L'enseignement de la cristallographie en sciences des matériaux

La cristallographie est une discipline scientifique clé à l’interface de nombreuses spécialités enseignées dans l’enseignement supérieur. Dans le cadre des formations « Matériaux » de l’Université Paul Sabatier Toulouse III, l’enseignement de cette discipline vise principalement à donner aux étudiants les moyens d’appréhender les problèmes liés aux aspects structuraux et microstructuraux de la matière. Leur mise en pratique via des méthodes actuelles d’analyse est au centre de ces enseignements et fait l’objet des quelques illustrations de cet article. Crystallography teaching in material sciences Crystallography is a key scientific discipline at the interface of many specialties taught in higher education. In the frame of the training in material sciences at the University Paul Sabatier Toulouse III, the teaching of this discipline is primarily intended to provide students with the means to understand the problems related to structural and microstructural aspects of the material. Their implementation via current methods of analysis is at the heart of this teaching and is the subject of this article through few illustrations

The composite structure of mixed τ-(Ag, Cu)xV2O5 bronzes—Evidence for T dependant guest-species ordering and mobility

The complex structural behavior of τ-[AgCu]∼0.92V4O10 has been elucidated by single crystal X-ray diffraction and thermal analysis. The τ-phase region is apparently composed of several distinct phases and this study identifies at least three: τ1rt, τ2rt and τlt. τ1rt and τ2rt have slightly different compositions and crystal habits. Both phases transform to τlt at low temperature. The room temperature modification τ1rt crystallizes in an incommensurately modulated structure with monoclinic symmetry C2(0β1/2) [equivalent to no 5.4, B2(01/2γ) in the Intnl. Tables for Crystallography, Volume C] and the cell parameters a=11.757(4)Å, b=3.6942(5)Å c=9.463(2)Å β=114.62(2)° and the q-vector (00.921/2), but it is more convenient to transform this to a setting with a non-standard centering X=(1/21/200; 001/21/2; 1/21/21/21/2;) and an axial q vector (00.920). The structure features a vanadate host lattice with Cu and Ag guests forming an incommensurate composite. The structural data indicates perfect Ag/Cu ordering. At low temperature this modification is replaced by a triclinic phase characterized by two independent q-vectors. The τ2rt phase is similar to the low temperature modification τlt but the satellite reflections are generally more diffuse

Autonomy Operating System for UAVs: Pilot-in-a-Box

The Autonomy Operating System (AOS) is an open flight software platform with Artificial Intelligence for smart UAVs. It is built to be extendable with new apps, similar to smartphones, to enable an expanding set of missions and capabilities. AOS has as its foundations NASAs core flight executive and core flight software (cFEcFS). Pilot-in-a-Box (PIB) is an expanding collection of interacting AOS apps that provide the knowledge and intelligence onboard a UAV to safely and autonomously fly in the National Air Space, eventually without a remote human ground crew. Longer-term, the goal of PIB is to provide the capability for pilotless air vehicles such as air taxis that will be key for new transportation concepts such as mobility-on-demand. PIB provides the procedural knowledge, situational awareness, and anticipatory planning (thinking ahead of the plane) that comprises pilot competencies. These competencies together with a natural language interface will enable Pilot-in-a-Box to dialogue directly with Air Traffic Management from takeoff through landing. This paper describes the overall AOS architecture, Artificial Intelligence reasoning engines, Pilot-in-a-box competencies, and selected experimental flight tests to date

R2U2: Monitoring and Diagnosis of Security Threats for Unmanned Aerial Systems

We present R2U2, a novel framework for runtime monitoring of security properties and diagnosing of security threats on-board Unmanned Aerial Systems (UAS). R2U2, implemented in FPGA hardware, is a real-time, REALIZABLE, RESPONSIVE, UNOBTRUSIVE Unit for security threat detection. R2U2 is designed to continuously monitor inputs from the GPS and the ground control station, sensor readings, actuator outputs, and flight software status. By simultaneously monitoring and performing statistical reasoning, attack patterns and post-attack discrepancies in the UAS behavior can be detected. R2U2 uses runtime observer pairs for linear and metric temporal logics for property monitoring and Bayesian networks for diagnosis of security threats. We discuss the design and implementation that now enables R2U2 to handle security threats and present simulation results of several attack scenarios on the NASA DragonEye UAS

Lithium conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 obtained via solution chemistry

NaSICON-type lithium conductor Li1.3Al0.3Ti1.7(PO4)3 (LATP) is synthesized with controlled grain size and composition using solution chemistry. After thermal treatment at 850 C, sub-micronic crystallized powders with high purity are obtained. They are converted into ceramic through Spark Plasma Sintering at 850–1000 C. By varying the processing parameters, pellet with conductivities up to 1.6 * 10−4 S/cm with density of 97% of the theoretical density have been obtained. XRD, FEG-SEM, ac-impedance and Vickers indentation were used to characterize the products. The influence of sintering parameters on pellet composition, microstructure and conductivity is discussed in addition to the analysis of the mechanical behavior of the grains interfaces

Facile Synthesis of a Common Na‐Ion Battery Cathode Material Na3V2(PO4)2F3 by Spark Plasma Sintering

In the pursuit of facile, fast, and efficient methods for the synthesis of various compounds for a variety of applications, spark plasma sintering (SPS) technique is considered to be a powerful and simple tool. Using this technique, a popular cathode material for Na‐ion batteries—Na3V2(PO4)2F3—is synthesized and characterized with X‐ray diffraction and scanning electron microscopy (SEM), and is electrochemically tested in Swagelok‐type cells in a galvanostatic mode. The obtained material is compared with the conventionally synthesized (via a solid‐state route) sample. SEM analysis shows 2 times smaller particles in the case of SPS‐synthesized material compared with the solid‐state‐synthesized material which is to be expected from the fast (40 min in total) SPS synthesis that practically excludes grain/particle growth and promotes much faster diffusion, thereby drastically enhancing the reaction kinetics. Electrochemical performance of the SPS‐obtained material shows an improvement in decreasing the overpotential and reducing the capacity loss at high C‐rates (8C)

Electrochemical performances of vitreous materials in the system Li2O–V2O5–P2O5 as electrode for lithium batteries

International audienceGlass composition 25Li2O–50V2O5–25P2O5 has been investigated as a potential material for electrode. Electrical properties as well as electrochemical performances of this glass composition have been characterized and results show a capacity less than 80mAhg−1 when tested in the [3–4.5V] potential window. To the best of our knowledge, this is the first lithiated amorphous material reported as a potential positive electrode material. Glasses, due to their wide available compositions in a given system and their easy processing, pave the way to new type of electrode material

Dense on Porous Solid LATP Electrolyte System: Preparation and Conductivity Measurement

A dense membrane of lithium aluminum titanium phosphate Li1+xAlxTi2-x(PO4)3, x=0.3 (LATP) is deposited on a porous LATP substrate via wet chemistry. In the polymerized complex process, phosphate precursors with different active groups and steric hindrance are selected to tune precursor’s reactivity. Rheological studies and microstructural observations lead to the selection of an LATP powder slurry charged with lithium, aluminum, titanium, and phosphate ion precursors. The optimized formulation is impregnated into a porous LATP substrate. After thermal treatment, dense LATP membranes on top of a porous LATP substrate are obtained with conductivities as high as 3 x 10-4 S/cm for the dense part, the porous part acting as a mechanical support. An original Van der Pauw impedance setup is validated for the measurement of the ionic conductivity of such dense/ porous systems

Optimization of Na-Ion Battery Systems Based on Polyanionic or Layered Positive Electrodes and Carbon Anodes

The revival of the Na-ion battery concept has prompted intense research activities toward new Na-based insertion compounds and their implementation in full Na-ion cells. Herein, we report the optimization of full Na-ion cells consisting of either a layered oxide Nax(Fe1/2Mn1/2)O2 or a polyanionic Na3V2(PO4)2F3 cathode associated with a hard carbon anode. From charge/discharge curves collected via 2 or 3-electrode measurements, the charge/discharge profiles of full cells are simulated to evaluate the maximum energy density these two systems can deliver. Similar energies of 235 W h kg−1 are found for both systems provided that a fully sodiated Na1(Fe1/2Mn1/2)O2 layered phase is used. Experimental cells confirm these values, and cells based on polyanionic compounds surpass the layered cathodes in terms of energy retention, average voltage and rate capabilities. By using Na sources to compensate for carbon's irreversible capacity, energy densities as high as 265 W h kg−1 can be reached with the Na3+xV2(PO4)2F3 / hard C system. Overall, such studies reveal that the gravimetric energy density advantage of layered over polyanionic compounds for Li-ion batteries vanishes by moving to Na-ion. We hope this information will be of great interest for battery manufacturers willing to enroll in the future commercialization of Na-ion batteries

Decoupling the effect of vacancies and electropositive cations on the anionic redox processes in Na based P2-type layered oxides

The activation of anionic redox couple is recognized as one of the best way to increase the energy density of positive electrode materials in both Li and Na-ion batteries. However, for such hope, to materialize a better understanding of the parameters governing the activation, reversibility and efficiency of the anionic redox in NaMO2 layered compounds is still sorely needed. Herein, we report a new P2–Na0.63[□0.036Mg0.143Mn0.820]O2 compound that combines vacancies and Mg doping as well-known sources for anionic redox activation and benchmark its electrochemical performances against P2–Na0.72[Mg0.31Mn0.69]O2. We found that vacancies and Mg doping trigger independently anionic redox processes that differ in terms of redox voltage and reversibility. The one associated to vacancies occurs at the lowest potential and is irreversible. Moreover, we evidenced by monitoring the structural evolution of the pristine phase during cycling the benefice of anionic processes in ensuring the stabilization of P2-type structure at high voltage over a wide range in Na content. These findings highlight the importance of the anionic redox process origin (e.g. vacancies vs. highly electropositive cations) in governing the material electrochemical properties, while providing a new way to efficiently stabilize, without capacity loss, the P2-type structure through the charge process in non A-rich compounds