Floating Zone Technique Research Articles

Effect of Marangoni number on thermocapillary convection and free-surface deformation in liquid bridges

Floating zone technique is a crucible-free process for growth of high quality single crystals. Unstable thermocapillary convection is a typical phenomenon during the process under microgravity. Therefore, it is very important to investigate the instability of thermocapillary convection in liquid bridges with deformable free-surface under microgravity. In this works, the Volume of Fluid (VOF) method is employed to track the free-surface movement. The results are presented as the behavior of flow structure and temperature distribution of the molten zone. The impact of Marangoni number (Ma) is also investigated on free-surface deformation as well as the instability of thermocapillary convection. The free-surface exhibits a noticeable axisymmetric (but it is non-centrosymmetric) and elliptical shape along the circumferential direction. This specific surface shape presents a typical narrow ‘neck-shaped’ structure with convex at two ends of the zone and concave at the mid-plane along the axial direction. At both θ = 0° and θ = 90°, the deformation ratio ξ increases rapidly with Ma at first, and then increases slowly. Moreover, the hydrothermal wave number m and the instability of thermocapillary convection increase with Ma.

Growth, mechanical, and magnetic study of SmFeO3 single crystal grown by optical floating zone technique

Single crystals of Samarium orthoferrite (SmFeO3) have been grown by the optical floating zone technique. The growth parameters to yield good quality crystals are 5 mm/h for pulling and 30–40 rpm for rotation. The mechanical behavior of the grown crystal has been investigated. Rosette pattern has been observed around the indentation and the microhardness has been found to decreases non-linearly with the applied load. For load higher than 1.96 N there is a transition from palmqvist to median crack due to plastic deformation of the crystal. The hardness parameters like fracture toughness, brittleness index, and yield strength have also been calculated for palmqvist and median cracks occurring on the crystal surface. The magnetic investigations revealed that a magnetic transition in the range of 300–180 K. Above 180 K, the magnetization decreases as Sm and Fe sublattices have opposite spins. At high temperature, two anomalies are observed, one due to near spin reorientation (TSR = 480 K) and the other is AFM to paramagnetic transitions (TN = 670 K). The M–H curves exhibit a shape change with temperature due to the emergence and enlargement of multi-domain state of the SmFeO3 crystals. Bloch parameter (3.28 × 10−5 K−3/2) has also been evaluated.

Magnetic anisotropy of large floating‐zone‐grown single‐crystals of SrRuO3

SrRuO3 is a highly interesting material due to its anomalous‐metal properties related with ferromagnetism and its relevance as conductive perovskite layer or substrate in heterostructure devices. We have used optical floating zone technique in an infrared image furnace to grow large single crystals of SrRuO3 with volumes attaining several hundred mm3. Crystals obtained for optimized growth parameters exhibit a high ferromagnetic Curie temperature of 165 K and a low‐temperature magnetization of 1.6 μB at a magnetic field of 6 T. The high quality of the crystals is further documented by large residual resistance ratios of 75 and by crystal structure and chemical analyzes. With these crystals the magnetic anisotropy could be determined.

On the Chemistry and Physical Properties of Flux and Floating Zone Grown SmB6 Single Crystals.

Recent theoretical and experimental findings suggest the long-known but not well understood low temperature resistance plateau of SmB6 may originate from protected surface states arising from a topologically non-trivial bulk band structure having strong Kondo hybridization. Yet others have ascribed this feature to impurities, vacancies, and surface reconstructions. Given the typical methods used to prepare SmB6 single crystals, flux and floating-zone procedures, such ascriptions should not be taken lightly. We demonstrate how compositional variations and/or observable amounts of impurities in SmB6 crystals grown using both procedures affect the physical properties. From X-ray diffraction, neutron diffraction, and X-ray computed tomography experiments we observe that natural isotope containing (SmB6) and doubly isotope enriched (154Sm11B6) crystals prepared using aluminum flux contain co-crystallized, epitaxial aluminum. Further, a large, nearly stoichiometric crystal of SmB6 was successfully grown using the float-zone technique; upon continuing the zone melting, samarium vacancies were introduced. These samarium vacancies drastically alter the resistance and plateauing magnitude of the low temperature resistance compared to stoichiometric SmB6. These results highlight that impurities and compositional variations, even at low concentrations, must be considered when collecting/analyzing physical property data of SmB6. Finally, a more accurate samarium-154 coherent neutron scattering length, 8.9(1) fm, is reported.

Thermal Conductivity and Thermoelectric Power of Yb-Substituted Bi-2212 Superconductor

In the present study, Bi2Sr2CaCu2-xYbxO8+y where x = 0.0, 0.05, 0.1 and 0.25, superconductor materials were textured using the Laser Floating Zone technique. After annealing the as-grown materials, they were characterized by thermal conductivity (κ-T), thermoelectric power (S-T), and electrical resistivity (R-T) measurements performed from room temperature down to 20 K. The thermoelectric power is positive in all cases and is found to increase with decreasing temperature, reaching the maximum value (peak) around the samples TC values and dropping rapidly to zero below TC. Electrical resistivity measurements show a slight decrease of TC when Yb substitution is raised. In spite of this effect, TC values are higher than 90 K in all cases. On the other hand, Yb substitution also decreases thermal conductivity, compared with the undoped samples.

Quantum spin liquid and electric quadrupolar states of single crystal Tb2+xTi2-xO7+y

The ground states of the frustrated pyrochlore oxide Tb2+xTi2-xO7+y, sensitively depending on the small off-stoichiometry parameter x, have been studied by specific heat measurements using well characterized samples. Single crystal Tb2+xTi2-xO7+y boules grown by the standard floating zone technique are shown to exhibit concentration (x) gradient. This off-stoichiometry parameter is determined by precisely measuring the lattice constant of small samples cut from a crystal boule. Specific heat shows that the phase boundary of the electric quadrupolar state has a dome structure in the x-T phase diagram with the highest Tc ≃ 0.5 K at about x = 0.01. This phase diagram suggests that the putative U(1) quantum spin-liquid state of Tb2+xTi2-xO7+y exists in the range x < xc ≃ –0.0025, which is separated from the quadrupolar state via a first-order phase-transition line x = xc.

Optical floating zone growth and dielectric constants of near-3:2 mullite crystals

Near-3:2 mullite crystals have been grown successfully with the optical floating zone technique. The growth direction of mullite crystals is along the c axis and growth rate can be reached 10mm/h. The effect of growth rates on the crystal quality has been studied. The crystalline phase, crystal quality, microstructure, composition distribution of the grown crystals were characterized by powder X-ray diffraction, single crystal X-ray diffraction, scanning electron microscope, electron probe micro-analyzer and Raman spectra, respectively. The grown mullite crystal is formed by peritectic structure with near 3:2 mullite crystal as main face and lamellar or needle-like SiO2-rich aluminosilicate as secondary phase that parallel to the crystal growth direction. The measured dielectric properties show large dielectric anisotropy and good temperature stability in near-3:2 mullite crystals.

Multiferroic interfaces in bismuth ferrite composite fibers grown by laser floating zone technique

In this work we explore the formation of enhanced multiferroic interfaces in bismuth ferrite crystalline fibers grown by laser floating zone technique. An underlying mechanism of self-segregation during the fibers growth process enables to establish a textured microstructure of a dominant BiFeO3 phase bordered by the presence of Bi25FeO40 secondary phase. The crystallites c axis of the BiFeO3 phase shows a preferential orientation along the longitudinal axis of the fibers, together with grain boundaries that also present a significant alignment with the same direction. These features induce a systematic disturbance of the antiferromagnetic structure of the BiFeO3 phase at the interfaces with the Bi25FeO40 diamagnetic phase. The structural anisotropy confirmed by High Resolution X-ray diffraction and scanning electron microscopy images is also manifested in the magnetic properties of the fibers, which reveal an enhanced susceptibility response in comparison to the conventional BiFeO3 phase diagram.

Magnetic Characterization and Low-Temperature Heat Transport Properties of the Orthoferrites &lt;italic&gt;R&lt;/italic&gt;FeO&lt;sub&gt;3&lt;/sub&gt; (&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$R =$ &lt;/tex-math&gt;&lt;/inline-formula&gt; Rare Earth) Single Crystals

Orthoferrites RFeO 3 (except R=Y, La and Lu) possess two sets of magnetic sublattice, that is, Fe3+ sub-system and R3+ sub-system. Magnetic properties and interactions between the two sub-systems including Fe-Fe, R-Fe, and R-R interactions depend on external parameters, such as temperature, magnetic field, etc.[1-3] So real magnetic materials can exhibt rich low temperature characteristics. We have successfully grown the orthoferrites RFeO 3 (R = Dy, Ho and Y) and Ho 1−x Y x FeO 3 (x = 0.1 and 0.3) by the floating zone technique using a four-mirror image furnace. The halogen lamp power and crystal growth atmosphere were identified to be the most important parameters. High-quality single crystals have been demonstrated by the X-ray diffraction data and X-ray Laue photograph. The magnetic transitions with decreasing temperature and the field-induced magnetic phase transitions in RFeO 3 for the rare earth ions and Fe3+ can be characterized by low-temperature magnetization and specific heat measurements. In addition, we report the low-temperature heat transport measurements of these orthoferrites single crystals to probe the magnetic properties and find that they show strong magnetic field dependence. The characteristic fields have a good correspondence with some transformations of the magnetic structure. These special behaviors demonstrate the magnetic field-induced transitions of the Fe3+ and R3+ spin structure.

Effect of Yttrium substitution on superconductivity in Bi-2212 textured rods prepared by a LFZ technique

In this study, the physical and superconducting properties of the Bi2Sr2Ca1−xYxCu2O8+δ with x=0.0, 0.05, 0.075 0.1, and 0.20 textured superconducting rods prepared by a laser floating zone technique were presented. The effects of Y3+ substitution for Ca2+ have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), dc-magnetization, magnetic hysteresis and critical current density calculation by using the Bean׳s critical state model. The powder XRD patterns of the samples have shown the Bi-2212 phase is the major one. Along with the powder samples, the textured rod surfaces also were investigated by XRD. The grains found to be well-oriented along the longitudinal rod axis which is a typical result for superconductors prepared by laser floating zone (LFZ) method, has been observed. The best critical temperature, TC, has been found as 92.9K for the sample with 0.15Y substitution, under DC magnetic field of 50Oe in ZFC mode. It has also been observed that the critical current density decreases with increasing Y-substitution. Using those values, the maximum JC value has been determined as 2.37×105A/cm2 for the undoped sample.

Engineering of ion-doping on the ground states and Bose–Einstein condensation of Sr3Cr2O8

Single crystals of Sr3Cr2O8, Sr3Cr1.9V0.1O8 and Sr3Cr1.9Fe0.1O8 were grown using the floating zone technique, and their magnetization behaviors were systematically investigated under pulsed field up to 54 T at various temperatures ranging from 2 K to 20 K. Temperature-induced transition from singlet ground state to triplet state and magnetic-field-induced Bose–Einstein condensation were observed, of which the critical temperature and the critical field are correlative to ion-dopants. The analysis of the ground state and low-field magnetization behaviors indicates that the ion-dopants lead to an enhancement of the intradimer exchange J0, which changes the transition temperatures, and increases the critical fields Hc1. The magnetic Fe ion dopant makes the transition from singlet to triplet states more sensitive to the applied magnetic field, in clearly contrast to the situation of the nonmagnetic V5+ dopant.

High thermoelectric performance in Bi2-xPbxBa2Co2Oy promoted by directional growth and annealing

Bi2-xPbxBa2Co2Oy (x=0.0, 0.2, 0.4, and 0.6) misfit compounds were grown by the laser floating zone technique. Microstructural analysis has shown the formation of thermoelectric grains together with high amount of secondary phases. Thermoelectric grains orientation is increased until 0.4Pb, while further substitution drastically destroys the preferential grain orientation. Electrical resistivity is very low compared with the values obtained in sintered materials, spectacularly increasing power factor. Moreover, the performance of these materials was further improved subjecting the as-grown samples to a postannealing step due to the rise of thermoelectric phase content. These microstructural modifications led to a high decrease of electrical resistivity, improving power factor in around a factor two at room temperature, compared with the as-grown samples. Moreover, the low thermal conductivity of the textured annealed samples leads to a maximum estimated ZT value of 0.53 for the 0.2 Pb-doped samples, much higher than the reported in literature.

A promising microstructure/deformability adjustment of β-stabilized γ-TiAl intermetallics

Ti–44Al–5Nb–3Cr–1.5Zr (at%) β-stabilized intermetallic was synthesized by the electron beam casting and afterwards re-solidified by the high-gradient (300°Ccm−1) induction float zone (FZ) technique. FZ-processing led to the ordered microstructure creation consisting of volumetrically prevailing (γ+α2) lamellar colonies separated by minor seam-like γ-granular interlayers, and the least intergranular quota of β(Ti)/B2 phase. The optimum phase balance, submicron interlamellar spacing and strict alignment of lamellae along the thermal gradient were controlled by FZ-conditions. Unique microstructural adjustment enhances drastically the yield and ultimate strengths, Young's modulus and creep resistance. Thus the high-temperature limit of γ-TiAl(Nb,Cr,Zr) structural applicability could be expanded from 750–800°C towards 900–950°C.

Directional solidification, thermo-mechanical and optical properties of (Mg(x)Ca(1-x))(3)Al(2)Si(3)O(12) glasses doped with Nd(3+) ions.

In this work glass rods of (Mg(x)Ca(1-x))(3)Al(2)Si(3)O(12) (x = 0, 0.5 and 1) doped with 1 wt% Nd(2)O(3) were produced by the laser floating zone technique. Thermo-mechanical and spectroscopic properties have been evaluated. The three glass samples present good thermo-mechanical properties, with similar hardness, toughness and glass transition temperatures. The spectroscopic characterization shows spectral shifts in absorption and emission spectra. These spectral shifts together with Judd-Ofelt intensity parameters and ionic packing ratio have been used to investigate the local structure surrounding the Nd(3+) ions and the covalency of the Nd-O bond. All obtained results agree and confirm the higher covalency of the Nd-O bond in the Ca(3)Al(2)Si(3)O(12) glass.

Powder diffraction data on Ca0.9Nd0.1Ti0.9Al0.1O3

Single crystals of Ca0.9Nd0.1Ti0.9Al0.1O3 (CNTAO) were grown using optical floating zone technique and the grown crystals were characterized by Laue diffraction and powder X-ray diffraction techniques for crystal quality and its composition, respectively. The powder pattern of CNTAO was indexed and refined using GSAS program to an orthorhombic structure with space group Pbnm (#62), a = 5.3832(1), b = 5.4343(1), c = 7.6389(2) Å, V = 223.4677 Å3′, and Z = 4.

Morphology and structural and electrical parameters of float-zone Si(111) single crystals

The surface structure of silicon single crystals grown in the [111] direction using the floating zone technique and the distribution of electric parameters of these crystals over the crystal length are investigated. Geometrical parameters of the morphological characteristics of deltoidal icositetrahedral habit are determined. It is demonstrated that, similarly to ridgelike protrusions, bulges are morphological elements of the ingot surface that characterize the rhombododecahedral and deltoidal icositetrahedral growth habits. It is established that, in the region of bulges, the nonequilibrium charge carriers lifetime distribution is more inhomogeneous due to instability of the crystallization rate.

Effect of Yb doping on the crystal structure, polarization dependent optical absorption and photoluminescence of Yb:YVO4 single crystal grown by optical floating zone technique

Single crystals of Yb doped YVO4 with dopant concentration in the range of 0.75–14.3 at.% were grown by optical floating zone technique. The lattice parameters of YVO4 remain unaffected up to 2.94 at.% doping of Yb but a contraction in the lattice volume was observed at higher concentrations. Spectral decomposition analysis of the broad absorption at 985 nm suggests that in addition to the contributions from three transitions from the ground state of the crystal field induced Stark multiplets of 2F7/2 and 2F5/2, it also has contribution from the transition from the first excited Stark level of 2F7/2 to the upper most Stark level of 2F5/2. Further, the absorption spectra exhibited significant polarization dependence. It was found that while for σ- (E⊥c) polarized light the absorption band at ∼972 dominates for π- (E||c) dominant absorption is at ∼985 nm. The absorption cross-section was found to be maximum at 2.94 at.% of doping for both the polarization signifying quenching at higher concentration. The emission spectra of the Yb doped crystals were characterized by two overlapped broad emissions centered at 985 and 1010 nm. The emission at 985 nm dominated over the emission at 1010 nm at lower doping concentrations which reversed at higher doping concentration. It is interesting to note that the PL intensity at 1010 nm is stronger for excitation at 972 nm in comparison to that for 985 nm.

Selective Crystal Growth and Structural, Optical, and Electronic Studies of Mn3Ta2O8.

Mn3Ta2O8, a stable targeted material with an unusual and complex cation topology in the complicated Mn-Ta-O phase space, has been grown as a ≈3-cm-long single crystal via the optical floating-zone technique. Single-crystal absorbance studies determine the band gap as 1.89 eV, which agrees with the value obtained from density functional theory electronic-band-structure calculations. The valence band consists of the hybridized Mn d-O p states, whereas the bottom of the conduction band is formed by the Ta d states. Furthermore, out of the three crystallographically distinct Mn atoms that are four-, seven-, or eight-coordinate, only the former two contribute their states near the top of the valence band and hence govern the electronic transitions across the band gap.

High pressure floating zone growth and structural properties of ferrimagnetic quantum paraelectric BaFe12O19

High quality single crystals of BaFe$_{12}$O$_{19}$ were grown using the floating zone technique in flowing oxygen pressurized to 100 atm. Single crystal neutron diffraction was used to determine the nuclear and magnetic structure of BaFe$_{12}$O$_{19}$ at 4 K and 295 K. At both temperatures, there exist local electric dipoles formed by the off-mirror-plane displacements of magnetic Fe$^{3+}$ ions at the bipyramidal sites. The displacement at 4 K is about half of that at room temperature. The temperature dependence of the specific heat shows no anomaly associated with long range polar ordering in the temperature range from 1.90-300 K. The inverse dielectric permittivity, $1/\varepsilon$, along the c-axis shows a $T^2$ temperature dependence between 10 K and 20 K, with a significantly reduced temperature dependence displayed below 10 K. Moreover, as the sample is cooled below 1.4 K there is an anomalous sharp upturn in $1/\varepsilon$. These features resemble those of classic quantum paraelectrics such as SrTiO$_3$. The presence of the upturn in $1/\varepsilon$ indicates that BaFe$_{12}$O$_{19}$ is a critical quantum paraelectric system with Fe$^{3+}$ ions involved in both magnetic and electric dipole formation.

Structural, electrical, and optical properties of CdMnTe crystals grown by modified floating-zone technique

Cadmium manganese telluride (CdMnTe or CMT), a compound semiconductor, is considered a promising material for the fabrication of high-performance room-temperature x-ray and gamma-ray detectors. The presence of material defects, e.g., high density of Te inclusions, has been a long-standing issue in CMT crystals grown by various Bridgman methods, since these defects degrade the device performance via charge-trapping. To address this issue, we employed the modified floating-zone method (MFZ) to grow CMT crystals and obtained as-grown crystals free of Te inclusions. This represents a new and distinct feature, absence of Te inclusions, compared to CMT crystals grown by Bridgman methods. White-beam x-ray diffraction topography (WBXDT) measurements demonstrated the existence of a high stress field within the MFZ-grown CMT crystals, which originates from the steep temperature gradient near the growth interface. Furthermore, we achieved a resistivity of 109 Ωcm for the MFZ-grown CMT crystals. The low-temperature photoluminescence (PL) measurements show that the intensity of the dislocation-related Y band is much higher than that of the principal exciton peaks, (D0,X) and (A0,X), confirming that the crystalline quality is affected by the high stress field. A long-term in-situ or post-growth thermal annealing will help to release such stress to improve the crystalline quality. Open image in new window