The exact molecular reaction pathway and crystallization mechanisms of LiNbO3 nanoparticles under solvothermal conditions are derived through extensive time- and temperature-resolved experiments allowing to track all the transient molecular and solid species. Starting with a simple mixing of Li/Nb ethoxides, water addition is used to promote condensation after ligand exchange with different co-solvents including alcohols and glycols of variable carbon-chain length. A nonclassical nucleation scheme is first demonstrated after the identification of new octanuclear complexes with a {Li4Nb4O10} core whose solvophobic interactions mediate their aggregation, thus, resulting in a colloidal gel at room-temperature. Upon heating, a more or less frustrated aggregation-mediated crystallization process is then evidenced leading to LiNbO3 nanocrystals of adjustable mean size between 20 and 100 nm. Such a fine control can be attributed to the variable Nb-OR (R = alkoxy/glycoxy ligand) binding interactions at the surface of crystalline intermediates. Demonstration of such a nonclassical nucleation process and crystallization mechanism for LiNbO3 not only sheds light on the entire growth process of multifunctional nanomaterials with non-perovskite crystalline structures, but also opens new avenues for the identification of novel bimetallic oxoclusters involved in the formation of several mixed oxides from the aqueous alkoxide route.

In the context of Human-Robot Collaboration (HRC) as System of Systems (SoS), motion planning and learning are a highly important subsystem. Dynamic Movement Primitives (DMP) are an elegant and efficient method for learning complex behaviours and representing them as stable, well understood dynamical systems. When applied for encoding a task by considering the behaviour of the end-effector of a robotic manipulator in Cartesian space, the common solution is to represent and to encode the pose separately as position and orientation using different but phase-coupled DMP formulations; resulting mathematically and algorithmically inefficient. Dual Quaternions are a mathematical tool capable of representing pose in a unified variable. Literature shows the interest of such a representation for rigid body kinematics, given its mathematical flexibility, efficiency and robustness. This article presents an existing formulation for Dual Quaternion Dynamic Movement Primitives based on screw theory. Then, we expand on our proposed improved formulation which considers obstacle avoidance as a contribution for the layer of Awareness and Intelligence in the context of Human-Robot Collaboration as a System of Systems.

Noncentrosymmetric Oxides In article number 2200992, Yannick Mugnier and co-workers critically review the solution-based synthesis methods for the preparation of noncentrosymmetric oxide nanocrystals with perovskite and non-perovskite crystalline structures. Special attention of the research community to the detailed understanding of their formation mechanisms is still needed for improving their resulting morphology and aggregation state in the future.

Dynamic Movement Primitives are an encoding method oriented to model the generalized behavior of a variable or set of variables over time, providing reproducibility and versatility. Originally designed for motor behavior, the method has demonstrated to be a highly promising tool for modeling tasks for robotic manipulators. An interesting use in literature is handwriting encoding. Close-shape graphemes are nearly impossible to model with existing DMP formulations. In this paper, we explore the operational definition of the method’s classic formulation in consideration, as well as a more tenacious form, focusing on cases which might not be possible to model. We then propose a solution to avoid such cases. Our modified formulation yields more consistent and coherent results regardless of the nature of the modelled handwritten graphemes.

With the miniaturization of electronic-based devices, the foreseen potential of new optical nanoprobes and the assessment of eventual size and shape effects, elaboration of multifunctional noncentrosymmetric nanocrystals with ferroelectric, pyroelectric, piezoelectric, and nonlinear optical properties are the subject of an increasing research interest. Here, the recent achievements from the solution-based methods (coprecipitation in homogeneous and nanostructured media, sol-gel processes including various chemistries and hydro/solvothermal techniques) to prepare 0-D perovskite and nonperovskite oxides in the 5-500 nm size range are critically reviewed. To cover a representative list of covalent- and ionic-type materials, BaTiO3 and its derivatives, niobate compounds (i.e., K/Na/LiNbO3 ), multiferroic BiFeO3, and crystals of lower symmetry including KTiOPO4 and some iodate compounds such as Fe(IO3 )3 and La(IO3 )3 are systematically in focus. The resulting size, morphology, and aggregation state are discussed in light of the proposed formation mechanisms. Because of a higher complexity related to their chemical composition and crystalline structures, improving the rational design of these multifunctional oxides in terms of finely-tuned compositions, crystalline hosts and structure-property relationships still need in the future a special attention of the research community to the detailed understanding of the reaction pathways and crystallization mechanisms.

Phase-pure, highly crystalline sub-50 nm LiNbO3 nanocrystals were prepared from a non-aqueous solvothermal process for 72 h at 230 °C and a commercial precursor solution of mixed lithium niobium ethoxide in its parent alcohol. A systematic variation of the reaction medium composition with the addition of different amounts of co-solvent including butanol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol resulted in the formation of nanocrystals of adjustable mean size and shape anisotropy, as demonstrated from XRD measurements and TEM imaging. Colloidal stability of ethanol- and water-based suspensions was evaluated from dynamic light scattering (DLS)/zeta potential studies and correlated with FTIR data. Thanks to the evolution in the nanocrystal size and shape distribution we observed, as well as to the available literature on the alkoxide chemistry, the reaction pathways and growth mechanisms were finally discussed with a special attention on the monomer formation rate, leading to the nucleation step. The polar, non-perovskite crystalline structure of LiNbO3 was also evidenced to play a major role in the nanocrystal shape anisotropy.

Synthesis and characterization of anhydrous LiZn(IO3)3 powders prepared from an aqueous solution are reported. Morphological and compositional analyses were carried out by using scanning electron microscopy and energy-dispersive X-ray measurements. The synthesized powders exhibited a needle-like morphology after annealing at 400 °C. A crystal structure for the synthesized compound was proposed from powder X-ray diffraction and density-functional theory calculations. Rietveld refinements led to a monoclinic structure, which can be described with space group P21, number 4, and unit-cell parameters a = 21.874(9) Å, b = 5.171(2) Å, c = 5.433(2) Å, and β = 120.93(4)°. Density-functional theory calculations supported the same crystal structure. Infrared spectra were also collected, and the vibrations associated with the different modes were discussed. The non-centrosymmetric space group determined for this new polymorph of LiZn(IO3)3, the characteristics of its infrared absorption spectrum, and the observed second-harmonic generation suggest it is a promising infrared non-linear optical material.

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We developed a wavelength-tunable second harmonic scattering experimental setup to investigate dispersion of the nonlinear optical response of three different nanocrystal suspensions (LiNbO3, ZnO and BiFeO3). Special attention was paid to reproducibility issues with the implementation of a detailed protocol that allows correcting for the setup spectral response. The absolute, orientation-averaged second order susceptibilities of the three nanomaterials were then assessed in the 700-1300 nm spectral range evidencing very specific optical signatures. The well-defined resonances observed for ZnO and BiFeO3 near their electronic transitions were found to be poorly described by the Miller's rule. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Synthesis and characterization of anhydrous LiZn(IO3)3 powders prepared from an aqueous solution are reported. Morphological and compositional analyses were carried out by using scanning electron microscopy and energy-dispersive X-ray measurements. The synthesized powders exhibited a needle-like morphology after annealing at 400 ◦C. A crystal structure for the synthesized compound was proposed from powder X-ray diffraction and density-functional theory calculations. Rietveld refinements led to a monoclinic structure, which can be described with space group P21, number 4, and unit-cell parameters a = 21.874(9) Å, b = 5.171(2) Å, c = 5.433(2) Å, and β = 120.93(4)◦. Density-functional theory calculations supported the same crystal structure. Infrared spectra were also collected, and the vibrations associated with the different modes were discussed. The non-centrosymmetric space group determined for this new polymorph of LiZn(IO3)3, the characteristics of its infrared absorption spectrum, and the observed second-harmonic generation suggest it is a promising infrared non-linear optical material.

Preparation of stable BiFeO3 nanocrystal suspensions through a simple, low-cost precipitation technique is described. Amorphous precursors are first precipitated from metal nitrate salts in highly basic KOH solutions, and a short high-temperature annealing step is then performed to induce crystallization. Nanoparticles are characterized by X-ray diffraction (XRD), TEM, DLS and ζ-potential measurements, and the synthesis conditions optimized after a systematic variation of the KOH concentration within the range of 1–12 M. The presence of residual impurities (mainly Bi25FeO39 and Bi2Fe4O9) quantified from XRD and mean nanocrystal size is found to be strongly influenced by the initial KOH solution content. A concentration at about 3–4 M is optimal in terms of BiFeO3 phase-purity and nanocrystal size. Stability of aqueous dispersions of the amorphous precursors and of the purest crystallized nanoparticles is also characterized between pH = 2 and pH = 13. After preparation of stable, almost phase-pure BiFeO3 nanocrystal suspensions, second and third harmonic scattering (SHS and THS) at excitation wavelengths of 1064 nm and 1250 nm are reported from nonlinear optical scattering measurements and compared with other recently published literature values.

Both coherent Third Harmonic Generation (THG) at the interfaces of a cuvette filled with a nanocrystal suspension and incoherent Second and Third Harmonic Scattering (THS) from the suspension volume have been studied to quantitatively assess the orientation-averaged third-order susceptibility of ZnO. These two complementary experimental approaches are based on different calibration routes with a nanocomposite model and fused-silica as a reference material for THG, and pNa molecules for THS. Similar and consistent absolute values of (above 10(-18) m(2)/V-2) are derived and discussed according to the particular orientation averaging procedure that holds for each experimental configuration for a 1064 nm excitation wavelength.

We present two new synthetic routes for bismuth ferrite harmonic nanoparticles (BiFeO 3 HNPs). Both phase-pure and mixed phase BiFeO 3 materials were produced after improvement of the solvent evaporation and sol-gel combustion routes. Metal nitrates with a series of dicarboxylic acids (tartronic, tartaric and mucic) were used to promote crystallization. We found that the longer the carbon backbone with a hydroxyl group attached to each carbon, the lower the annealing temperature. We also demonstrate that nanocrystals more readily formed at a given temperature by adding glycerol but to the detriment of phase purity, whereas addition of NaCl in excess with mucic acid promotes the formation of phase-pure, monocrystalline nanoparticles. This effect was possibly associated with a better dispersion of the primary amorphous precursors and formation of intermediate complexes. The nanoparticles have been characterized by XRD, TEM, ζ-potential, photon correlation spectroscopy, two-photon microscopy and Hyper-Rayleigh Scattering measurements. The improved crystallization leads to BiFeO 3 HNPs without defect-induced luminescence and with a very high averaged second harmonic efficiency (220 pm/V), almost triple the efficiency previously reported. This development of simple, scalable synthesis routes which yield phase-pure and, crucially, monocrystalline BiFeO 3 HNPs demonstrates a significant advance in engineering the properties of nanocrystals for bio-imaging and diagnostics applications.

Second Harmonic Generation (SHG) from BiFeO3 nanocrystals is investigated for the first time to determine their potential as biomarkers for multiphoton imaging. Nanocrystals are produced by an auto-combustion method with 2-amino-2-hydroxymethyl-propane-1,3-diol as a fuel. Stable colloidal suspensions with mean particle diameters in the range 100–120 nm are then obtained after wet-milling and sonication steps. SHG properties are determined using two complementary experimental techniques, Hyper Rayleigh Scattering and nonlinear polarization microscopy. BiFeO3 shows a very high second harmonic efficiency with an averaged 〈d〉 coefficient of 79 ± 12 pm/V. From the nonlinear polarization response of individual nanocrystals, relative values of the independent dij coefficients are also determined and compared with recent theoretical and experimental studies. Additionally, the particles show a moderate magnetic response, which is attributed to γ-Fe2O3 impurities. A combination of high nonlinear optical efficiency and magnetic response within the same particle is of great interest for future bio-imaging and diagnostic applications.