Bridgman Technique Research Articles

Bridgman grown CuSbS2 single crystal and its application as photodetector and potential thermoelectric material

Crystal of copper antimony disulphide (CuSbS2) measuring 4.5 cm in length and 0.8 cm in diameter was successfully grown using the vertical Bridgman technique (VBT). The orthorhombic unit cell structure and pure CuSbS2 phase of the grown crystal was confirmed by the powder X-ray diffraction and was well supported by Raman spectra. The stoichiometry of the grown crystal was confirmed by energy dispersive X-ray analysis and field emission scanning electron microscopy revealed that crystal is grown by layer growth mechanism. The Raman spectra has shown the presence of peak at 319.32 cm−1 corresponding to Sb-S bonds whereas peaks at 445.03 cm−1 and 257.27 cm−1 corresponds to S-S and Cu-S bonds. The photoluminescence spectra taken at room temperature with 488 nm excitation wavelength displays emission in different regions of the visible spectrum. Optical absorbance spectra shows that CuSbS2 single crystal possess direct bandgap of 1.57 eV which is suitable for solar cell application. The Seebeck coefficient is positive over the entire temperature range, demonstrating the sample's p-type semiconducting nature and corroborates our Hall effect measurements. Using electrical conductivity and lattice thermal conductivity values we calculated thermoelectric figure of merit i.e., ZT whose value comes nearly 0.988 at 503 K which stands in competition with reported values of the other grown crystal. Thermogravimetric (TG) curve has shown two step decomposition at four different heating rates of 5, 10, 15 and 20 K/min which is also confirmed from DTG (differential thermogravimetric analysis) curves. At room temperature, the I-V characteristics of prepared CuSbS2 single crystal photodetector are measured for parallel to plane and perpendicular to plane configuration, with various biasing voltages at 50 mW/cm2. At room temperature, a bias voltage of 0.1 V with a light intensity of 50 mW/cm2 yields responsivity and detectivity of 30 mA/W and 32.84 × 106 Jones for ⊥ to plane, which is comparable to the reported values of other materials.

Enhanced orange-red emission in Eu3+/Li+ co-doped Na5Lu9F32 fluoride single crystal upon excitation of 394 nm

In this study, a series of transparent 0.5 Eu3+/χ Li+ (χ = 0, 0.3, 0.6, 0.9, and 1.2): Na5Lu9F32 fluoride single crystals with high-quality were successfully grown by a modified Bridgman technique. The impacts of Li+ ion dopant on the luminous properties of Na5Lu9F32 doped Eu3+ single crystals were studied by fluorescence spectra, decay curves and absorption spectra. The doping of Li+ was beneficial for improvement of the orange-red emission, and the emission intensity of Eu3+ singly doped crystal could be doubled by co-doping 0.9 mol% Li+ ions. The variations of local environment around the Eu3+ ions after Li+ ions doping were probed by the emission spectra and the changes of ratios between red and orange emission intensities (R/O). Additionally, internal quantum efficiency of Eu3+/Li+: Na5Lu9F32 single crystal could be reached to ∼18.25%. Therefore, Eu3+/Li+: Na5Lu9F32 single crystal was considered as a potential material for orange-red laser and related optical devices.

Optimizing the temperature gradient for CdZnTe crystal growth using the vertical Bridgman–Stockbarger method

CdZnTe (CZT) is considered an ideal material for the growth of HgCdTe (MCT) epitaxial layers and nuclear detection devices. The crystal quality of CZT is the key factor in the MCT-based infrared plane array and the performance of nuclear devices. Herein, we report the growth of CZT by optimizing the temperature gradient vertical Bridgman–Stockbarger method. The crystalline character of the obtained CZT has been examined using optical microscopy, IR transmission microscopy, high-resolution X-ray diffraction, X-ray tomography (XRT), Fourier-transform infrared spectroscopy and glow discharge mass spectrometry. The etch pit dislocation density of the CZT sliced wafers (111)-B was less than 4.0 × 103 cm−2, the triangular shape inclusions in the CZT volume of the double-grinding wafers have a sparse distribution, and the size can be controlled to be less than 5 μm, the typical full-width at half-maximum of the Bragg diffraction peak was 17.4″. The XRT image of polished CZT wafers (111)-B showed a uniform structure without strain and defects. About 100 % of the CZT wafers showed transmittance >50 % at 20 µm and the detected impurities in the crystal were low, Li 4.9 ppb and Na 2.9 ppb, indicating the formation of high-quality CZT crystals. This work provides a scheme to improve the crystal quality of CZT for high-performance device applications.

Mn2+ doped LiBaF3 fluoride perovskite single crystal with broadband infrared luminescence pumped by blue LED

In this study, Mn2+ ions doped lithium barium fluoride single crystals (LiBaF3: Mn2+) with perovskite structure were successfully prepared by a reformative Bridgman technique. A near-infrared (NIR) emitting broadband of the single crystal with a peak wavelength of 767 nm and a full width half maxima (FWHM) of 77 nm is owing to the 4T1g(4G)→6A1g(6S) transition of the Mn2+ ions in strong crystal field. Mn2+ ions replace the lattices of Li+ ions from the results of Rietveld structure refinements of the crystals performed by General Structure Analysis System (GSAS) program. A high internal quantum efficiency (41.4%) can be obtained in the synthesized single crystal upon excitation of 494 nm, and the emission intensity of this single crystal at 473 K remains at 42.9% of that at 298 K. Therefore, the LiBaF3: Mn2+ single crystal is a promising candidate for NIR solid-state light-emitting material due to its effective broadband NIR emission. This work offers a novel route to rational design of efficient broadband NIR luminescence and provides a new insight into Mn2+ luminescence and its applications.

An overview of microstructure, mechanical properties and processing of high entropy alloys and its future perspectives in aeroengine applications

Modern engineering applications continually strive to develop greater performance mechanical components with good microstructural stability, improved mechanical properties, corrosion resistance and decreased cost of repairing and maintenance. This necessitates the broad use of advanced high performance materials like high entropy alloys (HEAs). These alloys are created by combining five or more alloying elements in equal or substantial amount. About 5 to 35 at. % of the alloying element is present in HEAs. It is characterized primarily by greater entropy, slow diffusion, severe lattice distortion, and cocktail effects. Due to its advanced microstructural stability throughout a larger temperature span and for longer length of time, it demonstrates improved mechanical characteristics at ambient temperature, cryogenic temperature, and elevated temperature. The diversity of elemental contents and significantly higher mixing entropy of HEAs make them mechanically superior to classic metals and alloys. It also shows better strength to weight ratio. Hence, it qualifies as a possible structural and functional material for aeroengine applications. In this work, the studies on the HEAs are briefly reviewed. A basic explanation of the four core effects of HEAs is given. Discussion is held on microstructure and mechanical properties of HEAs. The processing routes for manufacturing of HEAs (arc melting, bridgman solidification, mechanical alloying and vapour deposition) are presented briefly. The influence of heat treatment on mechanical behavior and microstructure of HEAs is presented. The simulation approach of CALPHAD modeling for designing of HEAs is discussed briefly. The future scope for research and development of HEAs in aeroengine applications is briefed.

Growth and Scintillation Properties of 6Li Containing Ce:LaCl3-Based Eutectic Scintillator for Neutron Detection

In this study, Ce:6LiCl/LaCl3 with a high 6Li concentration was developed as a novel thermal neutron scintillator, in which Ce3+ serves as an activator for the LaCl3 phase. The Ce:6LiCl/LaCl3 eutectic was grown in a quartz ampoule (inner diameter: 4.0 mm) using the Bridgman–Stockbarger technique. The grown eutectic contained 0.038 mol/cm3 6Li, which is greater than that found in commercially available scintillators such as LiCaAlF6 single crystals and Li glass. The Ce:6LiCl/LaCl3 eutectic has a lamellar eutectic structure and is optically transparent. A 350 nm emission due to Ce3+ 4f-5d transition was observed. The light yield under neutron irradiation was estimated to be 5.0 times higher than that of Li-glass. In this eutectic, the 6Li (n, a) 3H reaction made the 6LiCl phase to act as the neutron capture phase and LaCl3 to act as the scintillator phase.

Thermal, dielectric, mechanical and structural behavior of 2-amino 4-methylpyridinium 4-nitrophenolate 4-nitrophenol bulk single crystal

Applications in both science and industry have received increased attention as a result of bulk single crystals with particular orientations. However, due to the instability of organic crystals at high temperatures and stress, there is an interest in growing good-quality bulk single crystals with stable thermal and mechanical properties. Here, the 2-amino 4-methylpyridinium 4-nitrophenolate 4-nitrophenol (2A4MPPP) crystal was prepared employing a single-wall ampoule and the vertical Bridgman technique. Structure and functional groups were determined by XRD, NMR, and FTIR studies. More importantly, detailed thermal and kinetic properties such as activation energy, frequency factor, rate constant, and Avrami exponent are discussed. The mechanical stability and dielectric studies are also demonstrated for the title compound. According to the single crystal XRD investigation, 2A4MPPP is a member of the orthorhombic crystal system with the Pna21 space group. Through the TGA and DTA analyses, it was confirmed that the compound starts to melt at 98 °C and complete melting occurs at 103.3 °C. The dielectric experiments reveal the crystal's poor dielectric constant and high-frequency dielectric loss. Vickers microhardness investigations show that grown 2A4MPPP belongs to the soft materials group. As a result of these findings, the 2A4MPPP crystal should be well suited for usage in thermomechanical, microelectronic, optical communications, and nonlinear optical applications.

Influence of Process Parameter and Alloy Composition on Misoriented Eutectics in Single-Crystal Nickel-Based Superalloys.

The nucleation and the growth of misoriented micro-structure components in single crystals depend on various process parameters and alloy compositions. Therefore, in this study, the influence of different cooling rates on carbon-free, as well as carbon-containing, nickel-based superalloys was investigated. Castings were carried out using the Bridgman and Bridgman-Stockbarger techniques under industrial and laboratory conditions, respectively, to analyze the impact of temperature gradients and withdrawing rates on six alloy compositions. Here, it was confirmed that eutectics could assume a random crystallographic orientation due to homogeneous nucleation in the residual melt. In carbon-containing alloys, eutectics also nucleated at low surface-to-volume ratio carbides due to the accumulation of eutectic-forming elements around the carbide. This mechanism occurred in alloys with high carbon contents and at low cooling rates. Furthermore, micro-stray grains were formed by the closure of residual melt in Chinese-script-shaped carbides. If the carbide structure was open in the growth direction, they could expand into the interdendritic region. Eutectics additionally nucleated on these micro-stray grains and consequently had a different crystallographic orientation compared with the single crystal. In conclusion, this study revealed the process parameters that induced the formation of misoriented micro-structures, which prevented the formation of these solidification defects by optimizing the cooling rate and the alloy composition.

Enhanced ∼2.85 μm mid-infrared emission of Na5Lu9F32: Pr3+/Ho3+ single crystal by introducing of non active Gd3+ ions

A series of novel Na5Lu9F32 fluoride single crystals by keeping the concentrations of Ho3+ (0.5 mol%) and Pr3+ (0.1 mol%) fixed and varying the concentrations of Gd3+ ions (i.e., 0, 0.5, 1.0, 1.2, 1.5 mol%) were prepared successfully by a reformative Bridgman technique for application of 2.85 μm mid-infrared. The impact of the non active Gd3+ ion on the crystallographic structure and optical properties of the single crystal were explored by the aid of the X-ray diffraction, Rietveld refinement, spectra of absorption and emission and decay curves of fluorescence. By leading Gd3+ (1.2 mol%) into Ho3+(0.5 mol%)/Pr3+(0.1 mol%) incorporated Na5Lu9F32 single crystal, the emission intensity at ∼ 2.85 μm was fulfilled significantly about two times enhancement. The destruction of [Ho3+-Ho3+] ion quench clusters and release more luminescent ions are in charge of the enhancement of the emission at 2.85 μm by leading Gd3+ into the fluoride single crystal. The maximum emission cross-section, ∼5.2 × 10−20 cm2, at ∼2.85 μm was estimated on the basis of the emission spectra. Thus, the grown Pr3+/Ho3+/Gd3+ incorporated Na5Lu9F32 fluoride single crystals could be an excellent candidate for source of ∼2.85 μm mid-infrared solid-state laser device.

Cubic-phase NaYF4:Pr3+, Yb3+ down-conversion phosphors for optical temperature sensing

The cubic phase NaYF4:Pr3+, Yb3+ single crystals were grown in the resistive furnace by the Bridgman-Stockbarger technique with following milling in an agate mortar. The luminescence intensity ratio (LIR) between 3P1 – 3H5 and 3P0 – 3H5 emissions of Pr3+ was taken a temperature-dependent parameter. The calculated absolute (Sa) temperature sensitivity was 0.0075 at 320 K. The LIR between 3P0 – 1G4 (Pr3+) and 2F5/2 – 2F7/2 (Yb3+) emissions is also temperature-dependent due to phonon-assisted nature of energy transfer between 1G4 of Pr3+ and 2F5/2 of Yb3+. Sr and Sa demonstrated the highest values in the 100–220 K temperature range (Sa (max) = 0.0047 K−1 at 150 K).NaYF4:Pr3+, Yb3+ samples are useful in optical temperature sensing in the broad temperature range from 100 up to 320 K.

Temperature-dependent luminescence in pure and In+-Activated Cs3Cu2I5 single crystals

We report our investigation of the low-temperature optical properties of high-quality Cs2Cu3I5:In+ perovskite single crystals grown by the vertical Bridgman technique. Temperature-dependent radioluminescence in the range 15–300K reveals two main emissions for In+ doped samples at ∼450 nm and the other at ∼620 nm assigned to self-trapping exciton and In+ emissions respectively. Wavelength-resolved thermoluminescence reveals that In+ emission centers are the preferred recombination center for trapped charges. Further investigation of photoluminescence emission/excitation maps reveals a complex electronic structure that arises from spin-orbit coupling-related transitions in In+ and is only observable at low temperatures. Temperature-dependent photoluminescence decay measurements reveal some instances of charge transfer between the self-trapped excitons and In+ ions, as well as some thermally-assisted radiative recombination processes.

Original Na5(Lu1–x–yGdxYy)9F32: Pr3+/Ho3+ Hybrid Single Crystals for Efficient ∼2.9 μm Mid-Infrared Emission

A novel Ho3+/Pr3+/Y3+/Gd3+ multiply doped Na5Lu9F32 mixed single crystal was successfully grown via a modified Bridgman technique. The structure of the mixed crystal was characterized by means of X-ray diffraction and Raman spectra. The impacts of Y3+ and Gd3+ ions on the 2.9 μm emission of Na5Lu9F32 single crystals, which incorporated fixed Ho3+/Pr3+, were investigated systematically with the aid of the optical spectra and decay curves of fluorescence. The 2.9 μm emission intensity (Ho3+: 5I6 → 5I7) was further heightened upon gradually introducing both Y3+ and Gd3+ ions into Ho3+/Pr3+-incorporated single crystals pumped at 640 nm. The brokenness of ionic quenching clusters of [Ho3+–Ho3+] and the release of more luminescent ions are in charge of the augment of emission at 2.9 μm by introducing Gd3+ or Y3+ ions into the Ho3+/Pr3+ codoped single crystals. A value of ∼8.2 × 10–21 cm2 was estimated for the maximum emission cross section at 2.9 μm of the mixed crystal. The processing of energy transfer among Ho3+, Pr3+, Y3+, and Gd3+ ions was investigated, and the energy transfer efficiency for Ho3+: 5I7 → Pr3+: 3F2 was approximately 57.32%. The Na5Lu9F32-doped Ho3+/Pr3+/Y3+/Gd3+ mixed crystals may be a new laser gain medium for 2.9 μm generation because of their special spectral and physicochemical properties.

Production of detector grade CdZnTe crystal with VGF furnace by analyzing segregation of Zn and In

Production of CdZnTe crystals for radiation detector applications through Bridgman and Vertical Gradient Freeze (VGF) techniques is challenging in many aspects. Due to the structural characteristics of CdZnTe, it is not possible to obtain a large single crystalline ingots from the melt growth technique. In addition, the segregation of dopants and Zn decrease the yield significantly. In order to achieve detector-grade CdZnTe crystals, zinc segregation behavior should be fully understood, and optimum dopant concentration (In) should be determined. In this work, indium-doped Cd0.9Zn0.1Te single crystals grown via the Vertical Gradient Freeze (VGF) technique were compared in terms of dopant segregation, defect concentration, electron mobility, and electrical resistivity. It is observed that Zn segregates towards the tip of the ingot while In segregates towards the heel. Zn segregation coefficient is calculated as 1.35 while In segregation coefficient is found to be 0.4 for the VGF method. The variation of Zn throughout the ingot and excessive In dopant concentration degraded the detector performance. CdZnTe crystals having In doping concentrations of more than 5 ppm were unresponsive to gamma radiation. (µτ)e of VGF-grown crystals in METU Crystal Growth Laboratory is calculated as 4–5 × 10−4 cm2/V.

Investigation of thermoelectric properties and photoresponse of Sb2S3−xSex crystals grown by Bridgman technique

Investigation of thermoelectric properties and photoresponse of Sb2S3−xSex crystals grown by Bridgman technique

Growth of Cd1-xMnxTe crystals by vertical Bridgman method and analysis of composition dependence on the bandgap

This article reports the growth of cadmium manganese telluride (Cd1-xMnxTe, CMT) single crystal by vertical Bridgman method and the property measurements for three different Mn compositions (x = 0.05, 0.10 & 0.15). The single crystalline nature of the grown crystals was confirmed with Laue back reflection method. The lattice constants were calculated using single-crystal X-ray diffraction analysis. Phase formation and zinc blende crystal structure were confirmed with powder X-ray diffraction analysis. The shifting of the diffraction peak position indicates the reduction in lattice parameter of Cd1-xMnxTe crystals with Mn concentration. Raman spectra exhibited two mode behavior having CdTe and MnTe-like structures and their longitudinal optical phonon modes displaying peak shift with Mn concentration. The increase in the Mn concentration in CMT lattice made a blueshift in photoluminescence emission band leading to changes in the bandgap from 1.5776 to 1.7250 eV. The experimentally observed IR transmittance was found to be in line with theoretically observed transmittance. The observed Mn concentration dependent structural and optical properties confirm the formation of high quality CMT single crystals by vertical Bridgman technique.

Dependence of microstructural evolution on the geometric structure for serviced DZ125 turbine blades

The turbine blades were directionally solidified by a high-rate solidification process by the Bridgman technique using directional solidified Ni-based master superalloy DZ125 and operated on the engine bench with a high-temperature gas environment of more than 1500 °C from combustor and high-speed rotation of more than 13500 rpm for 400 h. A service-environment-based model was put forward to simulate the distribution of temperature and stress on the DZ125 blade in service. It was found that the distribution of temperature and stress on the serviced DZ125 blade was closely related to its geometric structure. The microstructural evolution of the serviced DZ125 blade was analyzed and the variations of microstructures with temperature and stress were investigated by using a scanning electron microscope. The results revealed that the evolution process of microstructures on the serviced DZ125 blade was different from that of the standard sample tested at constant temperature and uniaxial tensile stress. The reason for this discrepancy was explored using a combination of finite-element calculation and diffusion coefficient calculation.

Optical Temperature Sensors Based on Down-Conversion Nd3+,Yb3+:LiYF4 Microparticles

Nd3+ (0.3 mol.%), Yb3+ (0, 1, 2, 3 and 5 mol.%): LiYF4 phosphors were grown by the Bridgman–Stockbarger technique. The luminescence intensity ratio (LIR) of Nd3+ (4F3/2–4I9/2, ~866 nm) and Yb3+ emission (2F5/2–2F7/2, ~980 nm) was taken as a parameter. The energy exchange between 4F3/2 (Nd3+) and 2F5/2 (Yb3+) occurs via phonons, which elucidates the LIR temperature dependence. The influence of the cross-relaxation process on the temperature sensitivity was estimated as negligible. The LIR function depends on the Yb3+ concentration at a fixed 0.3 mol.% Nd3+. The maximum Sa and Sr value were reached for Nd3+ (0.3%), Yb3+ (1.0%): LiYF4 (Sa = 0.007 K−1 at 320 K) and Nd3+ (0.3%), Yb3+ (5.0%): LiYF4 (Sr = 1, 1.03%*K−1 at 260 K), respectively.

Effective enhancement of ∼2.86 µm mid-infrared emission of Na5Y9F32 single crystal co-doped Ho3+/Pr3+ introduced by Gd3+ ions

The optical spectral properties of high-quality Na5Y9F32 single crystals triply incorporated Ho3+/Pr3+/Gd3+ ions prepared successfully via a Bridgman technique were characterized with the help of their absorption spectra, emission spectra, and fluorescence lifetimes. It was discovered that the emission intensity at ∼2.86 µm of Na5Y9F32 co-doped Pr3+/Ho3+ single crystal was boosted obviously by introducing of Gd3+ ions, and it reached its maximum when the concentration of Gd3+ ion dopant was ∼0.7 mol%. The release of more luminescent centers due to the destruction of [Ho3+-Ho3+] ion quenching clusters and variation of the symmetry of crystal field around Ho3+ ions are responsible for the augmentation of ∼2.86 µm fluorescence emission. In addition, the introduction of Gd3+ ion reduced the fluorescence lifetime of Ho3+: 5I7 level, while the Ho3+:5I6 level remained slightly changed, which is beneficial to improve the particle inversion of Ho3+ ion between the 5I6 and 5I7 energy levels to enhance the ∼2.86 µm emission. The results showed that the triply doped fluoride single crystal can become a potentially prospective material for ∼2.86 µm mid-infrared lasers.

Crystal growth and characterization of mixed elpasolite scintillators Ce:Cs2Li(LaBr6)x(YCl6)1-x (0 < x ≤ 0.4)

Over the past two decades, substantial research has been done on the typical elpasolite scintillators Ce:Cs2LiYCl6 (CLYC) and Ce:Cs2LiLaBr6 (CLLB) for their potential use as neutron/gamma dual-mode detectors. Commonly, the cation or anion alloying will change the luminescence and scintillation properties of the scintillators, such as the good energy resolution of the Ce:Cs2LiLa(Br–Cl)6 (CLLBC) crystal. In this work, ⌀8 mm Ce:Cs2Li(LaBr6)x(YCl6)1-x crystals with x = 0.1, 0.2, 0.3 and 0.4 were grown by the vertical Bridgman technique. Then, ⌀25 mm Ce:Cs2LiLa0.1Y0.9Br0.6Cl5.4 crystal was grown for its relatively high optical quality and phase purity. The luminescence and scintillation properties were also investigated. The energy resolution of Ce:Cs2LiLa0.1Y0.9Br0.6Cl5.4 crystal was calculated to be 9.3%. The scintillation decay time were 38 ns and 623 ns under 137Cs irradiation.

Thermal Stability of LiRF4 (R = Gd, Tb) Compounds

AbstractLiGdF4 and LiTbF4 single crystals are grown by the Bridgman–Stockbarger method from the nonstoichiometric melt comprising 32 mol% RF3 (R = Gd, Tb) and 68 mol% LiF, respectively. Incongruent melting of the single crystals LiGdF4 and LiTbF4 is confirmed by differential scanning calorimetry. For the first time, the crystal structures of LiGdF4 and LiTbF4 are determined by Rietveld method. Also, rare‐earth lithium fluoride syntheses from lithium nitrate melts at 400 °С are performed for LiTbF4, LiGdF4, LiYF4, and LiDyF4 compounds. For terbium, the product is a mixture of LiTbF4 and TbF3; and for gadolinium, GdF3 is thus produced. With reference to the related literature, it is concluded that LiGdF4 and LiTbF4 are the thermodynamically stable phases in the ranges from 750 ± 5 to 425 ± 15 °С, and from 782 ± 5 to 400 ± 15 °С, respectively. The metastability of LiGdF4 and LiTbF4, however, does not prevent the use of their single crystals as photonic materials.