Traveling Solvent Floating Zone Method Research Articles

Single-crystal growth of Bi 2Sr 2Ca 2Cu 3O 10+ δ (Bi-2223) by TSFZ method

The traveling solvent floating-zone (TSFZ) method has the potential advantage over the usual flux method that crystal growth can be performed at one point on the temperature–composition phase diagram, and provides an opportunity to grow large single crystals even if their crystallization field is very narrow. Here, we report the first successful preparation of the triple-layered system Bi 2Sr 2Ca 2Cu 3O 10+ δ (Bi-2223) single crystals by improving the TSFZ method condition by applying slow growth velocity and higher temperature gradient. The obtained crystals are as large as 4×2×0.1 mm 3. X-ray diffraction pattern shows only sharp Bi-2223 peaks, confirming its good crystallinity. DC susceptibility of the as-grown samples exhibits a sharp superconducting transition with T c =105 K . After annealing the sample under O 2 flow at 600°C, T c increased to the maximum value (=110 K). High-resolution transmission electron microscope images were taken to investigate the phase purity. It confirms that the crystals cleaved from the last part of grown boule are almost single-phase Bi-2223.

Investigation on crystal growth of BiSrCuO system under high oxygen pressure using TSFZ method

Crystal growth was investigated in the system BiSrCuO using the travelling solvent floating zone (TSFZ) method. Crystal of formula Bi 2+xSr 2−xCuO 6+δ was obtained under oxygen pressure between 200–700 kPa. Platelet with an a- b surface of several cm 2 and along the c-axis > 1 mm was cleaved mechanically. A tetragonal phase was determined from the crystal grown under 700 kPa. Solubility of strontium was in the range of 0.09< xx<0.21, increasing with the applied oxygen pressure. Oxygen content of the as-grown crystals increased with increasing the pressure. A superconducting phase, T c∼5–10 K, was found for the crystals. The electric properties of the crystals were affected by the amount of oxygen as well as Sr content.

Crystal growth and structure analysis of Sm2−xCexCuO4

The phase diagram of the Sm2O3–CuO system was investigated by the combination of the differential thermal analysis and the quench method. The results showed that Sm2CuO4 incongruently melts at about 1220 °C, and that the solid Sm2CuO4 exists in equilibrium with the liquid consisting of 81–95 mol% CuO in the range of 1060–1220 °C. On the basis of the phase diagram, Sm2−xCexCuO4 single crystals were grown by the traveling solvent floating zone method. The crystal structure [space group I4/mmm, a = 3.917(1), c 4 11.899(2) Å] has been refined using single-crystal x-ray diffraction data with a precision corresponding to an R index of 0.02.

X-ray topography investigation of La 2− xSr xCuO 4 single crystals

La 2− x Sr x CuO 4 (LSCO) single crystals have been studied by X-ray topography methods. Particularities of grain structure connected with the growth methods travelling solvent floating zone (TSFZ) and slow cooling (SC) are explored. It was found that average disorientation between grains for the TSFZ method is 0.2–0.3°. For the SC method, the disorientation varies from 0.01–0.03° up to 0.3° depending on cooling rate. It was shown that TSFZ grown LSCO single crystals are more preferable as substrates for liquid phase epitaxy technique.

Vortex state in aNd1.85Ce0.15CuO4−δsingle crystal

Magnetization data of a ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ single crystal prepared by the traveling solvent floating zone method reveal a feature showing a sharply defined temperature range for the occurrence of the second-peak effect. A vortex phase diagram derived from these data on the basis of some of the existing models displays a number of perceptible changes in the temperature dependencies of the penetration field ${H}_{p},$ the irrevesibility line ${H}_{\mathrm{irr}},$ and the symmetry of the hysteresis loop, in conjunction with the observation of the peak effect. It is shown that effective penetration of the external magnetic field in the three-dimensional vortex regime is a prerequisite to the transition from its quasilattice to disordered glass vortex state associated with occurence of the peak effect. Comparison with previous results on a similar sample further indicates certain sample-dependent nature of the data.

Growth of Y 2Cu 2O 5 single crystals by the traveling solvent floating zone method

Sufficiently large single crystals of Y 2Cu 2O 5 for use in neutron diffraction experiments were successfully grown by the traveling-solvent floating zone method under an oxygen partial pressure of 40–100%. The optimum composition for growth from a high-temperature solution was determined in situ using high-temperature optical microscopy. The growth direction was parallel to the crystallographic b -axis. This crystal exhibited well-defined metamagnetic transitions.

Properties of a large La 1.92Sr 0.08CuO 4+ δ single crystal grown by the travelling-solvent floating-zone method

A centimeter size single crystal of La 2− x Sr x CuO 4+ δ (volume=1.32 cm 3) with x Sr=0.08 has been grown by the travelling-solvent floating-zone (TSFZ) method using a double ellipsoidal-type optical furnace as the heat source. The crystallised phase was checked solvent free by X-ray powder diffraction experiments, the crystal dimensions and quality being investigated by X-ray and neutron Laüe techniques. Several rocking curves of the Bragg peaks were performed by neutron diffraction giving a full width at half maximum (FWHM) of 0.200° for (006) reflection and clearly showing the presence of twin domains as expected for such an orthorhombic structure. The superconducting critical temperature of the as-grown crystal under 2 oxygen bar was determined by SQUID measurements with T c=18–20 K. Thermal treatments at different oxygen pressures were carried out showing no significant improvement of the transition sharpness and the T c value. Normal state susceptibility was also measured from 6 to 800 K for two different field orientations and can be interpreted as an antiferromagnetic insulating state behaviour. The resistivity measurements display an insulating behaviour perpendicular to the CuO 2 planes and a metallic behaviour in the planes, with a high anisotropy ratio R c / R b ∼350 at room temperature and a zero resistivity achieved at 27 K in both directions. The specific heat measurements have revealed no anomalies in the temperature range 15–300 K.

Crystal growth of the spin-ladder compound (Ca,La) 14Cu 24O 41 and observation of one-dimensional disorder

Centimeter size single crystals of Ca 14− x La x Cu 24O 41 have been successfully grown by the travelling solvent floating zone method using an image furnace. Crystals grown under oxygen pressure of several bar are single phase for 2⩽ x⩽5. Single crystal X-ray studies on Ca 8.4La 5.6Cu 24O 41 and Ca 9La 5Cu 24O 41 samples, using precession and Weissenberg methods, show diffraction streaks from the CuO 2 chains of the structure which are interpreted as an indication of a one-dimensional initial phase disorder along the a-direction.

Necking effect on the growth of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystal by TSFZ method

High-quality Bi 2 Sr 2 CaCu 2 O 8+δ single crystals have been grown by a travelling solvent floating zone method with a necking technique using a single crystal seed. The full-width at half maximum of the X-ray rocking curves was improved from 120 arcsec to 70 arcsec by the necking technique. The topographic results show that the crystals grown using the necking technique have better crystallinity. Especially, this technique is very effective on the growth of the atomically substituted single crystals. It results not only in the improvement of crystallinity but also in the enhancement of the single crystal size, especially for the crystals substituted by other elements.

Ｂｉ２Ｓｒ２ＣａＣｕ２Ｏ８＋δ系高温超伝導体の高品質単結晶育成

High-quality Bi2Sr2CaCu2O8+δ single crystals have been grown by a traveling solvent floating zone method with a necking technique. The full-width at half maximum of the rocking curves by a X-ray diffraction was improved from 120 arcsec to 70 arcsec by the necking technique. Especially, this technique is very effective on the growth of the single crystals substituted by lanthnoid elements.

Crystal Growth by the TSFZ Method and Superconducting Properties of the Tetragonal 1-2-3 Type Cuprates

Single crystals of Ca0.5La1.25Ba1.25Cu3Oyand NdBaSrCu3Oywith the dimensions of the order of 1×1×0.5 mm3have been grown by the travelling-solvent floating zone method. As-grown single-crystals are tetragonal and non-superconducting. Through the annealing in oxygen, single crystals of Ca0.5La1.25Ba1.25Cu3Oyhave become superconductors with Tc= 55 - 65 K, keeping the tetragonal structure. On the other hand, single crystals of NdBaSrCu3Oyhave changed from tetragonal to orthorhombic through the annealing in oxygen, though they have become superconductors with Tc= 55 K.

Flux Pinning by substitution in Nd1Ba2Cu3Oy Single Crystals

Magnetization and magneto-transport studies have been performed on high quality Nd1Ba2Cu3Oy (Nd123) single crystals grown by traveling solvent floating zone method in a reduced oxygen partial pressure. The angle dependent magnetization scales well. The magnetization loop splits into two peaks for H∥c. The first peak disappears when the c-axis is tilted away from the field displaying the influence of twin boundary for H∥c. The magnetotransport measurement by a six-terminal configuration shows correlation of the vortices along the c-direction of the Nd123 crystal. The pinning force increases markedly in the twinned crystal in comparison to the detwinned Nd123 crystal. The above measurements along with the studies of volume pinning forces in twinned and detwinned crystals and their microstructure reveal that the interplay between the twin planes and the substitutional Nd–Ba sites are responsible for high pinning in this material, especially in the high field region.

Magnetic and structural properties of superconducting PrBa2Cu3Oy grown by the TSFZ method

We report the magnetic and structural properties of single crystal PrBa2Cu3Oy grown by the travelling solvent floating-zone (TSFZ) method. Magnetic susceptibility measurements show that TSFZ PrBa2Cu3Oy has a superconducting transition below 80K. Zero-field-cooled magnetization shows diamagnetism with full volume fraction. The magnetic moment μeff approaches 2.0μB, and is in good agreement with that of the Pr3+ ion in the presence of a crystal field. The as-grown TSFZ PrBa2Cu3Oy is tetragonal and has a longer c-axis lattice constant than previously reported. Structural analysis revealed a larger z positional parameter of the Ba site in as-grown TSFZ PrBa2Cu3Oy.

Growth of orthorhombic SrCuO 2 by a traveling solvent floating zone method and its phase transformation under high pressure

Single crystals of the orthorhombic SrCuO 2 were grown by a traveling solvent floating zone (TSFZ) method. It was found that a suitable chemical composition of the traveling solvent for the TSFZ growth was Sr : Cu=3 : 7 in molar ratio. Lattice constants of the grown crystal were a 0=0.392, b 0=1.635 and c 0=0.357 nm and the chemical composition of them was Sr : Cu=1.00 : 0.98 in molar ratio. The grown crystal was compressed at 1000°C and 6 GPa for 1 h. The orthorhombic crystal was transformed to polycrystalline tetragonal SrCuO 2 with a 0=0.393 and c 0=0.343 nm by the high-pressure treatment. Preferable orientation of crystalline axis was found in the obtained polycrystalline sample of the tetragonal SrCuO 2. The axial relationship between the single crystalline precursor of the orthorhombic SrCuO 2 and the obtained tetragonal SrCuO 2 was discussed from the viewpoint of the orientation of the [CuO 4] square planer coordination.

SuperconductingPrBa2Cu3Ox

${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ grown by the traveling-solvent floating-zone method shows a large inhomogeneity both in structural and physical properties, such as lattice parameters and transport and magnetic properties. Some parts of this sample exhibit bulk superconductivity. The c-axis lattice constant is longer than that of nonsuperconducting samples grown by the flux method. However, the magnetic susceptibility of the superconducting sample suggests the valence of Pr is $+3$. The superconducting transition temperature exceeds 100 K under a pressure over 8 GPa and still has a potential to increase.

Oxygen dependence on superconducting properties of La 1.85Sr 0.15CuO 4− δ ceramic and crystal samples

We have produced LSCO ceramic samples by a sol–gel method, whose high quality is demonstrated by NQR and specific heat measurements. Many studies concerning the influence of phase purity, strontium homogeneity and oxygen stoichiometry on the superconducting properties of La 1.85Sr 0.15CuO 4− δ were carried out using X-ray diffraction, SQUID magnetization and specific heat measurements. The control of strontium and oxygen content achieved on ceramic samples gave us the opportunity to optimize our LSCO `crystal' grown by the travelling solvent floating zone method. Low-temperature specific heat measurements were also performed between 0.3 and 8 K on both La 1.85Sr 0.15CuO 4 ceramic and `crystal' samples in the T-range 0.3–8 K and the results revealed that the specific heat residuals of our samples were lower than those already measured and published by other groups.

Phase Diagrams in the Solid Solution Nd–Ba–Cu–O System and NdBa2Cu3O7-δ Single Crystals Growth by the Traveling-Solvent Floating-Zone Method

We have investigated the pseudo-binary phase diagrams between NdBa2Cu3O7-δ (Nd123) and several Ba–Cu–O compositions in air and reduced oxygen atmosphere by DTA, quenching, and X-ray powder diffraction measurements. We found that in air the wider liquidus line exists in the 60–90% concentration of (1/13) Ba3Cu10O13 [40–10% (1/6) Nd123] at 940–1090° C. Under 0.1% O2 in Ar, the liquidus line on the same pseudo-binary line shifts to the 65–92.5% concentration of (1/13) Ba3Cu10O13 [35–7.5% (1/6) Nd123] at 850–1000° C. Furthermore, we tried to grow single crystals of Nd123 based on these phase diagrams by traveling-solvent floating-zone method under 0.1% O2 in Ar. We could get a single crystal rod having the composition of Nd1.02Ba1.98Cu3O7-δ and the T C∼93 K in all through the length of the crystal rod.

Microstructural study of the Ni-doped 2212-phase of BiSrCaCuO superconductor single crystals

The microstructure of Bi 2Sr 2Ca 1Cu 2− x Ni x O y ( x=0.0, 0.02, 0.04) single crystals grown by the travelling solvent floating zone method have been investigated using transmission electron microscopy. High-resolution observations and diffraction patterns at the [100] zone axis show a very small change in the direction of the modulation wave with increasing of Ni concentration. Streak-shaped diffuse scattering along the row of modulation reflections was observed in all the specimens. Convergent beam diffraction patterns at the [001] zone axis showed two distinct symmetries: either a very strong asymmetry or a weak asymmetry in the b-plane. The strong asymmetry was attributed to the presence of intergrowth layers on the c-plane. The positions of Ni atoms within the structure of the crystal and their influence on the electric resistivity was discussed by considering the present experimental observation results.

NdBa2Cu3O7 − δ single crystal growth by the traveling-solvent floating-zone method

We have succeeded in growing large size NdBa 2 Cu 3 O 7 − δ crystals (the cross-section was elliptical, the major and minor axes were about 4.5 and 3.5 mm, respectively, and the length about 30–60 mm that depended on the length of the feed rod) by improving the traveling-solvent floating-zone method. A typical one of these crystals has been proved to be of single crystal from X-ray Laue diffraction measurements. These crystals show superconducting properties throughout the crystal length, whose transition temperature T C (onset) is 94 K and transition width ΔT C is about 5 K. The success of growing these single crystals was achieved by selecting the optimum solvent composition, increasing the density of the feed rod, interchanging the crystal growing direction, setting up the temperature gradient for the region of the solvent and finding the appropriate growing rate for the crystal growth in the TSFZ method. The compositions of grown crystals deviate slightly from the stoichiometric ratio, Nd : Ba : Cu = 1 : 2 : 3. It seems that there are regions in the crystals in which Nd atoms substitute for the Ba-site. Therefore, these crystals have broad ΔT C compared to stoichiometric crystals.

Field-induced pinning effect of Nd(Ba 1− xNd x) 2Cu 3O 7−δ single crystals grown by the traveling-solvent floating-zone method

We have studied the superconducting properties of Nd(Ba 1− x Nd x ) 2Cu 3O 7−δ (Nd123, x ≈ 0.1) single crystals grown by the traveling-solvent floating-zone method under 0.1% O 2 in Ar atmosphere. The enhancement of the magnetization with increasing field is observed in the hysteresis ( M- H) loop in fields both parallel and perpendicular to the c-axis of the Nd123 single crystals as well as in the bulk crystals prepared by the oxygen-controlled-melt-growth (OCMG) method. The composition variation of Ba/Nd is observed in the matrix of Nd123 crystals by an analytical TEM equipped with a cold field-emission gun. It turns out that the enhancement is due to the field-induced pinning effect ascribed to the weak superconducting NdBa substitution regions in the Nd123 matrix.