Growth Of Large Crystals Research Articles

Large size crystal growth and structural, thermal, optical and electrical properties of KCl1−xBrx mixed crystals

Large size and high quality KCl1−xBrx mixed crystals [with x = 0.0 (pure KCl), 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0 (pure KBr)] have been grown with suitable raw material proportion by the melt (Czochralski) method using the miscible alkali halides KCl and KBr. The grown crystals have been characterized by determining their density, refractive index, lattice constant, chemical composition, thermal parameters (Debye-Waller factor, Debye temperature and Debye frequency), optical absorption, micro hardness and electrical parameters (dielectric constant, dielectric loss factor, AC, and DC electrical conductivities and AC, and DC activation energies) through X-ray diffraction, optical, mechanical and electrical (both AC and DC at various temperatures in the range 30–150 °C) measurements. Results obtained in the present study indicate that mixing KCl with KBr leads to significant tuning of thermal, optical, mechanical and electrical properties without disturbing the crystal structure. The dielectric constant is found to increase several times due to mixing and KCl0.5Br0.5 crystal has the maximum value.

Seeded Chemical Vapor Transport Growth of Cu2OSeO3

We present an optimized seeded chemical vapor transport method for the growth of Cu2OSeO3 that allows for chemical control in a system with many stable phases to selectively produce large phase-pure single crystals. This method is shown to consistently produce single crystals in the range of 120 to 180 mg. A Wulff construction model of a representative crystal shows that the minimum energy surface is {1 1 0}, followed by {1 0 0}. Analysis of the lowest index planes revealed that cleavage of Se–O bonds has a large energy cost, leading to an overall high surface energy. The seeded chemical vapor transport demonstrated here shows promise for large single crystal growth of other functional materials such as Weyl semimetals, frustrated magnets, and superconductors.

High pressure floating-zone growth and property characterization of Cr-doped hexagonal YMnO3 crystals

Large crystal growth of Cr-doped h-YMnO3 has been investigated by using a high pressure optical floating-zone method. The size of the grown crystals is typically 60–70mm in length and 4–5mm in diameter. The structure of the grown crystals is analyzed by powder X-ray diffraction and scanning electron microscopy. The defects in the as-grown crystals, including low-angle grain boundary and inclusions are studied. An off-stoichiometric phenomenon is found with a slight Cr deficiency in different parts. The relationship between defects and growth conditions during crystal growth is also discussed. The magnetic properties show spin-glass phase features with weak ferromagnetic behavior below 30K.

Preliminary neutron diffraction analysis of challenging human manganese superoxide dismutase crystals.

Superoxide dismutases (SODs) are enzymes that protect against oxidative stress by dismutation of superoxide into oxygen and hydrogen peroxide through cyclic reduction and oxidation of the active-site metal. The complete enzymatic mechanisms of SODs are unknown since data on the positions of hydrogen are limited. Here, methods are presented for large crystal growth and neutron data collection of human manganese SOD (MnSOD) using perdeuteration and the MaNDi beamline at Oak Ridge National Laboratory. The crystal from which the human MnSOD data set was obtained is the crystal with the largest unit-cell edge (240 Å) from which data have been collected via neutron diffraction to sufficient resolution (2.30 Å) where hydrogen positions can be observed.

Method development for the synthesis of large crystals of pyromorphite

In the UK, water utilities add phosphate to drinking water in order to prevent lead being released from older properties that are supplied by lead water pipes. The mechanism of reduction is thought to involve the formation of insoluble lead phosphates. This research was carried out to optimise the growth of large lead apatite crystals for use in future atomic force microscopy work. In this case study, pyromorphite crystals exhibiting both prismatic hexagonal and needle-like structures with sizes up to 0.2mm were successfully grown using a caesium chloride flux. They were produced both at lower temperatures and in less time than previous studies. All samples were characterised using a variety of analytical techniques such as X-ray diffraction, infrared spectrometry, energy dispersive X-ray analysis, scanning electron microscopy and thermogravimetric analysis.

Improved lithium iodide neutron scintillator with Eu2+ activation: The elimination of Suzuki-Phase precipitates

Monovalent alkali halides such as NaI, CsI, and LiI are widely used as inorganic scintillators for radiation detection due to their light yield, the capability for the growth of large single crystals, relatively low cost, and other favorable characteristics. These materials are frequently activated through the addition of small amounts (e.g., a few hundred ppm) of elements such as thallium - or sodium in the case of CsI. The monovalent alkali halide scintillators can also be activated with low concentrations of Eu2+, however Eu activation has previously not been widely employed due to the non-uniform segregation of the divalent Eu dopant that leads to the formation of unwanted phases during Bridgman or other solidification crystal-growth methods. Specifically, for Eu concentrations near and above ~0.5%, Suzuki Phase precipitates form in the course of the melt-growth process, and these Suzuki Phase particles scatter the scintillation light. This adversely affects the scintillator performance via reduction in the optical transmission of the material, and depending on the crystal thickness and precipitated-particle concentration, this reduction can occur up to the point of opacity. Here we describe a post-growth process for the removal of Suzuki Phase precipitates from single crystals of the neutron scintillator LiI activated with Eu2+ at concentrations up to and in excess of 3wt%, and we correlate the resulting neutron-detection performance with the thermal processing methods used to remove the Suzuki Phase particles. The resulting improved scintillator properties using increased Eu activator levels are applicable to neutron imaging and active interrogation systems, and pulse-height gamma-ray spectroscopy rather than pulse-shape discrimination can be used to discriminate between gamma ray and neutron interaction events.

Black Phosphorus Quantum Dots for Hole Extraction of Typical Planar Hybrid Perovskite Solar Cells.

Black phosphorus, famous as two-dimensional (2D) materials, shows such excellent properties for optoelectronic devices such as tunable direct band gap, extremely high hole mobility (300-1000 cm2/(V s)), and so forth. In this Letter, facile processed black phosphorus quantum dots (BPQDs) were successfully applied to enhance hole extraction at the anode side of the typical p-i-n planar hybrid perovskite solar cells, which remarkably improved the performance of devices with photon conversion efficiency ramping up from 14.10 to 16.69%. Moreover, more detailed investigations by c-AFM, SKPM, SEM, hole-only devices, and photon physics measurements discover further the hole extraction effect and work mechanism of the BPQDs, such as nucleation assistance for the growth of large grain size perovskite crystals, fast hole extraction, more efficient hole transfer, and suppression of energy-loss recombination at the anode interface. This work definitely paves the way for discovering more and more 2D materials with high electronic properties to be used in photovoltaics and optoelectronics.

Two‐Step Sequential Deposition of Organometal Halide Perovskite for Photovoltaic Application

Organometal halide perovskite materials have become a superstar in the photovoltaic (PV) field because of their advantageous properties, which boost the power conversion efficiency (PCE) of perovskite solar cells (PSCs) from about 3.8% to above 22% in just seven years. Most importantly, such promising achievement is mainly based on its low‐cost and solution‐processed fabrication technique. One of the most promising and famous approaches to fabricating perovskite is a two‐step sequential deposition method because precursor (e.g., PbI2) deposition is controllable, versatile, and flexible. Due to tremendous efforts, great progress has been achieved on the two‐step sequential deposition method, which helps to promote the development of PSCs. Herein, the progresses on the two‐step sequential deposition method of perovskite layers is reviewed thoroughly. At first, the reaction process and principle is introduced and discussed. Then, the research on the deposition techniques, structures, and compositions of precursors (the first step) is presented. Subsequently, the developments on the conversion techniques, conversion solutions, and growth of large crystals at the second step are introduced. Finally, four important issues on the two‐step sequential deposition method will be stated, accompanied with proposed solutions.

Synthesis of PdS/ZnS--CdS-type photocatalysts using ZnS as sulphide source

In this work, a new method for the growth of large CdS crystals into PdS/ZnS--CdS-type photocatalysts is presented. In order to accomplish this, in the first stage zinc sulphide was synthesised and hydrothermally crystallised. In the second stage, after PdS decoration, the recrystallised zinc sulphide was utilised as sulphur source for the synthesis of PdS/ZnS--CdS-type photocatalysts. The photocatalysts were characterised by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, and diffuse reflectance spectroscopy. In the third stage magnetic polymer supports were manufactured and loaded with photocatalyst. Finally photocatalysis experiments under blue light illumination were conducted for the hydrogen evolution reaction in the presence of sulphite and sulphide ions on both suspension and polymer supported photocatalysts. The photocatalysts' efficiency increased by about 70% along with the PdS quantity increase from 0.11% to 0.89%. The use of magnetic polymer may be a solution for reducing the costs necessary to maintain the photocatalysts in suspension.

Crystal growth of the triangular-lattice antiferromagnet Ba3CoSb2O9

We report growth of large single crystals of the triangular-lattice antiferromagnetic compound Ba3CoSb2O9 by the floating-zone technique in an image furnace. Evaporation of Sb due to its high volatility was controlled by high pressure and addition of excess Sb in the starting materials to compensate for the losses. The crystal quality was analysed using different X-ray techniques, and the magnetic transition temperature was confirmed by magnetization and heat capacity measurements.

ChemInform Abstract: Deep Ultraviolet Nonlinear Optical Materials

AbstractReview: 185 refs.

Cathode Design for High Energy Molten Salt Lithium-Oxygen Batteries

State of the art commercial lithium ion batteries use cathodes such as lithium cobalt oxide which rely on insertion and removal of lithium ions from a host material. However, insertion cathode materials are limited in their capacity, and replacing them with a cathode that employs growth and dissolution of new phases could significantly increase a battery’s energy density. For example, oxygen and sulfur cathodes have been widely researched to this end, with both cases involving the growth of a lithium-rich compound on a current collector/catalyst support. While the lithium-oxygen battery is promising with regard to its energy density, there are many practical challenges that remain to be solved. For instance, traditional organic electrolytes decompose in the presence of superoxide anions, intermediates in the growth of the lithium peroxide discharge product. However, by replacing the organic electrolyte with a molten salt, we can inherently avoid this organic electrolyte decomposition. In addition, the use of a molten salt electrolyte results in a system operating at elevated temperature with a large concentration of lithium ions, encouraging faster diffusion and kinetics. The morphology of the lithium peroxide grown in this molten salt lithium-oxygen battery is notably different from that previously observed in literature. While previous works have observed thin films, platelets, and “toroids” on the order of several hundred nanometers, we observe much larger (several micron) structures which appear to be stacks of hexagonal layers. We believe these stacks to be a new morphology of lithium peroxide growth. These new lithium peroxide morphologies are characterized with SEM, EDS, and XRD. In addition to the lithium-oxygen system described above, we introduce another phase-forming chemistry, whereby a molten nitrate salt serves as both an active material and the electrolyte. Molten nitrate salts have been previously studied as an active material in a primary lithium battery where lithium oxide irreversibly forms as nitrate converts to nitrite. We will describe how the use of a nanoparticle heterogeneous catalyst allows the reversible growth and dissolution of large (several micron) lithium oxide crystals in this system, as substantiated by SEM, XRD, and TEM. After introducing these molten salt lithium batteries, we address the effect of cathode geometry on the discharge capacity. In particular, we note that the growth of such large, solid phase species on the surface of the catalyst support imposes new design restrictions when optimizing a cathode for energy density. For instance, it is not just the surface area of the catalyst support that determines the discharge capacity, but also the amount of usable pore volume to allow this solid phase discharge product to form. As a proof of concept, we design and implement an architected electrode with large pore volume and relatively small surface area. Such cathode design principles could be extended to other phase-forming chemistries.

Large single crystal growth of MnWO4-type materials from high-temperature solutions

A simple high-temperature growth apparatus was constructed to obtain large crystals of chemically gradient (In, Na)-doped MnWO4solid-solutions. This paper presents the crystal growth and characterisation of both MnWO4and epitaxially grown (In, Na): MnWO4crystals on MnWO4. These large monolithic crystals were made in two steps: A MnWO4 crystal was grown in the crystallographic main direction [001] applying the Czochralski method, followed by the top seeded growth of (In, Na): MnWO4 solid-solutions with an oriented seed crystal of MnWO4. Such a monolithic crystal will serve to fundamental investigation of coupling properties at boundaries between various multiferroic MnWO4-typesolid-solutions.

Deep Ultraviolet Nonlinear Optical Materials

Deep ultraviolet (absorption edge 6.2 eV) nonlinear optical (NLO) materials are of current interest owing to their technological applications and materials design challenges. Technologically, the materials are used in laser systems, atto-second pulse generation, semiconductor manufacturing, and photolithography. Designing and synthesizing a deep UV NLO material requires crystallographic non-centrosymmetry, a wide UV transparency range, a large second-harmonic generating coefficient (dij > 0.39 pm/V), moderate birefringence (Δn ∼ 0.07), chemical stability and resistance to laser damage, and ease in the growth of large high-quality single crystals. This review examines the known deep UV NLO materials with respect to their crystal structure, band gap, SHG efficiency, laser damage threshold, and birefringence. Finally, future directions with respect to new deep UV NLO materials are discussed.

Arrays of Pentacene Single Crystals by Stencil Evaporation

In order to realize high-performance organic thin-film transistors (TFT), two parameters of the organic semiconducting layer are desired: single crystallinity for high mobility and patterning for low off currents. High-quality single crystals can be fabricated using vapor techniques such as physical vapor transport (PVT), but they require high temperatures close to thermodynamic equilibrium, for example, 240 °C for pentacene. Such high temperatures are not ideal for TFT fabrication on plastic substrates and limit the use of PVT in flexible electronics applications. In this work arrays of pentacene single crystals were directly deposited at low temperature of 40 °C by vacuum thermal evaporation through microfabricated stencil masks (stencil lithography). By decreasing the stencil aperture size down to 1 μm × 1 μm, we were able to limit the nucleation area until only one grain per aperture is nucleated and grown. We studied systematically scaling effects for large singe crystal growth and discuss details of...

Isothermal crystallization kinetics of talc-filled poly(lactic acid) and poly(butylene succinate) blends

Blends comprising poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and talc were prepared via a solution casting method. The weight ratios of PLA to PBS (PLA/PBS) blends were 80:20 and 60:40, whereas the talc content was varied from 0 to 5.0 parts per hundred resin (phr). The crystallization halftime (t 1/2) of PLA/PBS (80:20) at 80 °C was higher than those of neat PLA, PBS, and PLA/PBS (60:40); this is due to its high PLA content. The t 1/2 value for neat PLA at 90 °C decreased when the talc content was increased, whereas the value for neat PBS gradually increased. These phenomena can be seen more clearly at 95 and 100 °C. This means that talc not only promotes PLA crystallization but also acts as a crystallization inhibitor for PBS. The isothermal crystallization kinetics and spherulitic morphology of these samples were investigated. The extent of talc loading showed a strong dependence on the isothermal crystallization rate and the extent of PLA crystallinity, whereas the contrary effect was observed for PBS due to the growth of large crystals. This suggests that talc not only promotes the crystallization of PLA but also inhibits the crystallization of PBS. The results are in agreement with the crystallization halftime and polarized optical microscopy analysis.

Growth and physical properties of large MoO3 single crystals

Molybdenum trioxide (MoO3) is an interesting material for smart windows, electrodes for batteries, and gas sensors. So far, it is known that the growth of large single crystal of MoO3 is elusive because of the rapid changing of activation energy at 650 °C. Small MoO3 crystals can be made by sublimation. In this study, we successfully grew large MoO3 single crystals through the modified vertical Bridgman method, which can prevent the sublimation of MoO3. Similar structural and optical properties were measured like those of nano/micro-crystalline MoO3. This study can provide evidence to contribute to the creation of large single crystals, which have a lower sublimation temperature than melting temperature.

Sublimation Growth of 4 and 6 Inch 4H-SiC Low Defect Bulk Crystals in Ta (TaC) Crucibles

Recently, the wide bandgap semiconductors, especially silicon carbide (SiC), have become more important due to the unique electrical and thermophysical properties that make them applicable to a variety of electronic devices (Schottky and PiN diodes, JFETs, MOSFETs, etc.). For these applications, the crystals need to be manufactured with highest possible quality, both structural and chemical, at reduced cost. This requirement places rather extreme constraints on the crystal growth as the simultaneous goals of high quality and low cost are generally incompatible.Refractory metal carbide technology, particularly, tantalum carbide (TaC), was originally developed for application in highly corrosive and reactive environments. Yu. Vodakov [1] demonstrated for the first time advantages of use of refractory metal carbides for PVT growth of SiC and later AlN bulk crystals. In the present paper we discuss the effect of refractory metal on PVT growth of large diameter 4H SiC bulk crystals.

Growth of 2 Inch Eu-doped SrI2 single crystals for scintillator applications

A vertical Bridgman (VB) crystal growth process was established using modified micro-pulling-down (μ-PD) crystal growth system with a removable chamber that was developed for the growth of deliquescent halide single crystals because conventional μ-PD method does not allow growth of large bulk single crystals. Eu:SrI2 crystals were grown from the melt of (Sr0.98Eu0.02)I2 composition using carbon crucibles. Undoped μ-PD SrI2 crystals were used as seeds that were affixed to the bottom of the crucible. All the preparations preceding the growths and the hot zone assembling were performed in a glove box with Ar gas. Then the removable chamber was taken out of the glove box, attached to the μ-PD system, connected with a Turbo Molecular pump, and evacuated down to 10−4Pa at ~300°C. After the baking procedure, high purity Ar gas (6N) was injected into the chamber. The crucible was heated by a high frequency induction coil up to the melting point of Eu:SrI2. After melting the starting materials, the crucible was displaced in downward direction for the crystal growth and then cooled down to room temperature. Thus, 2in. and crack-free Eu:SrI2 bulk crystals were produced. The crystals had high transparency and did not contain any visible inclusions. The crystals were cut and polished in the glove box and then sealed in an aluminum container with an optical window for characterization. The details of the crystal growth are discussed.

Large Ti-doped sapphire single crystals grown by the kyropoulos technique for petawatt power laser application

Large diameter Ti-doped sapphire single crystals were grown by the Kyropoulos technique. The optical characterizations (luminescence, transmittance, evaluation of the FOM) of these bulk crystals are presented. The presented results are promising for the growth of large Ti-doped sapphire crystals by Kyroupolos technology for petawatt scale amplifier.