High Growth Temperature Research Articles

Growth and characterization of novel piezo-/ferroelectric single crystals from the PSN-BS-PT ternary system

Bismuth-based single crystals with the nominal composition of 0.1Pb(Sc1/2Nb1/2)O3-0.315BiScO3-0.585PbTiO3 (0.1PSN-0.315BS-0.585PT) ternary complex perovskite system were successfully grown using a high-temperature solution growth (HTSG) method. A mixture of PbO and Bi2O3 in a molar ratio of 73:27 was used as flux, and the flux to charge ratio was optimized to be 70:30 (wt%). The grown crystals, with dimensions up to 3 mm, exhibit a pseudo-cubic morphology. The XRD patterns of the ground powder and naturally formed pseudo-cubic facets confirm that the grown single crystals crystallize in the perovskite structure with the rhombohedral symmetry as the major phase, and the naturally grown pseudo-cubic facets are parallel to {100}C. The domain structures in the (001)-oriented single crystals examined by polarized light microscopy (PLM) and optical crystallography reveal the coexistence of rhombohedral and monoclinic phases in majority, with the presence of a minor tetragonal phase likely grown at the late stage of the growth, demonstrating the morphotropic phase boundary (MPB) characteristics for the grown crystals. Upon heating, phase transition from the major rhombohedral and monoclinic to the cubic phase take place at TC = 370 °C. The ferroelectric properties are displayed by polarization-electric field (P-E) hysteresis loops with a remanent polarization of 17 µC/cm2 and a high coercive field of 68 kV/cm. The piezoelectric coefficient (d33) is found to be 478 pC/N. The high Curie temperature and decent piezo- and ferroelectric performance of the PSN-BS-PT crystals make this ternary complex perovskite system a promising candidate for potential applications in high-temperature and high-power electromechanical transduction.

Effects of environmental temperature during maturation on protein characteristics in spring wheat (Triticum aestivum cv. Haruyokoi)

Wheat (Triticum aestivum cv. Haruyokoi) gluten proteins are important contributors to wheat flour quality. Numerous studies have examined the effects of heat stress on gluten proteins. We clarified the relationship between growth temperature and the characteristics of storage proteins in spring wheat grown under mild conditions (<30 °C). As the growth temperature increased, crude protein content also increased and the activity of protein disulfide isomerase (PDI), which is involved in the folding and transport of gluten proteins, decreased. The growth temperature also affected the amount of aggregated storage proteins, with an increase in sodium dodecyl sulfate (SDS)-insoluble proteins observed under high-temperature conditions. From these results, it was inferred that high growth temperatures caused an environment where nonspecific aggregation is likely to occur. The accumulation of specific proteins was also affected. The high-molecular-weight glutenin subunit (HMW-GS) Dx5 encoded by Glu-D1d allele, which has a marked impact on the viscoelastic properties of dough characteristics, showed high accumulation under high growth temperatures. These effects of growth temperature on storage proteins appear to affect the formation of glutenin macropolymer, which in turn affects the physical properties of the dough. As global warming continues, this study could provide helpful information for long-term predictions of wheat quality.

GeSn-on-GaAs with photoconductive carrier lifetime >400 ns: role of substrate orientation and atomistic simulation.

Group IV GeSn quantum material finds application in electronics and silicon-compatible photonics. Synthesizing these materials with low defect density and high carrier lifetime is a potential challenge due to lattice mismatch induced defects and tin segregation at higher growth temperature. Recent advancements in the growth of these GeSn materials on Si, Ge, GaAs, and with substrate orientations, demonstrated different properties using epitaxial and chemical deposition methods. This article addresses the effect of GaAs substrate orientation and misorientation on the materials' properties and carrier lifetimes in epitaxial Ge0.94Sn0.06 layers. With starting GaAs substrates of (100)/2°, (100)/6°, (110) and (111)A orientations, Ge0.94Sn0.06 epitaxial layers were grown with an intermediate Ge buffer layer by molecular beam epitaxy and analyzed by several analytical tools. X-ray analysis displayed good crystalline quality, and Raman spectroscopy measurements showed blue shifts in phonon wavenumber due to biaxial compressive strain in Ge0.94Sn0.06 epilayers. Cross-sectional transmission electron microscopy analysis confirmed the defect-free heterointerface of Ge0.94Sn0.06/Ge/GaAs heterostructure. Minority carrier lifetimes of the unintentionally doped n-type Ge0.94Sn0.06 epilayers displayed photoconductive carrier lifetimes of >400 ns on (100)/6°, 319 ns on (100)/2°, and 434 ns on (110) GaAs substrate at 1500 nm excitation wavelength. On the other hand, Ge0.94Sn0.06 layer showed poor carrier lifetime on (111)A GaAs substrate. The observed differences in carrier lifetimes were correlated with the formation energy of the Ge on (100)/6° and (100)/2° GaAs heterointerface using Stillinger-Weber interatomic potential model-based atomistic simulation with different heterointerfacial bonding by Synopsys QuantumATK tool. Total energy computation of 6280-atom Ge/GaAs supercell on (100)/6° leads to lower formation energy than (100)/2°, making it more thermodynamically stable. Hence, the growth of the GeSn/III-V material system using misoriented (100) substrates that are more thermodynamically stable will enhance the performances of optoelectronic devices.

Morphologies and magnetic properties of α-Fe2O3 nanoparticles calcined at different temperatures.

Different morphologies and sizes of α-Fe2O3 were prepared by a coprecipitation method using polyvinylpyrrolidone as a dispersant. In the preparation process, homogeneous and dispersed nanoscale FeOOH particles were first obtained by the coprecipitation method, and then the FeOOH particles were calcined at high temperature to form α-Fe2O3. The growth and aggregation of the α-Fe2O3 particles at different calcination temperatures resulted in α-Fe2O3 powders with diversiform morphologies (nanoscale microsphere, pinecone ellipsoidal, polyhedral, and quasi-spherical structures). By analyzing the SEM images, it was inferred that the polyhedral structure of α-Fe2O3 particles was formed by the accumulation of rhomboid sheet structures and high-temperature growth. In terms of the magnetic properties, the samples belonged to the class of canted antiferromagnetic materials, and the morphology, particle size, and crystallite size of the α-Fe2O3 particles were important factors affecting the coercivity. Among these, when the calcination temperature was increased from 700 °C to 800 °C, the growth rate of the particle size was significantly faster than that of the crystallite size, and the coercivity increased substantially from 1411 Oe to 2688 Oe.

Salt-inclusion chalcogenides with d-orbital components: unveiling remarkable nonlinear optical properties and dual-band photoluminescence.

Metals containing d-orbitals are typically characterized by strong deformation and polarization, yet they tend to induce narrow bandgaps that render them little-appreciated by high-power nonlinear optical (NLO) crystals. Incorporating highly electropositive polycations into d-orbital-containing chalcogenides to modify them into salt-inclusion chalcogenides (SICs) that are competitive in NLO materials, is a viable solution to this predicament. In the present work, two isostructural SICs [K4Cl][MGa9S16] (M = Mn, 1; Hg, 2) are successfully synthesized by the high-temperature molten-salt growth method. Both compounds demonstrate commendable second-harmonic-generation (SHG) responses (0.6-1.0 × AgGaS2 @1910 nm), which can be attributed to their well-designed [MGa9S16]3- anionic frameworks; and compound 2 exhibits the widest optical bandgap (3.41 eV) among the Hg-based NLO chalcogenides. Also, an interesting dual-band photoluminescence emission centered at ∼650 and ∼718 nm is detected in 1 at 77 K, with long lifetimes of 0.94 and 1.35 ms, respectively.

Molecular dynamics simulation of effect of nickel transition layer on deposition of carbon atoms and graphene growth on cemented carbide surfaces

&lt;sec&gt;WC-Co cemented carbide has excellent cutting performance, which is a potential tool material. But when it is used as cutting ultra-high strength and high hardness materials, the machining accuracy and service life of the tool are significantly reduced. Graphene is a potential coating material for cemented carbide cutting tools due to its excellent mechanical properties. In this work, molecular dynamics (MD) is used to simulate the deposition of nickel transition layer and high-temperature catalytic growth of graphene in cemented carbide. The Ni and C atomic deposition process and the high temperature annealing process are simulated, and a combination of potential functions is adopted to continuously simulate these two deposition processes. The effect of deposition temperature and the effect of incident energy on the growth of graphene are analyzed. The healing mechanism of nickel-based catalytic defective graphene under high-temperature annealing is explored in detail.&lt;/sec&gt;&lt;sec&gt;The simulation results show that at the deposition temperature of 1100 K, the coverage of graphene is higher and the microstructure is flat. The higher temperature helps to provide enough kinetic energy for carbon atoms to overcome the potential energy barrier of nucleation, thereby promoting the migration and rearrangement of carbon atoms and reducing graphene growth defects. Too high a temperature will lead to continuous accumulation of carbon atoms on the deposited carbon rings, forming a multilayered reticulation and disordered structure, which will cause a low coverage rate of graphene. The increase of incident energy helps to reduce the vacancy defects in the film, but excessive energy leads to poor continuity of the film, agglomeration, the more obvious stacking effect of carbon atoms and the tendency of epitaxial growth. When the incident energy is 1 eV, the surface roughness of the film is lower, and more monolayer graphene can be grown. During annealing at 1100 K, the carbon film dissolves and nucleates simultaneously in the Ni transition layer, and the nickel transition layer catalyzes the repair of defective graphene. The graphene film becomes more uniform, and the number of hexagonal carbon rings increases. Appropriate high-temperature annealing can help to repair and reconstruct defective carbon rings and rearrange carbon chains into rings. Therefore, when the deposition temperature is 1100 K and the incident energy is 1 eV, graphene can be deposited and annealed to grow a high-quality graphene coatings. The simulation results provide the reference for preparing the cemented carbide graphene coated tools.&lt;/sec&gt;

Flux growth and characterization of gallium-rare earth borates

YGa3(BO3)4 single crystals were grown from a K2Mo3O10-based flux, and also RGa3(BO3)4 (R = Y, Pr–Yb) spontaneous crystals (RGB) were obtained by a high-temperature flux growth technique from a complex R2O3–Bi2O3–B2O3–Ga2O3 solvent.

Bright and Stable Yellow Quantum Dot Light-Emitting Diodes Through Core-Shell Nanostructure Engineering.

Solution-processed and efficient yellow quantum dot light-emitting diodes (QLEDs) are considered key optoelectronic devices for lighting, display, and signal indication. However, limited synthesis routes for yellow quantum dots (QDs), combined with inferior stress-relaxation of the core-shell interface, pose challenges to their commercialization. Herein, a nanostructure tailoring strategy for high-quality yellow CdZnSe/ZnSe/ZnS core/shell QDs using a "stepwise high-temperature nucleation-shell growth" method is introduced. The synthesized CdZnSe-based QDs effectively smoothed the release stress of the core-shell interface and revealed a near-unit photoluminescence quantum yield, with nonblinking behavior and matched energy level, which accelerated radiative recombination and charge injection balance for device operation. Consequently, the yellow CdZnSe-based QLEDs exhibited a peak external quantum efficiency of 23.7%, a maximum luminance of 686050cdm-2, and a current efficiency of 103.2cdA-1, along with an operating half-lifetime of 428523h at 100cdm-2. To the best of the knowledge, the luminance and operational stability of the device are found to be the highest values reported for yellow LEDs. Moreover, devices with electroluminescence (EL) peaks at 570-605nm exhibited excellent EQEs, surpassing 20%. The work is expected to significantly push the development of RGBY-based display panels and white LEDs.

Investigation of the CdZnTe (2 1 1) and (1 3 3) films grown on GaAs (2 1 1) controlled by temperature: Experiment and first-principles calculations

The origin and evolution of dual epitaxy in CdZnTe epilayer grown on GaAs substrates by close spaced sublimation has been studied, both (211) and (133) films are suitable for HgCdTe growth. And the effect of growth temperature on the orientation and crystalline quality of CdZnTe films has been investigated, more uniform orientation of adjoining growth islands in the growth of (133) film leads to a smoother surface with less threading dislocations and roughness. The interfacial properties of CdZnTe films were studied by the first-principles calculations combined with scanning transmission electron microscopy observations. By calculation the work of adhesion between the CdTe films and GaAs (211), obtain the CdTe (211)/GaAs (211) interface is the more stable interface structure at the initial nucleation stage. Combining to the results of experiment, at higher growth temperature, only (133) nucleus can reach the critical size and thus stabilize the growth. More importantly, the results on the dual epitaxy of CdZnTe films are expected to play a crucial role in guiding the dual epitaxy growth of other zincblende-type crystal.

Modulating microstructure and thermal properties of diamond/SiNx/GaN multilayer structure by diamond growth temperature

Numerous growth conditions affect thermal properties in diamond/SiNx/GaN multilayer structures, where diamond growth temperature is an important parameter and has not been adequately studied in the past. This article studies the relationship between the microstructure and thermal properties of diamond/SiNx/GaN multilayer structures under different diamond growth temperatures (740 °C–860 °C). The thermal boundary resistance of the diamond/GaN (TBReff, Dia/GaN) and thermal conductivity of the diamond (kDiamond) are measured using transient thermoreflectance (TTR). The lowest TBReff, Dia/GaN and highest kDiamond are achieved simultaneously at a growth temperature of 800 °C, and the difference in TBReff, Dia/GaN and kDiamond at different temperatures is up to 3–4 times. At the low growth temperature (740 °C), the thick transition layer is formed due to the insufficient ability of etching amorphous carbon and a significant carbon diffusion, resulting in significantly increased TBReff, Dia/GaN. At the high growth temperature (860 °C), the lattice distortion of GaN at the interface and the graphite phase in the transition layer contributed to the increase of TBReff, Dia/GaN. The thin diamond layer thickness and secondary nucleation result in low kDiamond except for 800 °C. The device simulation using the experimental kDiamond and TBReff, Dia/GaN at 800 °C predicts a 23 % reduction in maximum device temperature (Tmax) when the surface of GaN HEMTs is grown with a thin diamond layer.

Nucleation Selectivity and Lateral Coalescence of GaAs over Graphene on Ge(111).

We use epitaxial lateral overgrowth (ELO) to produce semimetallic graphene nanostructures embedded in a semiconducting GaAs matrix for potential applications in plasmonics, THz generation and detection, and tunnel junctions in multijunction solar cells. We show that (1) the combination of low sticking coefficient and fast surface diffusion on graphene enhances nucleation selectivity at exposed regions of the substrate and (2) high growth temperatures favor efficient lateral overgrowth, coalescence, and planarization of epitaxial GaAs films over the graphene nanostructures. Our work provides a more complete understanding of ELO using graphene masks, as opposed to more conventional dielectric masks, and enables new types of metal/semiconductor nanocomposites.

2D-Material-Assisted GaN Growth on GaN Template by MOCVD and Its Exfoliation Strategy.

The production of freestanding membranes using two-dimensional (2D) materials often involves techniques such as van der Waals (vdW) epitaxy, quasi-vdW epitaxy, and remote epitaxy. However, a challenge arises when attempting to manufacture freestanding GaN by using these 2D-material-assisted growth techniques. The issue lies in securing stability, as high-temperature growth conditions under metal-organic chemical vapor deposition (MOCVD) can cause damage to the 2D materials due to GaN decomposition of the substrate. Even when GaN is successfully grown using this method, damage to the 2D material leads to direct bonding with the substrate, making the exfoliation of the grown GaN nearly impossible. This study introduces an approach for GaN growth and exfoliation on 2D material/GaN templates. First, graphene and hexagonal boron nitride (h-BN) were transferred onto the GaN template, creating stable conditions under high temperatures and various gases in MOCVD. GaN was grown in a two-step process at 750 and 900 °C, ensuring exfoliation in cases where the 2D materials remained intact. Essentially, while it is challenging to grow GaN on 2D material/GaN using only MOCVD, this study demonstrates that with effective protection of the 2D material, the grown GaN can endure high temperatures and still be exfoliated. Furthermore, these results support that vdW epitaxy and remote epitaxy principle are not only possible with specific equipment but also applicable generally.

A systematic study on the efficacy of low-temperature GaN regrown on p-GaN to suppress Mg out-diffusion

Embedding p-type gallium nitride (p-GaN) in AlxGa1-xN-based thin films has garnered significant interest as a versatile structure for bandgap engineering such as tunnel/super-junctions or current blocking/guiding functions in electronic devices. However, Mg, a p-GaN dopant, has an undesirable diffusive capacity into the nearby thin films at a high growth temperature (&amp;gt;1,000°C), resulting in structural challenges in device design. This study systematically investigated the low-temperature GaN (LT-GaN) layer regrown on p-GaN that suppresses Mg diffusion according to metal–organic chemical vapor deposition growth conditions. Prototype Al0.3Ga0.7N (40 nm)/GaN (140 nm) high-electron-mobility transistors (HEMTs) were regrown with LT-GaN on p-GaN (300 nm), and a high two-dimensional electron gas (2DEG) density of 3.13E12 cm−2 was achieved by inserting a 100-nm-thick LT-GaN layer grown at 750°C; in contrast, only 1.76E10 cm−2 2DEG density was obtained from Al0.3Ga0.7N/GaN HEMTs regrown directly on p-GaN (Mg: 4.0E19 cm−3). The fabricated Al0.3Ga0.7N/GaN HEMTs with 100-nm-thick LT-GaN demonstrated a high drain current density of 84.5 mA/mm with a low on-state resistance of 31 Ω·mm. The AlxGa1-xN/LT-GaN/p-GaN platform demonstrated here paves the way for various III-nitride-based structures with embedded p-GaN.

High growth rate magnetron sputter epitaxy of GaN using a solid Ga target

Magnetron sputter epitaxy (MSE) is a promising processing route for group-III nitride semiconductors, with the potential to enable high-quality and low cost GaN growth for widespread use. However, fundamental technological hurdles must be overcome to enable the adoption of MSE in industrial production. Here, we present a new UHV-compatible magnetron design with high-performance cooling, enabling high GaN growth rates at high growth temperatures using a solid Ga target. The magnetron is tested with a wide range of process parameters and a stable process is feasible while maintaining the solid state of the Ga target. High GaN growth rates of up to 5 μm/h are achieved at room temperature and a growth rate of 4 μm/h at high temperature, which is one order of magnitude higher compared to MSE with a liquid target. We grow GaN on c-plane sapphire substrates and show the impact of partial pressure ratio and target-to-substrate distance (TSD) on growth rate, film morphology and crystal quality of GaN films with scanning electron microscopy and X-ray diffraction. While the growth rate and film morphology are strongly impacted by the process parameter variation, the crystal quality is further impacted by the overall film thickness. For a 2 μm thick GaN film a full width at half maximum of X-ray rocking curve (ω-FWHM) of GaN 10 1‾ 1 reflection of 0.32° is achieved. We demonstrate a process window for growth of dense and smooth GaN films with high crystal quality using low N2 flow rates and high TSD. By introducing a 20 nm AlN nucleation layer prior to the growth of 390 nm GaN, the ω-FWHM of GaN 0002 reflection of 0.19° is achieved. The epitaxially grown crystalline structure is precisely examined by transmission electron microscopy.

Atmospheric-pressure CVD-grown h-BN for the detector with deep ultraviolet response

Hexagonal boron nitride (h-BN) has a wide range of applications, especially as a protective coating, dielectric layer/substrate, transparent film, or deep ultraviolet detectors. High-quality h-BN thick films are indispensable for practical deep-ultraviolet (DUV) photodetector applications. However, the controlled synthesis of h-BN films in terms of thicknesses and crystallinity often requires high growth temperatures, low pressures, and catalytic transition metal substrates, which will ultimately hinder their applicability. In this work, we conducted a detailed study of h-BN films with thickness ranging from 50 nm to 160 nm directly synthesized by chemical vapor deposition (CVD) on SiO2/Si substrate under atmospheric pressure. The synthesized h-BN is clean, uniform, and exhibits excellent optical and photoelectrical properties for ultraviolet light in the range of 210 nm-280 nm. This sensitive h-BN photodetector has a high repulsion rate (R220nm/R280nm > 102 and R220nm/ R290nm > 103), a large detection rate (2.8 × 1010 Jones). This work presented here demonstrates the great potential of this h-BN thick film for the development of DUV photodetectors.

Leaf thermal safety margins decline at hotter temperatures in a natural warming 'experiment' in the Amazon.

The threat of rising global temperatures may be especially pronounced for low-latitude, lowland plant species that have evolved under stable climatic conditions. However, little is known about how these species may acclimate to elevated temperatures. Here, we leveraged a strong, steep thermal gradient along a natural geothermal river to assess the ability of woody plants in the Amazon to acclimate to elevated air temperatures. We measured leaf traits in six common tropical woody species along the thermal gradient to investigate whether individuals of these species: acclimate their thermoregulatory traits to maintain stable leaf temperatures despite higher ambient temperatures; acclimate their photosynthetic thermal tolerances to withstand hotter leaf temperatures; and whether acclimation is sufficient to maintain stable leaf thermal safety margins (TSMs) across different growth temperatures. Individuals of three species acclimated their thermoregulatory traits, and three species increased their thermal tolerances with growth temperature. However, acclimation was generally insufficient to maintain constant TSMs. Notwithstanding, leaf health was generally consistent across growth temperatures. Acclimation in woody Amazonian plants is generally too weak to maintain TSMs at high growth temperatures, supporting previous findings that Amazonian plants will be increasingly vulnerable to thermal stress as temperatures rise.

Sb-saturated high-temperature growth of extended, self-catalyzed GaAsSb nanowires on silicon with high quality

Ternary GaAsSb nanowires (NW) are key materials for integrated high-speed photonic applications on silicon (Si), where homogeneous, high aspect-ratio dimensions and high-quality properties for controlled absorption, mode confinement and waveguiding are much desired. Here, we demonstrate a unique high-temperature (high-T >650 °C) molecular beam epitaxial (MBE) approach to realize self-catalyzed GaAsSb NWs site-selectively on Si with high aspect-ratio and non-tapered morphologies under antimony (Sb)-saturated conditions. While hitherto reported low-moderate temperature growth processes result in early growth termination and inhomogeneous morphologies, the non-tapered nature of NWs under high-T growth is independent of the supply rates of relevant growth species. Analysis of dedicated Ga-flux and growth time series, allows us to pinpoint the microscopic mechanisms responsible for the elimination of tapering, namely concurrent vapor–solid, step-flow growth along NW side-facets enabled by enhanced Ga diffusion under the high-T growth. Performing growth in an Sb-saturated regime, leads to high Sb-content in VLS-GaAsSb NW close to 30% that is independent of Ga-flux. This independence enables multi-step growth via sequentially increased Ga-flux to realize uniform and very long (>7 μm) GaAsSb NWs. The excellent properties of these NWs are confirmed by a completely phase-pure, twin-free zincblende (ZB) crystal structure, a homogeneous Sb-content along the VLS-GaAsSb NW growth axis, along with remarkably narrow, single-peak low-temperature photoluminescence linewidth (<15 meV) at wavelengths of ∼1100–1200 nm.

Chemical vapor deposition growth of [formula omitted] on Si- and C- face off-axis 4H–SiC at high temperature

Realization of β‐Ga2O3 on a high-thermal-conductivity substrate is crucial to overcome the poor thermal conductivity of β‐Ga2O3 which is one of the major roadblocks against its era in power electronics. We investigated low-pressure chemical vapor deposition (LPCVD) growth on both Si and C- face (0001) 4H–SiC at a high growth temperature of 925 °C using Ga metal and O2 gas source. Growths on C-face 4H–SiC resulted polycrystalline β‐Ga2O3 for the entire O2-flow range, whereas under optimized O2-flow conditions, step flow growth of (−201) β‐Ga2O3 was achieved on Si-face 4H–SiC with 3.7 nm rms surface roughness and rocking curve FWHM of 0.54° at a growth rate reaching 2.48 μm/h 4° off-axis nature of the substrate promoted the growth of some of the in-plane rotational domains while suppressing others. Raman measurements further verified the pure β‐Ga2O3 nature of the grown films. Using a customized LPCVD with solid source Ga, a cost-effective, safe and industrially scalable method was shown to pave the way to enable β‐Ga2O3 heteroepitaxy on 4H–SiC for high-power electronics.

Adsorption, dissociation, and diffusion of borazine on Pt(111)

Using first-principles calculations, we investigate the adsorption, dissociation, and diffusion of borazine, a common precursor for the growth of two-dimensional hexagonal boron nitride (h-BN), on a Pt(111) surface. Our calculations show that borazine adsorbs on Pt(111) both molecularly and dissociatively. The molecular borazine has a planar structure, whereas the dissociated borazine is either in a tilted or vertical configuration. The energy differences between the structures are only ∼0.1 eV although the dissociated ones are more stable, and the energy barriers for conversion between the structures are also of the order of 0.1 eV. For molecular adsorption, borazine migrates through direct (0.87 eV barrier) or rotational (0.67 eV barrier) mechanisms. In the dissociated state, with alternating parallel and perpendicular structures, the borazine radical can migrate via a “slinky” movement. This results in a much lower diffusion barrier of 0.2 eV. In the case of vertical diffusion, the radical migrates with an energy barrier of 0.29 eV. Our results are consistent with experimental observations of borazine dehydrogenation and may be helpful in understanding h-BN formation at room temperature. We also discuss the atomistic processes for h-BN formation at high growth temperatures.

Growth of large-sized relaxor ferroelectric PZN-PT single crystals by modified flux growth method

A novel bottom-cooling high-temperature solution growth technique is developed for growing large-sized relaxor ferroelectric 0.91Pb(Zn1/3Nb2/3O3)-0.09PbTiO3 (PZN-PT) single crystals. During the growth, an inverse temperature gradient is maintained in the crucible base by flowing air at a controlled rate. This method restricts the number of spontaneously nucleated crystals at crucible bottom, reduces loss of volatile PbO component and favours the growth of large-sized PZN-PT single crystals. Large-sized PZN-PT single crystals of dimensions ∼ 22 × 20 × 14 mm3 are reproducibly grown by the proposed method. The electrical characteristics of the PZN-PT wafers oriented along the 〈100〉, 〈010〉 and 〈001〉 directions are investigated. PZN-PT wafers oriented along the 〈001〉 direction exhibited superior piezoelectric coefficient (d33) of ∼ 2221 pm/V. The homogeneity of the physical parameters is analysed by preparing 10 elements with dimensions of ∼ 5 × 2.5 × 2.5 mm3 which were cut from single wafer oriented along the 〈001〉 direction. The ferro-, piezo- and dielectric characteristics of these wafers were found to be highly uniform with small standard deviation. The observation of d33 value with less than 2 % deviation from mean value confirms the growth of highly quality PZN-PT single crystals.