thin films of ferroelectric BLT on specific silicon substrates, using a specific spin coating process. The thin films have been characterized by XRD, SEM and ellipsometry. Electrical polarization analyses have been finally performed on these films, and performing remnant polarization has been obtained. [ABSTRACT FROM AUTHOR]

Films of a catalytic compound (RuO2) were deposited by spin-coating process on ferroelectric films mainly constituted of SrBi2Ta2O9 (SBT) and Ba2NaNb5O15 (BNN) phases. SBT films were deposited by MOCVD method, and BNN films were deposited by sputtering. After thermal treatment under air, these ferroelectric-catalytic systems were characterized by X-ray diffraction and scanning electron microscopy (SEM). SEM images showed that RuO2 film morphology depended on substrate nature. A study of CH4 conversion into CO2 and H2O was carried out using these catalytic-ferroelectric multilayers: the conversion was analyzed from Fourier Transform Infrared (FT-IR) spectroscopy, at various temperatures. Improved catalytic properties were observed for RuO2 films deposited on BNN oxide layer. [ABSTRACT FROM AUTHOR]

Abstract: Catalytic ruthenium dioxide films were deposited by spin-coating process on ferroelectric films mainly constituted of SrBi2Ta2O9 (SBT) and Ba2NaNb5O15 (BNN) phases. After thermal treatment under air, these ferroelectric–catalytic systems were characterized by X-ray diffraction and scanning electron microscopy (SEM). SEM images showed that RuO2 film morphology depended on substrate nature. A study of CH4 conversion into CO2 and H2O was carried out using these catalytic–ferroelectric multilayers: the conversion was analyzed from Fourier transform infrared (FTIR) spectroscopy, at various temperatures. Improved catalytic properties were observed for RuO2 films deposited on BNN oxide layer. [Copyright &y& Elsevier]

A new ferroelectric rare earth family Pb1.6K1.2R0.2Nb5O15 with R=La, Nd, Sm, Eu and Gd (PKRN) of tetragonal tungsten bronze type ferroelectrics was synthesized. The ferroelectric transition with nonuniform distribution of critical temperature over a ceramic sample was found from dielectric measurements. According to X-ray diffraction measurements, the ferroelectric phase has an orthorhombic symmetry. The transition temperature was shown to decrease weakly with increasing radius of the rare earth ion R. [Copyright &y& Elsevier]

At high temperature, the A2BX4crystals exhibit P63/mmc structure. With temperature decreasing, a rich diagram of structural phases and phase transitions are observed, including different incommensurate phases. Ordering of the BX4tetrahedra orientation in the unit cell drives the transitions, and they can be well described by an Ising model with competing interactions. Raman and infrared spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry (TGA) are used to characterize the phase transitions in Cs2HgBr4and Rb2WO4crystals. [ABSTRACT FROM AUTHOR]

The old problem of the anomalous light scattering close to the α-β phase transition in quartz has led recently to diverging explanations. One model involves ferroelasticity of the novel incommensurate phase of Elongated Triangles ( ELT ) whereas another one is based on the temperature and stress induced metastability of blocks in the incommensurate phase of Equilateral Triangles ( EQT ). In the present paper we present new evidences of the ferroelastic ELT texture by means of transmission electron microscopy and give new arguments why the ELT is more advantageous than non equilibrium EQT model in describing the anomalous light scattering. [ABSTRACT FROM AUTHOR]

We present evidence for a thermodynamically stable incommensurate elongated-triangle (ELT) phase in quartz, observed by transmission electron microscopy at the α–β structural transition. The phase sequence on cooling is: incommensurate equilateral-triangle (EQT) phase (ferroelectric)—incommensurate ELT (ferroelectric and ferroelastic)—uniform α phase. The ELT blocks could be responsible for the large light scattering in the vicinity of the α–β transition. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]