CdSe single crystals with n- and p-type of conductivity approaching intrinsic

The properties of CdSe single crystals grown by static sublimation in an atmosphere of the excess selenium vapor both in the presence of argon and without it have been analyzed. The conditions for obtaining p- and n-type single crystals are given.     

弛豫铁电单晶及织构陶瓷的研究进展

综述了近年来弛豫铁电单晶和织构陶瓷的制备及其介电、压电性能的研究进展。弛豫铁电单晶的制备方法主要有高温溶液法、布里奇曼法和固态再结晶法，尺寸可达40mm以上，(001)切片压电常数d33最大可达3000pC／N，k3达到0.93，但是成分不均匀仍是影响晶体压电性能的一个主要因素。织构陶瓷的制备方法主要为固态再结晶法(TGG法和RTGG法)，其耗时短、成本低，压电性能可达到单晶的60％～80％，介电常数甚至可以超过部分单晶，是一个新的发展方向。     

Transport Property of C60 and C70 Single Crystals

Since a few years ago, many studies have been carried out for C₆₀ single crystals in the interest of superconductivity¹⁾ and other physical and chemical properties as a new device material. Recently, such related properties have been also interested for C₇₀ single crystals. In order to clarify the mechanism of superconductivity of C₆₀ or to discover the superconductivity of C₇₀, it is necessary to investigate the fundamental transport properties of the non-doped single crystal. In this work, to compare those transport properties of non-doped C₆₀ and C₇₀ single crystals, temperature dependence of the resistance was measured for the both single crystals prepared by a sublimation method. Each activation energy for C₆₀ or C₇₀ at high temperature was determined and phase transition temperatures for the both were discussed.     

Growth and characterization of a new non-linear optical l-histidinium dihydrogen phosphate single crystal

New non-linear optical single crystal of l-histidinium dihydrogen phosphate was grown by slow evaporation and temperature lowering technique from aqueous solution. Solubility studies have been carried out for three different solvents (water, acetone and ethanol). The grown crystals have been subjected to single crystal X-ray diffraction analysis to identify the cell parameters and morphology. Optical transmission spectra reveal the optical properties of the grown crystals. The NLO property of the crystal has been confirmed by Kurtz SHG test. Comparing the output power it has been confirmed that l-HDP crystals possess higher SHG efficiency than KDP. Thermal studies were carried out to check the thermal stability of the crystals.     

Growth and properties of benzil doped benzimidazole (BMZ) single crystals

In the present work, we have made an attempt to study the effect of benzil doping on the properties of benzimidazole single crystals. For this purpose we have grown pure and benzil doped benzimidazole single crystals by vertical Bridgman technique. The grown crystals were characterized by various characterization techniques. The presence of dopants confirmed by powder X-ray diffraction (XRD). Crystalline perfection of the grown crystals has been analysed by high-resolution X-ray diffraction (HRXRD). The transmittance, electrical property and mechanical strength have been analysed using UV-vis-NIR spectroscopic, dielectric and Vicker's hardness studies. The relative second harmonic generation efficiency of pure and doped benzimidazole crystals measured using Kurtz powder test.     

Crystal growth in tellurium fluxes and characterization of RuS2 single crystals

RuS₂ single crystals have been grown in tellurium flux either by slow cooling or by concentrating the flux through an evaporation of Te. The initial ratio of Ru, S and Te is defined over a short range in order to obtain RuS₂; sulfur amounts lower than 1.5% gave rise to RuTe₂ single crystals.Single crystals were characterized by microprobe analysis and X-ray diffraction. Electrical properties were measured and the magnetic susceptibility was determined down to 4.2K. Photoelectrochemical studies shows that the properties of single crystals are strongly dependent on Te amount. Conditions of growth of pure RuS₂ are discussed.     

Growth and characterization of l-proline cadmium chloride monohydrate single crystals

A novel semi-organic material of l-proline cadmium chloride monohydrate (l-PCCM) has been successfully synthesized and single crystal was grown by slow evaporation solution growth technique at room temperature. The grown single crystals have been characterized by different instrumentation techniques like XRD, FTIR, UV-Vis-NIR and TG/DTA measurements. Its nonlinear optical property has been tested by Kurtz powder method. The mechanical properties of grown crystals have been studied using Vickers microhardness tester. Its relative SHG efficiency is two times higher than that of potassium dihydrogen phosphate (KDP) single crystal.     

Preparation of new ferroelectric glycine phosphite single crystals

An experimental procedure adopted to prepare the recent ferroelectric glycine phosphite single crystals is presented. As the crystal solubility in water depends on temperature, single crystals were grown from fine seed crystals in a saturated solution by employing the slow cooling technique. Transparent, colourless crystals with habit morphology weighing about 8 g were obtained within a month. The same procedure was used to grow single crystals with urea (UGPI). Powder X-ray diffraction studies as well as FTIR studies were carried out on both the crystals. The thermal properties of glycine phosphite (GPI) and UGPI across the ferroelectric phase transition temperature has been carried out. The results will be discussed in detail.     

Growth and single crystal XRD characterization of undoped and doped 4-hydroxyacetophenone

Good quality 4-hydroxyacetophenone and nitro-doped 4-hydroxyacetophenone crystals have been successfully grown from saturated methanol solution by slow cooling method. Then, 3-nitro-4-hydroxyacetophenone is incorporated as a dopant into single crystals of 4-hydroxyacetophenone to enhance the NLO property. The crystal structure and the packaging of molecules along the “a” and “c” directions have been obtained by single crystal X-ray diffraction studies. The mechanical properties of the grown crystals have been analysed using Vicker's microhardness tester.     

Growth and electrical characterization of the lead magnesium niobate-lead titanate (PMN-PT) single crystals for piezoelectric devices

The lead magnesium niobate-lead titanate is one of the new generations of piezoelectric materials with outstanding properties. Single crystals of 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) show superior properties as compared to piezoelectric ceramics and piezoelectric films in device applications. Large size crystals are required for specific applications. Previously, transparent and high quality PMN-PT single crystals have been grown in our laboratory using the high temperature flux method. The size of the obtained crystals was small and varied from 2 to 8 mm³, mostly showing regular prismatic shape. In present attempt, PMN-PT crystals are grown from the vertical gradient freeze method with no flux using congruent melt. Processing conditions and growth parameters have been optimized to increase the size and yield of the perovskite crystals including cooling rate, soak time and soak temperature. The size of the grown crystals obtained by this method is very large relatively and varied from 5 to 30 mm³. The microstructure of the as grown single crystals is investigated by scanning electron microscopy. Piezoelectric properties of the grown crystals are also investigated. PMN-PT plates show excellent piezoelectric properties. Samples were poled under an applied electric field of 5 kV/cm. Dielectric properties at a frequency of 1 kHz are examined. Finally, the variation of pyroelectric coefficient with temperature is studied. The grown PMN-PT crystals show typical relaxor dielectric properties.     

Tensile plastic strain localization in single crystals of austenite steel electrolytically saturated with hydrogen

The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested Fe-18Cr-12Ni-2Mo single crystals of austenite steel with low stacking-fault energy has been studied using a double-exposure speckle photography technique. The main parameters of plastic-flow localization at various stages of the deformation hardening of crystals have been determined in single crystals of steel electrolytically saturated with hydrogen in a three-electrode electrochemical cell at a controlled constant cathode potential.     

弛豫型铁电体PZNT制备与性能研究的进展

本文综述了近年来国际上弛豫型铁电体PZNT的制备与介电、压电及电致伸缩性能研究的进展．PZNT单晶体的制备方法以高温PbO熔剂法为主,其尺寸已达40mm．随PT含量的变化,PZNT的顺电一铁电相交由弥散性、混合型变为一级相变;其铁电-铁电相变可由组份或电场诱导,由介电性能表征．压电性能在MPB处及偏向三方相一侧达到最佳,＜001＞切向的三方相与四方相单晶可分别作为频带宽、分辨率高、且阻抗匹配好的新一代声阵列与单个器件传感器．＜001＞向的PZNT单晶具有巨大的电致伸缩应变,可望成为高性能的固体驱动器．     

弛豫型铁电体PZNT制备与性能研究的进展

本文综述了近年来国际上弛豫型铁电体PZNT的制备与介电、压电及电致伸缩性能研究的进展．PZNT单晶体的制备方法以高温PbO熔剂法为主,其尺寸已达40mm．随PT含量的变化,PZNT的顺电一铁电相交由弥散性、混合型变为一级相变;其铁电-铁电相变可由组份或电场诱导,由介电性能表征．压电性能在MPB处及偏向三方相一侧达到最佳,＜001＞切向的三方相与四方相单晶可分别作为频带宽、分辨率高、且阻抗匹配好的新一代声阵列与单个器件传感器．＜001＞向的PZNT单晶具有巨大的电致伸缩应变,可望成为高性能的固体驱动器．     

Application of single crystals to achieve quantitative understanding of weld microstructures

Abstract

The inter-relationship between the weld pool shape and the weld microstructure is a critical factor that determines the physical integrity and other important properties offusion welds. In the present work, large single crystals of an Fe–15Ni–15Cr alloy have been used to increase basic understanding of the factors that influence the development of weld microstructures. Oriented ternary alloy single crystals were used to make electron beam welds along various principal directions lying in different principal crystallographic planes. Using oriented single crystals it was possible to obtain crucial microstructural information that is ordinarily lost when welds are made on normal polycrystalline specimens. This quantitative information regarding the microstructural properties of electron beam welds has provided valuable new insight into the fundamentals of the relationships between weld pool shapes and weld microstructures. A new three-dimensional geometrical analytical method has been developed to interpret the microstructural information resulting from welds made using oriented single crystals. This analytical method establishes a direct correlation between the three-dimensional weld pool shape and the dendritic microstructures that are observed in two-dimensional transverse micrographs, and can be used to reconstruct the three-dimensional weld pool shape. Single crystal multipass and single pass bicrystal welds have also been examined. Overlapping multipass single crystal welds showed remarkable reproducibility from pass to pass and replicated the microstructural patterns observed in single pass welds. The microstructure of butt welds joining two single crystals with different orientations showed a one to one correspondence with that associated with each individual crystallographic orientation, and the microstructure essentially represented a composite of two single pass microstructures corresponding to the individual crystal orientations.

MST/3166     

Linear and nonlinear optical properties of organic crystals: MBANP and its derivatives

In addition to possessing strong optical nonlinearity, the (−)-2-(α-methylbenzylamino)-5-nitropyridine (MBANP) crystal has been shown to have unusual linear optical properties. Two methyl derivatives of MBANP have now been synthesized and grown as large single crystals; their refractive indices have been measured as a function of frequency and second-harmonic generation, including the determination of the phase matching loci has been investigated. Data is also available on the racemic form of crystalline MBANP. The properties of this family of crystals have been reviewed and an attempt is made to relate the experimental responses of the crystals to their molecular structure and the calculated properties of the molecules.     

β-Ga2O3 crystal growing from its own melt

The applicability of several nonnoble materials for growing of β-Ga₂O₃ crystals using free crystallization in a crucible has been studied. The possibility of growing β-Ga₂O₃ crystals in crucibles made of single crystal sapphire has been demonstrated. Main features of the growth and properties of the obtained crystals have been investigated.     

Structure cristalline et proprietes physiques du spinelle Cu1−xTi2S4

The preparation, crystal structure and physical properties of normal spinel Cu_1−xTi₂S₄ are reported. A large range of compositions (0x0.44) has been observed. Single crystals have been obtained by chemical vapor transport reaction with iodine or chlorine pressure. The refinement of the structure (67 reflexions) corroborates the previous normal spinel structure and indicates for this crystal a composition of Cu_0.93Ti₂S₄. Electrical and magnetic properties have been measured for some single crystals. They are consistent with the metallic conductivity as shown by the proposed band structure model.     

Ni2+掺杂近化学计量比铌酸锂晶体的近红外发光特性

研究了Ni2+掺杂近化学计量比铌酸锂(Ni2+:SLN)晶体的近红外发光特性.用980 nm LD光激发,Ni2+:SLN单晶的近红外发光中心位于1087 nm,荧光峰半高宽约为72 nm.晶体荧光衰减特性的测定结果表明,其室温荧光寿命为～240μs.晶体的近红外的宽带发光,源于Ni2+离子八面体格位的3T2g(3F)...     

Relaxor properties of single crystals of Na1/2Bi1/2TiO3-KTaO3 solid solutions

Single crystals of Na_1/2Bi_1/2TiO₃-KTaO₃ (NBT-KT) solid solutions have been grown for the first time. The elemental composition of as-grown single crystals determined by X-ray diffraction corresponds to 0.81 NBT-0.19 KT. Measurements of the temperature dependences of dielectric characteristics showed that the obtained NBT-KT crystals possess clearly pronounced relaxor properties.     

Growth and magnetic characterization of large R2NiO4+δ (R=Pr, Nd) single crystals

To study the static and dynamic properties of the charge stripe phases in the nickelates by neutron scattering, single crystals are needed with a large volume (>1 cm³). We will report the optimization and growth of large R₂NiO₄₊ (R=Pr, Nd) crystals by the floating-zone technique in an image furnace. Crack-free single crystals of diameter 8–10 mm and length 80–90 mm have been obtained. The phase-purity of the crystals has been checked by powder X-ray diffraction, and information on the crystal quality has been obtained by X-ray and neutron diffraction. We will give an account of our investigations into the conditions needed to obtain the highest quality crystals, and we will discuss the magnetic studies by SQUID magnetometry.