As-grown Single Crystals Research Articles

Solid state growth of Na 1/2Bi 1/2TiO 3–BaTiO 3 single crystals and their enhanced piezoelectric properties

High quality 95Na 1/2Bi 1/2TiO 3–5BaTiO 3 (NBT–5BT) single crystals of 10 mm×10 mm×3 mm in size were fabricated by the solid state single crystal growth technique involving the sintering of proportioned powder compacts in contact with a seed. Structural studies with X-ray diffraction and Raman spectroscopy revealed that the as-grown single crystals have a rhombohedral (pseudo-cubic) single phase. The (0 0 1) cubic -oriented single crystals showed excellent dielectric and piezoelectric properties: ε r =723 , tan δ=0.01 (1 kHz at 25 °C), d 33=207 pC/N, and k 33=0.5. These values are comparable to the best reported properties of melt-grown single crystals.

Formation and suppression of misoriented grains in 6H-SiC crystals

The availability of high-quality silicon carbide (SiC) single crystals with large diameter is a key issue in the development of the full potential of SiC-based device technology. The formation and suppression of misoriented grains (MGs) in the marginal area of as-grown 6H-SiC single crystals are mainly discussed in this paper. The polytype of the MGs is identified to be mainly 6H-SiC by Raman spectroscopy and XRD. Results of modulation growth, in which different stages are decorated with nitrogen, reveal that the growth rate of MG is higher than that of the matrix. Owing to the MG orientation deviating from [0001], no micropipe has been observed in the etched MG samples. At the same time, there exist many thermal decomposition cavities (TDCs) at the initial growth stage, which indicates that the MG may result from a TDC. Based on this possible formation process, a method viasputtering carbon film on C-terminated (0001) 6H-SiC surface for eliminating TDCs is proposed, which may be helpful to suppress formation of MGs, hence to effectively grow SiC crystals with high quality and large diameter by moderate controls of critical growth conditions in the PVT technique.

Kinetic model of growth and coalescence of oxygen and carbon precipitates during cooling of As-grown silicon crystals

A kinetic model of growth and coalescence of oxygen and carbon precipitates has been proposed. This model in combination with the kinetic model of the formation of oxygen and carbon precipitates represents a unified model of precipitation in as-grown dislocation-free silicon single crystals during their cooling in the temperature range from 1683 to 300 K. It has been demonstrated that the results of the calculations are in good agreement with the experimental data obtained from investigations of grown-in microdefects.

Unconventional Growth Mechanism in Optical Traveling Solvent Floating Zone Growth of Large β-CuNb2O6 Single Crystals

A large single crystal (5mm x 4 mm x 15 mm) of CuNb 2 O 6 has been grown in a four-mirror-type optical floating-zone furnace by the traveling solvent floating zone (TSFZ) method using a composition having excess CuO as flux. The as-grown single crystal was found to be phase-pure orthorhombic β-CuNb 2 O 6 , excellent in quality and with a spontaneous growth direction along the crystallographic b-axis. A novel growth mechanism as observed for β-CuNb 2 O 6 in the floating-zone machine is illustrated, and characteristics of the magnetic susceptibility and magnetization along different crystallographic axes are also shown.

Stacking fault in Bi2Te3 and Sb2Te3 single crystals

The structural characterizations of the Bi2Te3 and Sb2Te3 single crystals grown by the Zone melting method have been carried out by XRD and Chemical Etching process. The top free surface of as-grown Bi2Te3 and Sb2Te3 single crystal were observed under optical microscope. The particle size was calculated for a number of reflections using Scherrer’s formula by X-ray diffraction method. By the use of XRD data, the growth and deformation fault probability has been estimated for the grown single crystals. The presence of stacking fault in the lattice structure of the grown crystals was verified by the probability of growth and dislocation fault. Also new dislocation etchant has been developed by the successive trial–error method. Dislocation etching was achieved on (111) crystal plane examined using a saturated solution of citric acid and nitric acid as the etchant. The dislocation etchant has been found to give reproducible etch pits on the cleavage surface for an appropriate etching time 30s. The use of citric acid and nitric acid proved to be especially advantageous for the basal plane, producing etched pits suitable for dislocation etch pit counting.

Growth and annealing characterization of ZnGeP2 crystal

Mid-infrared ZnGeP2 single crystal was successfully grown by the vertical Bridgman technique under the condition of spontaneous nucleation. By the X-ray Fluorescence analysis method, the constitution of Zn, Ge and P in as-grown ZnGeP2 single crystal was measured. Its defects were studied with an optical microscope. The laser damage threshold of ZnGeP2 crystals was measured to be 55.67MW/cm2 at the wavelength of 1064nm. The transmission spectra of ZnGeP2 were measured at room temperature. By annealing treatment in vacuum, ZnGeP2 powder and a pressure, its optical absorption in the region 0.7–2.5μm was found to decrease.

Vertical Bridgman growth and characterization of large ZnGeP 2 single crystals

The growth of ZnGeP 2 crystals by seeded Vertical Bridgman method was studied. High-quality near-stoichiometric ZnGeP 2 single crystals obtained were of 20–30 mm in diameter and 90–120 mm in length. By selection of the seed crystallographic orientation the single crystal ingots without cracks and twins were grown, as shown by X-ray diffraction. The infrared transmission property of the ZnGeP 2 crystals was studied by the calculated optical absorption coefficient spectra. The results showed that after thermal annealing of the crystals the optical absorption coefficient was ∼0.10 cm −1 at 2.05 μm, and ∼0.01 cm −1 at 3–8 μm. The rocking curves patterns of the (4 0 0) reflection demonstrated that the as-grown single crystals possessed a good structural quality. The composition of the crystals was close to the ideal stoichiometry ratio of 1:1:2. The low-loss typical ZnGeP 2 samples of 6 mm×6 mm×15 mm in sizes were cut from the annealed ingots for optical parametric oscillation experiments. The output power of 3.2 W was obtained at 3–5 μm when the incident pumping power of 2.05 μm laser was 9.4 W, and the corresponding slope efficiency and the conversion efficiency were 44% and 34%, respectively.

Studies on the growth and characterization of tris (glycine) calcium(ΙΙ) dichloride—a nonlinear optical crystal

A systematic characterization of a novel nonlinear optical material tris (glycine) calcium(ΙΙ) dichloride (TGCC) is performed. The solubility and metastable zone width of TGCC were studied. TGCC single crystal of dimensions 34×23×5 mm 3 was grown by the slow evaporation technique. Single crystal X-ray diffraction studies reveal that the crystal belongs to orthorhombic system. Energy dispersive X-ray analysis confirms the presence of elements in the crystal. Structural perfection of the as-grown single crystal was studied through multicrystal X-ray diffraction analysis. The thermal characteristics of TGCC were analyzed by thermogravimetric and differential thermal analysis and differential scanning calorimetry. The transmittance of TGCC crystal has been used to calculate the optical band gap of the crystal. Chemical etching studies of TGCC crystal was carried out. The dielectric and mechanical behavior of the crystals were analyzed. The second harmonic conversion property of TGCC was identified by the Kurtz and Perry powder technique and was observed to be higher than that of KDP.

Single Crystal Growth and Structural Characterization of ${\rm FeTe}_{1-x}{\rm S}_{x}$

We have synthesized single crystals of FeTe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> S <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> and investigated the structural and physical properties. The actual S concentration was found to be significantly smaller than the starting nominal value. The solubility limit of S for the Te site for the crystals grown using a self-flux method was estimated to be around 12%. Although a suppression of antiferromagnetic transition was observed by S substitution, bulk superconductivity was not observed. A phase diagram of as-grown FeTe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> S <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> single crystal was established on the basis of the structural and physical properties.

Co와 Ce를 첨가한 큐빅지르코니아(YSZ) 단결정의 이온화에너지 및 격자상수

Co-(0.5 mol%) and Ce-(0~0.3 mol%) doped cubic zirconia (ZrO :Y O = 64 : 36 mol%) single crystals grown by a skull melting method were heat-treated in N at 1200 C for 3 hrs. The brown-colored as-grown single crystals were changed into either green or blue color after the heat treatment. Before and after the heat treatment, the YSZ (yttria- stabilized zirconia) single crystals were cut for wafer form (φ7 mm × t2 mm) and round brilliant cut (φ12 mm). The optical and structural properties were examined by UV-VIS spectrophotometer and X-ray diffraction. Absorption by Ce ( F (4f) → T (5d )), Co ( A ( F) → T ( F) or T ( P)) and Co , change of ionization energy and lattice parameter were confirmed.

Synthesis, crystal growth, structural, spectral and optical properties of tri-allylthiourea mercury bromide (ATMB) single crystals

Metal-organic tri-allylthiourea mercury bromide (ATMB) is a new kind of double ligand complex single crystal. Incorporation of metals into NLO systems give a new dimension of study and introduce many new variables. Transfer of unlocalized electrons from the double ligand allylthiourea to the central metal ion (Hg 2+) through the sulphur atom display a large molecular hyperpolarizability. Experimental results show that the solubility of ATMB in aqueous solution is very low and also it is difficult to grow a large size crystal. Attempts were made to grow single crystals of ATMB by solution growth methods. Structural, spectral, optical and surface features of ATMB were studied with different characterization techniques. Trigonal crystal structure of the as-grown single crystals was identified from the powder X-ray diffraction. X-ray rocking curve contains a single sharp peak and indicates that the specimen is free from structural grain boundaries. Vibrational spectral analyses reveal that the metal–ligand coordination occur, only through sulphur and not with nitrogen by shifting the vibration frequencies of υ (N–C–N) to the higher and υ(C=S) to the lower values. ATMB has UV cut-off wavelength at 340 nm and there is no absorption up to 1500 nm which is more desirable for non-linear applications.

Photoelectrical characteristics of as-grown highresistance GaAs single crystals

The electrophysical and photoelectrical properties of high-resistance GaAs produced by single crystal growth are studied and analyzed. The electron (τ n ) and hole (τ p ) lifetimes are estimated. The charge-carrier lifetimes are compared in as-grown and diffusion high-resistance GaAs. The conclusion is made that in high-resistance GaAs produced by chromium diffusion, the charge-carrier recombination mechanism qualitatively differs from that in as-grown GaAs. The charge-carrier recombination in diffusion GaAs is determined by the occurrence of recombination barriers due to chromium diffusion.

Bulk properties of the UCoGe Kondo-like system

We report on extensive experimental investigations of a single crystal of the orthorhombic uranium compound UCoGe. Bulk measurements on as-grown and annealed single crystals, recording magnetization, magnetic susceptibility, electrical resistivity, magnetoresistivity, thermopower, thermal conductivity and heat capacity data do not reproduce the previously reported coexistence of ferromagnetism with superconductivity. The latter phenomenon was only observed for the annealed sample at T SC = 0.65 K. New observations show a crossover at around 13 K, visible in thermal and transport measurements as well as the coherent state around 50 K, signaled by a wide knee in ρ(T). Above this temperature, UCoGe exhibits a single-ion Kondo-like effect. The magnetoresistivity of the annealed single crystal increases negatively down to 4.2 K, reaching as a large value about −27% at a field of 8 T. The latter may be interpreted in terms of fairly strong magnetic fluctuations existing in UCoGe at low temperatures.

Synthesis, crystal growth and characterization of an organic NLO material: Bis(2-aminopyridinium) maleate

A novel organic nonlinear optical material bis(2-aminopyridinium) maleate (B2AM) was synthesized and crystals were grown from aqueous solution. The solubility and metastable zone width were determined. Single crystal X-ray diffraction and Fourier transform infrared spectral analysis were carried out to confirm the B2AM crystals. Crystalline perfection of the as-grown single crystal was studied through multicrystal X-ray diffraction analysis. The thermal characteristics of as-grown crystals were analyzed by thermogravimetric and differential thermal analysis and differential scanning calorimetry. The transmittance of B2AM crystal has been used to calculate the optical band gap of the crystal. The dielectric and mechanical behavior of the crystals were analyzed. The second harmonic conversion efficiency of B2AM was determined using the Kurtz and Perry powder technique; it was observed greater than that of KDP.

Enhancement of second harmonic generation, optical and dielectric properties inL-asparagine monohydrate single crystals due to an improvement in crystalline perfection by annealing

Single crystals of the relatively new nonlinear optical material L-asparagine monohydrate have been successfully grown by the slow evaporation solution growth technique at room temperature in aqueous solution. The crystal system of the title material has been confirmed by powder X-ray diffraction. The crystalline perfection of the as-grown and annealed crystals has been evaluated by high-resolution X-ray diffraction. The as-grown single crystals (particularly when their size is large) were found to contain internal structural grain boundaries, and the crystalline perfection of these crystals was found to be improved substantially by annealing at low temperatures. The crystalline perfection and the measured physical properties were found to be correlated such that the second harmonic generation efficiency, optical transparency, fluorescence and dielectric properties are enhanced as the crystal quality improves.

The M A-type monoclinic phase and its dc electric/temperature responses studies in Pb(In 1/2Nb 1/2)O 3–Pb(Mg 1/3Nb 2/3)O 3–PbTiO 3 ternary single crystals by polarized light microscopy

The method to distinguish two types of monoclinic phases (M A and M B) in perovskite crystals by polarized light microscopy was developed. The M A-type monoclinic phase was observed in xPb(In 1/2Nb 1/2)O 3– yPb(Mg 1/3Nb 2/3)O 3– zPbTiO 3 ternary crystal by polarized light microscopy at room temperature. The phase transition of these monoclinic phases under dc electric field along [1 1 0] cub direction was investigated in real time. Two dielectric peaks were found in ferroelectric phases of the as-grown ternary single crystals near the morphotropic phase boundary (MPB) with increasing temperature, which indicate the phase transition of monoclinic M A → orthorhombic (O) → tetragonal (T).

Growth of PrFeAsO1−y single crystals and its characterization

Single crystals of oxygen deficient oxypnictide superconductor PrFeAsO1−y have been grown by using belt-type anvil high-pressure synthesis apparatus. Superconducting transition temperature (Tc) of the obtained single crystal is 45K, and typical size is about 800×1000×30μm3. In-plane electrical resistivity shows s-shaped behavior, and can well be fitted by T1.2 temperature dependence near 150K. In addition, we obtained non-superconducting parent single crystal by annealing the as-grown single crystal under ambient pressure. Resistivity of parent single crystal is characterized by the kink near 150K corresponding to the structural transition, and the structure near 12K, which is thought to be originating from the magnetic order of Pr ion.

Oxygen and zinc vacancies in as-grown ZnO single crystals

Oxygen and zinc vacancies are unambiguously shown to be formed in as-grown ZnO bulk crystals grown from melt without being subjected to irradiation, from electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) studies. Concentrations of the defects in their paramagnetic charge states and are estimated to be ∼2 × 1014 cm−3 and ∼1015 cm−3, respectively. The defect is concluded to act as a deep acceptor and to exhibit large Jahn–Teller distortion by 0.8 eV. The energy level of the defect corresponding to the (2–/–) transition is Ev + 1.0 eV. The isolated Zn vacancy is found to be an important recombination centre and is concluded to be responsible for the red luminescence centred at around 1.6 eV. On the other hand, the oxygen vacancy seems to be less important in carrier recombination as it could be detected only in EPR but not in ODMR measurements. Neither isolated nor centres participate in the so-called ‘green’ emission. It is also shown that whereas the concentrations of both defects can be reduced by post-growth annealing, the Zn vacancy exhibits higher thermal stability. The important role of residual contaminants such as Li in the annealing process is underlined.

Colour centre-free perovskite single crystals

Yb 3+:YAlO 3 (YAP) and Yb 3+:GdAlO 3 (GAP) are interesting 1 μm high-power laser media thanks to their very good thermo-mechanical properties. However, as-grown perovskite single crystals exhibit colour centres. Parasitic thermal load generated by these centres is deleterious for high-power laser action and can lead to crystal damages. Moreover these defects decrease Yb 3+ lifetime. They are related to trapped holes on the oxygen network. In the present work, several schemes to remove colour centres are presented. Attention is focused on cerium codoping, thermal annealing under reducing atmosphere and growth of non-stoechiometric compounds.

Thermal Creation of Defects in GaTe

Photoluminescence spectra of as-grown and annealed GaTe single crystals in the 0.7–1.8 eV range have been analyzed at different temperatures. Annealing up to 200 °C produces an increase in the recombination intensity of an excitonic characteristic. The annealing at 400 °C generates an intense optically active recombination in the infrared region (0.76 eV). The thermal generation of defects is possible, owing to the low melting temperature of GaTe (800 °C).