Pure Polycrystalline Samples Research Articles

Thermoelectric and photovoltaic properties of 12-BaBi2S4

In this report, we have investigated the structure and properties of the 12-BaBi2S4. A single crystal X-ray diffraction study shows that the 12-BaBi2S4 crystallizes in the hexagonal crystal system (space group = P63/m) with refined lattice parameters of a = b = 25.2687(10) Å, c = 4.1859(2) Å, and formula unit = Z = 12 at room temperature. The structure contains fifteen crystallographic independent sites, including three Ba, four Bi, and eight types of S atoms. A phase pure polycrystalline sample of 12-BaBi2S4 was synthesized by heating stoichiometric amounts of BaCO3 and Bi2O3 under a CS2 atmosphere. The phase pure sample is found to be a semiconductor with a direct bandgap of 1.3(1) eV. The polycrystalline 12-BaBi2S4 exhibits ultra-low thermal conductivity values, varying from 0.47 Wm−1K−1 at 323 K to 0.43 Wm−1K−1 at 773 K. The sample shows high values of the Seebeck coefficient (S = −300 μV/K to −210 μV/K) in the 323 K–773 K range with poor electrical conductivity values. The negative sign of the S implies that the sample is a n-type semiconductor. DFT studies of the 12-BaBi2S4 also predict semiconducting properties. We have explored the 12-BaBi2S4 sample for photovoltaic (PV) applications by fabricating a liquid junction solar cell, TiO2/CdS/12-BaBi2S4/Sn2−/S2−/MWCNTs@Ni, which delivered an efficiency enhanced by ∼12 % to the control cell based on sole CdS as the photo-sensitizer. Theoretical electronic structure calculations suggest the semiconducting nature of the 12-BaBi2S4 in agreement with the optical absorption and electrical resistivity studies.

Synthesis, Crystal and Electronic Structures, Nonlinear Optical Properties, and Magnetic Properties of Two Thiophosphates: KInP2S7 and KCrP2S7

Two thiophosphates, KInP2S7 and KCrP2S7, were structurally characterized without investigating any optical properties. Herein in this work, KInP2S7 and KCrP2S7 were revisited to investigate their optical and magnetic properties, respectively. Pure polycrystalline samples and crystals of KInP2S7 and KCrP2S7 were grown by high temperature solid state reactions, where mm-sized crystals of KCrP2S7 were collected. KCrP2S7 is isostructural to KInP2S7, which features a layered structure. KInP2S7 and KCrP2S7 possess close relationship to the layered thiophosphate M2P2S6 (M = Fe, Co, Zn, etc.). The bonding pictures of KInP2S7 were studied using the electron localization function (ELF) coupled with crystal orbital Hamilton population (COHP) calculations. The intrinsically distorted [PS4] tetrahedra and [InS6] octahedra are made by strong covalent P-S interactions and ionic In-S interactions, respectively. Electronic structure analysis confirmed that the optical properties of KInP2S7 are mainly contributed to by [PS4] tetrahedra together with small amounts of the contributions coming from [InS6] octahedra. Magnetic measurement on mm-sized crystals of KCrP2S7 verified that there is an antiferromagnetic transition around 21 K, and the Cr atoms are trivalent. KInP2S7 is predicated to be an indirect bandgap semiconductor of 2.38 eV, which is confirmed by the UV-Vis measurement of 2.4(1) eV. KInP2S7 is not a type-I phase-matching material and exhibits moderate second harmonic generation (SHG) response (0.51 × AgGaS2, sample of particle size of 100 µm). The laser damage threshold (LDT) of KInP2S7 is very high of 5.2 × AgGaS2. Bandgap engineering were undergone to enhance the SHG response of KInP2S7.

Computational Investigation of Known and Predicted Li Boracites Li4B7O12Cl and Li4B7S12Cl as Solid Electrolytes Having Possible Applications for Developing All Solid-state Li Ion Batteries

The lithium chloroboracite Li4B7O12Cl with fractionally occupied Li sites located in diffusion channels formed by a rigid B7O12 framework possesses essential features of an ideal Li-ion conductor. Early experimental work in 1977 [1] identified three structural modifications related to a face-centered cubic pattern. The room-temperature α form was suggested to have a rhombohedral distortion, but was not fully characterized. Our first-principles calculations find the optimized structure of the α phase to have a face centered rhombohedral structure with space group R3c (No. 161) and structurally very similar to the higher temperature cubic structures of the ꞵ and ɣ forms apart from the fractional occupancy patterns of the Li configurations. Using the convex hull approach, we estimate α-Li4B7O12Cl to be thermodynamically stable within the composition space of Li2O, B2O3, and LiCl. Our analysis of Li ion mechanisms indicates that a concerted process, involving two host Li sites and a neighboring unoccupied site based on the face-centered cubic structure, provides the most efficient ion transport in Li4B7O12Cl. The room-temperature ionic conductivity calculated from molecular dynamic (MD) simulations is on the order of 10-4 S/cm, showing good agreement with the recent experimental measurement for pure polycrystalline samples of Li4B7O12Cl [2]. The temperature-dependent occupancies of Li sites, as the main structural distinction of the three reported modifications of Li4B7O12Cl, are also observed in the MD simulations performed at various temperatures. We also predict that the Li ion conductivity can be enhanced by substituting S for O to form Li4B7S12Cl, which has the same R3c ground state structure with an expanded lattice. Our preliminary studies show that Li4B7S12Cl has better Li conducting performance than Li4B7O12Cl and therefore also shows promise as a solid-state electrolyte for all-solid-state Li-ion batteries.------------------------------------------[1] W. Jeitschko, T. A. Bither, and P. E. Bierstedt. Crystal structure and ionic conductivity of Li boracites. Acta Crystallographica Section B, 33(9): 2767-2775, 1977.[2] D. Tan, F. Wang, T. Pietsch, M. A. Grasser, T. Doert, and M. Ruck. Low-Temperature Ionothermal Synthesis of Li-Ion Conductive Li4B7O12Cl Solid-State Electrolyte. ACS Applied Energy Materials, 2(7): 5140-5145, 2019.------------------------------------------Acknowledgements -- This work was supported by NSF grant DMR-1940324. Computations were performed on the Wake Forest University DEAC cluster, a centrally managed resource with support provided in part by the university.

Spin and Orbital Effects on Asymmetric Exchange Interaction in Polar Magnets: M(IO3)2 (M = Cu and Mn).

Magnetic polar materials feature an astonishing range of physical properties, such as magnetoelectric coupling, chiral spin textures, and related new spin topology physics. This is primarily attributable to their lack of space inversion symmetry in conjunction with unpaired electrons, potentially facilitating an asymmetric Dzyaloshinskii-Moriya (DM) exchange interaction supported by spin-orbital and electron-lattice coupling. However, engineering the appropriate ensemble of coupled degrees of freedom necessary for enhanced DM exchange has remained elusive for polar magnets. Here, we study how spin and orbital components influence the capability of promoting the magnetic interaction by studying two magnetic polar materials, α-Cu(IO3)2 (2D) and Mn(IO3)2 (6S), and connecting their electronic and magnetic properties with their structures. The chemically controlled low-temperature synthesis of these complexes resulted in pure polycrystalline samples, providing a viable pathway to prepare bulk forms of transition-metal iodates. Rietveld refinements of the powder synchrotron X-ray diffraction data reveal that these materials exhibit different crystal structures but crystallize in the same polar and chiral P21 space group, giving rise to an electric polarization along the b-axis direction. The presence and absence of an evident phase transition to a possible topologically distinct state observed in α-Cu(IO3)2 and Mn(IO3)2, respectively, imply the important role of spin-orbit coupling. Neutron diffraction experiments reveal helpful insights into the magnetic ground state of these materials. While the long-wavelength incommensurability of α-Cu(IO3)2 is in harmony with sizable asymmetric DM interaction and low dimensionality of the electronic structure, the commensurate stripe AFM ground state of Mn(IO3)2 is attributed to negligible DM exchange and isotropic orbital overlapping. The work demonstrates connections between combined spin and orbital effects, magnetic coupling dimensionality, and DM exchange, providing a worthwhile approach for tuning asymmetric interaction, which promotes evolution of topologically distinct spin phases.

Magnetic Properties of theRE2Pt6X15(RE= Y, La–Nd, Sm, Gd–Lu;X= Al, Ga) Series

The members of theRE2Pt6Al15(RE= Ce–Nd, Sm, Gd–Yb) andRE2Pt6Ga15(RE= Y, La–Nd, Sm, Gd–Lu) series have been synthesized from the elements via arc‐melting followed by annealing in an induction furnace. Isotypism of Ho2Pt6Al15with orthorhombic (3+1)D commensurately modulated Sc2Pt6Al15[Cmcm(α,0,0)0s0,α= 2/3] was observed from single‐crystal diffraction data. The diffraction pattern shows the same satellite reflections pattern as the prototype, therefore the same modulated superstructure was refined. Full ordering of the Pt and Al atoms within the [Pt6Al15]δ–polyanion was observed. The lattice parameters of the averaged hexagonal structure were refined from powder X‐ray diffraction experiments and agree well with previous reports on these compounds. The X‐ray pure polycrystalline samples of both series were studied with respect to their magnetic properties. The susceptibility data of all investigated compounds show experimental magnetic moments close to the free ion values of theRE3+cations and antiferro‐/ferrimagnetic ordering at low temperatures with Curie temperatures up toTC= 16.8(1) K for Gd2Pt6Ga15. Both, Sm2Pt6Al15and Sm2Pt6Ga15show the typicalvan Vlecktype behavior along with antiferromagnetic ordering at a Néel temperature ofTN= 4.5(1) K (Al) and ferrimagnetic ordering atTC= 6.5(1) K (Ga). Yb2Pt6Al15exhibits ytterbium in the trivalent oxidation state, while for Yb2Pt6Ga15a divalent state of the Yb atoms was observed.

Synthesis, structure, and third-harmonic generation measurements of a mixed alkali metal iodate, KLi2(IO3)3

Pure polycrystalline samples and single crystals of a mixed alkali metal iodate, KLi2(IO3)3 were synthesized through standard solid state and hydrothermal reactions, respectively, by using Li2CO3, K2CO3, and I2O5 as reagents. Single-crystal X-ray diffraction analysis suggests that KLi2(IO3)3 exhibits a corrugated layered structure consisting of IO3 distorted trigonal pyramids, LiO4 tetrahedra, and K+ cations. Within the layer, both five-membered rings (5-MRs) and six-membered rings (6-MRs) exist. UV–vis diffuse reflectance spectral data suggest that KLi2(IO3)3 has a wide optical band gap of ca. 4.25 ​eV. Infrared spectrum of the title compound clearly confirms the existence of IO3 groups in the backbone. The framework of the iodate is thermally stable to ca. 450 ​°C. Third-harmonic generation measurements using 1500 ​nm radiation indicate that the third-order nonlinear optical susceptibility of KLi2(IO3)3 is ca. 3 times that of α-SiO2. The laser-induced damage threshold of KLi2(IO3)3 is comparable to that of α-SiO2. Calculated local dipole moment values of IO3 polyhedra are also reported to better understand the asymmetric coordination environment.

Compressibility behaviour of conducting ceramic TiB2

To address the large spread in the bulk modulus value of TiB2 reported in literature, high pressure compressibility study of a phase pure polycrystalline sample has been carried out using in situ high pressure x-ray diffraction technique (HPXRD) in angle dispersive mode. The study has been done up to 23 GPa at ambient temperature with methanol-ethanol-water (MEW) as pressure transmitting medium. The hexagonal lattice has been found to be stable in the pressure range studied. The isothermal bulk modulus is estimated to be 333(6) GPa by employing 3rd order Birch–Murnaghan equation of state. The obtained high value of bulk modulus is understood in terms of band filling effect, and the nature of bonding between B–B and Ti–B in TiB2. Compressibility along ‘a’ and ‘c’ axis is found to be anisotropic with compressibility values of 0.93(2) TPa−1 and 1.14(2) TPa−1 respectively. From the estimated bond lengths for Ti–B and B–B it is found that B–B bonds are less compressible compared to Ti–B bonds which is in accordance with the respective nature of Ti–B and B–B bonds. A change in the rate of bond contraction was seen around 12 GPa which is due to the bond hardening for both Ti–B and B–B bonds with pressure.

Magnetism on quasi-1-D lattices in novel non-centrosymmetric Ba3CrVS4O3 and in centrosymmetric La3TMWS3O6 (TM = Cr, Fe, Co)

La3TMWS3O6 (TM=Fe, Co) and novel Ba3CrVS4O3 can be obtained as pure polycrystalline samples by mineralizer aided solid-state reactions and a solid-state reaction with further purification by water, respectively. In contrast, La3CrWS3O6 needs a standard solid-state reaction to form but the final product contains observable impurities. All four compounds contain similar quasi-1-D magnetic lattices although La-based ones are centrosymmetric (P63/m) and the Ba-containing one is polar and non-centrosymmetric (P63). Strong antiferromagnetic couplings are observed along the magnetic chains in the Fe and Cr containing compounds. As a result, short-range magnetic order is suggested at low temperatures for the Fe-chain, which can be related to magneto-electric couplings. The Co3+-homologue shows typical diamagnetic behavior, as supported by its insulating nature, which is due to a low-spin state. The polar Cr3+-compound exhibits very different magnetic behavior compared to its corresponding non-polar relative. This proves a strong influence on the physical properties from the crystallographic symmetry.

Characterization of YbNi4(P1–xAsx)2, x = 0, 0.2 single crystals grown by Czochralski method

We have investigated large single crystals of YbNi4P2 that were grown from a levitating melt by the Czochralski method. The new samples facilitate the determination of the absolute values of the electrical resistivity. Phase pure polycrystalline samples of the non-magnetic reference LuNi4P2 were prepared and the electrical resistivity was measured. Furthermore we have grown a single crystal of the As substituted compound YbNi4(P1–xAsx)2, x = 0.2 and investigated the homogenity of the As distribution.

Preparation of strontium W-type hexaferrites in a low oxygen pressure and their magnetic properties

We report a successful preparation of strontium W-type hexaferrite (SrW: SrFe18O27) without a quenching method in a reduced oxygen atmosphere and its magnetic properties. The pure SrW polycrystalline samples except their surface layer could be prepared by solid state reaction at 1300–1315 °C and subsequent furnace-cooling to room temperature in a low oxygen partial pressure of 10−3 atm. As-sintered SrW samples exhibited soft magnetic properties possessing high saturation magnetization values of 78.8(8)–81.3(8) emu/g and low coercivity values below 100 Oe. With increasing the sintering temperature, both saturation magnetization and anisotropy field values of samples were increased, which is attributable to an increased ratio of Fe2+/Fe3+ ions in the SrW phase induced by enhanced oxygen deficiency.

Synthesis and Structural Characterization of Ca<sub>14</sub>Nb<i><sub>x</sub></i>In<sub>1<i>-</i></sub><i><sub>x</sub></i>As<sub>11</sub> (<i>x</i> ≈ 0.85)

Single-crystals of the new compound Ca14NbxIn1–xAs11 have been obtained from a solid-state reaction in a sealed Nb ampoule. The initial experiment had been set up with the aim to investigate the effect of electron doping (via In) on the crystal structure and physical properties of Ca14MnAs11. Subsequent single-crystal X-ray diffraction and elemental analysis work suggested that instead of Ca14MnxIn1–xAs11, the major product of the reaction is the phase Ca14NbxIn1–xAs11. This supposition was corroborated when the title compound was synthesized from a reaction of Ca, In and As in a sealed Nb ampoule, proving that, 1) Mn metal is not included in the structure, and 2) that the inadvertent side reaction of As with the walls of the Nb container is the source of the niobium. The overall structure is isotypic with the tetragonal Ca14AlSb11 structure type (space group I41/acd), although some marked differences between the two must be noted. Current ongoing work is focused on the synthesis of phase pure polycrystalline samples and determination of the physical properties of this unusual transition metal Zintl phase.

Crystal growth and crystal structures of six novel phases in the Mn/As/O/Cl(Br) system, as well as magnetic properties of α-Mn3(AsO4)2

Chemical vapour transport reactions (900°C → 820°C, Cl2 or Br2 as transport agent) of in situ formed Mn3(AsO4)2 yielded the orthoarsenates(V) α-Mn3(AsO4)2 and β-Mn3(AsO4)2 as well as the oxoarsenate(V) halide compounds Mn7(AsO4)4Cl2, Mn11(AsO4)7Cl, Mn11(AsO4)7Br and Mn5(AsO4)3Cl. The crystal structures of all six phases were determined from single crystal X-ray diffraction data. The crystal structures of α-and β-Mn3(AsO4)2 are isotypic with the corresponding phosphate phases γ- and α-Mn3(PO4)2, respectively, and are reported here for the first time. A comparative discussion with other structures of general composition M3(AsO4)2 (М = Mg; divalent first-row transition metal) is given. The unique crystal structures of Mn7(AsO4)4Cl2 and that of the two isotypic Mn11(AsO4)7X (X = Cl, Br) structures are composed of two [MnO5] polyhedra, two [MnO4Cl2] polyhedra (one with site symmetry 1¯), two AsO4 tetrahedra, and one [MnO5] polyhedron, three [MnO6] octahedra (one with site symmetry.m.), one [MnO4X], one [MnO5X] polyhedron and four AsO4 tetrahedra, respectively. The various polyhedra of the three arsenate(V) halides are condensed into three-dimensional framework structures by corner- and edge-sharing. Mn5(AsO4)3Cl adopts the chloroapatite structure. The magnetic and thermal properties of pure polycrystalline samples of a-Mn3(AsO4)2 were investigated in more detail. The magnetic susceptibility proves all Mn atoms to be in the oxidation state +2 yielding an effective magnetic moment per Mn atom of 5.9μB. Long-range antiferromagnetic ordering is observed below 8.2K consistent with the negative Curie-Weiss temperature of −50K derived from the high temperature susceptibility data.

Slow Relaxation of Magnetization in an Isostructural Series of Zinc-Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study.

We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %.

Structure-Directing Effect of Alkali Metal Cations in New Molybdenum Selenites, Na2Mo2O5(SeO3)2, K2Mo2O5(SeO3)2, and Rb2Mo3O7(SeO3)3.

Both single crystals and pure polycrystalline samples of three new quaternary alkali metal molybdenum selenites, Na2Mo2O5(SeO3)2, K2Mo2O5(SeO3)2, and Rb2Mo3O7(SeO3)3, have been synthesized through hydrothermal and solid-state reactions using A2CO3 (A = Na, K, and Rb), MoO3, and SeO2 as reagents. The frameworks of all three materials consist of both families of second-order Jahn-Teller distortive cations, i.e., the d(0) cation (Mo(6+)) and the lone pair cation (Se(4+)). Although the extent of framework distortions and the resulting occupation sites of alkali metal cations are dissimilar, Na2Mo2O5(SeO3)2 and K2Mo2O5(SeO3)2 exhibit similar three-dimensional networks that are composed of highly asymmetric Mo2O11 dimers and SeO3 polyhedra. Rb2Mo3O7(SeO3)3 reveals a two-dimensional structure that is built with Mo3O15 trimers and SeO3 intralayer linkers. Close structural examinations suggest that the structure-directing effect of alkali metal cations is significant in determining the framework distortions and the dimensions of the molybdenum selenites. UV-vis diffuse reflectance and infrared spectroscopy, thermogravimetric analyses, and ion-exchange reactions are reported, as are out-of-center distortion and dipole moment calculations.

Characteristics of Friedel pairs and diffraction contrast tomography with non-perpendicular rotation axis.

The characteristics of Friedel pairs in diffraction contrast tomography (DCT) are studied in the condition that the rotation axis of the sample is not exactly perpendicular to the incident X-ray direction. For the rotation axis approximately aligned along the vertical direction, the Friedel pairs close to the horizontal plane are insensitive to the non-perpendicularity of the rotation axis, and can be used to refine the sample-to-detector distance and X-ray energy, while the Friedel pairs close to the vertical direction are sensitive to the non-perpendicularity of the rotation axis, and can be used to determine the rotation axis orientation. The correct matching proportion of Friedel pairs decreases with increasing non-perpendicularity of the rotation axis. A method of data processing considering rotation axis misalignment is proposed, which significantly increases the correct matching and indexing proportions of the diffraction spots. A pure aluminium polycrystalline sample is investigated using DCT at beamline 4W1A of Beijing Synchrotron Radiation Facility. Based on the analysis of Friedel pairs, the sample-to-detector distance and X-ray energy are refined to be 8.67 mm and 20.04 keV, respectively. The non-perpendicular angle of the rotation axis is calculated to be 0.10°. With these refined geometric parameters, the matching proportion of the spatial position of diffraction spots is 90.62%. Three-dimensional reconstruction of the sample with 13 grains is realised using the algebraic reconstruction technique. It is demonstrated that the precise correction of the orientation of the sample rotation axis is effective in DCT suffering from rotation axis misalignment, and the higher accuracy in determining the rotation axis is expected to improve the reconstruction precision of grains.

Novel P-T Phase Diagram of the Multiorbital Mott Insulator Sr2VO4.

The electrical and optical properties of the Mott insulator Sr2VO4 are investigated under high pressure on a phase pure polycrystalline sample. The system undergoes a pressure-driven insulator to metal transition (IMT) with a crossover between 20 and 24 GPa. The effect of pressure on the thermally driven electronic changes resulting from spin-orbital ordering transitions is studied. A multiorbital analysis of the low frequency optical conductivity spectra suggests a bandwidth-controlled and orbital selective nature of the Mott IMT transition. Dramatic enhancement of the low energy spectral weight in the high pressure correlated metallic phase is explained in terms of the formation of a quasiparticle peak in the spectral function of the narrow and degenerate d(yz,zx) orbitals. Our results overall establish a novel electronic phase diagram of tetragonal Sr2VO4.

Interparticle and collective states of interactions in mechanically milled Fe/CoO nanocomposites

The effect of high-energy milling on magnetic properties of Fe/CoO nanocomposites has been studied. Formation of pure phase polycrystalline sample having size in the range 15–20 nm is confirmed from micro-structural analysis. Mossbauer spectroscopy indicates the formation of a broad distribution of particle sizes in the samples milled for higher duration. Enhancement in coercivity as well as exchange field is confirmed from magnetic hysteresis measurements. High-field bifurcation in temperature dependent magnetization measurement points toward the formation of spin-glass like state. Wait time dependent magnetization relaxation confirmed this possibility and is supported by the field cooled memory effect. Complexity arises when the absence of memory effect is observed in time dependent magnetic relaxation measurement. Polydispersity and defects are argued to be possible causes for observed spin-glass behavior.

Imaging Quantum Mechanical Effects in Superconductors with Polarized Neutrons

Abstract Macroscopic Quantum effects such as the Meissner effect and magnetic flux trapping in massive, pure poly-crystalline lead samples and in a low purity crystalline sample having non-superconducting parts could be visualized and quantified by radiography with polarized neutrons. A uniform poly-crystalline Pb sample with a high purity of 1−1×10 −4 weight% and one with a low purity of approx. 85 weight% Pb having non-superconducting parts showed a partial Meissner effect and for B ext = 0 and T T c a non-uniform magnetic flux trapping. Based on radiographies with polarized neutrons the trapped and expelled magnetic fields could be calculated for the uniform lead sample, in the case of the sample which contains non-superconducting parts an asymmetric (also squeezed) field distribution yielded the best fit.

Polarized neutron imaging and three-dimensional calculation of magnetic flux trapping in bulk of superconductors

Polarized neutron radiography was used to study the three-dimensional magnetic flux distribution inside of single-crystal and polycrystalline Pb cylinders with large (cm${}^{3}$) volume and virtually zero demagnetization. Experiments with single crystals being in the Meissner phase ($T<{T}_{c}$) showed the expected expulsion of magnetic field. 99.9999 wt $%$ pure polycrystalline samples were exposed to the same homogeneous magnetic field (6.4 mT) and only a portion of the applied field was expelled. The trapped field in the sample ($T<{T}_{c}$, ${B}_{\mathrm{ext}}=0$ T) showed a nearly Gaussian spatial distribution, centered on the cylinder axis and decreasing towards the surface of the cylinder. In the direction along the cylinder axis the trapped flux was nearly constant. The expelled field outside of the samples followed $1/R$ dependence. These measurements provided a unique and detailed picture of macroscopic superconducting samples, confirming the existence of both uniform bulk Meissner expulsion in single crystals and bulk flux trapping with nearly-Bean-model profiles due to flux pinning in polycrystalline samples.

ChemInform Abstract: Mg11Cu6Al12, a New Link in the Structural Chemistry of MgCu2‐Type Clusters.

AbstractThe title compound is prepared by direct reaction of the elements at 550 °C for 24 h followed by annealing at 450 °C for 165 h (for single crystals), or at 1000 °C for 5 h followed by annealing at 500 °C for 357 h (for phase pure polycrystalline samples).