Abstract: Design of 3D computer model has been started with a scheme of uni- and invariant states in both tabular and 3D forms. Firstly, the analysis of the geometric structure of T-x-y diagram is depicted in the form of template (prototype). Then experimental data are introduced, and the prototype is converted into the model of real diagram. It is convenient to use the Reference of 3D computer models of T-x-y diagrams of basic topological types, which contains the computer models of nearly 300 phase diagrams of ternary and quaternary systems and include the commentaries in the case of questionable (or incorrectly depicted in the literature source) geometric elements. Since the combined diagrams include the majority of real systems, then, composing the combinations of the known topology diagrams from the Reference, it is possible to obtain the computer models of necessary configuration. Based on the example of complex combined diagrams it is more easily to understand as with the aid of the scheme of uni- and invariant states to decode the geometric structure, given by liquidus and several isothermal sections and isopleths in the sub-solidus. E.g. the high-temperature part (above 914^oC) of the T-x-y diagram of the subsystem Fe-FeS-Cu₂S-Cu contains 68 surfaces, including the liquid immiscibility surface, and 32 phase regions. The analysis of geometric structure is carried out with the aid of the computer models of phase diagrams with the liquid immiscibility, which are formed by binary systems with monotectics, either with monotectic transformations in the ternary system without the immiscibility in binary systems, with immiscibility of three and even four liquid phases in the ternary system, and also diagrams with the syntectic uni- and invariant transformations have been designed. The coordinates of the prototype invariant points are given taking into account a temperature row, so as to most clearly show the diagram geometric structure.

Keywords: Phase Diagram, Space Computer Model, Quaternary System

Abstract: Cold production goes through refrigerant gases (coolants) describing a classic Carnot cycle. These gases are unfortunately harmful and cause the "greenhouse effect" as soon as they escape from their containers during production or in the various heat exchange devices already manufactured. It is therefore urgent to find alternatives; less energy consuming and environmentally friendly solutions. Ferroelectric materials constitute a solution due to their electrocaloric property in solid phase, described by the presence of permanent dipole moments. The ferroelectric-paraelectric phase transition takes place by a crystal symmetry break and a heat exchange takes place in the material, in a reversible process which can be exploited for cooling applications. To the latent heat at phase transition is added the temperature variation due to the change of entropy, compensated by the creation of phonons entropy in the material in a reversible transformation with a constant internal energy.
In order to have amplification of the electrocaloric effect, several avenues are currently being explored, in particular; studies on composites and multiferroics and heterostructures.
In this presentation we will show the recent results obtained on ceramics manufactured from a powder mixture of nanometric grain size that were ferroelectric oxides well chosen (for example, BCT and BCZT) for optimal dielectric and electro-caloric performances. We will also show the perspectives of this study

Keywords: Cooling, Electrocaloric, Nanomaterial, Multiferroic, Heterostructure

Abstract: For earth-moving machinery which are operated in areas with danger of falling objects on its cabin, an important performance requirements imposed on the machine is the protection of the human operator in case the cabin is hit by a falling object. As a result, the mechanical system formed by the cab's strength structure and its supporting elements must have the ability to dissipate high impact energies, so that the deformed system does not penetrate the deflection limiting volume (DLV). In general, the support on the chassis of the falling-object protective structures is rigid, so almost all impact energy is dissipated in the deformation of the cabin's strength structure. The present article proposes that most of the impact energy be dissipated in the post-critical deformation of some dissipative removable supporting elements interposed between the chassis of the machine and the falling-object protective structure. In addition, the article proposes the numerical evaluation of the post-critical behavior of the analyzed mechanical system, using finite element analysis. The first part of the article briefly presents the main regulations in the field of falling-object protective structures, as well as the methods of approaching the evaluation of the performances imposed on these structures, with their advantages and disadvantages. Following are given the main aspects of the optimal modeling of structures for numerical analysis of their behavior, the particularities of numerical evaluation of post-critical behavior and some constructive solutions of dissipative elements. The final part of the article is dedicated to a case study and the author's conclusions.

Keywords: FOPS, Post-critical Behavior, Dissipative Element, Finite Element Analysis.

Abstract: Platinum-transition metal bimetallic alloys have attracted enormous attention in the field of proton-exchange membrane fuel cells (PEMFC). It was suggested to replace seemingly indispensable platinum cathode catalyst. Along with reducing the cost, addition of transition metal to Pt induces its electronic and/or structural modifications so that it improves a sluggish kinetics of the oxygen reduction reaction (ORR). However, other than activity and cost, durability is another key issue that certainly deserves an attention as it is a prerequisite for of PEMFCs commercialization. The cathode catalyst in fuel cell needs to withstand corrosive conditions under high potentials and low pH which lead to its degradation. The corrosive degradation of fuel cell catalysts during its operation is a complex phenomenon involving an interplay between multiple mechanisms such as dissolution of both platinum and transition metal, Ostwald ripening, coalescence and carbon support corrosion. As a result, the PEMFC undergoes performance deterioration. Despite numerous works, a clear link between specific operating conditions of a fuel cell and above listed phenomena remains superficial. This is mainly because a vast majority of studies were limited by ex situ characterization techniques investigating catalyst only before and after reaction and lack true information about catalyst operando behavior. With the rising of the state-of-the-art in situ techniques, the behavior of fuel cell catalysts directly under reaction conditions is becoming a growing focus of researchers. Herein, I will present our recent results on the lifetime degradation of bimetallic fuel cell catalysts obtained using novel in situ techniques.

Keywords: Fuel Cells, Cathode Catalyst, Bimetallic Alloy, Degradation.

Abstract: The present work is a serious effort in providing a Comprehensive Technical Analysis and Overview of the Recent Theoretical and Experimental Advances in Metamaterials. The Talk deals with the analytical treatment, conceptual explanation and unique characteristics of Artificial Dielectrics in the form of Dual-band Metamaterial Absorbers. A Qualitative Review of the available experimental results for better understanding of the concepts has been given. The technical analysis of the theoretical aspects of Concepts and Characterization of the dielectric materials in the form of Photonic Crystals, their Band Structure, and Devices based on them, with Emphasis on Designing of Fibers, and Novel lasers with Nanostructures, and Plasmonic Photonic Crystals along with the modeling and designing considerations for maximizing the efficiency of some of such devices, has been done very briefly in order to give a comprehensive picture about the various aspects of such materials. Their role as Hydrogel Sensors in Medicine and Biosensors, has also been briefly mentioned. This invited talk is expected to be immensely useful for the Researchers and Designers in this novel evolving field, and also in choosing a direction for their Research work on Artificial Dielectric Materials.

Keywords: Artificial Dielectrics, Dual-band Metamaterial Absorbers, Spatial Light Modulators, and Dielectric Materials based Hydrogel Sensors.

Abstract: Organic solar cells (OSCs) employ semi-transparent active layers deposited through solution processes. Combining these low-cost active layers with transparent electrodes, one can produce smart windows that harvest energy from the sun. To fulfill their role as energy source for sustainable urban designs, OSC-based photovoltaic windows have to overcome major drawbacks such as reducing materials and hazardous solvent wastes generated during active layer fabrication. Additionally, to replace conventional windows, the photovoltaic windows should transmit enough visible light and avoid having a colored-glass aspect which would change the spectrum of the transmitted light.

Here, we demonstrate that employing ternary active layers (three active materials) can simultaneously increase the photovoltaic performances and optical properties of light-harvesting windows. Following this strategy, we fabricated efficient neutral color photovoltaic windows with a color rendering index and an average visible transparency over 95 and 40%, respectively. Furthermore, to increase the sustainability and environment-friendliness of their production, we developed a new thin film fabrication process called push-coating. Using push-coating, uniform thin films that generate similar photovoltaic performances to spin-coated ones can be fabricated with no material waste and 20 times less hazardous solvents than with spin-coating.

Our results thus open the path to extremely low-cost and eco-friendly fabrication of innovative photovoltaic technologies which could strongly impact the global energy roadmap.



Keywords: Organic Solar Cells, Green & Sustainable Fabrication, Emerging Photovoltaic Technology.

[1] Sano et al. ACS Applied Energy Materials 2, 2534-2540 (2019)
[2] Inaba et al. ACS Applied Materials & Interfaces 11, 10785-10793 (2019)
[3] Vohra et al. ACS Applied Materials & Interfaces 9, 25434-25444 (2017)

Abstract: The main features of high-voltage electropulse consolidation (H-VEC) of powder refractory materials and the unique possibilities of the method caused by them are considered. The electro-thermal processes in the H-VEC at the contacts between the powder particles and in the macroscale of the whole consolidated sample are analyzed. The results of calculations of the dynamics of closure (collapse) of interparticle pores in the consolidated material are presented.

The experimental results of high voltage consolidation W-based heavy alloys are discussed and a theoretical analysis of the kinetics of compaction of powder materials is made. The results of investigation of the macro- and microstructure of consolidated materials and the stress - strain testing are presented. Compression testing showed that all tested alloys bear compressive stress at room temperature without failure. The plasticity of the heavy tungsten alloy is one of the objectives of the current research. The high-voltage consolidation contributes to maintaining an initial fine-grained structure, more uniform distribution of iron-nickel binder and almost total absence of porosity. The optimal modes of high voltage consolidation W-based heavy alloys on the results of tests of short cylinders according to the “Brazilian test” scheme were obtained.

The process of high-voltage electropulse consolidation of hafnium carbide powder was experimentally studied. A criterion is established that defines the range of technological parameters for creating dense consolidated materials. The results of an experimental study of the microstructure of the obtained hafnium carbide are presented.

Examples of the use of high-voltage electropulse consolidation of powder materials and the direction of further research are considered.

Abstract: Development of giant-permittivity and high-tunability dielectric materials has attracted great interest because of growing demand for smaller and faster energy-storage and electronic devices. Materials such as CaCu₃Ti₄O₁₂, displaying the giant dielectric permittivity due to extrinsic Maxwell-Wagner interfacial polarization effect, have previously been reported. Ferroelectric materials possessing intrinsic ionic polarization due to a phase transition to the polar state have also been indicated to possess high dielectric permittivity. Here, a class of the giant-permittivity materials based on SrTiO₃ ceramics doped with about 1% of trivalent ions like yttrium, dysprosium and gadolinium as well as their processing concept, which yields the dielectric permittivity up to ~209 000 at 10 kHz, is reported. The giant permittivity is explained by a coupling of the polar clusters relaxation mode with the donor substitution induced electrons at low temperatures and by the Maxwell-Wagner relaxation around room temperature. Besides the fundamental understanding, this discovery opens a new development window for high-frequency and low-temperature electronic and energy-storage applications.

Keywords: Electroceramics, Doping, Sintering Atmosphere, Polar order, Maxwell-Wagner Polarisation

Abstract: Vacuum ultraviolet (VUV) light are important for various applications such as surface treatment, optical cleaning of semi-conductor substrates and sterilization. Constant monitoring of high intensity VUV radiation is required to maintain the high standard of manufactured products in many industrial applications. Currently, VUV detectors based on oxide, nitride and diamond have been developed. However, these detectors require filters to block out deep-UV, leading to the reduction of the sensing area. The band gap of the photodetector material is an important consideration when developing the next generation of VUV detectors as the band gap determines the spectral response of the detector. Here, a filterless VUV detector using mixed crystals of calcium fluoride and strontium fluoride (CaF2 – SrF2, CaxSr1-xF2) will be presented [1]. Generally, fluoride compounds have significantly wider band gaps that allow them to be highly transparent in the deep UV region. Unwanted low energy photons are therefore intrinsically blocked out without having to use filters. We experimentally demonstrate that the band gap of these mixed crystals can be engineered by modulating the composition ratio of CaF2 and SrF2. By increasing the CaF2 content, the band gap increases, and the absorption edge is blue shifted. A range of band gap energies can be obtained between 9.73 eV for pure SrF2 and 10.24 eV for pure CaF2. The ability to manipulate the band gap is maintained even at very low temperatures. VUV photoconductive detectors were fabricated to explore the effect of varying composition ratios on spectral sensitivity. The spectral response of the photodetectors shifts to shorter wavelengths as the band gap increases. This allows the spectral response to be controlled by appropriately choosing the CaF2 – SrF2 ratio. Using CaxSr1-xF2 sensors also eliminate the need for extra filters to cut off unwanted longer wavelengths as the onset of their absorption occur in the VUV region. The controllable spectral response and the filterless feature of CaxSr1-xF2 photodetectors provide an advantage over currently available oxide-, nitride-, and diamond-based ones.

Keywords: photoconductive detector, vacuum ultraviolet, fluoride crystal, band gap control

Reference [1] K. Suzuki, M. Cadatal-Raduban, M. Kase, S. Ono, Opt. Mater, 88, 576-579 (2019)

Abstract: We analyze the systematic trends in BaTiO₃, SrTiO₃, SrZrO₃ and PbZrO₃ bulk as well as very rarely performed (001) surface F-center ab initio calculations [1,2]. The nearest neighbour atomic displacements around the bulk F-center in the ABO₃ perovskites are considerably smaller than the relevant neighbour atomic dispalcements around the (001) surface F-centers. The F-center electrons are more delocalized for the ABO₃ perovskite (001) surface F-center than for the bulk F-center. The calculated formation energy difference between the BaTiO₃, SrTiO₃, SrZrO₃ and PbZrO₃ bulk and (001) surface F-centers triggers the F-center segregation from the bulk towards the (001) surface.

Keywords: Ab initio Calculations; ABO₃ Perovskites; Surfaces; F-centers

1. R.I. Eglitis and S. Piskunov, Comput. Condens. Matter 7, 1-6 (2016)
2. M. Sokolov, R.I. Eglitis, S. Piskunov and Y.F. Zhukovskii, Int. J. Mod. Phys. B 31, 1750251 (2017)
3. R.I. Eglitis and D. Vanderbilt, Phys. Rev. B 76, 155439 (2007)
4. R.I. Eglitis and D. Vanderbilt, Phys. Rev. B 77, 195408 (2008)
5. R.I. Eglitis and D. Vanderbilt, Phys. Rev. B 78, 155420 (2008)
6. R.I. Eglitis, Applied Surface Science 358, 556-562 (2015)
7. R.I. Eglitis and A.I. Popov, J. Saudi Chem. Soc. 22, 459-468 (2018)
8. R.I. Eglitis, J. Kleperis, J. Purans, A.I. Popov and Ran Jia, Journal of Materials Science 55, 203-217 (2020)

Abstract: Welding is a process of joining materials into one piece. Welding is used extensively for pipe welding, aerospace, aviation, biomedical implants, fabrication of race cars, choppers, etc. Welding processes include thermal fusion joining processes and solid-state joining processes. Arc welding process belongs to thermal fusion joining process. Generally, the metallurgy of the welded joint can be categorised into two major regions, the fusion zone (FZ) and the heat-affected zone (HAZ). The heat-affected zone (HAZ) is a region that is thermally affected by the welding treatment. The heat-affected zone (HAZ)is a transition zone, because it is composed with the microstructure of the BM and the HAZ. The changes of microstructures in the HAZ depend on the level of thermal exposure and are varying with distance from the weld metal zone. The main difficulty associated with welding is the prevention of unexpected deterioration of properties as a result of the microstructure evolutions which reduce the resistance to brittle fracture in the heat-affected zone (HAZ) [7]. Properties of the HAZ are different from those of the base material. According to the literature, the HAZ is the most problematic area in the high strength steels weld. For this reason, many research works investigated this critical zone in welded joint. The main research questions and results related to the HAZ will be presented.

Abstract: Banana is the most consumed fruit in Brazil, mainly due to their all-year harvesting, ease of handling, and rapidity of ripening. The large volume of consumption generates a large amount of waste, as barks and stalks, which, in turn, have great potential for scientific technical exploitation. These stalks and banana peels are rich in polysaccharides with potential applications as raw material for the production of nanocellulose fibers (NCF). Carbon nanotubes (CNTs) are very promising materials for many distinct applications. Nonetheless, most of the known applications of CNTs require a well dispersed solution of nanotubes, hence the best way to disperse these nanotubes is the use of highly concentrated acid functionalization. In this work, we produced NCF from banana peel stalks to use as a replacement for surfactants and acid functionalization in the dispersion of CNTs. The usage of NCF as a surfactant can be useful when seeking waterbased, efficient, and green pathways for their preparation, making the process less hazardous to the environment and keeping the structure of CNTs intact. Among possible applications, well dispersed CNT/NCF solution can be used to obtain conductive papers and additive 3D manufacture. Alkaline treatment followed by bleaching were carried out at the banana peel pulp to obtain the cellulose. Later, the pulp was exposed to acid hydrolysis in order to obtain the NCF. The nanofibers were confirmed by characterization methods as x-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy. Aqueous suspension of CNT/NCF were analysed for up to 10 days and remained dispersed, indicating that the NCF may be a good dispersing agent for CNTs.

Abstract: A study of drilling-induced damage in barely visible impact damaged (BVID) carbon fibre reinforced polymer (CFRP) laminates where small circular holes were intentionally drilled into the impacted zone as an intermediate step of the resin-injection repair process was reported. The pristine CFRP laminates were quasi-statically indented to yield damage that were barely visible. Following the drilling of open/blind, single and binary holes in the impacted laminates at selective locations within the BVID zone, the holed laminates were subjected to in-plane compression test until they broke apart. Binary-hole specimens at fixed distance apart were tested in parallel/normal to the external load. Statistical analysis was used to assess for diminution of laminate mechanical properties contributed by hole-hole interaction and hole-hole orientation effects. BVID specimens showed significant diminution of property value (compared to pristine ones). No dependence of mechanical properties on hole-hole orientation was observed. Owing to the large hole-hole separation, this significantly mitigated the hole-hole interactions. Finally single/binary-hole BVID laminates revealed laminate stiffening effects: the stiffness was significantly higher than that of undrilled BVID specimens.

Abstract: The wave propagation in elastic solids is widely treated as plane waves with Cartesian coordinates for known modes such as Rayleigh and Love waves in broad engineering applications. Such distinct wave phenomena also exist in other coordinate systems but the essential property such as the velocity should be the same as known ones while many other special features related to coordinate systems are not presented in details in earlier literature. In a series of recent research, it confirmed that typical wave modes can be found in cylindrical coordinate system with axisymmetric feature and wave velocities are independent from coordinate systems of elastic solids. In general, the deformation solution is given in Bessel functions with a decaying feature along the radius that is different from the constant amplitude in Cartesian coordinates. Such feature is consistent with the energy decaying along the wavefront away from the origin. Consequently, there is a distinct feature of enhancement or reduction of signal strength and amplitudes related to the direction of wave propagation. Clearly, this feature can be exploited further through the consideration of wave modes and direction of propagation in relation with the source in measurement and detection by sensors utilizing the axisymmetric waves. Furthermore, it also showed through the properties of Bessel functions that wave modes are consistent with Cartesian coordinates from the asymptotic expansions, confirming the plane wave characteristics we are familiar with. However, in the vicinity of origin, wave properties can be better represented with cylindrical coordinates and solutions. These results, similar with major wave modes in cylindrical coordinates including Rayleigh, Love, Sezawa, and others, are analyzed in details for better understanding of their special properties to aid future applications involving elastic solids with axisymmetric configurations and required interests near the origin of typical wave propagation problems in engineering applications. These analyses are essential in future study of axisymmetric waves in finite elastic solids with practical engineering applications.

Abstract: Investigations of flexoelectric effect is a hot topic. Since the flexoeffect is defined by gradients of polarization and elastic strains, which obligatory exist in nanos, where all the properties change strongly from the surface to the bulk, we introduced the spontaneous flexoeffect [1], and establish its key role for explanation of mysterious experimental results. The strong influence of spontaneous flexoeffect explains unexpected phenomenon in nanos – the critical size disappearance at size-induced phase transition and reentrant ferroelectric phase appearance. This phenomenon was observed in BaTiO₃ nanospheres of radii 5–50 nm and was a puzzle up to our paper [2], where we explained it by the spontaneous flexoeffect and Vegard strains, created by oxygen vacancies. The developed mechanism opens the ways for miniaturization of electronic devices up to a few nm sizes. More than 15 years ago the appearance of ferroelectricity was observed in bulk PZN-PLZT relaxor sintered in nitrogen atmosphere, which induce high concentration of oxygen vacancies. This phenomenon stayed unexplained, until we have shown [3] that the transition from relaxor to ferroelectric state is possible at high concentration of the vacancies, which are elastic dipoles, due to electrostriction, flexoelectric and Vegard effects. The flexoelectric origin of morphotropic region with high electromechanical properties in relaxors is very important for high-sensitive ultrasound devices. Recently we study the polar phenomenon in low-dimensional transition metals dichalcogenides, and have shown that spontaneous out-of-plane polarization arises from the flexoeffect due to spontaneous bending and inversion symmetry breaking in the vicinity of surface/substrate. [4].

Keywords: Spontaneous Flexoelectric Effect, Nanomaterials, Vacancies, Ferroelectricity.

1. E.A.Eliseev et al, Phys. Rev. B 79, 165433(10) (2009).
2. A. N. Morozovska, M. D. Glinchuk, J. Appl. Phys. 119, 094109(8) (2016).
3. M. D. Glinchuk et al, Phys.Rev. B 98, 094102 (2018).
4. A. N. Morozovska et al., Phys. Rev. B 102, 075417 (2020).

Abstract: The international trend nowadays is to use natural insulating materials in buildings to be safe for human beings and to lower the environmental impact. Fibers extracted from the pods of the Apple of Sodom (AOS) plant are confirmed to have lower thermal conductivity compared to those extracted from synthetic fibers and close to the ASME standard. The fibers extracted from its seed pods can be used as a thermal insulating and absorbing sound materials in building. Palm tree surface fibers (PTSF), Agave fibers, wheat straw fibers, and palm tree leaves are all considered as agro wasted materials. These agro-wasted materials are tested for their promising side to be thermal insulating and sound absorbing materials. Hybrid samples are made of these agro materials on the lab scale. Thermal analysis, acoustic characteristics and the microstructure of these wasted materials are made. Sample specimens are made using different binders such as cornstarch, wood adhesive and others to determine their thermal conductivity and their applicability to be used as insulating material for buildings. Thermogravimetric analysis (TGA and DTGA) are obtained showing the stability of all agro fibers. The differential scanning calorimetry (DSC) analysis is also reported for all fibers and shows a broad endothermic transition indicating the melting point of the fibers. Sound absorption coefficients are obtained for the hybrid samples and indicate the potential of using these samples for sound absorption. Results also show that the average thermal conductivity at temperature range 10^oC to 60^oC of the developed specimens has average values of 0.0418 - 0.0568 W/m K.