Traveling Solvent Floating Zone Technique Research Articles

Evolution of incommensurate superstructure and electronic structure with Pb substitution in (Bi2−xPbx)Sr2CaCu2O8+δ superconductors**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300300 and 2017YFA0302900), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant Nos. XDB07020300 and XDB25000000), the National Natural Science Foundation of China (Grant Nos. 11334010 and 11534007), and the

High-quality Bi2−xPbxSr2CaCu2O8+δ (Bi2212) single crystals have been successfully grown by the traveling solvent floating zone technique with a wide range of Pb substitution (x = 0–0.8). The samples are characterized by transmission electron microscope (TEM) and measured by high resolution laser-based angle-resolved photoemission spectroscopy (ARPES) with different photon energies. A systematic evolution of the electronic structure and superstructure with Pb substitution has been revealed for the first time. The superstructure shows a significant change with Pb substitution and the incommensurate modulation vector () decreases with increasing Pb substitution. In the meantime, the superstructure intensity from ARPES measurements also decreases dramatically with increasing Pb concentration. The superstructure in Bi2212 can be effectively suppressed by Pb substitution and it nearly disappears with a Pb substitution of x=0.8. We also find that the superstructure bands in ARPES measurements depend sensitively on the photon energy of lasers used; they can become even stronger than the main band when using a laser photon energy of 10.897 eV. These results provide important information on the origin of the incommensurate superstructure and its control and suppression in bismuth-based high temperature superconductors.

Synthesis, crystal growth and characterization of the pyrochlore Er2Ti2O7

A stoichiometric and high crystalline quality Er2Ti2O7 single crystal was successfully grown using the traveling solvent floating zone technique for the first time.

Superdislocations and point defects in pyrochlore Yb2Ti2O7 single crystals and implication on magnetic ground states

This study reports atomic-scale characterization of structural defects in Yb2Ti2O7, a pyrochlore oxide whose subtle magnetic interactions is prone to small perturbations. Due to discrepancies in the reported magnetic ground states, it has become a pressing issue to determine the nature of defects in this system. In the present study, we use atomic resolution scanning transmission electron microscopy techniques to identify the type of defects in the ytterbium titanate single crystals grown by the conventional optical floating zone (FZ) method. In addition to the known point defects of substitution Yb on Ti B-sites, extended defects such as dissociated superdislocations and anti-phase boundaries were discovered for the first time in this material. Such defects were prevalently observed in the FZ grown single crystals (of a darker color), in contrast to the stoichiometric white polycrystalline powders or high quality colorless single crystals grown by the traveling solvent floating zone technique. The lattice strains from these extended defects result in distortions of Yb-tetrahedron. A change of Ti valance was not detected at the defects. Our findings provide new insights into understanding the nature of defects that are of great importance for the physical property studies of geometrically frustrated compounds. Furthermore, this work sheds light on the complicated core structure of superdislocations that have large Burgers vectors in oxides with complex unit cells.

Magnetocrystalline Anisotropy of Single Crystals of M-, X-, and W-Type Strontium Hexaferrites

We have grown single crystals of non-substituted M-, X-, and W-type strontium hexaferrites by utilizing the traveling solvent floating zone technique and investigated their magnetic and electrical ...

Growth and physical properties of Bi2Sr2CaCu2O8+x crystals grown by a simple pressure technique and comparison with regrowth self-flux technique

Single crystals of a high temperature superconductor Bi2Sr2CaCu2O8+x (2212) were grown using two different techniques, namely, regrowth technique as well as a pressure technique and the results are compared. Single crystal X-ray diffraction (XRD) performed on crystals grown using both techniques show no impurity or intergrowth phase. However, powder XRD reveals the presence of only Bi2Sr2CuO6+x(2201) intergrowth phase in crystals grown using pressure technique, with additional impurity phases also found in the crystals grown using regrowth technique. Rietveld refinement showed the weight fraction of 2212 as 93% in crystals grown from pressure technique, confirming the excellent quality of the as-grown crystals. The transition temperature of crystals grown using both techniques was ∼90 K. It was found that pressure technique gives crystals that have a higher superconducting volume fraction (∼100) than that of crystals grown using regrowth technique. Structural and magnetization measurements reveal that the as-grown crystals grown using pressure technique are of high quality, comparable to those grown using traveling solvent floating zone technique. Crystals grown by both the techniques exhibit second magnetization peak anomaly.

Magnetocrystalline anisotropy of La- and Co-substituted M -type strontium ferrites: Role of Co2+ and Fe2+

We have systematically investigated the magnetic properties of ${\mathrm{La}}_{}$- and ${\mathrm{Co}}_{}$-substituted ${\mathrm{Sr}}_{}{\mathrm{Fe}}_{12}{\mathrm{O}}_{19}$ using single crystals. By utilizing the traveling solvent floating zone technique, we have grown single crystals over a wide range of substitution content, and examined their saturation moments and magnetocrystalline anisotropy. With increasing content of ${\mathrm{La}}_{}$ and ${\mathrm{Co}}_{}$, the saturation moment at $300\phantom{\rule{4pt}{0ex}}\mathrm{K}$ monotonically increases. The increment of magnetocrystalline anisotropy is almost proportional to the content of Co. In addition, further La substitution also enhances magnetocrystalline anisotropy, which demonstrates that ${\mathrm{Fe}}^{2+}$ plays an important role to enhance magnetocrystalline anisotropy. We have analyzed magnetocrystalline anisotropy energy as a function of substitution content, and elucidate the effects of ${\mathrm{Co}}^{2+}$ and ${\mathrm{Fe}}^{2+}$.

Impact of stoichiometry ofYb2Ti2O7on its physical properties

A series of Yb2Ti2O7 doped samples demonstrates the effects of off-stoichiometry on Yb2Ti2O7's structure, properties, and magnetic ground state via x-ray diffraction, specific heat, and magnetization measurements. A stoichiometric single crystal of Yb2Ti2O7 grown by the traveling solvent floating zone technique (solvent = 30 wt% rutile TiO2 and 70 wt% Yb2Ti2O7) is characterized and evaluated in light of this series. Our data shows that upon positive x doping, the cubic lattice parameter a increases and the Curie-Weiss temperature decreases. Heat capacity measurements of stoichiometric Yb2Ti2O7 samples exhibit a sharp, first-order peak at T = 268(4) mK that is suppressed in magnitude and temperature in samples doped off ideal stoichiometry. The full entropy recovered per Yb ion is 5.7 J/K ~ Rln2. Our work establishes the effects of doping on Yb2Ti2O7's physical properties, which provides further evidence indicating that previous crystals grown by the traditional floating zone method are doped off ideal stoichiometry. Additionally, we present how to grow high-quality colorless single crystals of Yb2Ti2O7 by the traveling solvent floating zone growth method.

Single-Crystal Growth of ZnO:Ga by the Traveling-Solvent Floating-Zone Method

Transparent and blue ZnO:Ga (GZO) single crystals have been grown by the traveling-solvent floating-zone technique using the solvent B2O3 + MoO3 + Nb2O5. The crystals were typically 9–14 mm in diameter and 46–120 mm in length. The largest one was Φ12 mm × 120 mm in size. All GZO crystals were grown along the direction. The growth rate was 0.3–0.5 mm/h, which was far faster than 0.1 mm/day of that grown by the hydrothermal method. The crystalline quality has been characterized by single crystal X-ray diffraction and X-ray rocking curve measurements. Ga substituted on Zn-site and was saturated at about 0.5 wt % of Ga2O3 addition. The GZO crystal doped with 0.5 wt % Ga2O3 has the lowest electrical resistivity of 1.083 × 10–3 Ω·cm and the highest carrier concentration of 1.78 × 1020 cm–3.

Single-crystal growth of Mg- and Ni-doped chain compound SrCuO2 by the traveling-solvent floating-zone method and chain breaking effect induced by the dopants

Pure and doped high-quality single-crystals of the non-congruently melting chain compound SrCuO2 were grown in an infra-red image furnace using the traveling solvent floating zone technique. The growth conditions, together with the characterization of the grown single crystals by optical microscopy, EDX, X-ray powder diffraction and magnetization in the 2–300K temperature range are presented. Doping by Mg2+ (S=0) and Ni2+ (S=1) on the Cu2+ (S=½) sites leads to breaking of the chains of the structure in finite segments.

Flux-free growth of large superconducting crystal of FeSe by traveling-solvent floating-zone technique

A flux-free solution to the growth of large and composition homogeneous superconducting FeSe crystal is reported for the first time, which is based on the traveling-solvent floating-zone technique. The size of the crystal samples prepared by this approach is up to 15 × 6 × 2 mm3, being far bigger than previously reported in all dimensions, and the main phase of the crystals is of a single preferred orientation along the tetragonal (101) plane. X-ray diffraction analysis identifies the main phase to be the superconducting tetragonal β-FeSe. The superconducting transition temperature (TC) is determined to be 9.4 K by AC magnetic susceptibility and electronic transport measurements. A nearly perfect diamagnetic shielding of −97% is observed, indicating a bulk superconductivity in the crystal sample.

Growth and Characterization of High-Quality Single Crystals of Ni- and Zn-Doped Bi2Sr2Ca(Cu2−xMx)O8+δ (M = Ni or Zn) High-Temperature Superconductors

High-quality large single crystals of Ni- and Zn-doped Bi2Sr2Ca(Cu2−xMx)O8+δ (M = Ni or Zn) have been successfully grown by the traveling solvent floating zone technique. The single crystals are characterized by compositional and structural analyses and their physical properties are investigated by magnetic susceptibility and resistivity measurements. A record high critical temperature with a Tc = 97.5 K has been achieved in the annealed pristine Bi2212 single crystal. Substitution of Cu by Ni or Zn reduces the superconducting transition temperature when compared with pristine Bi2Sr2CaCu2O8+δ (Bi2212) grown under similar conditions. The successful growth of such pristine Ni- and Zn-doped Bi2212 single crystals will facilitate studies of the relationship between the magnetism and superconductivity in high-temperature cuprate superconductors.

Floating zone crystal growth and magnetic properties of bilayer manganites Pr(Sr1−xCax)2Mn2O7

Single crystals of a bilayer manganite series Pr(Sr1−xCax)2Mn2O7 (x=0, 0.4, 0.9, 1) have been grown using traveling solvent floating zone technique under various oxygen partial pressure. It was found that the crystal quality is very sensitive to oxygen partial pressure applied during growth and highly Ca doped crystals could only be obtained at elevated oxygen pressure. Whereas a secondary phase was observed for PrCa2Mn2O7 grown at oxygen partial pressure below 1bar, a pure phase can be achieved at 8bar of oxygen. This was evidenced studying composition mapping by X-ray fluorescence spectroscopy. X-ray Laue diffraction and X-ray powder diffraction have been carried out on the samples for the quality check of the grown crystals. Susceptibility measurements indicate that all samples are antiferromagnetic at low temperature. They also reveal the existence of two anomalies at ∼320K and 370K, which coincide with the charge ordering/orbital ordering transitions described in the literature.

Disorder-dependent superconducting phase diagram at high magnetic fields in Fe1+ySexTe1−x(x∼0.4)

We compare the superconducting phase-diagram under high magnetic fields (up to $H = 45$ T) of Fe$_{1+y}$Se$_{0.4}$Te$_{0.6}$ single crystals originally grown by the Bridgman-Stockbarger (BRST) technique, which were annealed to display narrow superconducting transitions and the optimal transition temperature $T_c \gtrsim 14$ K, with the diagram for samples of similar stoichiometry grown by the traveling-solvent floating-zone technique as well as with the phase-diagram reported for crystals grown by a self-flux method. We find that the so-annealed samples tend to display higher ratios $H_{c2}/T_c$, particularly for fields applied along the inter-planar direction, where the upper critical field $H_{c2}(T)$ exhibits a pronounced downward curvature followed by saturation at lower temperatures $T$. This last observation is consistent with previous studies indicating that this system is Pauli limited. An analysis of our $H_{c2}(T)$ data using a multiband theory suggests the emergence of the Farrel-Fulde-Larkin-Ovchnikov state at low temperatures. A detailed structural x-ray analysis, reveals no impurity phases but an appreciable degree of mosaicity in as-grown BRST single-crystals which remains unaffected by the annealing process. Energy-dispersive x-ray analysis showed that the annealed samples have a more homogeneous stoichiometric distribution of both Fe and Se with virtually the same content of interstitial Fe as the non-annealed ones. Thus, we conclude that stoichiometric disorder, in contrast to structural disorder, is detrimental to the superconducting phase diagram of this series under high magnetic fields. Finally, a scaling analysis of the fluctuation conductivity in the superconducting critical regime, suggests that the superconducting fluctuations have a two-dimensional character in this system.

Advances in single crystal growth and annealing treatment of electron-doped HTSC

High quality electron-doped HTSC single crystals of Pr2−xCexCuO4+δ and Nd2−xCexCuO4+δ have been successfully grown by the container-free traveling solvent floating zone technique. The optimally doped Pr2−xCexCuO4+δ and Nd2−xCexCuO4+δ crystals have transition temperatures T c of 25 K and 23.5 K, respectively, with a transition width of less than 1 K. We found a strong dependence of the optimal growth parameters on the Ce content x. We discuss the optimization of the post-growth annealing treatment of the samples, the doping extension of the superconducting dome for both compounds as well as the role of excess oxygen. The absolute oxygen content of the as-grown crystals is determined from thermogravimetric experiments and is found to be ≥ 4.0. This oxygen surplus is nearly completely removed by a post-growth annealing treatment. The reduction process is reversible as demonstrated by magnetization measurements. In as-grown samples the excess oxygen resides on the apical site O(3). This apical oxygen has nearly no doping effect, but rather influences the evolution of superconductivity by inducing additional disorder in the CuO2 layers. The very high crystal quality of Nd2−xCexCuO4+δ is particularly manifest in magnetic quantum oscillations observed on several samples at different doping levels. They provide a unique opportunity of studying the Fermi surface and its dependence on the carrier concentration in the bulk of the crystals.

High-Quality Large-Sized Single Crystals of Pb-Doped Bi2Sr2CuO6+δ High-Tc Superconductors Grown with Traveling Solvent Floating Zone Method

High quality Pb-doped Bi2Sr2CuO6+δ (Pb-Bi2201) single crystals are grown by the traveling solvent floating zone technique, with dimensions as large as ∼ 50 mm× ∼ 5.0 mm× ∼ 2 mm. The Pb-Bi2201 single crystals with different doping levels are obtained by the annealing process which covers a wide doping range of the overdoped region. We describe in detail the growth and annealing procedures and the characterization and physical property measurements of the Pb-Bi2201 crystals. The availability of these crystals provides a good opportunity to experimentally investigate high-Tc cuprate superconductors, particularly in the overdoped region.

Investigations for the growth of large underdoped Bi 2Sr 2CaCu 2O 8+δ single crystals

In order to study superconducting physical properties by neutron scattering technique, the necessity to obtain large and high quality optimally doped Bi 2Sr 2CaCu 2O 8+ δ (Bi-2212) and underdoped Bi-2212 single crystals is prominent. Three routes have been investigated to reach this goal: synthesis under low oxygen pressure by travelling solvent floating zone technique (TSFZ), TSFZ synthesis of yttrium doped Bi 2Sr 2Ca 1− x Y x Cu 2O 8+ δ and TSFZ synthesis under air followed by post-annealing treatments. With decreasing p(O 2 ) from ambient pressure to 0.1 atm during the TSFZ growth, the superconducting transition temperature, T c, transits from 87 K (slightly overdoped) to 93 K. On yttrium doped growth, a systematic study of Bi 2 Sr 2Ca 1− x Y x Cu 2O 8+δ, where x=0–0.5, was undertaken to correlate the nominal yttrium composition with the yttrium crystal composition and to control the T c as a function of yttrium composition. 85 K underdoped Bi-2212 crystals with a size up to 220 mm 3 and a 5 K transition width, Δ T c, were obtained by post-annealing under p(O 2 )=0.1 atm at 450 °C.

Floating-zone growth and property characterizations of high-quality La2–xSrxCuO4 superconductor crystals

We have grown underdoped (x = 0.11, 0.12) and optimally doped (x = 0.16) La2–xSrxCuO4 single crystals by the traveling-solvent floating-zone technique. In order to prepare good quality cuprate crystals, we have made much effort to optimize the preparation procedures. For example, we haveadopted the sol–gel route to prepare a highly fine and homogeneous La2–xSrxCuO4 precursor powder for fabricating a very dense ceramic feed rod used for the floating-zone growth, and we have also used quite a slow growth rate. The high quality of the grown crystals has been verified by double-crystal x-ray rocking curves, with the full-width-at-half-maximum being only 113–150 arcseconds, which are the best data reported so far for La2–xSrxCuO4 crystals. The superconducting critical temperatures of the grown crystals are 30, 31 and 38.5 K for x = 0.11, 0.12 and 0.16 samples, respectively, according to magnetic measurements.

Crystal growth and characterization of two-leg spin ladder compounds: Sr 14Cu 24O 41 and Sr 2Ca 12Cu 24O 41

Single crystals of Sr 14− x Ca x Cu 24O 41 ( x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr 14Cu 24O 41 show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. T c onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with T c max=9.4 K and T N=5 K at 56 kbars.

Growth, characterization and physical properties of high-quality large single crystals ofBi2(Sr2−xLax)CuO6+δ high-temperature superconductors

High-quality large Bi2(Sr2−xLax)CuO6+δ (La–Bi2201) single crystals have been successfully grown by the traveling solventfloating zone technique. The samples are characterized by compositional andstructural analyses and their physical properties are investigated by magneticsusceptibility and resistivity measurements. Superconducting samples with sharpsuperconducting transitions are obtained, covering a wide range of doping from overdoped(x<0.40), optimallydoped (x∼0.40),underdoped (0.40<x<0.84) to heavily underdoped without superconducting transition(x>0.84). Crystals aslarge as ∼40 × 2.0 × 1 mm3 areobtained for x = 0.73. A sharp superconducting transition with a width less than 2 K anda nearly perfect Meissner signal of superconductivity are achieved forx = 0.40. The availability of the La–Bi2201 single crystals will provide an ideal system to studythe physical properties, electronic structure and mechanism of high-temperaturesuperconductivity.

Single-crystal growth of LiMnPO 4 by the floating-zone method

LiMnPO 4 crystals with orthorhombic Pnma crystal structure containing large grains have been grown successfully for the first time by the traveling-solvent floating-zone technique under elevated argon pressure. The grains achieve sizes of about 3 mm 2×10 mm and display an orange transparent color. During the growth process, the traveling zone is continuously enriched with PO 4- and Li-ions, due to the self-adjustment of the liquid zone, which hinders grain selection and leads to constitutional supercooling with the formation of a secondary phase in a later stage of the process. Magnetic measurements performed on oriented cuboids reveal antiferromagnetic ordering of the Mn 2+-ions below T N≈34 K. The c-axis is the easy magnetic axis.