The superconducting transition and mixed state of YBa2Cu3O6.95: an undergraduate experiment

We describe a simple AC susceptometer built in-house that can be used to make high-resolution measurements of the magnetic susceptibility of high-temperature superconductors in an undergraduate physics lab. Our system, cooled using liquid nitrogen, can reach a base temperature of 77 K. Our apparatus does not require gas handling systems or PID temperature controllers. Instead, it makes use of a thermal circuit that is designed to allow the sample to cool on a time scale that is suitable for an undergraduate lab. Furthermore, the temperature drift rate at the superconducting transition temperature T c is low enough to allow for precise measurements of the complex magnetic susceptibility through T c, even for single-crystal samples with exceedingly sharp superconducting transitions. Using an electromagnet, we were able to apply static magnetic fields up to 63 mT at the sample site. By measuring the change in susceptibility as a function of the strength of an applied of static magnetic field, we were able to estimate the lower critical field H c1 of a single-crystal sample of optimally-doped YBa2Cu3O6.95 at 77 K. We also investigated the mixed state of a sintered polycrystalline sample of YBa2Cu3O6+y .

Influence of an electric field on flexopolarization induced by acoustic action on a liquid crystal

The work experimentally investigated the influence of an electric field on the direct flexoelectric effect that occurs under the influence of an acoustic field in liquid crystals. Thin layers of nematics 10-100 μm thick were studied. In this case, the liquid crystal sample was exposed to the piston method with an acoustic wave with a frequency of 1 kHz. The dependences of the first and second harmonics for different NLCs on the bias voltage value, shear amplitude, and crystal thickness were obtained. It was revealed that the flexosignal harmonics depend on the direction of the electric field; when a positive potential is applied to the movable plate, they take on smaller values than when negative. It was found that in low fields the magnitude of the flexosignal increases due to an increase in the amplitude of the director deviation, but at a critical value of the field it is suppressed, since the layer is stabilized by a constant electric field.

Photoinduced anisotropic lattice dynamic response and domain formation in thermoelectric SnSe

Identifying and understanding the mechanisms behind strong phonon–phonon scattering in condensed matter systems is critical to maximizing the efficiency of thermoelectric devices. To date, the leading method to address this has been to meticulously survey the full phonon dispersion of the material in order to isolate modes with anomalously large linewidth and temperature-dependence. Here we combine quantitative MeV ultrafast electron diffraction (UED) analysis with Monte Carlo based dynamic diffraction simulation and first-principles calculations to directly unveil the soft, anharmonic lattice distortions of model thermoelectric material SnSe. A small single-crystal sample is photoexcited with ultrafast optical pulses and the soft, anharmonic lattice distortions are isolated using MeV-UED as those associated with long relaxation time and large displacements. We reveal that these modes have interlayer shear strain character, induced mainly by c-axis atomic displacements, resulting in domain formation in the transient state. These findings provide an innovative approach to identify mechanisms for ultralow and anisotropic thermal conductivity and a promising route to optimizing thermoelectric devices.

Dynamic and equilibrium precipitation of struvite from the concentrated cellulosic ethanol stillage

The phosphate rock mineral is the main source of P-fertilizer production. It is estimated to become depleted in next century. Thus, the recovery of phosphorus from waste streams have attracted great interest. The cellulosic ethanol production is seen more and more important in future. During the production of cellulosic ethanol, the phosphorus element is released from lignocellulosic biomasses and end up dissolved as phosphate ions in the stillage stream. In this study, the struvite (MgNH4PO4 · 6 H2O) recovery from the concentrated cellulosic ethanol stillage (ES) was conducted under room conditions with an initial pH at 7–9. The effect of Mg2+, PO43−, NH4+ and Ca2+ during struvite precipitation testes are investigated. The optimized pH value for struvite recovery is estimated at 8.5, by which 85% of PO43− and 46% of Mg2+ are removed from the liquid stream. The mass fraction of struvite in recovered crystal sample reaches 82 wt.%. The economic evaluation of struvite recovery from ES was also investigated. This work proves that the struvite is potentially to be recovered with high purity from the concentrated cellulosic ethanol stillage.

Features of trace element composition of beryl from the Uralian Izumrudnye kopi

It was found as a result of SIMS study of beryl with various color zoning from the Uralian Izumrudnye Kopi that the content of a number of trace elements regularly varies to the margin of the crystal regardless of the color nature of the central and marginal crystal parts. The Na, Mn, Ga, Fe and Rb content increases towards the periphery of both crystals forming a U-shaped zoning. This pattern is less pronounced for Ni and Co. The Ti content, on the contrary, decreases towards the crystal margin forming a bell-shaped zoning. The distribution of a number of elements demonstrates another zoning pattern. For the beryl crystal (sample 24), the color saturation and transparency of which increases from a colorless to green-yellow from the center to the periphery of the crystal, the Sc, Cr and V forms U-shaped zoning with an increasing content to the margin of the crystal and Li exhibits a bell-shaped zoning. In transparent beryl crystal with more intense green color in the center (sample 25), the zoning pattern is dramatically distinct: bell-shaped for Sc, Cr and V and U-shaped for Li. The content of each element for both crystals coincides in the marginal zones, which have color comparable in intensity and transparency, despite the diferent color pattern with a sharply contrast¬ing distribution in the central part. In discriminant diagrams proposed for the identifcation of emeralds from various world regions, the composition of beryl from the Uralian Izumrudnye Kopi correspond to the feld of compositions of the Uralian emeralds or is close to them.

Stability and equation of state of face-centered cubic and hexagonal close packed phases of argon under pressure

The compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.2–13 GPa. Hcp phase forms through stacking faults in fcc-Ar and its amount depends on pressurizing conditions and starting fcc-Ar microstructure. The quasi-hydrostatic equation of state of the fcc phase is well described by a quasi-harmonic Mie–Grüneisen–Debye formalism, with the following 0 K parameters for Rydberg-Vinet equation: $$V_0$$ V 0 = 38.0 Å$$^3$$ 3 /at, $$K_0$$ K 0 = 2.65 GPa, $$K'_0$$ K 0 ′ = 7.423. Under the current experimental conditions, non-hydrostaticity affects measured P–V points mostly at moderate pressure ($$\le$$ ≤ 20 GPa).

Polyimide mesh-based sample holder with irregular crystal mounting holes for fixed-target serial crystallography

The serial crystallography (SX) technique enables the determination of the room-temperature structure of a macromolecule while causing minimal radiation damage, as well as the visualization of the molecular dynamics by time-resolved studies. The fixed-target (FT) scanning approach is one method for SX sample delivery that minimizes sample consumption and minimizes physical damage to crystals during data collection. Settling of the crystals on the sample holder in random orientation is important for complete three dimensional data collection. To increase the random orientation of crystals on the sample holder, we developed a polyimide mesh-based sample holder with irregular crystal mounting holes for FT-SX. The polyimide mesh was fabricated using a picosecond laser. Each hole in the polyimide mesh has irregularly shaped holes because of laser thermal damage, which may cause more crystals to settle at random orientations compared to regular shaped sample holders. A crystal sample was spread onto a polyimide-mesh, and a polyimide film was added to both sides to prevent dehydration. Using this sample holder, FT-SX was performed at synchrotron and determined the room-temperature lysozyme structure at 1.65 Å. The polyimide mesh with irregularly shaped holes will allow for expanded applications in sample delivery for FT-SX experiments.

Modeling of diffusion motion of In nanoparticles in a CdTe crystal during laser-induced doping

In order to solve the problem of the ohmic contact between the crystal surface and the metal electrode in the manufacturing process of the X/γ-ray detector, this paper uses a laser to probe the doping process of In/CdTe crystals in different media. In this experiment, the Traveling Heater Method (THM) is used to obtain CdTe(111) crystals that meet the requirements (ρ >109Ω∙cm). In and Au materials are respectively coated on the surface of the crystal sample by the vacuum thermal evaporation method to obtain the crystal sample meeting the requirements. The high-resistance p-type CdTe crystal of a relatively thick In film is irradiated with nanosecond laser pulses, the In film is used as an n-type doping source and as an electrode after laser irradiation.