The ferroelectric transition in YMnO3_3 from first principles

We have studied the structural phase transition of multiferroic YMnO$_3$ from first principles. Using group-theoretical analysis and first-principles density functional calculations of the total energy and phonons, we perform a systematic study of the energy surface around the prototypic phase. We find a single instability at the zone-boundary which couples strongly to the polarization. This coupling is the mechanism that allows multiferroicity in this class of materials. Our results imply that YMnO$_3$ is an improper ferroelectric. We suggest further experiments to clarify this point.Comment: published version, PRB (rapid comm), slight change in presentatio

Direct observation of the proliferation of ferroelectric loop domains and vortex-antivortex pairs

We discovered "stripe" patterns of trimerization-ferroelectric domains in hexagonal REMnO3 (RE=Ho, ---, Lu) crystals (grown below ferroelectric transition temperatures (Tc), reaching up to 1435 oC), in contrast with the vortex patterns in YMnO3. These stripe patterns roughen with the appearance of numerous loop domains through thermal annealing just below Tc, but the stripe domain patterns turn to vortex-antivortex domain patterns through a freezing process when crystals cross Tc even though the phase transition appears not to be Kosterlitz-Thouless-type. The experimental systematics are compared with the results of our six-state clock model simulation and also the Kibble-Zurek Mechanism for trapped topological defects

Measurements and ab initio Molecular Dynamics Simulations of the High Temperature Ferroelectric Transition in Hexagonal RMnO3

Measurements of the structure of hexagonal RMnO3 (R=rare earths (Ho) and Y) for temperatures significantly above the ferroelectric transition temperature (TFE) were conducted to determine the nature of the transition. The local and long range structural measurements were complemented by ab initio molecular dynamics simulations. With respect to the Mn sites in YMnO3 and HoMnO3, we find no large atomic (bond distances or thermal factors), electronic structure changes or rehybridization on crossing TFE from local structural methods. The local symmetry about the Mn sites is preserved. With respect to the local structure about the Ho sites, a reduction of the average Ho-O bond with increased temperature is found. Ab initio molecular dynamics calculations on HoMnO3 reveal the detailed motions of all ions. Above ~900 K there are large displacements of the Ho, O3 and O4 ions along the z-axis which reduce the buckling of the MnO3/O4 planes. The changes result in O3/O4 ions moving to towards central points between pairs of Ho ions on the z-axis. These structural changes make the coordination of Ho sites more symmetric thus extinguishing the electric polarization. At significantly higher temperatures, rotation of the MnO5 polyhedra occurs without a significant change in electric polarization. The born effective charge tensor is found to be highly anisotropic at the O sites but does not change appreciably at high temperatures

Azerbaijan’s Contribution to the Chinese Belt & Road Initiative

The Belt and Road Initiative (BRI) was initiated by the Chinese government in 2013 to promote regional trade and increase Chinese political and economic presence in the region. The main instrument for realising the ambition of this initiative is the Chinese provision of financial support to the countries located on the Ancient Silk Road to implement infrastructure projects. It includes the construction of roads, railroads, seaports, logistic centres, and communication facilities. Azerbaijan is a BRI partner country in the South Caucasus strategically located between Asia and Europe. It can play the role of a strategic partner and hub connecting China with the Middle East and Europe. The paper finds out that China accepts Azerbaijan as a reliable partner. Azerbaijan perceives BRI as a promising initiative. The Azerbaijani government has a political will and the capacity to contribute to the BRI. By offering some key recommendations, the paper concludes that China and Azerbaijan should closely work to strengthen the BRI's influence in Central Asia and South Caucasus and priorities the Trans-Caspian International Transport Route (TITR) passing through Azerbaijan

Experimental evidence for an intermediate phase in the multiferroic YMnO3

We have studied YMnO$_{3}$ by high-temperature synchrotron X-ray powder diffraction, and have carried out differential thermal analysis and dilatometry on a single crystal sample. These experiments show two phase transitions at about 1100K and 1350K, respectively. This demonstrates the existence of an intermediate phase between the room temperature ferroelectric and the high temperature centrosymmetric phase. This study identifies for the first time the different high-temperature phase transitions in YMnO$_{3}$.Comment: 10 pages 5 figures. New version, Additional data, Journal of Physics: Condensed Matter, in Pres

Migration and Ethnopolitical Heritage of Sabirs in Southeastern Europe

The purpose of the research paper is to systematise and analyse the migration and ethnopolitical heritage of Sabirs in Southeastern Europe. The main focus is on their role in military conflicts, interaction with Byzantium and the Sasanian Empire, as well as their influence on the formation of early medieval political entities such as the Bulgarian and Onogur Confederations. The research aims to identify the cultural and linguistic heritage of the Sabirs, which is preserved in place names and linguistic data, as well as to study their unique social structure, including the role of women in Sabir society. The scientific novelty. The novelty of the research lies in a comprehensive approach to the study of Sabirs, combining the analysis of ancient, Byzantine and Arabic sources with modern research. Special attention is paid to previously insufficiently studied aspects, such as the influence of the Sabirs on Hungarian culture and their participation in the formation of early medieval political formations. For the first time, the role of women in Sabir society is considered in detail, in particular, the ruler of Boaryk, who led the army and entered into an alliance with Byzantium. The study also contributes to the understanding of Sabir military innovations, such as the development of siege engines, which influenced the military art of Byzantium and the Sasanian Empire. Conclusions. The study showed that the Sabirs played a significant role in shaping the ethnopolitical map of Southeastern Europe and the Caucasus. Their migrations, caused by external threats and internal changes, have led to their settlement in vast territories and participation in key military conflicts. The Sabirs not only acted as mercenaries, but also influenced the cultural and political development of the region. Their cultural heritage can be traced through geographical names and linguistic data, and their unique social structure, including the role of women, highlights their contribution to the development of steppe traditions. Thus, the Sabirs represent an important link in the chain of migrations and cultural interactions that determined the development of Eurasia in the early Middle Ages

Microstructural and high-temperature impedance spectroscopy study of Ba6MNb9O30 (M=Ga, Sc, In) relaxor dielectric ceramics with tetragonal tungsten bronze structure

The authors would like to thank to the following funding organisations: the Royal Society for providing a research fellowship (F.D.M.), EPSRC for providing the PhD student grant (A.R.) and Roberto Rocca Education Program for providing an additional fellowship (A.R.).This work reports on the microstructural and high-temperature impedance spectroscopy study of a family of dielectric ceramics Ba6MNb9O30 (M=Ga, Sc, In) of tetragonal tungsten bronze (TTB) structure with relaxor properties. For Ba6GaNb9O30 and Ba6InNb9O30 pellets, the SEM images have revealed good, dense internal microstructures, with well-bonded grains and only discrete porosity; in contrast Ba6ScNb9O30 pellets had a poorer microstructure, with many small and poorly-bonded grains gathered in agglomerates, resulting in significant continuous porosity and poorly defined grain boundary regions. The electroactive regions were characterised by the bulk and grain boundaries capacitances and resistances, while their contribution to the electrical conduction process was estimated by determining activation energies from the temperature (Arrhenius) dependence of both electric conductivities and time constants. For Ga and In analogues the electronic conductivity are dominated by the bulk response, while for Sc analogue, the poorly defined grain boundaries give a bulk-like response, mixing with the main bulk contribution.PostprintPeer reviewe

The Economic Importance of the South Caucasus Zangazur Corridor

Azerbaijan, Russia, and Armenia signed a trilateral declaration to end the Nagorno-Karabakh conflict in November 2020. The declaration put an end to the conflict in Karabakh and laid the groundwork for future cooperation, stability, and security in the South Caucasus and the Caspian region. The South Caucasus is at a crossroads of transportation routes connecting Russia and India, as well as Europe and China. The region also acts as an energy corridor, carrying energy supplies from the Caspian region to the western energy market. For Azerbaijan, one of the most significant achievements of the November trilateral declaration was the inclusion of the article on the opening of all regional transport routes, including the Zangazur corridor, which connects Azerbaijan with Turkey via Armenia and is currently under discussion. The opening of the Zangazur corridor means the opening of trade routes linking Central Asia, the Caspian, Azerbaijan, and Armenia from the Pacific to Turkey. It is also an opportunity to expand the railway network between Russia, Azerbaijan, Turkey and Armenia in order to increase regional trade volume. This policy brief discusses the economic importance of the South Caucasus' Zangazur Corridor in terms of reaching lasting peace, connectivity and integration in the South Caucasus and acceleration of local development. It also argues that the Zangazur Corridor will be instrumental to future South Caucasus reconciliation and economic cooperation

The δ-phase of SrTeO3 at 780 K1

As part of a structural investigation of strontium tellurate(IV) (STO), SrTeO3, with particular emphasis on the crystal chemistry and phase transitions, the structure of the δ-phase has been determined at 780 K using a single-crystal analysis. Both structural and non-linear optical measurements indicate that STO undergoes a γ→δ second-order ferroelectric phase transition at 633 K from the C2 (γ) to the C2/m (δ) modification. Systematic differences between the similar γ- and δ-phase structures were determined and it was found that this phase transformation can be described by a displacive mechanism

Research of instruments and mechanisms of financing and managing competitiveness of international airports in the world market

В статті проаналізовані особливості управління конкурентоспроможністю міжнародних аеропортів на світовому ринку авіаційних перевезень шляхом реалізації інструментів і механізмів державної підтримки авіабізнесу. Фінансування розвитку аеропортів відбувається шляхом залучення урядових джерел та приватних інвесторів з метою підвищення конкурентоспроможності міжнародних аеропортів.The article analyzes the peculiarities of managing the competitiveness of international airports in the world aviation transport market through the implementation of instruments and mechanisms of state support for aviation business. The financing of airport development is through government sources and private investors in order to increase the competitiveness of international airports