Crystal growth and characterization of the CMR compound La1.2(Sr,Ca)1.8Mn2O7

High-quality centimeter-sized single crystals of La_1.2Sr_1.8−yCa_yMn₂O₇ (0.0y0.2) were successfully grown using a floating zone method associated with an image furnace. We present the growth conditions together with a characterization of the single crystals by means of optical and electron microscopy, EDX and ICPAES analysis, DTA-TGA measurements and redox titration, X-ray powder diffraction, Laue X-ray back-reflection and neutron diffraction. We also stress the main aspects of the complex thermodynamical and kinetic behaviors of these compounds.     

Effect of Yb content on purity and crystal growth of Ba2NaNb5O15

Growth by the micro-pulling-down technique (μ-PD) of homogeneous and crack-free fiber single crystals with composition Ba₂Na_1−xYb_xNb₅O₁₅ (0<x<0.08) is reported. The effect of Yb³⁺ addition to barium sodium niobate (BNN, x=0), having the tungsten bronze-type structure, was examined by room temperature X-ray powder diffraction and differential thermal analysis coupled to thermogravimetry. In the region of the monophased field the structure is tetragonal from x=0.02 to 0.16. Volume change is mainly by variation of the a-axis length. Addition of Yb³⁺ to BNN could be effective for the production of high optical quality, crack-free, bulk crystals by the Czochralski technique.     

Growth by self-flux method and post-annealing effect of Bi2Sr2Ca1Cu2Ox single crystals

Post-annealing effects on superconducting characteristics have been studied in Bi₂Sr₂Ca₁Cu₂O_x single crystals grown by a conventional flux method. Also, favorable growth conditions and the effect of the pre-sintering process on the starting materials for flux growth have been examined. The best superconducting behavior is obtained in post-annealed crystals grown from pre-sintered powder materials. The critical current density J_c estimated from magnetization hysteresis in annealed crystals grown with pre-sintered materials is roughly 8×10⁵ A/cm² (Hc) and 5×10⁴ A/cm² (Hc) at 4.2 K at zero field.     

Growth and properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals directly from melt

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg_1/3Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d₃₃, remnant polarization P_r, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm², and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions.     

The effects of As and Te on the crystallization and optical gaps of selenium

Glasses with compositions Te_xSe_100−x (0x25 at.%), As_ySe_100−y (0y40 at.%) and As₂Te_zSe_98−z (0z25 at.%) were prepared. The effects of the additives As and Te on the crystallization behaviour and optical gaps of selenium were studied. The relationship between the above properties and the chemical bond nature of the glass constituents is discussed. Materials with long lifetime and high sensitivity can be obtained by the addition of certain amounts of As and Te into Se.     

Flux growth of PbMg1/3Ta2/3O3 single crystals

Single crystals of PbMg_1/3Ta_2/3O₃ (PMT) were grown by the flux method. The PbO–Pb₃O₄–B₂O₃ system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm³ were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz).     

Growth of pyroxene-type MnGeO3 and (Mn,Mg)GeO3 crystals by the floating-zone method

Pyroxene-type solid–solution crystals of (Mn_1−xMg_x)GeO₃ with x=0.06, 0.10 and 0.20 have been grown by the floating-zone method. The end member crystal of MnGeO₃ is broken into small pieces by the orthorhombic-to-monoclonic phase transition during cooling after growth. On the other hand, the solid–solution crystals keep the orthorhombic structure between the melting points and room temperature and no crack is formed. The unit cell volumes are significantly decreased with an increase in Mg content.     

Low-temperature growth of epitaxial layers of ZnSe1−xTex solid solutions

The layers of ZnSe_1−xTe_x (0 < x < 1.0) solid solutions have been grown by liquid-phase epitaxy in a closed tube at 620–680 °C. Zinc chloride served as a solvent. ZnTe and ZnSe crystals were used as sources and substrates with orienting surfaces (110) and (111) for ZnSe and (110) for ZnTe. The composition of the grown layer was specified by the relative content of the ZnSe and the ZnTe in the solution and was controlled by X-ray analysis. The position of the exciton bands in the photoluminescence spectra of ZnSe_1−xTe_x over the interval 0.3 < x < 1.0 is in agreement with the free exciton energies calculated for these compositions. Relatively low-ohmic (of about 10² Ω cm) epitaxial layers of ZnSe_1−xTe_x solid solutions were grown.     

Growth and characterization of a new nonlinear optical material: Potassium p-nitrophenolate dihydrate (NO2–C6H4–OK·2H2O) with new bonding properties

Single crystals of potassium p-nitrophenolate dihydrate (NPK·2H₂O) have been grown successfully using the isothermal solvent evaporation technique. It is a new semiorganic nonlinear optical crystal, possessing a d_eff of about 1.5 times that of lithium niobate and in which the K⁺ ions are bonded to the nitro group instead of bonding with the phenolic O⁻. Large single crystals of dimension upto 20×6×4 mm³ are harvested within a period of 60 days. The grown crystals are subjected to single crystal X-ray, FTIR and DRS-UV visible spectral, thermal and microhardness analyses. Single crystal X-ray analysis confirms the molecular formula and the structure of the crystal. FTIR spectral studies verify the functional groups present in the crystal. The DRS-UV visible spectrum proved the optical transparency of the crystal in the entire visible and near infrared region. Thermal studies reveal that the crystals are stable upto 180 °C. Microhardness measurements on the cleaved plane (1 1 0) explain the strength and slip direction in the crystal. The SHG efficiency of the crystal is examined by performing the Kurtz powder test using Nd:YAG laser.     

A glass-forming system with compound-forming tendency: As4S6---P4S10

Glasses in the quasi-binary system (As₄S₆)_x(P₄S₁₀)_1−x x = 0.1, …, 1.0, are produced and studied by thermal analysis, X-ray, and Raman spectroscopy. The phase diagram of the system and the critical cooling rate for glass formation both have their maximum at x = 0.5, corresponding to the compound As₂P₂S₈; the X-ray structure of recrystallized samples can be described as a sum of the As₂P₂S₈ (x = 0.5)- and the P₄S₁₀-structure (As₄S₆ not visible); Raman spectra of the glasses are again sums of As₂P₂S₈- and As₄S₆/P₄S₁₀-spectra. All these observations support the assumption that a stable building block corresponding to the 1:1 compound As₂P₂S₈ and surplus As₄S₆ (or P₄₁₀) are the essential elements of the structure in the glasses.     

Preparation and characterization of Ni-incorporated FeS2 single crystals

Nickel-incorporated FeS₂ single crystals with various Ni compositions of Fe_0.99S₂:Ni_0.01, Fe_0.98S₂:Ni_0.02, Fe_0.96S₂:Ni_0.04, and Fe_0.9S₂:Ni_0.1 were grown by chemical vapor transport (CVT) method using ICl₃ as a transport agent. Physical properties of the Ni-incorporated FeS₂ single crystals were characterized using X-ray diffraction, Raman spectroscopy, electrical conductivity, and photoconductivity (PC) measurements. By means of the analyses of the X-ray diffraction patterns, the whole series of Ni-doped FeS₂ single crystals were determined to be single-phase and isostructural. Raman spectroscopy of the Ni-doped FeS₂ crystals was carried out at room temperature. Raman resonant peaks of the Ni-doped FeS₂ crystals demonstrate an energy red-shift behavior with respect to the increase of the dopant densities. Conductivity measurements show the resistivity of the Ni-doped FeS₂ decreased as the doping concentration of Ni is increased. Nickel is an n-type dopant, which behaves like a donor level existed near the conduction band edge of the synthetic FeS₂. On the other hand, dopant effect of nickel on the synthetic FeS₂ also destroys the photoconductive sensitivity in the photoconductivity measurements.     

Solubility of YBa2Cu3O7−δ and Nd1+xBa2−xCu3O7±δ in the BaO/CuO flux

The knowledge of the phase relations and solubilities in the Y–Ba–Cu–O and Nd–Ba–Cu–O systems are of fundamental importance for crystal growth and liquid-phase epitaxy of YBa₂Cu₃O_7−δ (YBCO) and Nd_1+xBa_2−xCu₃O_7±δ (NdBCO). The determination of the solubility curve of YBCO and NdBCO in a BaO/CuO flux containing 31 mol% BaO was done by observation of the formation and dissolution of crystals on the surface of the high-temperature solution. The heat of the solution of YBCO at 1000°C was found to be 34.7 kcal/mol, and for NdBCO at 1060°C, it was found to be 28.1 kcal/mol. The determination of the solubility curves requires special care, and the problems of the time-dependent shift of the solution composition due to the corrosion of the crucible is discussed. The scatter of the solubility data published by different authors could be due to the use of solutions with different Ba : Cu ratios, different determination methods, i.e. different crystallization mechanisms, different crucibles and starting chemicals.     

Crystal growth of NdAl3(BO3)4 from K2O/MoO3/Nd2O3/B2O3/KF flux

NdAl₃(BO₃)₄ single crystals were grown by the flux method and the TSSG technique using a K₂O/3MoO₃/B₂O₃/0.5Nd₂O₃/KF flux system. Light-violet clear crystals could be obtained. The effects of fluoride on the growth of NAB crystals were investigated. As the content of KF was gradually increased, the growth form of NAB was changed from the equant to the columnar and the primary crystalline region of NAB was shrinked. At the ratio of KF/K₂O = 0.75, NAB crystals could not be grown.     

Growth of (CH3)2NH2CuCl3 single crystals using evaporation method with different temperatures and solvents

The bulk single crystals of low-dimensional magnet (CH₃)₂NH₂CuCl₃ (DMACuCl₃ or MCCL) are grown by a slow evaporation method with different kinds of solvents, different degrees of super-saturation of solution and different temperatures of solution, respectively. Among three kinds of solvent, methanol, alcohol and water, alcohol is found to be the best one for growing MCCL crystals because of its structural similarity to the raw materials and suitable evaporation rate. The best growth temperature is in the vicinity of 35 °C. The problem of the crystals deliquescing in air has been solved through recrystallization process. The crystals are characterized by means of X-ray diffraction, specific heat and magnetic susceptibility.     

Phase relations around langasite (La3Ga5SiO14) in the system La2O3–Ga2O3–SiO2 in air

Phase relations around langasite (LGS, La₃Ga₅SiO₁₄) were studied on the basis of phase assemblage observed during calcination and crystallization process of samples of various compositions in the ternary system La₂O₃–Ga₂O₃–SiO₂. A ternary compound of apatite structure, La₁₄Ga_xSi_9–xO_39–x/2 was found for the first time. Crystallization of this compound was observed in the cooling process of molten samples of stoichiometric LGS as well as LGS single crystal, demonstrating that LGS is an incongruent-melting compound. A phase diagram was established primarily based on the crystallization sequence in the cooling process.     

Tb2Fe17和Tb2（Fe,Si）17磁性单晶的生长和相图

利用磁悬浮冷坩埚提拉法技术生长了Tb2Fe17和Tb2(Fe,Si)17的单晶,并用差热分析等方法研究了材料的相图。研究结果表明：Tb2Fe17的相关系并非以往报道的包晶反应。而是同成分熔化。本文还给出了Tb2Fe17化合物附近的新相图。采用优化后的生长条件,获得了缺陷较少的Tb2Fe17和Tb2(Fe,Si)17高质量单晶,分析了Si替代对于化合物结构的影响,测量了Tb2Fe17单晶样品的基本磁性。从材料的一级磁化过程的测量可以看出,在理想配比条件下最容易获得缺陷密度低的单晶样品,这种磁性测量方法为了解单晶的完整性提供了一个有效的间接观察方法。     

Growth of Cu(AlxGa1−x)SSe pentenary alloy crystals by iodine chemical vapor transport method

Single crystals of Cu(Al_xGa_1−x)SSe pentenary alloys were successfully grown by the vapor transport technique using iodine as a transport agent. Systematic measurements of the basic crystal properties were carried out using powder X-ray, photoluminescence (PL), photoreflectance (PR), and Van der Pauw methods. Dependence of the lattice constants, exciton transition energies, and PL peak energies on Al composition, x, were examined in detail. The lattice constants obeyed Vegard's law. A quadratic dependence of exciton transition energies on x was found. The broadening parameters in the PR spectrum increase monotonically with increasing x, the results showing that the crystal quality degrades with increasing x. Exciton-related PL peaks were found for 0 ≤ x ≤ 0.77 at 77 K.     

XPS and electroluminescence studies on SrS1−xSex and ZnS1−xSex thin films deposited by atomic layer deposition technique

SrS_1−xSe_x and ZnS_1−xSe_x thin films were deposited by the atomic layer deposition (ALD) technique using elemental selenium as the Se source, thus avoiding use of H₂Se or organometallic selenium compounds. X-ray diffraction (XRD) analysis showed that the films were solid solutions and X-ray photoelectron spectroscopy (XPS) data showed that the surface of both ZnS_1−xSe_x and SrS_1−xSe_x were covered with an oxide and carbon-containing contaminants from exposure to air. The oxidation of SrS_1−xSe_x extended into the film and peak shifts from sulfate were found on the surface. Luminance measurements showed that emission intensity of the ZnS_1−xSe_x:Mn alternating current thin film electroluminescent (ACTFEL) devices at fixed voltage was almost the same as that of the ZnS:Mn device, while emission intensity of the SrS_1−xSe_x:Ce devices decreased markedly as compared to the SrS:Ce device. Emission colors of the devices were altered only slightly due to selenium addition.     

Growth, morphological and structural characterization of Pb1−xSnxTe single crystals

Pb_1−xSn_xTe single crystals have been grown by a vertical Bridgman method. They have typical Hall mobilities and carrier concentration values of 10³ cm²/V · s and 10¹⁸ cm^-3, respectively, and change from p- to n-type as the Sn content increases. The ingots were single crystal with a subgrain structure that has a misorientation no higher than 2′. The segregation of Sn has been determined and it suggests that there is a convective flow in the liquid.     

Growth, dielectric, ferroelectric and optical properties of Ca0.28Ba0.72Nb2O6 single crystals

Calcium barium niobate Ca_0.28Ba_0.72Nb₂O₆ (CBN-28) crystals were grown by the Czochralski method. The effective segregation coefficients of Ca, Ba, Na elements in CBN-28 crystal growth were measured, and the rocking curve from 0 0 2 reflection of CBN-28 wafer was also measured by the high-resolution X-ray diffractometer D5005, and the full-width at half-maximum value was measured to be 70.6″. The measured dependence of dielectric constants on temperature showed the Curie temperature of the CBN-28 crystals is between 246.8 and 260 °C. Typical polarization–electric field (P–E) hysteresis loops were measured at room temperature. Ferroelectric 180° domains were observed by scanning electron microscopy (SEM) on the etched (0 0 1) surface of the CBN-28 crystals. The transmittance of [0 0 1]-oriented CBN-28 crystals was measured and the result shows that optical properties of CBN-28 crystal are almost the same as those of SBN for wavelengths between 2500 and 7500 nm.