Low-alloyed molybdenum single crystals: preparation, structure and properties

Investigation concerns the method of preparation of low-alloyed molybdenum single crystals directly from molybdenum rods and wire, rod or foil containing the appropriate alloying metal, excluding the stage of pre-fusion of the components in an arc furnace, which is more economical than traditional method. In this way Mo-W, Mo-Ta (1,5 wt.% alloying elements of each) and Mo-Re (2 and 3 wt.%) single crystals were prepared by electron-beam zone melting. Authors discuss in more detail the structure and structural parameters of prepared single crystals. Some structural features of Mo-2 wt.% Re and Mo-3 wt.% Re single crystals are explained. Moreover the coefficient thermal linear expansion (CTLE) was measured for Mo-Re single crystals. As shown the proposed method ensures the preparation of single crystal even in single stage melt. The structural imperfections may be removed by following re-melting.

Source:IOPscience

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A novel in situ method for simultaneous growth of smart material single crystals and thin films

Development of a novel in situ method for simultaneous growth of single crystals and thin films of a smart material spinel is achieved. Material to be grown as metal-incorporated single crystal and thin film was taken as a precursor and put into a bath containing acid as a reaction speed-up reagent (catalyst) as well as a solvent with a metal foil as cation scavenger. By this novel method, zinc aluminate crystals having hexagonal facets and thin films having single crystalline orientation were prepared from a single optimized bath. Properties of both crystals and thin films were studied using an x-ray diffractometer and EDAX. ZnAl2O4 is a well-known wide bandgap compound semiconductor (Eg = 3.8 eV), ceramic, opto-mechanical and anti-thermal coating in aerospace vehicles. Thus a space_ gmr technique was found to be a new low cost and advantageous method for in situ and simultaneous growth of single crystals and thin films of a smart material.

Source:IOPscience

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Refined crystal structures and phase transitions in 0.24Pb(In1/2Nb1/2)O3–0.43Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystal

Local lattice structures of 0.24Pb(In1/2Nb1/2)O3–0.43Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (0.24PIN–0.43PMN–0.33PT) single crystal have been investigated by Micro-Raman spectroscopy. A total of 12 Raman active modes were ascertained using the Gauss–Lorentzian line shape approximation, which confirmed that the 0.43PIN–0.26PMN–0.33PT single crystal has monoclinic symmetry at room temperature. The phase transitions were investigated by analyzing the temperature-dependent relative dielectric permittivity of both poled and unpoled 0.43PIN–0.26PMN–0.33PT single crystals measured upon heating. The monoclinic–tetragonal phase transition occurs at TM–T = 82 °C, and the Curie temperature is 199 °C. The splitting of (200) and (002) peaks in detailed X-ray diffraction spectra in the 2θ range of 44.6–45.2° during heating from room temperature to 200 °C was also studied. For a sample being poled along [111]c pseudo-cubic direction, several sharp peaks arise in the thermally stimulated depolarization current from 67 to 82 °C with the main peak occurs at 67 °C, which indicates that the depolarization temperature is 15 °C lower than the monoclinic to tetragonal phase transition and there are coexistence of monoclinic and rhombohedral phases in the [111]cpoled single crystal.

Source:IOPscience

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Influence of Mn doping on CuGaS2 single crystals grown by CVT method and their characterization

1 and 2 mole% of Mn doped CuGaS2 (CGS) single crystals were grown by the chemical vapour transport (CVT) technique using iodine as the transporting agent. The analysis of the single crystal x-ray diffraction data suggests that the doping of 1 and 2 mole% Mn in the CGS single crystal does not affect the tetragonal (chalcopyrite) crystal structure. The optical absorption spectrum shows that the Mn ion induces a very strong absorption band in the UV–visible–near IR regions. The values of the crystal parameter (Dq) and the Racah parameter (B) calculated from the absorption spectra show d electron delocalization in the host crystal CGS. Room temperature photoluminescence spectra of undoped CGS only exhibited a band–band emission. But 1 and 2 mole% Mn doped CGS single crystals show two distinct CGS and Mn2+ related emissions, both of which are excited via the CGS host lattice. Raman spectra of 1 and 2 mole% Mn doped CGS single crystals exhibit a high intensity peak of the A1 mode at 310 cm−1 and 300 cm−1, respectively. EDAX, optical absorption and Raman spectrum studies reveal that Mn2+ ions are substituted in the Ga3+ ions and incorporated into the CGS lattice. The magnetization of Mn doped CGS single crystals was measured as a function of the magnetic field and temperature. Paramagnetic behaviour typical of spin S = 5/2 expected for Mn2+(d5) magnetic centres was observed in the temperature range 2 K < T < 300 K. In Mn doping, the increase in bulk conductivity of the Mn doped CGS single crystals at room temperature indicates an increase in the hole concentration.

Source:IOPscience

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Effect of sintering temperature on the growth of (K0.5Na0.5)NbO3 single crystals fabricated by the solid-state crystal growth method

The effect of sintering temperature on the growth of (K0.5Na0.5)NbO3 (KNN) single crystals fabricated by a solid-state crystal growth method with a sintering aid of 2 wt%Co3O4 and the seed crystals of (110) and (100) KTaO3 was investigated. For the KNN single crystals fabricated with the (110) KTaO3 seed crystal, crystal growth length was gradually increased with increasing sintering temperature at the temperatures of 1020 °C–1120 °C. At the temperatures of 1130 °C–1200 °C, rapid growth was observed and a grown single crystal reached the surfaces of the ceramic compact containing the seed crystal. The length of the KNN crystal sintered at 1140 °C for 24 h was 690 μm. On the other hand, such rapid growth was not observed for the KNN single crystals fabricated with the (100) KTaO3 seed crystal. The length of the KNN crystal sintered at 1140 °C for 24 h was 160 μm. The dielectric, ferroelectric, and piezoelectric properties of the KNN single crystal fabricated with the (110) KTaO3 seed crystal at a sintering temperature of 1140 °C were reported.

Source:IOPscience


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Synthesis and optical characterization of Nickel doped Thiourea Barium Chloride (TBC) single crystals

Organometallic Thiourea barium chloride (TBC) single crystals were synthesized using solution evaporation process at room temperature. Synthesized thiourea barium chloride crystals were recrystallized and during the recrystallization process 1M%, 2M% and 5M% of nickel (Ni) was added to the solution and kept for crystallization. The variation of intensity peaks and the shift in the XRD peaks were observed due to the incorporation of nickel in the host matrix. Variations in the absorbance and transmittance spectra of the pure and Ni doped crystals further confirms the presence of nickel in TBC single crystal. The optical bandgap of the pure and nickel doped single crystals were calculated using Touc's relation. The results show that bandgap decreased with the dopant concentration in the thiourea barium chloride crystal. The optical constants such as extinction coefficient and reflectance were also studied using the absorption spectrum. The FTIR absorption also shows minute shift in the absorption peaks due to the presence of nickel in the host matrix. Photoluminescence spectra of pure and doped crystals were studied.

Source:IOPscience
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Distributed Feedback Laser Based on Single Crystal Perovskite

We demonstrate a single crystal perovskite based, with grating-structured photoresist on top, highly polarized distributed feedback laser. A lower laser threshold than the Fabry–Perot mode lasers from the same single crystal CH3NH3PbBr3 microplate was obtained. Single crystal CH3NH3PbBr3microplates was synthesized with one-step solution processed precipitation method. Once the photoresist on top of the microplate was patterned with electron beam, the device was realized. This one-step fabrication process utilized the advantage of single crystal to the greatest extend. The ultra-low defect density in single crystalline microplate offer an opportunity for lower threshold lasing action compare with poly-crystal perovskite films. In the experiment, the lasing action based on the distributed feedback grating design was found with lower threshold and higher intensity than the Fabry-Perot mode lasers supported by the flat facets of the same microplate.

Source:IOPscience

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Heavy ion induced luminescence studies of YAlO3:Tb3+, Tm3+ single crystals

Ionoluminescence (IL), photoluminescence (PL) and thermoluminescence (TL) studies of YAlO3:Tb3+, Tm3+ (1 at %) single crystals are carried out using 100 MeV Si7+ ions for the fluence 3.91 × 1012 ions cm−2. IL peaks are recorded in the range 385–450, 493, 544, 585 and 624 nm in Tb3+- and 353, 459, 523, 651 and 763 nm in Tm3+-doped YAlO3 single crystals, respectively. PL studies also show similar characteristic emission peaks. The variation of IL intensity is studied in a YAlO3:Tb3+ crystal for a wide fluence range of 3.91 × 1012 –17.57 × 1012 ions cm−2. The IL intensity is found to be higher in lower ion fluences, and it decreases with the increase of ion fluence. Thermoluminescence (TL) studies are carried out for ion fluence– (3.91 × 1012 ions cm−2) and UV-exposed (05–60 min) single crystals. A single well-resolved glow peak at 242 °C, along with a shouldered peak at 272 °C, is recorded in the Tm3+-doped sample. In the Tb3+-doped samples, a well-resolved glow peak at 218 °C, along with a shouldered peak at 147 °C, is recorded at the lower temperature side. In the UV-exposed crystals, two glow peaks at 168 °C and 223 °C are recorded. The glow peaks are found to be shifted towards the lower temperature side with an increase in UV exposure time. Good linearity over a large span of UV exposure time and a single glow peak with a simple trap distribution are observed in YAlO3:Tb3+ single crystals, which makes them suitable as a dosimeter for UV-rays. The kinetic parameters (E, b, s) are estimated using the glow peak shape method for both ion and UV-exposed crystals, and the results are discussed in detail.

Source:IOPscience

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Defect-driven synthesis of self-assembled single crystal titanium nanowires via electrochemistry

One-dimensional single crystal nanostructures have garnered much attention, from their low-dimensional physics to their technological uses, due to their unique properties and potential applications, from sensors to interconnects. There is an increasing interest in metallic titanium nanowires, yet their single crystal form has not been actualized. Vapor–liquid–solid (VLS) and template-assisted top-down methods are common means for nanowire synthesis; however, each has limitations with respect to nanowire composition and crystallinity. Here we show a simple electrochemical method to generate single crystal titanium nanowires on monocrystalline NiTi substrates. This work is a significant advance in addressing the challenge of growing single crystal titanium nanowires, which had been precluded by titanium's reactivity. Nanowires grew non-parallel to the surface and in a periodic arrangement along specific substrate directions; this behavior is attributed to a defect-driven mechanism. This synthesis technique ushers in new and rapid routes for single crystal metallic nanostructures, which have considerable implications for nanoscale 

Source:IOPscience

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Precipitation of thin-film organic single crystals by a novel crystal growth method using electrospray and ionic liquid film

We report an organic single crystal growth technique, which uses a nonvolatile liquid thin film as a crystal growth field and supplies fine droplets containing solute from the surface of the liquid thin film uniformly and continuously by electrospray deposition. Here, we investigated the relationships between the solute concentration of the supplied solution and the morphology and size of precipitated crystals for four types of fluorescent organic low molecule material [tris(8-hydroxyquinoline)aluminum (Alq3), 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD), and N,N-bis(naphthalene-1-yl)-N,N-diphenyl-benzidine (NPB)] using an ionic liquid as the nonvolatile liquid. As the concentration of the supplied solution decreased, the morphology of precipitated crystals changed from dendritic or leaf shape to platelike one. At the solution concentration of 0.1 mg/ml, relatively large platelike single crystals with a diagonal length of over 100 µm were obtained for all types of material. In the experiment using ionic liquid and dioctyl sebacate as nonvolatile liquids, it was confirmed that there is a clear positive correlation between the maximum volume of the precipitated single crystal and the solubility of solute under the same solution supply conditions.

Source:IOPscience

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Enhanced mobility in organic field-effect transistors due to semiconductor/dielectric interface control and very thin single crystal

A perfect organic crystal while keeping high quality semiconductor/dielectric interface with minimal defects and disorder is crucial for the realization of high performance organic single crystal field-effect transistors (OSCFETs). However, in most reported OSCFET devices, the crystal transfer processes is extensively used. Therefore, the semiconductor/dielectric interface is inevitably damaged. Carrier traps and scattering centers are brought into the conduction channel, so that the intrinsic high mobility of OSCFET devices is entirely disguised. Here, very thin pentacene single crystal is grown directly on bare SiO2 by developing a 'seed-controlled' pentacene single crystal method. The interface quality is controlled by an in situ fabrication of OSCFETs. The interface is kept intact without any transfer process. Furthermore, we quantitatively analyze the influence of crystal thickness on device performance. With a pristine interface and very thin crystal, we have achieved the highest mobility: 5.7 cm2 V−1 s−1—more than twice the highest ever reported pentacene OSCFET mobility on bare SiO2. This study may provide a universal route for the use of small organic molecules to achieve high performance in lamellar single crystal field-effect devices.

Source:IOPscience

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Spectroscopic properties of Nd3+:Lu3ScAl4O12 single crystal

Nd:Lu3ScAl4O12 single crystal has been grown by the Czochralski method. The segregation coefficient of Nd3+ ions in LuSAG crystal is 0.22. X-ray powder diffraction (XRD) experiments show that the Nd:LuSAG crystal crystallizes in cubic structure with space group Ia3d and its cell parameters are a = 1.1953 nm. The absorption and fluorescence spectra of Nd:LuSAG crystal were investigated at room temperature. The spectral parameters were calculated based on Judd–Ofelt (J–O) theory, and the intensity parameters Ω2, Ω4 and Ω6 were obtained to be 0.14, 3.38, and 4.88 × 10−20 cm2, respectively. The calculated spontaneous radiative probabilities, branching ratios, radiative lifetime and quantum efficiency have been evaluated for the 4F3/2 excited state using the calculated intensity parameters. The results indicate that this crystal can be considered as a promising material for solid-state laser application.

Source:IOPscience

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Analytical development of single crystal Macro Fiber Composite actuators for active twist rotor blades

A Macro Fiber Composite (MFC) is a piezoelectric fiber composite which has an interdigitated electrode, rectangular cross-section and unidirectional polycrystalline piezoceramic (PZT) fibers embedded in the polymer matrix. A MFC actuator has much higher actuation performance and flexibility than a monolithic piezoceramic actuator. Moreover, the single crystal piezoelectric material exhibits much higher induced strain levels, energy density and coupling than those of polycrystalline piezoceramic materials. Thus, the performance of an MFC can be improved by using single crystal piezoelectric fiber instead of polycrystalline piezoceramic fiber. This study investigates the analytical modeling, material properties and actuation performance of an MFC using single crystal piezoelectric material (single crystal MFC). For single crystal MFC, the mechanical properties are calculated by the classical lamination theory, and the uniform fields model (UFM) is adopted to predict piezoelectric strain constants. In addition, the actuation performance of the single crystal MFC with the active twist rotor blade is studied. The material properties and actuation performance of single crystal MFC are compared with those of standard MFC.

Source:IOPscience

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The density and compositional analysis of titanium doped sapphire single crystal grown by the Czocharlski method

Titanium doped sapphire (Ti:Al2O3) crystal has attracted attention not only as beautiful gemstones, but also due to their applications as high power laser action. It is very important crystal for tunable solid state laser. Ti:Al2O3 crystals have been success grown using the Czocharlski method with automatic diameter control (ADC) system. The crystals were grown with different pull rates. The structure of the crystal was characterized with X-Ray Diffraction (XRD). The density of the crystal was measurement based on the Archimedes principle and the chemical composition of the crystal was confirmed by the Energy Dispersive X-ray (EDX) Spectroscopy. The XRD patterns of crystals are showed single main peak with a high intensity. Its shows that the samples are single crystal. The Ti:Al2O3 grown with different pull rate will affect the distribution of the concentration of dopant Ti3+ and densities on the sapphire crystals boules as well on the crystal growth process. The increment of the pull rate will increase the percentage distribution of Ti3+ and on the densities of the Ti:Al2O3 crystal boules. This may be attributed to the speed factor of the pull rate of the crystal that then caused changes in the heat flow in the furnace and then causes the homogeneities is changed of species distribution of atoms along crystal.

Source:IOPscience

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Bi-2212 and Y123 highly curved single-crystal-like objects: whiskers, bows and ring-like structures

High-temperature superconducting objects of Bi2Sr2CaCu2O8 and Y Ba2Cu3O7 highly curved in the ab-plane, such as curved/kinked whiskers, bows and ring-like structures, were obtained within a solid–liquid–solid (SLS) grass-like growth mechanism. As-grown objects are crystals with three-dimensional epitaxy similar to conventional single crystals: they can be viewed as crystal parts 'cut' from a conventional rectangular crystal. Between our curved objects and conventional crystals, whiskers or thin films there are some differences in the superconducting properties induced only by the shape factors and no new physics is observed. Some details of the growth mechanism are discussed, emphasizing curved-line formation.

Source:IOPscience

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A thickness-mode piezoelectric micromachined ultrasound transducer annular array using a PMN–PZT single crystal

Micro-electromechanical system (MEMS) technologies were used to develop a thickness-mode piezoelectric micromachined ultrasonic transducer (Tm-pMUT) annular array utilizing a lead magnesium niobate–lead zirconate titanate (PMN–PZT) single crystal prepared by the solid-state single-crystal-growth method. Dicing is a conventional processing method for PMN–PZT single crystals, but MEMS technology can be adopted for the development of Tm-pMUT annular arrays and has various advantages, including fabrication reliability, repeatability, and a curved element shape. An inductively coupled plasma–reactive ion etching process was used to etch a brittle PMN–PZT single crystal selectively. Using this process, eight ring-shaped elements were realized in an area of 1  ×  1 cm2. The resonance frequency and effective electromechanical coupling coefficient of the Tm-pMUT annular array were 2.66 (±0.04) MHz, 3.18 (±0.03) MHz, and 30.05%, respectively, in the air. The maximum positive acoustic pressure in water, measured at a distance of 7.27 mm, was 40 kPa from the Tm-pMUT annular array driven by a 10 Vpp sine wave at 2.66 MHz without beamforming. The proposed Tm-pMUT annular array using a PMN–PZT single crystal has the potential for various applications, such as a fingerprint sensor, and for ultrasonic cell stimulation and low-intensity tissue stimulation.

Source:IOPscience

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High infrared transmittance CdS single crystal grown by physical vapor transport

Φ55 × 15 mm2 CdS bulk single crystal with high infrared transmittance was grown by physical vapor transport. The single crystal has a consistent structure from top to bottom, which was confirmed by X-ray diffraction. The (002) full-width at half-maximum of the X-ray diffraction was measured to be 60.00 arcsec, indicating a good quality of the structure. Hall mobility, specific resistivity, and carrier concentration for the top and bottom of the crystal were observed as well. Transmittance for the CdS single crystal was measured to be higher than 70% from 2.5 to 4.5 µm, making the single crystal an important candidate for infrared window materials. Furthermore, the absorption mechanism of the CdS single crystal was analyzed.

Source:IOPscience

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Growth, structural and mechanical studies of phthalic acid single crystals grown in two different solutions

Good quality pure Phthalic acid single crystals were grown by slow evaporation solution growth method. Phthalic acid 1(PA1) crystals were grown in Ammonium Oxalate aqueous solution. From the aqueous solution of Ammonium Bromide, Phthalic acid 2 (PA2) crystals were grown. Single crystal x-ray diffraction and Mechanical characterizations of slow evaporation grown single crystals of PA1 and PA2 were analyzed in this article. Lattice parameters, space group and crytal system were found from Single crystal x-ray diffraction analysis. Optical tranmittance study reaveal the optical perfection of the crystals. Mechanical properties such as Vicker's microhardness number, work hardening index, standard hardness values, Yield strength, fracture toughness, brittleness index and elastic Stiffness constant values were determined using Vicker's microhardness tester.

Source:IOPscience

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Structural and optical properties of LuVO4 single crystals

The synthesis of large single crystals with good optical quality which is a preliminary condition for the practical applications of these materials frequently is complicated. It is found that large LuVO4 single crystals with high optical quality are possible to be prepared using high temperature solution growth method. It is obtained by X-ray crystallographic analysis that the grown crystals possess centrosymmetric tetragonal structure with the point group symmetry D4h and space group I41/amd (zircon-type structure). The unit cell parameters of a = 7.0236 Å, b = 7.0236 Å, c = 6.2293 Å, volume = 307.30(3) Å3 are measured. The crystals composition as well as vanadium oxidation state were measured in order to confirm that the crystal phase is mainly LuVO4. Optical transmission and Raman Spectroscopy are further performed on LuVO4 single crystal to reveal the optical quality and structure details

Source:IOPscience

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PVT growth of AlN single crystals with the diameter from nano- to centi-meter level

Physical vapor transport (PVT) is the most successful and widely used approach for bulk aluminum nitride (AlN) single crystals. During the process of PVT growing AlN crystals, crucible materials, the growth setup, and the growth parameters (e.g., temperature distribution, growth pressure) are crucial. This work proposes a detailed study on the PVT growth of single AlN crystals with sizes ranging from nanometers to centimeters. AlN crystals with different sizes are grown by spontaneous nucleation. Furthermore, it discusses and contrasts the growth conditions and mechanisms of AlN crystals with different sizes. The structural and optical properties of the AlN crystals are also involved.

Source:IOPscience

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Growth of square Si single bulk crystals with large side-face widths using noncontact crucible method

The noncontact crucible method was used to prepare square Si single bulk crystals. The size of the square part of the ingots was determined by the side-face width of the four-cornered pattern that appeared on the top surface. We obtained square Si single crystals with sizes of 9.4 × 9.7 and 10.9 × 11.0 cm2 that had no fan-shaped {110} faces and had diagonal lengths of up to 91% of the crucible diameter. To obtain large square Si single bulk crystals with a large side-face width using the present method, the importance of establishing a larger low-temperature region in the Si melt while maintaining a smaller initial temperature reduction was considered.

Source:IOPscience

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Coefficients of sliding friction of single crystals of high explosives under different rubbing conditions

The coefficients of sliding friction of single crystals of commonly used high explosives pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitramine (RDX) and beta-cyclotetramethylene tetranitramine (β-HMX) under several rubbing configurations and at a relative sliding speed of 0.22 mm s−1 were measured. The sliding configurations were (1) crystal–polished steel pairs, (2) like-crystal pairs and (3) unlike-crystal pairs. For every rubbing configuration the friction force showed oscillations, which are thought to be caused by the formation and shearing of the adhesive junctions formed at the surface of the rubbing crystals. This shearing of the adhesive junctions led to the formation of microscopic and sub-microscopic particles, which were confirmed by an environmental scanning electron microscope study. For every rubbing configuration and for relatively high normal loads pressing the rubbing crystals together, the coefficient of friction was generally in the range 0.2–0.25 and it has been concluded that the coefficient of friction is controlled by the adhesion with almost negligible contribution from the ploughing component. From a knowledge of the coefficient of friction and the uniaxial yield stress values of single crystals of RDX and β-HMX, the shear strength of these crystals were determined to be ~13.4 MPa and ~16.8 MPa, respectively.

Source:IOPscience

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The influence of crack face electrical boundary conditions on the nonlinear behavior of ferroelectric single crystal

The nonlinear electromechanical behavior of a cracked ferroelectric single crystal subjected to pure electrical loading is investigated by a three-dimensional phase field model for different crack face electrical boundary conditions. Phase field simulations show that crack face electrical boundary conditions have significant influence on the electrical and mechanical responses of the ferroelectric single crystal to an external electric field. The coercive field for the polarization switching of a single crystal with an electrically permeable crack is about 50% larger than that for a single crystal with an electrically impermeable crack. The remanent strain and the strain variation induced by polarization switching in a single crystal with a permeable crack are larger than those with an impermeable crack. The different macroscopic nonlinear behaviors are attributed to different polarization switching processes. It is found that domain switching takes place from the surface of a single crystal with a permeable crack, while it begins from the vicinity of the crack tip when the crack is impermeable. A ferroelectric single crystal with an impermeable crack exhibits strip 90° domain switching under a negative electric field, which is consistent with experimental observation.

Source:IOPscience

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On the optical properties of undoped and rare-earth-doped yttrium aluminium garnet single crystals

Optical absorption and photoluminescence (PL) measurements were performed on single crystals of undoped Y3Al5O12 (YAG) and a number of rare-earth-doped YAG to study the effect of dopant type and concentration, growth atmosphere, post-growth annealing and UV irradiation on the optical properties of YAG crystals. The presence of hydrogen in the growth atmosphere was found to be essential for enhancing the incorporation of Ce ions in the Ce3+ state in Ce-doped YAG (Ce : YAG). Annealing in air was shown to have no effect on the PL emission of Ce : YAG crystals. An absorption peak around 256 nm was observed in the undoped YAG and Ce : YAG crystals after air anneal at 1200 °C. Optical absorption and annealing experiments support the association of the 256 nm peak with Fe impurities and oxygen ions. UV irradiation modifies the valency of impurities and generates electronic defects leading to an increase in the optical density of YAG crystals. Optimizing the growth and annealing conditions is critical in order to develop Ce : YAG single crystals as efficient scintillators.

Source:IOPscience

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Float zone single crystals for testing rods, pulled under electron beam heating

The article is devoted to the description of mathematical modelling and attempts to grow silicon single crystals from a pedestal. The crystals are intended to be used for impurity composition testing in rods with a diameter of 300 mm grown with electron beam heating. The testing is being planned both by the method of FTIR spectroscopy and by functional testing of devices that might be manufactured using single crystals grown from pedestal. The article also describes the improvements of equipment, which were necessary for crystal growth attempts, and substantial difficulties that occurred in the process and hindered single crystal growth, allowing to obtain only a polycrystalline sample.

Source:IOPscience

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Light emission from organic single crystals operated by electrolyte doping

Light-emitting devices based on electrolytes, such as light-emitting electrochemical cells (LECs) and electric double-layer transistors (EDLTs), are solution-processable devices with a very simple structure. Therefore, it is necessary to apply this device structure into highly fluorescent organic materials for future printed applications. However, owing to compatibility problems between electrolytes and organic crystals, electrolyte-based single-crystal light-emitting devices have not yet been demonstrated. Here, we report on light-emitting devices based on organic single crystals and electrolytes. As the fluorescent materials, α,ω-bis(biphenylyl)terthiophene (BP3T) and 5,6,11,12-tetraphenylnaphthacene (rubrene) single crystals were selected. Using ionic liquids as electrolytes, we observed clear light emission from BP3T LECs and rubrene EDLTs.

Source:IOPscience

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Segmentation Effect on Inhomogeneity of [110]-Single Crystal Deformation

This work presents a detailed analysis of segmentation process in FCC single crystals with compression axis [110] and side faces( ̅110) and (001) considering effect of octahedral shear crystal-geometry and basic stress concentrators. Sequence of meso-band systems formation on side faces is determined. Macro-segmentation patterns are specified, that are common to the FCC single crystals under investigation. It is proved that rectangular shape of highly compressed crystals, elongated in direction of operating planes, is conditioned by orientation symmetry of compression axis, single crystal side faces and shears directions, which are characteristic for the given orientation. The specified patterns are characteristic only for the samples with initial height-to-width ratio equal to 2. When varying sample height relative to the initial one, segmentation patterns will also vary due to crystal geometry variations.

Source:IOPscience

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Magnetic properties and spin structure of MnO single crystal and powder

Zero field cooled (ZFC)/Field Cooled (FC) magnetization curves of a bulk MnO single crystal show a peculiar peak at low temperatures (~ 40 K) similar to the low temperature peak observed in MnO nanoparticles. In order to investigate the origin of this peak, the spin structure of a MnO single crystal has been studied and compared with a single phase powder sample using magnetometry and polarized neutron scattering. Both magnetometry and polarized neutron diffraction results confirm the antiferromagnetic (AF) phase transition at the Néel temperature TN of 118 K, in both powder and single crystal form. However, the low temperature peak in the ZFC/FC magnetization curves is not observed in single phase MnO powder. To better understand the observed behavior, ac susceptibility measurements have been employed. We conclude that the clear peak in the magnetic signal from the single crystal originates from a small amount of ferrimagnetic (FiM) Mn2O3 or Mn3O4 impurities, which is grown at the interfaces between MnO crystal twins.

Source:IOPscience

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Optical non-linearities by Z-scan measurements, thermal characterization of single crystal: 8-hydroxyquinolinium 3-carboxy-4-hydroxy benzene sulfonate monohydrate

Single crystals of 8-hydroxyquinolinium 3-carboxy-4-hydroxy benzene sulfonate monohydrate were grown by slow evaporation technique at room temperature by using ethanol as solvent. Single crystal X-ray diffraction study elucidated that the crystal structure of8-hydroxyquinolinium 3-carboxy-4-hydroxy benzene sulfonate monohydrate belongs to monoclinic crystal system with space group P21/n. The solid state physical parameters have been also determined for the grown crystal from the single crystal data. The cut-off wavelength and optical band gap energy of grown crystal was found to be 420 nm and 2.67 eV respectively.Thermogravimetric and differential thermal analysis reveals that the 8-hydroxyquinolinium 3-carboxy-4-hydroxy benzene sulfonate monohydrate single crystal is thermally stable up to 144˚C without any weight loss. The mechanical properties of the grown crystal were studied by Vickers microhardness technique and it is found that 8-hydroxyquinolinium 3-carboxy-4-hydroxybenzene sulfonate monohydrate belongs to hard material category. The third order nonlinear refractive index (n2), nonlinear absorption coefficient (β) and nonlinear optical susceptibility (χ3) of the grown crystal were also measured by Z-scan studies.

Source:IOPscience

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Single Crystal growth of mixed anion Zr(P, Se)2 superconductor and related materials

A new method to grow single crystals of PbFCl-type mixed anion AP2-x Xx (A = Zr, Hf, X = S, Se) superconductor is examined. Using a wedge-type, cubic-anvil, high-pressure apparatus, single crystals of ZrP1.25Se0.75 (A = Zr, X = Se) were grain grown from nominal composition melts under a pressure of 2.0 GPa. Obtained Plate-like single crystal with approximate edge sizes of 160 × 160 × 20 μ m3 was measured on electron probe microanalysis and X-ray diffraction indicate that the as-grown boules are a single phase ZrP1.25Se0.75. Superconducting transition temperature (T c) is 6.31 K for ZrP1.25Se0.75 single crystal. It also succeeded in single crystal growth of substitution of nonmagnetic rare earth atoms for A (A = Zr) site, T c = 6.91 K was reached in the (Zr0.50Lu0.50)PSe nominal composition. In this paper, the crystal growth of these compound are also reported.

Source:IOPscience

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The growth of 122 and 11 iron-based superconductor single crystals and the influence of doping

This review focuses on the various single crystal growth techniques applied to the new class of high temperature superconductors—iron-based layered pnictides, such as the parent compounds AFe2As2 (A = Ba, Sr, Ca) (122), hole-doped A1 − xK x Fe2As2, electron/hole-doped AFe2 − xM x As2 (M = Co, Ni, Mn, Cr), isovalently doped AFe2As2 − xP x , the chalcogenides A x Fe2 − ySe2(A = K, Rb, Cs) (122), and Fe1 − δTe1 − xSe x (11). Detailed single crystal growth methods (fluxes, Bridgman, floating zone(FZ)), the associated procedures, and their impact on crystal size and quality are presented. We also discuss the influence of doping on the structure, and the electric, magnetic, and superconducting properties of these compounds by a comparative study of different growth methods.

Source:IOPscience

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Chemical mechanical polishing and nanomechanics of semiconductor CdZnTe single crystals

Cd0.96Zn0.04Te and  Cd0.9Zn0.1Te semiconductor wafers grown by the modified vertical Bridgman method with dimensions of 10 mm × 10 mm × 2.5 mm were lapped with a 2–5 µm polygonal Al2O3 powder solution, and then chemically mechanically polished by an acid solution having nanoparticles with a diameter of around 5 nm, corresponding to the surface roughnesses Ra of 2.135 nm, 1.968 nm and 1.856 nm. The hardness and elastic modulus of,Cd0.96Zn0.04Te and  Cd0.9Zn0.1Te single crystals are 1.21 GPa, 42.5 GPa; 1.02 GPa, 44.0 GPa; and 1.19 GPa, 43.4 GPa, respectively. After nanocutting is performed by the Berkovich nanoindenter, the surface roughness Ra of the Cd0.9Zn0.1Te single crystal attains a 0.215 nm ultra-smooth surface. The hardness and elastic modulus of three kinds of CdZnTe single crystals decrease with the increase of indentation load. When the nanoindenter departs the surface of the crystals, the adherence effects are obvious for the three kinds of single crystals. This is attributed to the plastic sticking behavior of CdZnTe material at a nanoscale level. When the indentation load of the three kinds of CdZnTe single crystals is in the range of 4000–12 000 µN, the adhered CdZnTe material on the nanoindenter falls onto the surface and accumulates around the nanoindentation.

Source:IOPscience

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Crystal growth and optical characterization of an organic single crystal for frequency conversion applications

Organic nonlinear optical 2-methylquinolinium L-malate single crystals have been grown by slow evaporation solution growth technique from a mixture of 2-methylqiunoline and L-malic acid in ethanol solution at ambient temperature. Single crystal X-ray diffraction analysis reveals that grown crystal in monoclinic system with non-centrosymmetric space group P21 and the lattice parameters are a = 7.35 Ǻ, b = 26.51 Ǻ, c = 10.83 Á, α = γ = 90° β = 102.95º and V = 2057.4 Ǻ3. UV-vis spectrum indicates that the crystal is transparent (75%) in the entire visible region with a cut-off wavelength of 437 nm and optical energy band gap Eg is found to be 2.71 eV. Microhardness measurement reveals the mechanical strength of the grown crystal. The photoluminescence spectrum shows the blue emission of the crystal. Laser damage threshold studies was carried out to ascertain the suitability of grown crystal for laser applications.The relative second harmonic generation efficiency of 2-methlquinolinium L-malate crystal was found to be two times greater than that of KDP.

Source:IOPscience

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Prediction of four, six or eight ears in drawn cups of single-crystal aluminum sheets

The new single crystal criterion developed by Cazacu, Revil and Chandola (2017) was implemented in a finite-element (FE) code and applied to forming of single-crystal cups of aluminum. Drawing simulations were conducted for circular single-crystal blanks of three different orientations: {100}〈001〉, {111} and [112] using the same set of parameters for the single-crystal yield criterion. A strong influence of anisotropy (single-crystal orientation) on the earing profile is found. While for the {100}〈001〉 orientation it is predicted that four ears develop, for the {111} and [112] crystal orientations six and eight ears are predicted, respectively. The FE simulation results are consistent with experimental observations of Tucker (1961). 

Source:IOPscience

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The effect of dopants on the brittle-to-ductile transition in silicon single crystals

The brittle-to-ductile transition (BDT) in boron, antimony and arsenic doped Cz silicon crystals has been experimentally studied, respectively. The BDT temperatures in antimony and arsenic doped silicon wafers are lower than that in a non-doped wafer while the BDT temperature in a boron doped wafer is almost the same as that in the non-doped wafer. The activation energy was obtained from the strain rate dependence of the BDT temperature. It was found that the values of the activation energy in the antimony and arsenic doped wafers are lower than that in the non-doped and boron doped wafers, indicating that the dislocation velocity in the antimony and arsenic doped silicon is faster than that in the non-doped while the dislocation velocity in the boron doped is the same as that in the non-doped. The effect of increasing in dislocation velocity on the BDT temperature was calculated by two-dimensional discrete dislocation dynamics simulations, indicating that the increasing in dislocation velocity decreases the BDT temperature in silicon single crystals.

Source:IOPscience

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Influence of Mn doping on CuGaS2 single crystals grown by CVT method and their characterization

1 and 2 mole% of Mn doped CuGaS2 (CGS) single crystals were grown by the chemical vapour transport (CVT) technique using iodine as the transporting agent. The analysis of the single crystal x-ray diffraction data suggests that the doping of 1 and 2 mole% Mn in the CGS single crystal does not affect the tetragonal (chalcopyrite) crystal structure. The optical absorption spectrum shows that the Mn ion induces a very strong absorption band in the UV–visible–near IR regions. The values of the crystal parameter (Dq) and the Racah parameter (B) calculated from the absorption spectra show d electron delocalization in the host crystal CGS. Room temperature photoluminescence spectra of undoped CGS only exhibited a band–band emission. But 1 and 2 mole% Mn doped CGS single crystals show two distinct CGS and Mn2+ related emissions, both of which are excited via the CGS host lattice. Raman spectra of 1 and 2 mole% Mn doped CGS single crystals exhibit a high intensity peak of the A1 mode at 310 cm−1 and 300 cm−1, respectively. EDAX, optical absorption and Raman spectrum studies reveal that Mn2+ ions are substituted in the Ga3+ ions and incorporated into the CGS lattice. The magnetization of Mn doped CGS single crystals was measured as a function of the magnetic field and temperature. Paramagnetic behaviour typical of spin S = 5/2 expected for Mn2+ (d5) magnetic centres was observed in the temperature range 2 K < T < 300 K. In Mn doping, the increase in bulk conductivity of the Mn doped CGS single crystals at room temperature indicates an increase in the hole concentration.

Source:IOPscience

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