Structural studies of the brass ingots from the Shcherbet historical complex of the Lower Kama region: neutron diffraction and tomography studies

The structural characteristics and phase composition of several ancient brass ingots obtained in the archeological Shcherbet complex has been studied using neutron diffraction and tomography methods. The XRF analysis and neutron diffraction provide high zinc content up to 30 wt.%. The neutron tomog- raphy yielded 3D data of the spatial distribution of chemical elements in the brass alloy of the studied ingots, as well as inner voids and cavities as a possible result of the gas output during casting process. The patina, as a cuprite phase, occupy volumes to 8 % of the volumes of the ingots

Synchronization of multi-phase oscillators: An Axelrod-inspired model

Inspired by Axelrod's model of culture dissemination, we introduce and analyze a model for a population of coupled oscillators where different levels of synchronization can be assimilated to different degrees of cultural organization. The state of each oscillator is represented by a set of phases, and the interaction --which occurs between homologous phases-- is weighted by a decreasing function of the distance between individual states. Both ordered arrays and random networks are considered. We find that the transition between synchronization and incoherent behaviour is mediated by a clustering regime with rich organizational structure, where some of the phases of a given oscillator can be synchronized to a certain cluster, while its other phases are synchronized to different clusters.Comment: 6 pages, 5 figure

Non-destructive structural studies of coins from the Uzundara Fortress using X-ray diffraction and neutron tomography

The copper Heliocles coin and two silver Demetrius coins dated to the II century BC from the archaeological works of the Uzundara fortress of the Greco-Bactrian Kingdom were studied using non-destructive structural diagnostics methods. The phase analysis of the coins was performed using the X-ray diffraction method. Also, the spatial distribution of the internal components of the coins was investigated by neutron imaging methods. It has been established that the dominant phase of the Heliocles coin is copper, however, a small volume of patina was found. It is mainly represented by tenorite CuO phase. The neutron tomography method indicates a deep penetration of tenorite into the thickness of the coin, and its volume fraction can reach 10% of the total volume. Two Demetrius coins consist entirely of silver. The complex profile of coins due to the features of a coinage was reconstructed. The phase composition, the content of the composite phases and three-dimensional models of the studied coins were obtained

Studies of Coins of Medieval Volga Bulgaria by Neutron Diffraction and Tomography

© 2020, Pleiades Publishing, Ltd. Abstract: The phase composition and spatial distribution of chemical components in the volume of coins of medieval Volga Bulgaria are studied using the neutron-diffraction- and neutron-tomography methods. Two coins belonging to different time periods of this medieval state are studied: a Samanid multidirham dating from the first half of the 10th Century and a silver dirham dating from the period of the reign of the Bulgarian emir Bulat-Timur. It is established that both coins consist of a copper-silver alloy. In the Samanid multidirham, the average volume contents of copper and silver are found to be about 50%. Minor spatial variations in the chemical composition are found in the volume of the multidirham under study. It is established that the volume average silver content in the Bulat-Timur dirham is about 95%

Spin-induced negative thermal expansion and spin–phonon coupling in van der Waals material CrBr<inf>3</inf>

The two-dimensional van der Waals (vdW) magnets retaining magnetic order in atomically thin limit demonstrate challenging physical phenomena and they are considered as prospective building blocks for construction of advanced spintronics and nanoelectronics devices. Here, we present experimental evidence for negative thermal expansion of lattice volume and vdW layers and strong spin–phonon coupling effects, caused by formation of the long-range ferromagnetic order in the vdW material CrBr3. The neutron and X-ray diffraction measurements revealed anomalous temperature variation of lattice parameters and interatomic distances and angles in the vicinity of Curie temperature (TC). A pronounced rise of the frequencies of the most of the observed vibrational modes and unusual reversal broadening of their full widths at half maximum below TC was found from Raman spectroscopy measurements

Pressure-induced structural phase transitions in bismuth tungstate Bi<inf>2</inf>WO<inf>6</inf>

The pressure-induced structural phase transitions in bismuth tungstate Bi2WO6 have been studied using neutron diffraction and Raman spectroscopy at high pressures up to 7 and 30GPa, respectively. A rich structural polymorphism was revealed. At P ≃ 3.5GPa a phase transition from the initial orthorhombic phase of P21 ab symmetry to an orthorhombic phase of B2cb symmetry was observed. This transition is caused by the complex spatial rotation of the WO6 octahedra. A subsequent isostructural phase transition to another orthorhombic phase of B2cb symmetry was detected at P ≃ 5.9GPa, accompanied by changes in both the mutual rotation and tilting of the oxygen octahedra with respect to the crystal b axis. Two more pressure-induced phase transitions in Bi2WO6 at high pressures of 11.5 and 20GPa were observed in the Raman spectra. These pressure-driven phase transitions in bismuth tungstate are accompanied by anomalies in the pressure dependences of the unit-cell parameters, bond lengths and angles, and in the vibrational modes