Flux growth of β-Mn2V2O7 single crystals

Large single crystals of β-Mn₂V₂O₇ are successfully grown at a slow cooling rate using flux method in a closed crucible. The grown crystals exhibit a characteristic morphology with natural (1 1 0) and (3 5 0) facets. X-ray diffraction and chemical analyses show that the grown crystals have high quality.     

Growth and characterization of InxBi2−xTe3 single crystals

The V–VI group narrow band gap compounds are known to have important photoconductivity and thermoelectric properties. Among these, Bi₂Te₃ is the most potential material for thermoelectric devices having a direct band gap of 0.16 eV. There has been ample study reported on crystal growth and polycrystalline thin films of both pure and indium doped Bi₂Te₃ pertaining to its basic semiconducting, optoelectronic and thermoelectric properties. It has been shown that on exceeding certain limiting concentration of indium in Bi₂Te₃, the conductivity changes from p-type to n-type. However, there is hardly any work reported in literature on crystal growth, dislocation etching and optical band gap of In_xBi_2?xTe₃ (x=0.1, 0.2, 0.5) single crystals. The authors have grown their single crystals using the zone melting method. The freezing interface temperature gradient of 70 °C/ cm^?1 has been found to yield the best quality crystals obtainable at the growth rate of 0.4 cm/h. The as-grown crystals have been observed to exhibit certain typical features on their top free surfaces. The crystals have been characterized using XRD technique. A chemical dislocation etchant has been used for estimating perfection in terms of dislocation density in the crystals. The optical absorption was measured in the wave number range 500 to 4000 cm^?1. The transitions in all the cases were observed to be allowed direct type. The detailed results are reported in the paper.     

Hydrothermal growth and optical properties of RbBe2BO3F2 crystals

Crystals of RbBe₂BO₃F₂ up to a size of 22×18×5 mm³ have been grown by the hydrothermal method. The growth conditions were optimized mainly by adjusting the mineralizers and growth temperature. The crystals linear and nonlinear optical properties, including its transmittance spectrum and second harmonic generation from 532 to 266 nm, were measured and compared with those of flux grown crystals. A maximum conversion efficiency of 20% was obtained with a 25 ps, 10 Hz laser system. The results indicate that RbBe₂BO₃F₂ crystals grown by the hydrothermal method show similar capability for frequency conversion compared with flux grown crystals and are promising for future deep-UV harmonic generation.     

Single crystal growth from the melt and magnetic properties of hexaferrites–aluminates

Single crystals of aluminum substituted barium hexaferrite were grown by the floating zone method with optical heating. Single crystals were produced from a melt of stoichiometric composition. The process was carried out under a pressure of 50 atm of oxygen. In the system BaO–(x)Al₂O₃–(6?x)Fe₂O₃ the region of single phase crystal growth from the melt is limited by the value x=3. For higher substitutions single-phase crystallization is not observed. The grown single crystals are cylindrical boules with a diameter of 4–5 mm and with lengths up to 50 mm. To avert cracking the crystals have been annealed during the process of growth at 1100 °C. The content of FeO in the composition of single crystals of barium hexaferrite, grown by zone melting under an oxygen pressure of 50 atm, is approximately 0.3 wt%. In the system of hexaferrite–aluminates the macroscopic magnetic moment of the material disappears at x=3.     

Magnetic and magnetostrictive behavior of Dy3+ doped CoFe2O4 single crystals grown by flux method

We studied the effect of Dy³⁺ content on the magnetic properties of cobalt ferrite single crystal. The single crystals of CoFe_1.9Dy_0.1O₄ were grown by the flux method using Na₂B₄O₇.10 H₂O (Borax) as a solvent (flux). The black and shiny single crystals were obtained as a product. The X-ray diffraction analysis at room temperature confirmed the spinel cubic structure with lattice constant a=8.42 Å of the single crystals. The compositional analysis endorses the presence of constituents Co, Fe and Dy elements after sintering at 1300 °C within the final structure. The magnetic hysteresis measurements at various temperatures viz. 10 K, 100 K, 200 K and 300 K reveal the soft ferrimagnetic nature of the single crystal than that of for pure CoFe₂O₄. The observed saturation magnetization (M_s) and coercivity (H_c) are found to be lower than that of pure CoFe₂O₄ single crystal. The magnetostriction (λ) measurement was carried out along the [001] direction. The magnetic measurements lead to conclude that the present single crystals can be used for magneto-optic recording media.     

Growth and characterization of the chalcopyrite LiGaTe2: A highly non-linear birefringent optical crystal for the mid-infrared

LiGaTe₂ crystals have been grown by the Bridgman–Stockbarger technique. The clear transparency range of LiGaTe₂ extends from 2.5 to 12 μm and its band-gap at room temperature is at 2.41 eV (515 nm). LiGaTe₂ is a positive uniaxial crystal which possesses sufficient birefringence for phase-matching. Its non-linear coefficient d₃₆ estimated by phase-matched second harmonic generation is 43 pm/V ± 10% at 4.5 μm. The properties of LiGaTe₂ are compared to those of other mid-IR chalcopyrite non-linear optical crystals with special emphasis on the frequency doubling potential for CO₂ lasers operating at 10.6 μm.     

Single crystal growth and physical properties of superconducting ferro-pnictides Ba(Fe,Co)2As2 grown using self-flux and Bridgman techniques

We have employed the high temperature solutions growth technique and the Bridgman technique to grow cm-size high-quality single crystals of pristine BaFe₂As₂ (Ba122) and its Co-doped superconducting variants. In the first approach, self-flux (Fe, Co)As was used to achieve a homogeneous melt of composition Ba(Fe, Co)_3.1As_3.1 at T=1463 K. The melt was then cooled slowly under a temperature gradient in a double-wall crucible assembly to obtain large and flux-free single crystals of Ba(Fe, Co)₂As₂. In the second approach, single crystals were grown directly from a stoichiometric Ba(Fe, Co)₂As₂ melt at T=1723 K employing the Bridgman technique associated with a vertical tube furnace. Using both techniques single crystals with lateral dimensions up to 25×10 mm² and thickness up to 1 mm were obtained. Details of the two methods are given and a comparative study of the magnetic and transport properties of the single crystals obtained using the two methods is presented.     

Growth and scintillation properties of Pr doped Gd3(Ga,Al)5O12 single crystals

Pr:Gd₃(Ga,Al)₅O₁₂ single crystals were grown by the micro-pulling down (μ-PD) method. All grown crystals were greenish and transparent with 3.0 mm in diameter, 15–30 mm in length. Neither visible inclusions nor cracks were observed. Luminescence and scintillation properties were measured. The substitution at the Al³⁺ sites by Ga³⁺ in garnet structure has been studied. In these crystals, Pr³⁺ 5d–4f emission is observed with 340 nm wavelength. Pr1%:Gd₃Ga₃Al₂O₁₂ shows highest emission intensity. The light yield of Pr:Gd₃Ga₃Al₂O₁₂ sample with 3 mmφ×1 mm size was around 4500 photon/MeV. Scintillation decay time was 7.9 ns (0.5%), 46 ns (0.7%) and 214 ns (98.8%).     

Growth of PBI2 single crystals from stoichiometric and Pb excess melts

We have successfully grown high-purity and -quality PbI₂ single crystals by the vertical Bridgman method. The rocking curves of four-crystal X-ray diffraction (XRD) show 120 arcsec in full-width at half-maximum (FWHM). The photoluminescence (PL) spectra at 7.8 K show the resolved intensive exciton emission line and the weak DAP emission band. The deep-level emissions are not observed. The measurement of the electrical and radiographic properties show that Leadiodide (PbI₂) single crystal has a resistivity of 5×10¹⁰ Ω cm and imager lag is 8 s, respectively. In order to improve the controllability of crystal growth, PbI₂ single crystals were also grown from a lead (Pb) excess PbI₂ source. The experimental results show very good reproducibility. In addition, the growth models of crystal are proposed, and the growth mechanism is discussed.     

Vapour diffusion growth and characterisation of fully deuterated triglycine sulphate (ND2CD2COOD)3D2SO4

A new vial-in-vial vapour diffusion method for growing single crystals of fully deuterated triglycine sulphate (TGS) has been developed. Single crystals of hydrogenous TGS were also grown for comparison purposes. The crystals have been characterised using x-ray diffraction and differential scanning calorimetry. The phase transition temperature was 334.0±0.5 K for fully deuterated TGS compared to 322.3±0.3 K for hydrogenous TGS. These values compare well with the expected T_C.     

Growth of CdSiP2 single crystals by self-seeding vertical Bridgman method

Using a high purity CdSiP₂ polycrystalline charge synthesized in a single-temperature zone furnace, a CdSiP₂ single crystal with dimensions of 8 mm in diameter and 40 mm in length was successfully grown by the vertical Bridgman method. The quality of the crystal was characterized by high resolution X-ray diffraction and the full width at half maximum (FWHM) of the rocking curve for the (200) face is 33″. Thermal property measurements show that: the mean specific heat of CdSiP₂ between 300 and 773 K is 0.476 J g^?1 K^?1; the thermal conductivity of the crystal along the a- and c-axes is 13.6 W m^?1 K^?1 and 13.7 W m^?1 K^?1 at 295 K, respectively; and the thermal expansion coefficient measured along the a- and c-axes is 8.4×10^?6 K^?1 and ?2.4×10^?6 K^?1, respectively. The optical transparency range of the crystal is 578–10,000 nm, and there is no absorption loss in the spectrum from 0.7 to 2.5 μm, as often exists with ZnGeP₂ crystals grown from the melt.     

Human 17β-hydroxysteroid dehydrogenase-ligand complexes: crystals of different space groups with various cations and combined seeding and co-crystallization

Human estrogenic 17β-hydroxysteroid dehydrogenase (17β-HSD1) is responsible for the synthesis of active estrogens that stimulate the proliferation of breast cancer cells. The enzyme has been crystallized using a Mg²⁺/PEG (3500)/β-octyl glucoside system [Zhu et al., J. Mol. Biol. 234 (1993) 242]. The space group of these crystals is C2. Here we report that cations can affect 17β-HSD1 crystallization significantly. In the presence of Mn²⁺ instead of Mg²⁺, crystals have been obtained in the same space group with similar unit cell dimensions. In the presence of Li⁺ and Na⁺ instead of Mg²⁺, the space group has been changed to P2₁2₁2₁. A whole data set for a crystal of 17ß-HSD1 complex with progesterone grown in the presence of Li⁺ has been collected to 1.95 Å resolution with a synchrotron source. The cell dimensions are a=41.91 Å, b=108.21 Å, c=117.00 Å. The structure has been preliminarily determined by molecular replacement, yielding important information on crystal packing in the presence of different cations. In order to further understand the structure–function relationship of 17β-HSD1, enzyme complexes with several ligands have been crystallized. As the steroids have very low aqueous solubility, we used a combined method of seeding and co-crystallization to obtain crystals of 17β-HSD1 complexed with various ligands. This method provides ideal conditions for growing complex crystals, with ligands such as 20α-hydroxysteroid progesterone, testosterone and 17β-methyl-estradiol-NADP⁺. Several complex structures have been determined with reliable electronic density of the bound ligands.     

Effect of tellurium deposition rate on the properties of Cu–In–Te based thin films and solar cells

To investigate the effects of tellurium (Te) deposition rate on the properties of Cu–In–Te based thin films (Cu/In=0.30–0.31), the films were grown on both bare and Mo-coated soda-lime glass substrates at 200 °C by co-evaporation using a molecular beam epitaxy system. The microstructural properties were examined by means of scanning electron microscopy and X-ray diffraction. The crystalline quality of the films was improved with increase in the deposition rate of Te, and exhibited a single CuIn₃Te₅ phase with a highly preferred (1 1 2) orientation. Te-deficient film (Te/(Cu+In)=1.07) grown with a low Te deposition rate showed a narrow bandgap of 0.99 eV at room temperature. The solar cell performance was affected by the deposition rate of Te. The best solar cell fabricated using CuIn₃Te₅ thin films grown with the highest deposition rate of Te (2.6 nm/s) yielded a total area (0.50 cm²) efficiency of 4.4% (V_oc=309 mV, J_sc=28.0 mA/cm², and FF=0.509) without light soaking.     

Electromechanical and electro-optic properties of xBiScO3–yBiGaO3–(1−x−y)PbTiO3 single crystals

Single crystals in the xBiScO₃–yBiGaO₃–(1−x−y)PbTiO₃ (BS–BG–PT) system were grown by the high temperature solution method using Pb₃O₄ and Bi₂O₃ as the flux. The dielectric permittivity (ε_r) at room temperature for unpoled tetragonal crystals was determined to be 500–600 with dielectric loss tangents less than 0.3%. The Curie temperature was found to be around ∼420–450°C, with a dielectric maximum, exhibiting relaxor behavior. The longitudinal piezoelectric coefficient (d₃₃) was found to be ∼300 pC/N for 〈0 0 1〉 oriented tetragonal crystals with electromechanical coupling factor (k₃₃) of 75%, with a shear mode, d₁₅∼290 pC/N and k₁₅∼45%, lateral mode, d₃₁∼−55 pC/N and k₃₁∼−37%. The remnant polarization (P_r) was 46 μC/cm² with a coercive field (E_c) of 43 kV/cm at 1 Hz and DC field of 60 kV/cm. The linear electro-optic (E-O) coefficients of poled crystals determined using an automated scanning Mach–Zehnder interferometer method at room temperature and wavelength of 632.8 nm were r₃₃=36 and r₁₃=4 pm/V, respectively.     

Characterization of Eu3+-doped fluorophosphate glasses for red emission

Fluorescence spectra and decay curves of the ⁵D₀ level for different concentrations of Eu³⁺ (4f⁶) ions in K–Ba–Al fluorophosphate glasses have been measured at room temperature and are analyzed. The Judd–Ofelt intensity parameters Ω₂ and Ω₄ have been determined from the intensity ratios of emission peaks corresponding to ⁵D₀ → ⁷F_J (J = 2 and 4) to ⁵D₀ → ⁷F₁ transitions for 1.0 mol% glass. The intensity parameters thus obtained are in turn used to calculate the radiative properties of the fluorescent levels of Eu³⁺ ions. Second and fourth rank crystal-field parameters have been evaluated by assuming a C_2V site symmetry for the local environment of Eu³⁺ ions to estimate the crystal-field strength experienced by Eu³⁺ ions in the present host. The decay profiles of the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions in the present glasses are found to be single exponential for all the studied Eu³⁺ ion concentrations. A marginal increase in lifetime of the ⁵D₀ level has been noticed with Eu³⁺ ion concentration up to 2.0 mol% and then the lifetime marginally decreases for higher Eu³⁺ ion concentrations.     

Growth improvement and characterization of AgGaxIn1−xSe2 chalcopyrite crystals using the horizontal Bridgman technique

AgGa_xIn_1?xSe₂ single crystals with x=0.4 have been grown by the horizontal Bridgman technique for nonlinear optical application requires phase matching. High purity polycrystalline synthesis of AgGa_xIn_1?xSe₂ was carried out at 850 °C, which is a relatively lower temperature compared to those in earlier reports, thus reducing secondary phase formation. An average Ga:In ratio of 62:38 (±3%) was measured using energy dispersive spectroscopy (EDS). As grown, a single crystal shows very high IR transmission of ～65% in the spectral range of 4000–600 cm^?1. There was no significant change in its IR transmission after annealing it at 500 °C for 20 days in vacuum in the presence of AgGa_xIn_1?xSe₂ powder. This indicates a low concentration of defects in the crystal. The results demonstrate that the improved new synthesis method for crystal growth was promising and that the quality of the crystal was good.     

Crystal growth and spectral properties of Nd3+:Ca9Gd(VO4)7 crystal

An Nd³⁺:Ca₉Gd(VO₄)₇ crystal with dimensions of ?25×30 mm³ was grown by the Czochralski method. The hardness, thermal expansion coefficient and thermal conductivity coefficient of the crystal were measured. The spectroscopic characteristics of Nd³⁺:Ca₉Gd(VO₄)₇ crystals were investigated. The absorption band at 810 nm has an FWHM of 10 nm, and absorption cross-sections are 5.81×10^?20 cm² for π-polarization and 7.47×10^?20 cm² for σ-polarization at 810 nm. The emission cross-sections at 1067 nm are 4.2×10^?20 and 6.5×10^?20 cm² for π- and σ-polarizations, respectively. The quantum efficiency η_c is equal to 94.3%. To sum up the above results, Nd³⁺:Ca₉Gd(VO₄)₇ crystal can be regarded as a highly efficient solid state laser material.     

Characterization of deep levels in a-plane GaN epi-layers grown using various growth techniques

To study the correlation between defects and deep levels in a-plane GaN films grown on r-plane sapphire substrates, transmission electron microscopy (TEM) and deep level transient spectroscopy (DLTS) have been performed on three types of a-plane GaN samples grown using modified two-step growth (sample I), SiN_x interlayer (sample II), and patterned insulator on sapphire substrate (sample III). From the microstructure evolution in cross-sectional TEM images, it was shown that combination of growth techniques is highly efficient in the reduction of dislocation densities. Average dislocation densities of samples I, II, and III were about 2.2×10⁹ cm^?2, 1.1×10⁹ cm^?2, and 3.4×10⁸ cm^?2, respectively. The trap a_t E_c–E_t～0.13 eV (E1) was observed in only sample I, and three electron traps at 0.28–0.33 eV (E2), 0.52–0.58 eV (E3), and 0.89–0.95 eV (E4) from the conduction band edge were measured common to all the samples. The analysis of trap properties indicated that E2 and E3 trap levels are strongly associated with the partial dislocations in a-plane GaN films.     

Lower dimer impurity incorporation may result in higher perfection of HEWL crystals grown in microgravity: A case study

Crystals of tetragonal hen egg white lysozyme (HEWL) grown on a series of space missions and their terrestrial counterparts were analyzed by gel electrophoresis and X-ray diffraction. The crystals were produced by vapor-diffusion and dialysis methods. The microgravity and terrestrial grown HEWL crystals were found to have effective partitioning coefficients (K_eff) for an oxidatively formed covalent dimer impurity (MW 28 K) of 2 and 9, respectively, i.e. the latter contain 4.5 times more dimers. The microgravity grown crystals allowed the collection of 24% more useful reflections and improved the resolution from 1.6 to 1.35 Å. Other improvements were also noted including lower isotropic B-factors of 16.9, versus 23.8 Å² for their terrestrial counterparts. High-resolution laser interferometry was applied quantitatively to evaluate the influence of dimer impurity on growth kinetics. It is shown that the growth of the (1 0 1) face from solution into which 1% dimers were introduced decelerates with increasing solution flow rate and the growth stops at a flow rate of about 0.2 mm/s. This effect occurs faster than in ultrapure solutions. The covalently bound dimers essentially increase the amplitudes of the striation-inducing growth rate fluctuations. The effect is ascribed to the enhanced transport of growth inhibiting HEWL dimer to the interface. Theoretical analysis shows that a stagnant solution around a growing crystal is strongly depleted with respect to impurity by about 60% for the measured growth parameters as compared to the solution bulk. Thus, a crystal in microgravity grows from essentially purer solution than the ones in the presence of convection flows. Therefore, it traps less stress inducing impurity and should be more perfect. For crystal/impurity systems where K_eff is small enough microgravity should have an opposite effect.