Single Crystalline Samples Research Articles

Transformation-induced fracture toughening in CuAlBe shape memory alloys: A phase-field study

Stress-induced martensitic transformation ahead of a crack tip can relax the stress concentration and produce fracture toughness in shape memory alloys (SMAs). In this manuscript, we utilize a non-isothermal phase-field model (PFM) to study the martensitic transformation induced crack tip toughening in CuAlBe SMA. The force-displacement curve, transformation zone and high stress zone in single crystalline samples show high dependency on the grain orientation with respect to the crack alignment. Comparison between isothermal and non-isothermal simulations reveals that the transformation-induced self-heating decreases the toughening capability by increasing the critical transformation stress. Investigating the high stress zones in CuAlBe and the non-transforming CuAl alloy shows that the toughening is obtained by redistributing the stress concentration far from the crack tip, as the high stress zone follows the moving tip of the transformation zone. Increasing the acuity of the crack tip is found to generate more symmetric martensite wings on both side of the crack axis, and a more localized high stress zone. The polycrystal specimen displays higher toughening due to the internal constraints related to the presence of various grains with difference orientations. Depending on the orientation of the grain inclosing the crack tip, the toughening effect can be lower or higher. Coincidence of the crack tip with a triple junction is found to improve the toughening behavior.

Strong magnetic anisotropy and unusual magnetic field reinforced phase in URhSn with a quasi-kagome structure

The physical properties of URhSn with quasi-kagome structure are studied using single-crystalline samples via electrical resistivity, magnetic susceptibility, heat capacity, thermal expansion, and high-field magnetization measurements. Remarkable magnetic anisotropy is found in the ferromagnetic (FM) state below ${T}_{\mathrm{C}}=16\phantom{\rule{4pt}{0ex}}\mathrm{K}$ as well as in the ordered state between ${T}_{\mathrm{C}}$ and ${T}_{\mathrm{O}}=54\phantom{\rule{4pt}{0ex}}\mathrm{K}$, where the easy and hard magnetization directions are the hexagonal [0001] and $[10\overline{1}0]$ axes. In the paramagnetic state, the magnetic susceptibility shows a Curie-Weiss behavior; the Weiss temperatures are positive and negative for [0001] and $[10\overline{1}0]$, respectively, indicating the presence of both FM and antiferromagnetic (AFM) correlations. The entropy release for $5f$ electrons is approximately $R\phantom{\rule{0.16em}{0ex}}\mathrm{ln}3$ at ${T}_{\mathrm{O}}$. The thermal expansion coefficient is strongly anisotropic around ${T}_{\mathrm{O}}$ between the hexagonal basal plane and the [0001] axis, indicating its remarkable anisotropic magnetoelastic response and uniaxial stress dependences. Interestingly, the magnetic field response of the higher-temperature ordered state is unusual: ${T}_{\mathrm{O}}(H)$ increases and the heat-capacity jump is enhanced with the magnetic field for $H\phantom{\rule{0.16em}{0ex}}||\phantom{\rule{4pt}{0ex}}[0001]$. Based on the established thermodynamic evidence for the second-order transition at ${T}_{\mathrm{O}}(H)$, a plausible scenario is the occurrence of a canted AFM ordering or a conical state under magnetic fields, which is stabilized when coupled with field-induced magnetic moments along the [0001] axis. Another possibility is the occurrence of quadrupole ordering at ${T}_{\mathrm{O}}(H)$.

Speckle correlation as a monitor of X-ray free-electron laser induced crystal lattice deformation

X-ray free-electron lasers (X-FELs) present new opportunities to study ultrafast lattice dynamics in complex materials. While the unprecedented source brilliance enables high fidelity measurement of structural dynamics, it also raises experimental challenges related to the understanding and control of beam-induced irreversible structural changes in samples that can ultimately impact the interpretation of experimental results. This is also important for designing reliable high performance X-ray optical components. In this work, X-FEL beam-induced lattice alterations are investigated by measuring the shot-to-shot evolution of near-Bragg coherent scattering from a single crystalline germanium sample. It is shown that X-ray photon correlation analysis of sequential speckle patterns measurements can be used to monitor the nature and extent of lattice rearrangements. Abrupt, irreversible changes are observed following intermittent high-fluence monochromatic X-ray pulses, thus revealing the existence of a threshold response to X-FEL pulse intensity.

Magnetic anisotropies of La–Co substituted M-type Sr hexaferrites studied by 57Fe Mössbauer spectroscopy with external magnetic fields

Magnetoplumbite-(M)-type hexaferrites are the most widely used base materials of permanent magnets. La–Co substitution in these M-type Sr hexaferrites improves these magnetic anisotropies. By 57Fe Mössbauer spectroscopy using the single-crystalline samples, we have investigated the Fe electronic states in the La–Co substituted M-type Sr hexaferrites, Sr1−xLaxFe12−yCoyO19, as a function of an external magnetic field to discuss the enhancement of these magnetic anisotropies. All observed 57Fe Mössbauer spectra were well analyzed using the five subspectra corresponding to the five crystallographic nonequivalent Fe sites. At one site of these five Fe sites, the 2a Fe site, the extracted hyperfine interaction parameters clearly show the Co substitution and external magnetic field dependences, revealing the increments of the 3d electrons in the Fe ions, which are caused by the substitution of Co2+ ions for Fe3+ ions at the neighbor 4f1 Fe site. This hybridization between the Fe ions and the Co ions induces the non-negligible unquenched orbital momentum in the Fe ions at the 2a Fe site. Our findings represent an enhancement of the magnetic anisotropies in Sr1−xLaxFe12−yCoyO19.

Ca14AlBi11—a new Zintl phase from earth-abundant elements with a great potential for thermoelectric energy conversion

The Zintl phase Ca14AlBi11 has been synthesized and structurally characterized for the first time. Its crystal structure has been carefully determined by single-crystal X-ray diffraction methods, and shown to crystallize in the tetragonal space group I41/acd, No. 142 (Z = 8). Not surprisingly, Ca14AlBi11 adopts the Ca14AlSb11-structure type, although Ca14AlBi11 is the first alumo-bismuthide among the ‘14–1–11’ family whose structure is unequivocally established. In the respective Ca–Al–Bi ternary system, so far, Ca14AlBi11 is only the second identified phase. Electronic structure calculations for this new bismuthide indicate the opening of a small gap at the Fermi level, suggestive of intrinsic semiconducting behavior. Resistivity measurements on as-synthesized single crystalline sample show temperature dependence akin to those of heavily doped semiconductors or the bad metals. In addition to the moderately high electrical conductivity (ρ300 = 1.05 mΩ cm), specimens of Ca14AlBi11 also exhibit excellent thermopower, with high-temperature (HT) values of the Seebeck coefficient approaching and possibly exceeding 200 μV/K. These metrics, coupled with preliminary HT conductivity estimates, are comparable with the best state-of-the-art p-type Zintl thermoelectric materials and are among the best within the known bismuthides with the same atomic arrangements. Therefore, Ca14AlBi11 represents a new platform for the development of a novel, low-cost thermoelectric materials family with first-class transport properties and enhanced thermal stability. Initial data suggest that Ca14AlBi11 is amenable to doping, which opens up many opportunities for tuning charge-carrier concentration and optimizing the transport properties in this new, HT thermoelectric material.

Aqueous Stability and Ligand Substitution of a Layered Cu(I)/Isocyanide-Based Organometallic Network Material with a Well-Defined Channel Structure.

Isocyanide coordination networks (ISOCNs), which consist of multitopic isocyanide linker groups and transition-metal-based secondary building units (SBUs), are a promising class of organometallic framework materials for the inclusion of low-valent metal centers as primary structural components. Previously, it was demonstrated that the ditopic m-terphenyl isocyanide ligand, [CNArMes2]2 (ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3), could provide single-metal node frameworks based on Cu(I) and Ni(0) centers. However, the relatively short linker length in [CNArMes2]2 precluded the formation of networks with significant porosity. Here, it is shown that expansion of the [CNArMes2]2 scaffold with a central phenylene spacer allows for the formation of a robust Cu(I)-based framework with a distinct and solvent accessible channel structure. This new framework, denoted Cu-ISOCN-4, is prepared as single-crystalline samples from a solvothermal reaction between [Cu(NCMe)4]PF6 and expanded linker 1,4-(CNArMes2)2C6H4. Crystallographic characterization of Cu-ISOCN-4 revealed mononuclear [Cu(THF)(CNR)3]+ structural nodes. The expanded diisocyanide linker results in fourfold interpenetrated (6,3) internal morphology. However, interpenetration in Cu-ISOCN-4 results in discrete layer domains, each of which possesses well-defined 29 × 19 Å channels along the crystallographic b axis. Thermogravimetric analysis on Cu-ISOCN-4 revealed THF solvent loss from the channels between 100-200 °C and dissociation of the Cu-coordinated THF ligand at 290 °C. The overall integrity of the network remains intact up to 400 °C, thereby signifying the robust nature of materials produced from metal-isocyanide M-C linkages. Aqueous stability studies revealed that Cu-ISOCN-4 remains chemically resistant to exposure to liquid water for several days. In addition, ligand exchange studies in both THF and aqueous solution demonstrate that the Cu-coordinated THF group in Cu-ISOCN-4 can be readily substituted with pyridine. This ligand exchange process occurs via single-crystal-to-single-crystal transformations and can also be readily monitored by infrared spectroscopy.

Ionic Conductivity in Copper Selenides

For the first time, the results of investigations of ion transport phenomena in high-temperature modifications of single-crystalline copper selenide are presented depending on the temperature and the composition within the homogeneity region as well as the effect of the degree of perfection of single-crystalline samples on the ion transfer. It is found that the activation energy estimated from the temperature dependences of the ionic conductivity for perfect single crystals is significantly higher than in polycrystalline samples and increases with a deviation from stoichiometry. For single crystals, lower values of ionic conductivity are observed. The ionic conductivity in the temperature range of 573–723 K is 1.5–2 times higher for polycrystalline samples than for single crystals.

Noncoplanar ferrimagnetism and local crystalline-electric-field anisotropy in the quasicrystal approximant Au70Si17Tb13

Neutron scattering experiments have been performed to elucidate magnetic properties of the quasicrystal approximant Au70Si17Tb13, consisting of icosahedral spin clusters in a body-centered-cubic lattice. Bulk magnetic measurements performed on the single crystalline sample unambiguously confirm long-range ordering at T C = 11.6 ± 1 K. In contrast to the simple ferromagnetic response in the bulk measurements, single crystal neutron diffraction confirms a formation of intriguing non-collinear and non-coplanar magnetic order. The magnetic moment direction was found to be nearly tangential to the icosahedral cluster surface in the local mirror plane, which is quite similar to that recently found in the antiferromagnetic quasicrystal approximant Au72Al14Tb14. Inelastic neutron scattering on the powdered sample exhibits a very broad peak centered at ℏω ≃ 4 meV. The observed inelastic spectrum was explained by the crystalline-electric-field model taking account of the chemical disorder at the fractional Au/Si sites. The resulting averaged anisotropy axis for the crystalline-electric-field ground state is consistent with the ordered moment direction determined in the magnetic structure analysis, confirming that the non-coplanar magnetic order is stabilized by the local uniaxial anisotropy.

Competing Exchange Interactions in Lanthanide Triangular Lattice Compounds LnZn3P3 (Ln = La–Nd, Sm, Gd)

Stacked triangular lanthanide compounds LnZn3P3 (Ln = La–Nd, Sm, Gd) are successfully grown as single-crystalline samples. Magnetic-susceptibility and specific-heat measurements reveal that the com...

Temperature and time-dependent luminescence of single crystals of KTb3F10

This work deals with the spectroscopic properties of single crystalline samples of KTb3F10. Green luminescing KTb3F10 is an efficient UV radiation converter with a quantum yield of about 40% upon UV-A excitation, while it is also an efficient scintillator upon excitation by 20–50 kV X-ray photons. The temperature dependence of the integral photoluminescence as well as the decay time of KTb3F10 monitored for the Tb3+ emission show that the internal quantum yield between 100 and 800 K is almost constant, while the external quantum yield is modulated, likely due to a change in reabsorption at elevated temperatures. In contrast, the low temperature range between 3 and 63 K reveals a change of the local Tb3+ environment in KTb3F10, which is indicated by an anomaly in the heat capacity and by a strong change of the decay time as well as by a distinct shift of the photoluminescence spectra at low temperatures. In addition, temperature dependent magnetic susceptibility measurements and a structure refinement based on single crystal X-ray diffraction data were performed.

Transformations of Crystalline Phases in Fe1 – xGaxBO3 Single Crystals at Annealing

Optical microscopy and X-ray phase analysis were used to study single-crystalline samples of FeBO3, GaBO3, and Fe0.27Ga0.73BO3, annealed at high temperatures. It was established that the nature of high-temperature structural transformations is significantly different for the “pure” phases (FeBO3, GaBO3) and for the mixed composition Fe0.27Ga0.73BO3.

An Extensive Study of the Electrical Conduction in HKUST-1 Single Crystals

Metal-Organic Frameworks (MOFs), which is three-dimensional (3-D) nanoporous materials composed of metal ions and organic ligands coordinated together, has recently attracted enormous attention as functional materials for electronic devices owing to their structural and functional flexibility in the design, as well as relatively high thermal stability [1, 2]. Although there are some reports so far that guest molecule doping drastically improves the electrical conduction of MOFs, e.g. the electrical conductivity of HKUST-1 (Cu3(btc)2) increases by infiltration of TCNQ, most of those experiments has been done using pellet or polycrystalline film samples [3, 4]. To extract an intrinsic electrical current conduction, avoiding the influences of grain boundaries and the residual stress introduced into the film due to the substrate mismatching, the use of single crystalline sample is essential. In this work, we investigated the dominant conduction mechanism of TCNQ-infiltrated bulk HKUST-1 single crystals which include much less grain boundaries and residual stress, by measuring the electrical conductivity as functions of a bias voltage, temperature, and pressure. Sub-mm sized HKUST-1 single crystals were fabricated and infiltrated with TCNQ using a saturated TCNQ/CH2Cl2 solution. The temperature dependence of DC current between 30 °C to 110 °C in the ambient shows that a current at 10 V decreases with increasing temperature down to undetectable value of less than 1 x 10-12 A, although the current value at 30 °C of around 1 x 10-6 A is similar to that of polycrystalline films [3]. We also confirmed that the temperature dependence of DC current for un-infiltrated HKUST-1 single crystals almost agrees with those of the TCNQ-infiltrated ones. Therefore, TCNQ infiltration is not effective in improving an electrical conductivity and the relatively high electrical conductivity at 30 °C is attributed to the presence of water absorbed by samples from the ambient, which was confirmed by thermogravimetric analysis. These results indicate that the current we measured was attributed to the ionic conduction probably due to the electrolysis of water inside the nanoporous structure not to the electronic conduction. Therefore, it is implied that the drastic improvement of the conductivity in the TCNQ-infiltrated HKUST-1 reported in ref. [3] is due to the use of film instead of bulk single crystal. It is suggested that the residual stress introduced into the HKUST-1 film by substrate mismatching plays a key role in the improved electronic conduction of the TCNQ-infiltrated HKUST-1 system. We will also discuss the effect of applying high pressure to the single crystals.

Experimental methods in chemical engineering: X‐ray diffraction spectroscopy—XRD

AbstractX‐ray diffraction (XRD) analysis identifies the long‐range order (ie, the structure) of crystalline materials and the short‐range order of non‐crystalline materials. From this information we deduce lattice constants and phases, average grain size, degree of crystallinity, and crystal defects. Advanced XRD provides information about strain, texture, crystalline symmetry, and electron density. When radiation impinges upon a solid, coherent scattering of the radiation by periodically spaced atoms results in scattered beams that produce spot patterns from single crystalline samples and ring patterns from polycrystalline samples. The pattern, intensities of the diffraction maxima (peaks or lines), and their position (Bragg angle θ or interplanar spacing dhkl), correlate to a specific crystal structure. In 2016 and 2017 close to 100 000 articles mention XRD—more than any other analytical technique, and it was the top analytical technique of researchers that published in Can. J. Chem. Eng. A bibliographic analysis based on the Web of Science groups articles referring to XRD into five clusters: the largest cluster includes research on nanoparticles, thin films, and optical properties; composites, electro‐chemistry, and synthesis are topics of the second largest cluster; crystal morphology and catalysis are next; photocatalysis and solar cells comprise the fourth largest cluster; and, waste water is among the topics of the cluster with the least number of occurrences. Researchers publishing in Can. J. Chem. Eng. focus most of the XRD analyses to characterize polymers, nanocomposite materials, and catalysts.

Superconductivity in single crystalline LuPd2Si2 probed by heat capacity measurements

Single-crystalline samples of LuPd2Si2 were studied by means of low-temperature specific heat measurements performed in a magnetic field oriented along two main crystallographic directions. The compound was found to be superconducting below 0.6 K, in agreement with previous reports. Detailed analysis of the phase-transition anomaly revealed that LuPd2Si2 is a BCS-like superconductor with anisotropic properties and a possible two-gap character.

Anisotropic electrical and thermal magnetotransport in the magnetic semimetal GdPtBi

The half-Heusler rare-earth intermetallic GdPtBi has recently gained attention due to peculiar magnetotransport phenomena that have been associated with the possible existence of Weyl fermions, thought to arise from the crossings of spin-split conduction and valence bands. On the other hand, similar magnetotransport phenomena observed in other rare-earth intermetallics have often been attributed to the interaction of itinerant carriers with localized magnetic moments stemming from the $4f$-shell of the rare-earth element. In order to address the origin of the magnetotransport phenomena in GdPtBi, we performed a comprehensive study of the magnetization, electrical and thermal magnetoresistivity on two single-crystalline GdPtBi samples. In addition, we performed an analysis of the Fermi surface via Shubnikov-de Haas oscillations in one of the samples and compared the results to \emph{ab initio} band structure calculations. Our findings indicate that the electrical and thermal magnetotransport in GdPtBi cannot be solely explained by Weyl physics and is strongly influenced by the interaction of both itinerant charge carriers and phonons with localized magnetic Gd-ions and possibly also paramagnetic impurities.

Magnetic properties of single-crystalline terbium and holmium – Experiment and modeling

The trend in modern experimental physics of magnetic phenomena is the increasing complexity of experimental methods, or a combination of methods to study even well studied “classical” magnetic materials. The development of related sciences (materials science, chemistry, nanotechnology), as well as the emergence of modern highly informative laboratory and research complexes allows simultaneous analysis of both bulk and local magnetic properties on the same samples. At the same time, the samples are subject to increased requirements in terms of chemical purity and degree of structural perfection. The combination of these factors leads to the discovery of new properties of well-known magnetic materials. This is particularly noticeable in the case of heavy rare earth metals, where a high degree of purity and absence of impurities can lead to the appearance of new magnetic phases and phase transitions. It is important to note that the complexity of the experimental detection of some non-collinear magnetic phases causes the need for theoretical analysis and mathematical modelling of the fundamental possibility of the existence of a type of magnetic ordering in rare-earth metals in order to exclude the experimental error. In this paper we present the modeling of the experimental results of high purity single-crystalline samples of Tb and Ho [5,6] trying to find theoretical and phenomenological patters which explain the existence of certain magnetic phases in the series of heavy lanthanides.

Crystal Systems and Lattice Parameters of CH3NH3Pb(I1–xBrx)3 Determined Using Single Crystals: Validity of Vegard’s Law

Metal halide perovskites are promising materials for light absorbers in solar cell applications. Use of the Br/I system enables us to control band gap energy and improves the efficiency of solar cells. Precise knowledge of lattice parameters and band gap energies as functions of compositions are crucially important for developing the devices using those materials. In this study, we have determined lattice parameters and band gap energies of CH3NH3Pb(I1-xBrx)3, one of the most intensively studied mix-halide perovskites, as functions of Br content x. We measured accurate Br contents and lattice parameters of CH3NH3Pb(I1-xBrx)3 (0 ≤ x ≤ 1) using single-crystalline samples by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements, respectively. The CH3NH3Pb(I1-xBrx)3 crystal system is tetragonal for x ≤ 0.06 and cubic for x ≥ 0.08 at 300 K. Lattice parameters of CH3NH3Pb(I1-xBrx)3 strictly follow Vegard's law; i.e., they are linearly dependent on x. We give linear expressions of x of lattice parameters for the tetragonal and cubic phases of CH3NH3Pb(I1-xBrx)3 at 300 K. We have shown that these expressions can be used for determining the Br contents of CH3NH3Pb(I1-xBrx)3 polycrystalline thin-film samples based on XRD measurements and, in addition, demonstrated that XPS measurements on polycrystalline samples may be erroneous because of impure ingredients in the samples. Furthermore, we determined band gap energies of CH3NH3Pb(I1-xBrx)3 (0 ≤ x ≤ 1) at room temperature using absorption spectra of polycrystalline thin films taking account of excitonic effects.

63,65Cu NMR study of the magnetically ordered state of the multiferroic CuFeO2

Field-swept 63,65Cu NMR spectra under magnetic fields up to 8.3 T at a constant NMR frequency and temperatures T < 12 K on a single crystalline sample of multiferroic CuFeO2 were measured and analyzed. When the magnetic field is applied along the c axis, a nearly zero internal magnetic field at the Cu site in magnetic ordered state was observed. This is explained by the perfect cancellation of the internal fields produced by the 6 nearest neighbor Fe3+ (S = 5/2) ions, revealing the magnetic structure to be a collinear four-sublattice structure. On the other hand, when the magnetic field is applied along the ab plane, we observed a finite internal field at the Cu sites, which is due to the canting of the Fe moments. Strong change in the NMR signal intensity is observed around 7–8 T, corresponding to the magnetic phase transition from the collinear magnetic to ferroelectric incommensurate states. The ratio of the two magnetic phases significantly depends on the history of the change in the external magnetic field and the temperature of the sample. The details of history dependence of the ratio were discussed.

Study of TAFF and vortex phase of FexTe0.60Se0.40 (0.970 ≤ x ≤ 1.030) single crystals

Single crystalline samples with starting compositions FexTe0.60Se0.40 (x = 0.970, 0.985, 1, 1.015 and 1.030) have been grown using the self-flux method to study the effect of Fe variation (x) on the structural and superconducting properties of the grown single crystalline samples. All the grown samples are found superconducting and among all, the FeTe0.60Se0.40 (x = 1) sample shows the highest superconducting transition temperature (TC). For the samples with x other than 1, a decrease in the superconducting properties, such as TC, activation energy (U0) and upper critical field (HC2(0)), has been observed. The thermal activation energy (TAE) of the flux flow has been calculated using the conventional method and modified thermally activated flux flow (TAFF) model. The values of U0(H) show transition from the single vortex pinning regime to the collective vortex pinning regime at 2T. Also, the presence of planer defects has been estimated via both models. Furthermore, the modified TAFF model suggests three dimentional (3D) behaviour for all the grown single crystals. The vortex phase diagrams have been established by analysing the magnetoresistance data. The analysis reveals the transitions from unpinned to pinned vortex liquid region and also from the pinned vortex liquid state to vortex glass state. In the vortex phase diagram, below the critical temperature (T*), the critical exponent (s) is in a good agreement with the ‘q’ values for the 3D behaviour of vortex states for all the grown samples.

Study of the ferromagnetic quantum phase transition in Ce3−x Mg x Co9

ABSTRACT The CeMgCo system evolves from a Pauli paramagnetic ground state for x = 0 to a ferromagnetic ground state for in single-phase, polycrystalline samples [Lamichhane, V. Taufour, A. Palasyuk, Q. Lin, S.L. Budko, and P.C. Canfield, : transformation of a Pauli paramagnet into a strong permanent magnet, Phys. Rev. Appl. 9 (2018), p. 024023]. In order to better understand this behaviour, single-crystalline samples of CeMgCo for x = 0.01, 0.16, 0.24, 0.35, 0.43 and 0.50 were grown using the flux growth technique, and electrical transport and magnetic properties were studied. The -x phase diagram we infer shows that the system has a quantum phase transition near x = 0.35, transforming to a ferromagnetic ground state.