Hexagonal High-Entropy Alloys

We report on the discovery of a high-entropy alloy with a hexagonal crystal structure. Equiatomic samples in the alloy system Ho-Dy-Y-Gd-Tb were found to solidify as homogeneous single-phase high-entropy alloys. The results of our electron diffraction investigations and high-resolution scanning transmission electron microscopy are consistent with a Mg-type hexagonal structure. The possibility of hexagonal high-entropy alloys in other alloy systems is discussed.Comment: Changes upon replacement: inserted submission date of manuscript to journal. No other changes were mad

Problems of creating an innovative ecosystem in Ukraine

Побудова інноваційної екосистеми в Україні є одним із першочергових завдань, з метою вирішення якого Кабінетом Міністрів України схвалена Стратегія розвитку сфери інноваційної діяльності на період до 2030 року, а також створюються нові інституції тощо. Проте створення такої інноваційної екосистеми неможливе без розуміння проблеми та без урахування попереднього досвіду. Досліджені поняття “екосистема”, “стійкість екосистеми” та визначений їх зв’язок з проєктами. Проведений аналіз міжнародного досвіду у створенні стійких інноваційних екосистем та ефективних мереж трансферу технологій, під час якого зроблені висновки щодо значущості усвідомлення закладами вищої освіти, що саме вони мають налагоджувати зв’язки з представниками реального сектору економіки та гнучко підлаштовуватись під вимоги ринку, а не проводити дослідження та не створювати розробки наосліп. Це є головною передумовою успішної реалізації трансферу технологій та розбудови інноваційної екосистеми в цілому. Визначені бар’єри на шляху ефективного трансферу технологій. Проведений аналіз стану суб’єктів трансферу технологій - закладів вищої освіти та промислових підприємств, та виявлені негативні тенденції, що потребують втручання. Виявлені проблеми управління трансфером технологій на загальнодержавному рівні, а саме віднесення питання трансферу технологій до відомства різних міністерств та інших органів державної влади, а також паралельне та одночасне створення на базі цих міністерств дублюючих інституцій, одним із завдань яких є супровід трансферу технологій. Запропоновано визначити єдиний орган, що здійснюватиме управління трансфером технологій та запровадить чіткий план дій щодо розбудови інноваційної екосистеми, а також буде відповідальним за його невиконання або незадовільне виконання.Building an innovative ecosystem in Ukraine is one of the priority tasks for the solution of which the Cabinet of Ministers of Ukraine has approved the Strategy of development of the innovative activity field for the period until 2030 as well as started creating new institutions and so on. However, the creation of such the innovative ecosystem is impossible without understanding the problem and previous experience. The terms “ecosystem” and “ecosystem sustainability” are studied and their relation to the projects is defined. An analysis of international experience in creating sustainable innovative ecosystems and efficient technology transfer networks is conducted, drawing conclusions about the importance of higher education institutions being aware that they should establish contacts with representatives of the real sector of the economy and adapt flexibly to the market demands rather than make unclaimed and undemanded researches and developments. This is a key prerequisite for the successful implementation of technology transfer and the development of the innovative ecosystem as a whole. The main impediments to the effective technology transfer are identified. The technology transfer subjects such as higher education institutions and industrial enterprises are analyzed and negative tendencies requiring intervention are defined. Problems of technology transfer management at the national level are identified, namely the relation of technology transfer issues to the departments of different ministries and other state authorities, as well as parallel and simultaneous creation of duplicate institutions based on these ministries, one of the tasks of which is supporting technology transfer. It is suggested to designate a single authority that would manage technology transfer and establish a clear actions plan for the development of the innovation ecosystem, and that also would be responsible for its failure or insufficient implementation

Untersuchung von Grenzflächen mit Hilfe der Elektronenenergieverlustspektroskopie in der höchstauflösenden Rastertransmissionselektronenmikroskopie

The development of the StripeSTEM technique enabled the investigation of microscopic defects and interfaces as well as electron beam sensitive materials by means of electron energy loss spectroscopy (EELS). Existing techniques require enormous efforts regarding microscope stability to ensure control over the measurement location. A possible miss-interpretation due to beam damage is another challenge of existing techniques. The StripeSTEM technique offers advantages regarding both obstacles. Experimental limits of the new method were measured on an indium doped zinc-oxide sample and showed a full width half maximum of the indium EELS signal of 2.5-3.0 angström. It was demonstrated by means of multislice calculations that the localization of the EELS signal is not only limited by the inelastic cross section but also by the dynamic dispersion of the electron probe inside the sample. Besides the calculations showed the dependence of the intensity of the EELS signal on the channeling effect of the different atomic columns. This circumstance requires the necessity of accompanying calculations for the proper analysis of experimental EELS data concerning the elemental concentration on the atomic scale. Besides the significant contribution to the methodical development concrete physical problems related to different materials were addressed. In order to prevent a possible miss-interpretation of the titanium-EELS-fine-structure in an investigation of the interface between lanthanum-aluminate and strontium-titanate experiments concerning the beam damage on strontium-titanate were conducted. The subsequent non-destructive characterization of the titanium-EELS-fine-structure did not show any change in the valence of the titanium atoms which would have been a proof for oxygen vacancies or electronic reconstruction. In fact a substitution of cations was found to avoid the polar catastrophe. The investigation of strained layers of barium-titanate revealed the ability of EELS to detect structural differences of the sample material in the range of 4-6 pm which implies that EELS shows similar performance like high resolution transmission electron microscopy (HRTEM). The advantage of EELS is the ability to examine thicker samples when compared to HRTEM. In the last application the stoichiometrie of a stacking fault in strontium-titanate was analyzed. Again the need for accompanying calculations was proven. The stacking fault in question turned out to be a double layer of strontium without any titanium inside

On the stability of metadislocations with 16 associated phason planes

High-resolution scanning transmission electron microscopy was used to investigate the core structure of a metadislocation in a plastically deformed sample of the complex metallic alloy ε 6-Al–Pd–Mn. The atomic-level characterization of a metadislocation with 16 associated phason planes showed dissociation into metadislocations with 6 and 10 phason planes. A structural model of the dissociated core region was developed. The Burgers vector of the dislocation View the MathML sourceb→16 = −0.07 nm [001] splits up into View the MathML sourceb→6 = −0.183 nm [001] and View the MathML sourceb→10 = 0.113 nm [001] increasing the strain at the metadislocation cores. Although unfavourable with respect to an increasing elastic strain energy the dissociation is realized due to a decrease in fault-plane energy. The latter arises from a size reduction of the ξ-phase area that is required to accommodate the metadislocation in the structure. A careful inspection of several exemplary metadislocations with 16 phason planes using electron microscopy indicates their dissociated structure which casts doubt on the stability of elementary metadislocations with 16 phason planes. The study includes a detailed analysis of the structure of a metadislocation core with 6 associated phason planes

Comprehensive model of metadislocation movement in Al13_{13}Co4_{4}

Metadislocations are highly complex defects mediating plasticity in several complex metallic alloys. Available models characterizing the atomic rearrangements during the movement of these defects are limited to two dimensions and heavy atomic species. Combining high-resolution scanning transmission electron microscopy, density functional theory and simulated annealing we develop a three-dimensional model of a metadislocation glide step of 12.3 Å in the complex metallic alloy Al13Co4 including all atomic species. The rearrangements within the core are shown to involve maximum atomic jump distances of 3.4 Å

Periodic Cation Segregation in Cs0.44_{0.44}[Nb2.54_{2.54}W2.46_{2.46}O14_{14}] Quantified by High-Resolution Scanning Transmission Electron Microscopy

The atomic structure of Cs0.44[Nb2.54W2.46O14] closely resembles the structure of the most active catalyst for the synthesis of acrylic acid, the M1 phase of . Consistently with observations made for the latter compound, the high-angle electron scattering signal recorded by scanning transmission electron microscopy shows a significant intensity variation, which repeats periodically with the projected crystallographic unit cell. The occupation factors for the individual mixed Nb/W atomic columns are extracted from the observed intensity variations. For this purpose, experimental images and simulated images are compared on an identical intensity scale, which enables a quantification of the cation distribution. According to our analysis specific sites possess low tungsten concentrations of 25%, whereas other sites have tungsten concentrations above 70%. These findings allow us to refine the existing structure model of the target compound, which has until now described a uniform distribution of the niobium and tungsten atoms in the unit cell, showing that the similarity between Cs0.44[Nb2.54W2.46O14] and the related catalytic compounds also extends to the level of the cation segregation

Structural anomaly in the high-entropy alloy ZrNbTiTaHf

We present a high-resolution scanning transmission electron microscopy study on the microstructure of a non-equiatomic high-entropy alloy with the composition of Zr12.7 Nb30.8 Ti17.7 Ta30.8 Hf8.0 (at.%). We identify a novel inter-grain phase (IGP) that compositionally and structurally differs from the surrounding body-centred cubic host. In particular, we find that the IGP has a composition of Zr52.8 Nb6.9 Ti4.6 Ta20.6 Hf15.1 (at.%) and that it solidifies in a face-centred cubic crystal lattice structure. The occurrence of the latter is unexpected and remarkable since all possible binary phase diagrams of the involved elements only show body-centred cubic and hexagonal close-packed crystal structures. Therefore, to validate our experimental findings we have conducted parameter-free ab-initio calculations based on density-functional theory and the coherent-potential approximation. The simulations support our experimental findings showing that for the composition of the IGP, the face-centred cubic crystal structure is indeed the most stable one