Synthesis and characterization of PbI2 polycrystals

Single‐phase PbI₂ polycrystalline material for single crystal growth was synthesized by two‐temperature vapor‐transporting method (TVM), directly from highly pure lead and iodine with excess lead without according to the PbI₂ stoichiometry. It is found that there is an immiscible phenomenon of two melts in the synthesis experiment, and the melts solidified until cooled down to room temperature. X‐ray diffraction (XRD) analysis and Energy dispersive X‐ray (EDX) microanalysis indicate that the solidified materials are single‐phase PbI₂ polycrystal and nearly pure lead. Considering the observed immiscible phenomenon and the data given in paper [1], it is able to confirm that there is a new immiscible region L₂+L₃ in Pb‐I phase diagram, which is very important to PbI₂ polycrystal synthesis and single crystal growth. Using single‐phase PbI₂ polycrystalline material synthesized by our method, PbI₂ single crystal with size of ?15mm×30mm was grown by vertical Bridgman method. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Growth of PbI2 single crystal by the top seed vertical zone melting method

PbI₂ is a type of syntectic compound, and its single crystal is one of the room temperature semiconductor nuclear radiation detector materials. A new method for the growth of the PbI₂ single crystal is proposed in this article, which was named the top seed vertical zone melting method (TSVZMM), directly from the synthesis of polycrystal with analytically pure lead and iodine, by controlling the decomposition and stratification of the melt and the stoichiometry of the PbI₂ crystal. Impurities in the crystal and the coagulating droplets of lead were eliminated during the PbI₂ crystal growth process from the top to bottom by TSVZMM. The PbI₂ single crystal was successfully grown with the size of Φ15 mm×15 mm, an infrared transmittance of more than 40%, a resistivity of 2×10¹² Ω cm magnitude and stoichiometry close to its theoretical value.     

Impurity induced structural phase transformations in melt grown single crystals of lead iodide

Lead iodide is a wide‐band gap and highly resistive semiconductor considered to be a promising room temperature nuclear detector. The phenomenon of polytypism is posing interesting problems of phase transformations among its polytypic modifications and formation of polytypic admixture during growth due to native impurities. Transformations have also been observed even when the material is stored for few months that causes deterioration in functioning of the PbI₂ devices. Lead iodide has been purified and single crystals were grown using zone‐refining system. The observed phase transformations during growth and storage have been explained in the light of distortion of [PbI₆]^4‐ octahedron due to impurities present in the material and the known crystal structures of PbI₂. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth,etching morphology and spectra of LiAlO2 crystal

γ‐LiAlO₂ single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X‐ray rocking curve and chemical etching. The effects of air‐annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO₂ were also investigated in detail. The results show that the as‐grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7‐22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×10³ cm^–2. The VTE‐treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air‐annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterisation of potassium cobalt nickel sulfate hexahydrate for UV light filters

A new single crystal for ultraviolet light filter, KCNSH (Potassium Cobalt Nickel Sulfate Hexahydrate) was designed and its crystal structure was studied using X‐ray diffraction in this paper. The empirical of the title compound is K₂Co_0.1Ni_0.9(SO₄)₂.6H₂O with formula weight 437.15. KCNSH crystal belongs to the monoclinic space group P2(1)/c, a=6.1390(3)Å, b=12.1839(6)Å, c=9.0095(4)Å, α=γ=90°, β=105.060(2)°, V=650.74(5)ų, Z=2, Dc=2.231g/cm³. Using the cooling solution method, we have grown a deep green KCNSH crystal with dimension of 12×12×40mm³. The transmission spectrum of KCNSH in the range from UV to near IR wavelengths, its thermal properties, and the relationship between the structure and optical transmission properties are also studied and further discussed in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure,growth and optical properties of Zn0.24Ni0.76(SO4)·7H2O single crystal

A new crystalline complex zinc nickel sulfate heptahydrate (ZNSH) has been prepared. The crystal structure was investigated by x‐ray single crystal diffraction method and the empirical formula is Zn_0.24Ni_0.76(SO₄)·7H₂O. The ZNSH crystal belongs to the orthorhombic space group P2₁2₁2₁ with cell parameters a = 6.7742(14) Å, b = 11.748(2) Å, c = 12.009(2) Å. The deep‐green ZNSH single crystal with dimension of 30 × 25 × 25 mm³ has been grown by the cooling solution method. The constituent ratio of ZNSH crystal grown from various compounding solutions at temperature range 40‐50 °C is approximate invariant. The crystal absorption spectra with theoretical analysis are reported. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Structural and Spectral Studies of ZnKPO4 · 6H2O Crystals

Zinc Potassium Phosphate Hexahydrate (ZPPH) is analogous to naturally occurring struvite. ZPPH crystals are grown by slow evaporation technique. These crystals are characterised by x‐ray and infrared studies. Powder x‐ray pattern indicates the orthorhombic crystal structure analogous to struvite with unit cell parameters a = 5.964, b = 5.808 and c = 12.495 Å. Infrared spectrum is characteristic of H₂O and PO₄^3‐ radicals.     

Growth of Inclusion Free KTP Crystals by Top Seeded Solution Growth and their Characterization

KTiOPO₄ single crystals of dimensions 34 × 15 × 15 mm³ have successfully been grown by Top Seeded Solution Growth (TSSG), using phosphate flux (K₆P₄O₁₃), employing a home made vertical cylindrical three zone resistive heated furnace. Growth experiments were carried out with <001> seed orientation. A method to grow inclusion free crystal with less dislocation density is proposed, by employing cooling rate of 0.5‐2 K/day and rotation rate of 60‐30 rpm. UV‐VIS transmission studies were performed and the dependence of absorption coefficient with wavelength is discussed. SHG elements of dimension 8 × 7.5 × 7.5 mm³ were fabricated and conversion efficiency of 58 % was achieved without antireflection coating. Nature of ionic conductivity and ferroelectric phase transition behavior of KTP crystals along the crystallographic polar axis in the frequency range of 100 Hz – 10 MHz are discussed.     

Preparation and Properties of a Novel Nonlinear Optical Crystal: MnHg(SCN)4(H2O)2.2(C3H6CONCH3)

In this article, diaquatetrakis (thiocyanato) manganese(II) mercury(II)‐N‐methyl‐2‐pyrrolidone, MnHg(SCN)₄(H2O)₂.2(C₃H₆CONCH₃), (abbreviated as MMTWMP), a new organometallic nonlinear optical crystal material is reported. The structure, optical and thermal characterizations were determined by elemental analysis, infrared and Raman spectroscopy, X‐ray powder diffraction, thermogravimetric analysis, differential scanning calorimetry, special heat, SHG measurements and UV/Vis/NIR optical transmission spectra. It belongs to the tetragonal crystallographic system, with cell parameters: a = 12.1294, c = 8.2238Å, V = 1211.27ų. Single crystals with dimensions up to 8 × 7 × 5 mm³ have been obtained. The morphology of the crystals was indexed. The MMTWMP crystal exhibits good physicochemical stability at normal temperature and pressure. Its UV transparency cutoff is 360 nm, which is shifted to the violet by 13 nm, as compared with MnHg(SCN)₄ (MMTC); the optical transmission is 44.82% at 404 nm, which is by 17.46% higher than that of MMTC.     

Enhancement of thermoelectric efficiency in vapor deposited Sb2Te3 and Sb1.8In0.2Te3 crystals

Pure and indium doped antimony telluride (Sb₂Te₃) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb_1.8In_0.2Te₃ crystals (155 μVK⁻¹, 2.669 × 10⁻³ W/mK²) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10⁻³ K⁻¹ for vapour grown Sb_1.8In_0.2Te₃ platelets indicates that it could be used as a potential thermoelectric candidate.     

Effect of γ‐irradiation on spectral properties of undoped Y2SiO5 crystals

The absorption spectra of undoped Y₂SiO₅ crystals were studied before and after γ‐irradiation. After γ‐irradiation, the additional absorption peaks at 260‐270 and 320nm were observed in as‐grown and H₂‐annealed Y₂SiO₅ crystal, but it did not occur in air‐annealed Y₂SiO₅ crystal. These absorption peaks were attributed to F color centers and O^– hole centers, respectively. Owing to more oxygen vacancies and color centers in H₂‐annealed Y₂SiO₅ crystal than that in as‐grown Y₂SiO₅ crystal after γ‐irradiation, the additional absorption peaks were more intense in the former than that in the latter. With the irradiation dose increasing from 20 to 220kGy, the intensity of additional absorption peaks increased. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Crystal data and some physical properties of Tl2InGaTe4 crystals

The room temperature crystal data, Debye temperature, dark and photoelectrical properties of the Bridgman method grown Tl₂InGaTe₄ crystals are reported for the first time. The X‐ray diffraction technique has revealed that Tl₂InGaTe₄ is a single phase crystal of tetragonal body‐centered structure belonging to the space group. A Debye temperature of 124 K is calculated from the results of the X‐ray data. The current‐voltage measurements have shown the existence of the switching property of the crystals at a critical voltage of 80 V. The dark electrical resistivity and Hall effect measurements indicated the n ‐type conduction with an electrical resistivity, electron density and Hall mobility of 2.49×10³ Ω cm, 4.76×10¹² cm^–3 and 527 cm²V^–1s^–1, respectively. The photosensitivity measurements on the crystal revealed that, the variation of photocurrent with illumination intensity is linear, indicating the domination of monomolecular recombination at room temperature. Moreover, the spectral distribution of the photocurrent allowed the determination of the energy band gap of the crystal studied as 0.88 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X‐Ray Powder Diffraction,DTA and Vibrational Studies of CdNH4PO4.6H2O Crystals

Cadmium Ammonium Phosphate Hexahydrate (CAPH) is analogous to naturally occurring struvite. CAPH crystals are grown by slow evaporation technique. These crystals are characterised by X‐ray, TG‐DTA and Infra‐red studies. Powder X‐ray pattern indicates the orthorhombic crystal structure analogous to struvite. TG‐DTA analysis suggests loss of water of hydration (6H₂O) between 113 and 391°C. Later the substance melts and only Cd remains around 780 °C. Infra Red spectrum is characteristic of H₂O, PO₄^3‐ and NH₄⁺ radicals.     

Growth and characterization of a new langasite‐type single crystal Sr3NbAl1.5Ga1.5Si2O14

Single crystals of Sr₃NbAl_1.5Ga_1.5Si₂O₁₄ (SNAGS) with langasite structure have been successfully grown by Czochralski method. The X‐ray diffraction (XRD) verified that the as‐grown crystal was isostructural with A₃BC₃D₂O₁₄ structure and the lattice parameters were calculated as follows: a = 8.242 Å, c = 5.041 Å, V = 296.6 ų. The piezoelectric coefficient d₁₁ was 5.7pC/N, which was 2.47 times of α‐quartz (d₁₁=2.31pC/N). The electric resistivity was up to 3.04×10⁶ Ωcm at 700 °C for X‐cut sample. In addition, the transmission spectrum of the SNAGS crystal showed that it had a high transmittance (>80%) in the range of 350‐800 nm and exceeded 90% above 520 nm. These results suggest that the SNAGS crystals have potential applications in high‐temperature piezoelectric sensors and optical techniques. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Top‐seeded growth,optical properties and theoretical studies of noncentrosymmetric Te2V2O9

A single crystal of Te₂V₂O₉ with dimensions of 15×15×5 mm³ has been grown by the top‐seeded growth method. Infrared and transmission spectra indicate the transmission cutoff wavelength of Te₂V₂O₉ crystal is about 620 nm in visible region and 6.2 μm in infrared region. In addition, band structure and density of states calculations of Te₂V₂O₉ were carried out using the total‐energy code CASTEP based on density functional theory. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal and infrared studies of calcium malate crystals grown in diffusion limited medium

Single crystals of the title compound Ca (C₄H₅O₅)₂.10H₂O are grown in silica gel using controlled chemical reaction method. Multifaceted single crystals of size up to 8 × 4 × 2 mm³ are obtained. Powder X‐ray Diffraction (XRD) pattern of the grown crystal and the Fourier Transform Infra‐Red (FTIR) spectrum in the range 400–4000 cm^–1 are recorded. The vibrational bands corresponding to different functional groups are assigned. Thermal decomposition stages observed in the Thermo‐gravimetric (TG) and Differential Thermal Analysis (DTA) studies are discussed. A six‐stage thermal decomposition scheme is proposed for the compound. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and spectral analysis of Dy3+ and Er3+ doped KPb2Cl5 as a mid‐infrared laser crystal

This paper reports crystal growth and optical characteristics of dysprosium (Dy³⁺) and erbium (Er³⁺) doped mid‐infrared laser crystal ternary‐potassium‐lead‐chloride (KPb₂Cl₅). Two transparent crystals with good optical quality have been grown successfully by using the Bridgman technique,the largest crystal size reaches up to ∅︁10×60mm². Measurements of X‐ray diffraction(XRD) and absorption spectra were carried out. Based on Judd‐Ofelt theory, the intensity parameters Ω_t(t=2,4,6), the experimental and theoretical oscillator strengths have been obtained.The intensity parameters Ω_t(t=2,4,6) of Er³⁺:KPb₂Cl₅ were calculated to be Ω₂=5.10×10^‐20 cm², Ω₄=1.25×10^‐20 cm², Ω₆=0.83×10^‐20 cm², and the values for Dy³⁺:KPb₂Cl₅ were calculated to be Ω₂=6.26×10^‐20 cm², Ω₄=2.45×10^‐20 cm², Ω₆=0.04×10^‐20 cm² respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and spectroscopic investigation of Yb/Nd co‐doped KLu(WO4)2 laser crystals

Single crystals of Yb, Nd: KLu(WO₄)₂ (Yb, Nd: KLW) of dimensions up to 40mm× 40mm×5mm have been grown by top‐seeded solution growth (TSSG) method. X‐ray powder diffraction pattern was measured and compared with that of Nd: KLuW and Yb: KLuW. Absorption and fluorescence spectra were measured at room temperature. The Judd‐Ofelt theory was applied to analyze the spectrum of Nd, Yb: KLuW crystal. The intensity parameters Ω_t (t=2, 4 and 6) were calculated as Ω₂=20.68×10^‐20cm², Ω₄=11.04×10^‐20cm², Ω₆=6.74×10^‐20cm² respectively, with a root mean square deviation of 0.58×10^‐20 cm². (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth,structure and spectroscopic studies of a novel organic single crystal: L‐lysine p‐nitrophenolate monohydrate (LLNP)

A novel organic crystal, L‐lysine p‐nitrophenolate monohydrate (LLNP) has been grown successfully from an aqueous solution by the slow cooling method. Transparent single crystal of dimensions 22 × 12 × 12 mm³ has been obtained. The single crystal X‐ray diffraction has shown that LLNP belongs to the orthorhombic crystallographic system with space group P2₁2₁2₁. The functional groups and vibrational frequencies of the crystal have been identified using IR and Raman spectra. The proton and carbon configurations have been confirmed through ¹H‐NMR and ¹³C‐NMR spectra analyses. The UV‐Vis‐NIR transmittance spectrum for LLNP crystal has been recorded in the range from 200 to 2500 nm. The second harmonic generation (SHG) intensity of LLNP has been measured by powder SHG method and found to be as 4.2 times as that of KDP. The thermal properties have been studied by using thermo gravimetric (TG) and differential thermal analysis (DTA).