Bulk crystal growth, optical, mechanical and ferroelectric properties of new semiorganic nonlinear optical and piezoelectric Lithium nitrate monohydrate oxalate single crystal

Highlights

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Solution grown LNO crystals showed sharp violet emission peak at 438 nm.

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Wide band gap and low Urbach energy was found in UV absorption spectra.

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Low dielectric constant along with phase change transition at 33 °C was found.

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A saturated hysteresis loop and piezoelectricity (d₃₃ & g₃₃) was observed.

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The SHG efficiency was found to be 1.2 times that of KDP.

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Abstract

New semiorganic nonlinear optical single crystals of Lithium nitrate oxalate monohydrate (LNO) were grown by slow evaporation solution technique. Single crystal X-ray diffraction study indicated that LNO crystal belongs to the triclinic system with space group P1. Various functional groups present in the material were identified by FTIR and Raman analysis. UV–vis study showed the high transparency of crystals with a wide band gap 5.01 eV. Various Optical constants i.e. Urbach energy (E_u), extinction coefficient (K), refractive index, optical conductivity, electric susceptibility with real and imaginary parts of dielectric constant were calculated using the transmittance data which have applications in optoelectronic devices. A sharp emission peak was found at 438 nm in photoluminescence measurement, which revealed suitability of crystal for fabricating violet lasers. In dielectric studies, a peak has been observed at 33 °C which is due to ferroelectric to paraelectric phase transition. Piezoelectric charge coefficients (d₃₃ = 9.2 pC/N and g₃₃) have been calculated, which make it a suitable for piezoelectric devices applications. In ferroelectric studies, a saturated loop was found in which the values of coercive field and remnant polarization were found to be 2.18 kV/cm and 0.39 μC/cm², respectively. Thermal behavior was studied by TGA and DSC studies. The relative SHG efficiency of LNO was found to be 1.2 times that of KDP crystal. In microhardness study, Meyer’s index value was found to be 1.78 which revealed its soft nature. These optical, dielectric, piezoelectric, ferroelectric, mechanical and non-linear optical properties of grown crystal establish the usefulness of this material for optoelectronics, non-volatile memory and piezoelectric devices applications.

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Graphical abstract

Keywords

• Single crystal growth; 
• Optical properties; 
• Dielectric; 
• Piezoelectricity; 
• Ferroelectricity;
• Mechanical properties
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    • Soure:Sciencedirect
      
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Quality improvement of single crystal 4H SiC grown with a purified β-SiC powder source

In the processing of single crystal SiC using the PVT method, defects such as micropipes and dislocations occur due to various reasons, including growth rate, temperature gradient, seed quality, pressure change and the SiC source powder. Among these factors, the SiC source powder was investigated to reduce defects in single crystal SiC. β-SiC powder was used to reduce the growth temperature and change basic properties of the particle, including microstructure, particle size and chemical composition, through the purification process. The structure of the purified β-SiC particle was changed into a spherical structure and its particle size expanded. Chemical analysis revealed reduced free carbon, oxide phases such as silica (SiO₂), silicon oxycarbide and metallic impurities. Purified β-SiC powder showed increased particle size of 37 µm and showed improved purity. With this, we grew single crystal 4H SiC and compared the micropipe and dislocation density to that of single crystal 4H SiC grown with non-purified β-SiC powder. The experimental results confirmed that the 4H SiC wafer grown by purified β-SiC powder exhibited improved quality.

Keywords

• Purified β-SiC powder; 
• Chemical composition; 
• Single crystal 4H SiC; 
• Micropipe and dislocation density
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    • Soure:Sciencedirect
      
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Multi-discharge EDM coring of single crystal SiC ingot by electrostatic induction feeding method

Highlights

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A novel tool electrode setup was developed for EDM coring of SiC ingot/wafer.

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EDM coring of 2 inch SiC ingot/wafer by rod electrode was carried out successfully.

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EDM by electrostatic induction feeding method was applied for rough machining.

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Multi-discharge EDM by electrostatic induction feeding method was developed.

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Multi-discharge EDM improves both the machining rate and the surface integrity.

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Abstract

A new technique of EDM coring of single crystal silicon carbide (SiC) ingot was proposed in this paper. Currently single crystal SiC devices are still of high cost due to the high cost of bulk crystal SiC material and the difficulty in the fabrication process of SiC. In the manufacturing process of SiC ingot/wafer, localized cracks or defects occasionally occur due to thermal or mechanical causes resulted from fabrication processes which may waste the whole piece of material. To save the part of ingot without defects and maximize the material utilization, the authors proposed EDM coring method to cut out a no defect ingot from a larger diameter ingot which has localized defects. A special experimental setup was developed for EDM coring of SiC ingot in this study and its feasibility and machining performance were investigated. Meanwhile, in order to improve the machining rate, a novel multi-discharge EDM coring method by electrostatic induction feeding was established, which can realize multiple discharges in single pulse duration. Experimental results make it clear that EDM coring of SiC ingot can be carried out stably using the developed experimental setup. Taking advantage of the newly developed multi-discharge EDM method, both the machining speed and surface integrity can be improved.

Keywords

• Electrical discharge machining (EDM); 
• EDM coring; 
• Multi-discharge EDM; 
• Single crystal silicon carbide (SiC); 
• Electrostatic induction feeding; 
• SiC wafer
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    • Soure:Sciencedirect
      
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Latent hardening effect under self- and coplanar dislocation interactions in Mg single crystals

Latent hardening experiments were carried out on Mg  single crystals under basal self- and coplanar dislocation interactions. For self-interactions the latent hardening ratio (LHR) is independent on the amount of primary deformation in the basal slip system. For coplanar interactions LHR increases linearly with primary strain and quadratically with primary stress, suggesting that during the stage A in Mg the coplanar slip systems harden proportionally to the dislocation density accumulated in the other coplanar slip system.

Keywords

• Magnesium single crystals; 
• Easy glide; 
• Basal slip; 
• Latent hardening; 
• Coplanar interactions
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  • Soure:Sciencedirect
    
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ZnO single crystal microtubes: synthesis, growth mechanism, and geometric structure using direct microwave irradiation

ZnO single crystal microtubes have been successfully synthesized using direct microwave irradiation via the catalyst-free vapor-solid (V-S) process. Field emission scanning electron microscopy (FE-SEM) showed that ZnO single crystal microtubes exhibit a symmetrical 6-facet structure with an exact hexagonal hollow. ZnO single crystal microtubes have an average outer diameter of 100 µm and a length of over 300 µm, and the wall thickness ranges from 1-2 µm. X-ray diffraction (XRD) reveals a single high-intensity diffraction peak along the (101) direction, suggesting good crystallization of the synthesized ZnO single crystal microtubes. Single crystal diffraction (SCD) reveals the obvious polar nature of the ZnO single crystal microtube structure. The room-temperature photoluminescence (PL) spectrum shows an intense ultraviolet (UV) emission at 375.68 nm, with weak and broad visible light emissions in the range between 435 nm and 700 nm at a maximum peak of 588.66 nm.

Keywords

• ZnO; 
• Microtubes; 
• Microwave; 
• Vapor-solid; 
• Crystal growth; 
• Single crystal
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    • Soure:Sciencedirect
      
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Surface atoms core-level shifts in single crystal GaAs surfaces: Interactions with trimethylaluminum and water prepared by atomic layer deposition

Highlights

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Demonstrations of high-resolution core-level photoelectron spectra of the untreated, atomically clean GaAs(1 1 1)A-2 × 2, GaAs(0 0 1)-4 × 6, and GaAs(0 0 1)-2 × 4 using synchrotron radiation as a probe.

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Demonstration of the interfacial electronic structure of the high k dielectrics on the clean GaAs surfaces prepared by atomic layer deposition.

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Demonstration of different surface structures resulting in different growth mode.

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The surface As/Ga atoms 3d core-level spectra of the atomically clean GaAs(1 1 1)A-2 × 2, GaAs(0 0 1)-2 × 4, and GaAs(0 0 1)-4 × 6 surfaces were firstly presented using high-resolution synchrotron radiation photoemission as a probe. The technique clearly explicates behaviors of the As atoms in different surface reconstruction. For GaAs(1 1 1)A-2 × 2, the surface As sits in the same plane as the Ga atoms. As to the GaAs(0 0 1)-2 × 4 surface, the As–As dimers dominate the surface layer, while for GaAs(001)-4 × 6, the As existed in two forms, the As in the As–Ga dimer and the 3-fold coordinated As. Next, we present a microscopic view of in situ atomic layer deposition (ALD) of Al₂O₃ on GaAs taking the two (0 0 1) surfaces as examples. The precursors were trimethylaluminum (TMA) and water. TMA could exist in either a chemisorbed or physisorbed form, depending on the charge environment of the associated surface atoms. The subsequent water purge resulted in both adsorbed forms being etched off or transformed the physisorbed TMA into the As-O-Al(CH₃)₂ configuration. We found that the ALD process rendered the precursors partially and selectively in forming bonds with the surface atoms without disturbing the atoms in the subsurface layer. Upon annealing, the interfacial bonding was dominated with the AsAl as well as GaO bonds.

Keywords

• GaAs; 
• Trimethylaluminum; 
• High K; 
• Atomic layer deposition; 
• Synchrotron radiation 
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    • Soure:Sciencedirect
      
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Flux growth and characterization of Sr2NiWO6 single crystals

Highlights

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In our manuscript, we report on the growth of high quality Sr₂NiWO₆ single crystals.

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Our single crystals enabled us to do the first magnetization measurements of Sr₂NiWO₆ along different crystallographic directions.

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The key point is to use a synthesis route for the polycrystalline precursors that differs from previous reports.

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Abstract

Single crystals of the double perovskite Sr₂NiWO₆ were synthesized via SrCl₂ flux growth using high quality, phase-pure polycrystalline Sr₂NiWO₆ as precursor material. This high quality precursor enabled us to grow large and phase pure crystals with sizes up to 1 mm ×1 mm in the basal plane and octahedral morphology. We measured the temperature dependence of the magnetization along the c-axis and along the ab plane. The analysis of the data allows a precise determination of the effective magnetic moment and the Curie–Weiss temperature. Sr₂NiWO₆ orders antiferromagnetically at T_N=54 K as revealed by magnetization and specific heat data.

Keywords

• A1. Characterization; 
• A1. Crystal structure; 
• A2. Growth from solutions; 
• A2. Single crystal growth; 
• B2. Perovskites; 
• B2. Magnetic materials
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• SOURCE:SCIENCEDIRECT
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