Showing papers in "Crystal Research and Technology in 2010"

A review of polytypism in lead iodide

Abstract: Lead Iodide (PbI2) is an important inorganic solid for both basic scientific research and possible technological applications and in this brief review we discuss the structure of PbI2. Although the basic structure is a simple I-Pb-I layered structure with a [PbI6]4- near-octahedron being the basic building block, there are many ways of stacking the layers which results in many polytypes. We present 20 of the 23 entries for the structure of PbI2 from the Inorganic Structural Database and order them by polytype. This represents more than 80 years of crystallographic research in the structure of this compound. We present a simple way to view the 2H, 4H, 6H, and 6R polytypes and extend the procedure to higher-order polytypes. We note a relationship, not generally appreciated, between the distortion of the near [PbI6]4- octahedrons and the polytype. We suggest that the significance of vacancies has only recently been appreciated. We suggest that small discrepancies in structure determination are probably due to different distributions of vacancies and that there are, in practice, very many structures for macroscopic or even mesoscopic samples of a given polytype when vacancies are considered. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure and electrical properties of Mg-doped ZnO nanoparticles

Abstract: MgxZn1-xO (x=0.01-0.3) nanoparticles were synthesized by the sol-gel technique using solutions of Mg and Zn based organometalic compounds. The electrical properties of Mg doped zinc oxide (ZnO) were studied within wide temperature range from 300 to 500 K under the N2 gas flow (flow rate: 20 sccm) and in the frequency range from 40 Hz to 1 MHz for ac electrical measurements. The dc conductivities and the activation energies were found to be in the range of 10-9-10-6 S/cm at the room temperature and 0.26-0.86 eV respectively depending on doping rate of these samples. The ac conductivity was well represented by the power law Aωs. The conduction mechanism for all doped ZnO could be related to correlated barrier hopping (CBH) model. The complex impedance plots (Nyquist plot) showed the data points lying on a single semicircle, implying the response originated from a single capacitive element corresponding to the nanoparticle grains. The crystal structures of the MgxZn1-xO nanoparticles were characterized using X-ray diffraction. The calculated average particle sizes values of Zn1-xMgxO samples are found between 29.72 and 22.43 nm using the Sherrer equation. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and characterization of L‐alanine doped KDP crystals

Abstract: Potassium Dihydrogen Phosphate (KDP) is an excellent inorganic nonlinear optical (NLO) material with different device applications. Most of amino acids possess NLO property; therefore, it is of interest to dope them in KDP crystals. In the present study, amino acid L-alanine doped KDP crystals were grown by slow aqueous solvent evaporation technique. The doping of L-alanine was confirmed by the paper chromatography, the CHN analysis and the FT-IR spectroscopy. The powder XRD was carried out to assess the single phase nature of the samples. The effect of doping on thermal stability of the crystals was studied by TGA and the kinetic and thermodynamic parameters of dehydration were evaluated. As the amount of doping increased the thermal stability of crystals decreased. However, the second harmonic generation (SHG) efficiency and the UV-Vis spectroscopy studies indicated that as the L-alanine doping increased the SHG efficiency and optical transmission percentage increased. The dielectric behavior of the samples has been studied. The variation of dielectric constant, dielectric loss (tanδ), a.c.resistivity and a.c.conductivity with frequency of applied field in the range from 100 Hz to 100 kHz was studied. The dielectric constant and dielectric loss decreased with increase the value of frequency of applied field. The dielectric constant and the dielectric loss values of L-alanine doped KDP crystals were lower than the pure KDP crystals. The results are discussed. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis, structure and optical properties of zinc oxide hexagonal microprisms

Abstract: Zinc oxide (ZnO) pencil-head-like (PHL) microprisms were synthesized by a hydrothermal route using a zinc (Zn) plate as a source and substrate. The structural analysis confirmed the formation of ZnO with hexagonal wurtzite phase on the hexagonal Zn substrate and the growth of the ZnO microparticles along the [101] direction. The room temperature photoluminescence (PL) of the ZnO microprisms showed a sharp UV emission band located at around 380 nm, which is expected to originate from the radiative recombination of free excitons. The sharp UV emission band, with a full width at half-maximum of about 15 nm and an extremely weak visible emission, confirms the high crystal quality of the synthesized ZnO microprisms. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and characterization of L‐valine ‐ a nonlinear optical crystal

Abstract: The growth of a new nonlinear optical material L-valine by solvent evaporation method is reported here. To grow good quality crystals pH value of growth solution has been optimized and solubility of L-valine in different solvents and different pH values was determined. The grown crystals were characterized by IR, single crystal XRD, DTA and TGA, optical transmission and second harmonic generation (SHG) efficiency measurement. SHG efficiency of L-valine was found equivalent to KDP and its transmission is 75%-80% from ultraviolet to near IR region. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and properties of α‐Fe2O3 nanorods

Abstract: We report synthesis of α-Fe2O3 (hematite) nanorods by reverse micelles method using cetyltrimethyl ammonium bromide (CTAB) as surfactant and calcined at 300 °C. The calcined α-Fe2O3 nanorods were characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The result showed that the α-Fe2O3 nanorods were hexagonal structure. The nanorods have diameter of 30-50 nm and length of 120-150 nm. The weak ferromagnetic behavior was observed with saturation magnetization = 0.6 emu/g, coercive force = 25 Oe and remanant magnetization = 0.03 emu/g. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and characterization of calcium hydrogen phosphate dihydrate crystals from single diffusion gel technique

Abstract: Calcium hydrogen phosphate dihydrate (CaHPO4·2H2O, CHPD) a dissolved mineral in urine is known to cause renal or bladder stones in both human and animals. Growth of CHPD or brushite using sodium metasilicate gel techniques followed by light and polarizing microscopic studies revealed its structural and morphological details. Crystal identity by powder x-ray diffraction confirmed the FT-IR and FT-Raman spectroscopic techniques as alternate methods for fast analysis of brushite crystals which could form as one type of renal stones. P-O-P asymmetric stretchings in both FT-IR (987.2, 874.1 and 792 cm-1) and FT-Raman (986.3 cm-1, 1057.6 cm-1 and 875.2 cm-1) were found as characteristics of brushite crystals. Differential Scanning Calorimetry (DSC) analysis revealed brushite crystallization purity using gel method by studying their endothermic peaks. This study incorporated a multidisciplinary approach in characterizing CHPD crystals grown in vitro to help formulate prevention or dissolution strategy in controlling urinary stone growth. Initial studies with 0.2 M citric acid ions as controlling agent in the nucleation of brushite crystals further support the presented approach. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Ba ions substitution on multiferroic properties of BiFeO3 perovskite

Abstract: Dielectric, magnetic and ferroelectric properties of Bi1-xBaxFeO3(x = 0.1, 0.2 and 0.3) synthesized by solid state reaction method are reported. X-ray diffraction pattern showed that Bi1-xBaxFeO3was single phase. Ba substitution has led to a decrease in grain size and hence an increase in the electrical resistivity. The variation of dielectric constant and loss has been studied over a frequency range of 1 kHz – 2 MHz at room temperature. Ba doping leads to effective suppression of the spiral spin structure of BiFeO3, resulting in the appearance of net magnetization. Improved multiferroic properties of Bi0.8Ba0.2FeO3 ceramic with remnant magnetization and polarization 0.093 emu/g and 0.808 µC/cm2, respectively, were obtained. The evidence of ferromagnetism and ferroelectric hysteresis loops in Bi1-xBaxFeO3system at room temperature makes it a good candidate for potential applications. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of the substrate temperature on the structural, optical, and electrical properties of tin selenide thin films deposited by thermal evaporation method

Abstract: Thin films of tin selenide (SnSe) were deposited on sodalime glass substrates, which were held at different temperatures in the range of 350-550 K, from the pulverized compound material using thermal evaporation method. The effect of substrate temperature (Ts) on the structural, morphological, optical, and electrical properties of the films were investigated using x-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission measurements, and Hall-effect characterization techniques. The temperature dependence of the resistance of the films was also studied in the temperature range of 80-330 K. The XRD spectra and the SEM image analyses suggest that the polycrystalline thin films having uniform distribution of grains along the (111) diffraction plane was obtained at all Ts. With the increase of Ts the intensity of the diffraction peaks increased and well-resolved peaks at 550 K, substrate temperature, were obtained. The analysis of the data of the optical transmission spectra suggests that the films had energy band gap in the range of 1.38-1.18 eV. Hall-effect measurements revealed the resistivity of films in the range 112-20 Ωcm for films deposited at different Ts. The activation energy for films deposited at different Ts was in the range of 0.14 eV-0.28 eV as derived from the analysis of the data of low-temperature resistivity measurements.

Impedance analysis and high temperature conduction mechanism of flux grown Pb(Zn1/3Nb2/3)0.91Ti0.09O3 single crystal

Abstract: The electrical properties of Pb(Zn1/3 Nb2/3)0.91Ti0.09O3 single crystals over a wide range of frequencies (20 Hz to 2 MHz) and temperature (30 to 490 °C) were studied using impedance spectroscopic technique. A strongly frequency dependant Debye type relaxation process in crystals was observed. The activation energy for relaxation was found to be 1.72 eV. The nature of Cole-Cole plot reveals the contribution of only grain (bulk) effect in the sample. The temperature dependant conductivity was found to different in different temperature regions, which shows the presence of different carrier for conduction. The activation energy for conduction in the order of 1.69 eV suggested that the conduction process in higher temperature region is governed by the presence of lead vacancy defect in the sample. Further, the negative temperature thermistor behaviour of the system was explored and various associated parameters were calculated. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Biomineralization of struvite crystals by Proteus mirabilis from artificial urine and their mesoscopic structure

Abstract: In order to investigate the mineralization of struvite we performed the experiment of struvite growth process from artificial urine. The crystallization process was induced by Proteus mirabilis, as these bacteria are mainly isolated from infectious stones. The crystallization process occurred at conditions mimicking the real urinary tract infection. Our results show that struvite exhibits polar properties. This feature of struvite crystals is potentially very important in the case of binding additives which may either enhance or inhibit crystallization process. It seems also that the differences in the polarity of opposite faces of c-axis play important role in directing the struvite mesoscopic arrangement. We also described recent developments concerning curcumin – pigment extracted from the roots of turmeric commonly known as a spice added to various food preparations. Curcumin exhibited the effect against Proteus mirabilis inhibiting the activity of urease and consequently decreasing the efficiency of struvite growth. Therefore, curcumin belongs to phytoterapheutic components, which may be the alternative with relation to the antibiotic therapy. The paper concludes with a future outlook and goals in this field of research. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanocrystalline transparent SnO2‐ZnO films fabricated at lower substrate temperature using a low‐cost and simplified spray technique

Abstract: Nanocrystalline and transparent conducting SnO2- ZnO films were fabricated by employing an inexpensive, simplified spray technique using a perfume atomizer at relatively low substrate temperature (360±5 °C) compared with conventional spray method. The structural studies reveal that the SnO2-ZnO films are polycrystalline in nature with preferential orientation along the (101) plane. The dislocation density is very low (1.48×1015lines/m2), indicating the good crystallinity of the films. The crystallite size of the films was found to be in the range of 26–34 nm. The optical transmittance in the visible range and the optical band gap are 85% and 3.6 eV respectively. The sheet resistance increases from 8.74 kΩ/□ to 32.4 kΩ/□ as the zinc concentration increases from 0 to 40 at.%. The films were found to have desirable figure of merit (1.63×10–2 (Ω/□)–1), low temperature coefficient of resistance (–1.191/K) and good thermal stability. This simplified spray technique may be considered as a promising alternative to conventional spray for the massive production of economic SnO2 - ZnO films for solar cells, sensors and opto-electronic applications. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of citric acid concentration as emulsifier on perovskite phase formation of nano-sized SrMnO3 and SrCoO3 samples

Abstract: In this study the effects of citric acid concentration, used as organic emulsifier, on the perovskite phase formation of the nano strontium manganite or cobaltite samples were studied. Stoichiometric perovskites in the absence and presence of citric acid were prepared by drying a solution containing molar ratio of Sr(NO3)2/Mn(NO3)2·4H2O and Sr(NO3)2/Co(NO3)2·6H2O = 1 followed by calcination at 900 °C for 5 h. Citric acid concentration, selected to be 0.0, 0.3, 0.6, 1.0, 1.3, 2.5 and 5 times of the total number of moles of the nitrate ions. The results revealed that increase in the citric acid concentration, larger than number of moles of the nitrate ions equivalent, deteriorates the perovskite phase formation. Instead, a new phase of carbonates and metal oxides are appeared. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis, characterization and gas sensing properties of flowerlike In2O3 composed of microrods

Abstract: Flowerlike structured In{sub 2}O{sub 3} were successfully synthesized via a hydrothermal process and the subsequent calcinations. The obtained sample consists of microrods with an average diameter of 0.5-1{mu}m and a length of 1-3{mu}m. Structure and property of the sample were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The sensing properties towards trimethylamine (TMA) were examined at 200-400 C, which showed high sensitivity, better selectivity, and prompt response/recovery merits. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Effect of annealing temperatures on properties of sol-gel grown ZnO-ZrO2 films

Abstract: Mixed ZnO-ZrO2 films have been obtained by sol-gel technology. By using spin coating method, the films were deposited on Si and glass substrates. The influence of thermal annealings (the temperatures vary from 400 °C to 750 °C) on their structural properties has been studied. The structural behavior has been investigated by the means of XRD and FTIR techniques. The results revealed no presence of mixed oxide phases, the detected crystal phases were related to the hexagonal ZnO and to crystalline ZrO2. The sol-gel ZnO-ZrO2 films showed polycrystalline structure with a certain degree of an amorphous fraction. The optical transmittance reached 91% and it diminished with increasing the annealing temperatures. The optical properties of the sol-gel ZnO-ZrO2 films, deposited on glass substrates are excellent with high transparency and better then those of pure ZrO2 films, obtained at similar technological conditions. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Micro‐Raman spectroscopic investigations of cobalt phthalocyanine thin films deposited on quartz and diamond substrates

Abstract: In this paper we present study of cobalt phthalocyanine (CoPc) thin films deposited on quartz and diamond substrates. The different diamond substrates were obtained using chemical vapour deposition method (CVD). The micro-Raman scattering spectra of CoPc thin films deposited onto quartz and diamond substrates were investigated in the spectral range 200 – 1800 cm-1 at room temperature for different wavelengths excitation (488 nm and 785 nm). The Raman modes A1g and B1g are connected with different polymorphic of metallophthalocyanine phase of CoPc thin films deposited on substrates (α and β form). Using confocal and surface Raman mapping we also obtained information on polymorphic phase of CoPc layers deposited on different diamond substrates. We observed both, change and distribution of polymorphic phase of CoPc thin films deposited on the surface. The observed feature can be probably caused by the change of crystalline form of CoPc thin layer and different size of crystallites of the diamond substrates. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optimization of process parameters by Taguchi method in the recovery of lactose from whey using sonocrystallization

Abstract: Anti-solvent crystallization of lactose in the presence of ultrasound will reduce crystal size and the level of agglomeration as compared to the commercial cooling crystallization. It offers a potential route to enhance the physical properties as well as the rapid recovery of lactose. Since lactose recovery itself can reduce biological oxygen demand of whey by more then 80%, recovery of lactose from dairy waste stream (whey) solves the problems of dairy industries by improving economics of whey utilization and pollution reduction. In the present study, recovery of lactose from partially deproteinated whey using an anti-solvent (acetone) by sonocrystallization was optimized for finding the most influencing operating parameters; such as sonication time, anti-solvent concentration, initial lactose concentration in the whey and initial pH of sample mixture at three levels using L9-orthogonal method. The responses were analyzed for recovery of lactose from whey. The anti-solvent concentration and the sonication time were found to be most influencing parameters for the recovery of lactose and the recovery of lactose was found to be 89.03% at the identified optimized level. The crystal size distribution of recovered lactose was found to be narrower (2.5 – 6.5 μm) as compared to the commercial lactose crystals (3.5 – 9.5 μm). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Debye temperature and melting point of II‐VI and III‐V semiconductors

Abstract: In this paper, simple relations are proposed for the calculation of Debye temperature θD and melting point Tmof II-VI and III-V zincblende semiconductors. Six relations are proposed to calculate the value of θD. Out of these six relations, two are based on plasmon energy data and the others on molecular weight, melting point, ionicity and energy gap. Three simple relations are proposed to calculate the value of Tm. They are based on plasmon energy, molecular weight and ionicity of the semiconductors. The average percentage deviation of all nine equations was calculated. In all cases, except one, it was estimated between 3.34 to 17.42 % for θD and between 2.37 to 10.45 % for Tm. However, in earlier correlations, it was reported between 10.59 to 33.38% for θD and 6.96 to 14.95% for Tm. The lower percentage deviation shows a significant improvement over the empirical relations proposed by earlier workers. The calculated values of θD and Tm from all equations are in good agreement with the available experimental values and the values reported by different workers. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation and crystallographic characterization of crystalline modifications of 3,4:9,10‐perylenetetracarboxylic dianhydride at room temperature

Abstract: 3,4:9,10-Perylenetetracarboxylic dianhydride (PTCDA) powder obtained from Sigma-Aldrich was purified by three cycles of temperature gradient sublimation in an evacuated quartz glass tube providing variable conditions. By means of X-ray diffraction (XRD) analysis, a crystallographic characterization of the powders obtained during the sublimation process and selected single crystals was carried out evidencing the presence of a major {alpha}- and a minor {beta}-PTCDA component in all samples. Lattice parameters of high precision were obtained for {alpha}-PTCDA (a = 3.73283(4)A, b = 12.0328(6)A, c = 17.3998(4)A, {beta} = 98.689(2) , V = 772.57(4)A{sup 3} and d{sub 102} = 3.219(3)A) by whole-X-ray-powder-pattern-fitting of the experimental XRD pattern using the Le Bail approach. Employing a (001) KCl wafer as substrate for the material purification results in formation of single phase {alpha}-PTCDA accompanied by a decrease in the size of the crystallites which is attributed to the presumed lower temperature of the KCl wafers. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Effect of strontium chloride on the optical and mechanical properties of γ-glycine crystals

Abstract: Single crystals of γ-glycine have been grown from aqueous solution in the presence of small amount of strontium chloride. Single crystal X-Ray diffraction analysis was used to measure the unit cell parameters and to confirm the crystal structure. The grown crystals have also been subjected to powder X-Ray diffraction study to identify the crystalline nature. The presence of all the functional groups of the γ-glycine has been confirmed by Fourier Transform Infrared (FTIR) spectral analysis. The presence of hydrogen and carbon in the glycine molecules was confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. Optical behavior of the crystal was studied using UV – Visible absorbance spectroscopy and second harmonic generation (SHG) studies. The SHG efficiency of γ-glycine is greater than that of standard potassium dihydrogen phosphate (KDP). Mechanical strength of the γ-glycine crystal has been determined by microhardness studies. Thermal stability of the grown crystal is probed using thermo gravimetric analysis and differential thermal analysis. Laser damage threshold value has been determined using Q-switched Nd:YAG laser operating at 1064 nm and with 13 ns pulse width in single shot mode. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of indium content and rapid solidification on microhardness and micro‐creep of Sn‐Zn eutectic lead free solder alloy

Abstract: The Sn-Zn alloys have been considered as lead-free solders. In this paper, the effect of 0.0, 0.5, 1.0, 1.5 and 2.0 wt.% Indium as ternary additions on melting temperature, structure, microhardness and micro-creep of the Sn-9Zn lead-free solders were investigated. It is shown that the alloying additions of Indium to the Sn-Zn binary system result in a suppression of the melting point to 187.9 °C. From x-ray diffraction analysis, a new intermetallic compound phase, designated β-In3Sn is detected. The formation of an intermetallic compound phase causes a pronounced increase in the electrical resistivity and mechanical strength. Also, an interesting connection between dynamic Young's modulus and the axial ratio (c/a) of the unit cell of the β-Sn was found in which Young's modulus increases with increasing the axial ratio (c/a). The ternary Sn-9Zn-xIn exhibits creep resistance superior to Sn-9Zn binary alloy. The better creep resistance of the ternary alloy is attributed to solid solution effect and precipitation of In3Sn in the Sn matrix. The addition of small amounts of In is found to refine the effective grain size and consequently, improves hardness. The 89%Sn-9%Zn-2%In alloy is a lead-free solder designed for possible drop-in replacement of Pb-Sn solders. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure and humidity sensing properties of SnO2 zigzag belts

Abstract: A novel method was developed for synthesizing ultralong SnO2 zigzag belts with the assistance of CuO powder. The crystalline structure and morphology of SnO2 zigzag belts were characterized using x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The growth mechanism of the ultralong SnO2 zigzag belts and the catalytic behavior of the copper were discussed. The humidity sensor based on as-synthesized product shows high sensitivity and fast response time due to unique structure of the SnO2 zigzag belts with large surface-to-volume ratio. It can be found that the resistance of the SnO2 materials decreases obviously with increasing relative humidity (RH) at room temperature (26 °C). The results demonstrate that these SnO2 nanostructures are potential to be used as effective and high performance humidity sensors. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and morphology of nanosized zeolite L

Abstract: AFM is a powerful tool for imaging nanoscale surface features; it provides two and three dimensional crystal structure images and other information about actual surface of zeolite crystallites. In this paper, nanosized zeolite L is synthesized in different crystallization times and a study of crystal growth of zeolite L is reported using atomic force microscopy (AFM). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques are used for characterization of the as synthesized samples. TEM and two-dimensional AFM images indicate that the zeolite particles are in a nano-range and they have hexagonal structure. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of L‐ascorbic acid single crystals grown from solution with different solvents

Abstract: Single crystals of L-ascorbic acid, popularly known as vitamin-C, were grown from solutions with different solvents and solvent combinations by low temperature solution growth methods. The suitability of different solvents and solvent combinations such as acetone, ethanol, methanol, isopropyl alcohol, water, water + acetone (1:1), water + ethanol (3:1), water + isopropyl alcohol (3:1) and isopropyl alcohol + methanol (1:1) for crystal growth of L-ascorbic acid was found out by assessing the solubility and crystallization behaviours. Solubility of L-ascorbic acid in selected solvents and solvent combinations in a range of temperatures was determined by gravimetric method. Solution prepared with water, water + acetone (1:1), water + ethanol (3:1) and water + isopropyl alcohol (3:1) were yielded crystals with tabular, columnar and prismatic habits and their morphologies were evaluated by goniometry. Grown single crystals were characterized with various instrumental techniques such as powder X-ray diffraction, Fourier infrared spectroscopy, optical transmittance study, differential scanning calorimetry and second harmonic generation studies. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

X-ray topography and crystal orientation study of a nickel-based CMSX-4 superalloy single crystal

Abstract: A study of the crystal orientation and structural perfection of single crystal blades obtained by Bridgeman method from CMSX-4 nickel superalloy at various withdrawal rates between 1 and 5 mm/min was carried out using the Laue diffraction method and X-ray diffraction topography methods as well as electron scanning microscopy. Blades consisted mainly of the regular γ' phase, with [001]γ'-type direction close to the blade axis. The angle of deviation of the [001]γ' direction in relation to the blade axis changes between the blade locking piece and end. The dependence this angle on the distance from the locking piece has been named as the crystal orientation distribution (COD). It was found that the nature of COD changes with a change in the withdrawal rate. The change in the withdrawal rate also results in a rotation of [001]γ'-type direction in relation to the blade axis. The best blades in terms of orientation and structural perfection were obtained for the withdrawal rate of 3 mm/min. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

On the interpretation of metastable zone width in anti‐solvent crystallization

Abstract: Considering nonlinear dependence of solute concentration on anti-solvent–solvent composition a modified Nývlt-like equation based on traditional power-law relation between nucleation rate and developing supersaturation and a new equation based on the classical theory of three-dimension nucleation are proposed to explain the dependence of anti-solvent addition rate on metastable zone width defined as excessive anti-solvent composition in anti-solvent crystallization. The experimental data on the metastable zone width in anti-solvent crystallization of benzoic acid are analyzed and discussed from the standpoint of these equations. It is found that the new approach based on the classical nucleation theory provides better insight into the processes involved in anti-solvent crystallization. Analysis of the experimental results on anti-solvent crystallization of benzoic acid [D. O'Grady, M. Barret, E. Casey, and B. Glennon, Trans. IChemE A 85, 945, (2007)] revealed that: (1) the value of metastable zone width for a solvent–anti-solvent system is determined by the solute–solvent and solute–anti-solvent interactions, (2) the dependence of the metastable zone width on stirring is associated with the enthalpy of mixing, and (3) the new approach predicts a threshold anti-solvent addition rate associated with the setting up of an equilibrium between solvent and anti-solvent and a maximum anti-solvent addition rate connected with the induction period tind for the onset of crystallization. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Microwave assisted synthesis of hydroxyapatite nano strips

Abstract: Synthesis of hydroxyapatite (HAP) nano strips was carried out by chemical precipitation method followed by microwave irradiation. The microwave assisted reactions proceed at fast rates. It is found that the presence of the complex reagent EDTA plays an important role in the morphological changes of nanostructure hydroxyapatite. EDTA acts as a hexadentate unit by wrapping itself around the Ca2+ metal ion with, four oxygen and two nitrogen atoms and forms several five member chelate rings. The relative specific surface energies associated with the facets of the crystal determines the shape of the crystal. Scanning electron microscopy revealed the presence of hydroxyapatite nano strips with the range 50-100 nm in EDTA influenced HAP powders. Fourier transform-infrared spectroscopy (FT-IR) result combined with the X-ray diffraction (XRD) indicates the presence of amorphous hydroxyapatite (HAP) in the as-prepared material. X-ray patterns collected on the powder after heat-treatment at 1100 °C for 2 h in air exhibits single phase of HAP. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and properties of PbGeO3 nanostructures

Abstract: PbGeO3 nanostructures including nanofibers and nanobelts, have been synthesized via a facile hydrothermal method by the reaction between GeO2 and Pb(CH3COO)2·3H2O in the absence of any surfactant. The influences of synthetic parameters, such as reaction time, reaction temperature, and the concentration of ethylenediamine, on the morphologies and sizes of PbGeO3 nanostructures have been investigated. It is found that an evolution of PbGeO3 nanostructures from nanobelts to nanofibers is observed for the first time with the reaction time increased from 1 h to 6 h. The diameters of PbGeO3 nanofibers can be controled from 300–900 nm to 80–120 nm by adjusting the concentration of ethylenediamine. Under similar conditions, PbGeO3: Eu3+ nanofibers with rough surfaces can also be obtained. The photoluminescent spectra of PbGeO3: Eu3+ nanofibers exhibits two fluorescence emission peaks centered at around 591 and 614 nm as the excitation wavelength is 395 nm. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

X‐ray diffraction and magnetization studies of BiFeO3 multiferroic compounds substituted by Sm3+, Gd3+, Ca2+

Abstract: The multiferroic compounds Bi0.9Sm0.1FeO3, Bi0.9Gd0.1FeO3, Bi0.9Ca0.1FeO3, Bi0.9Sm0.05Ca0.05FeO3, and Bi0.9Gd0.05Ca0.05FeO3 were prepared by the conventional ceramic method and were characterized by X-ray diffraction, vibrating sample magnetometry, and differential scanning calorimetry. The compounds were found to have the rhombohedral perovskite-like structure, accompanied by a small residual Bi2Fe4O9 impurity phase. Magnetic hysteresis loops with enhanced remnant magnetization and coercive field were obtained for the Gd-containing compounds. The improvement of magnetic behavior of the Gd-containing compounds is thought to arise mainly from the partial suppression of the spiral spin structure and the stronger interaction between magnetic ions. The magnetic transition temperatures of the compounds were found to be in the range 300-310 °C. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)