Traveling Solvent Floating Zone Research Articles

Traveling solvent floating zone growth and anisotropic ionic conductivity of Li<i><sub>x</sub></i>La<sub>(1−</sub><i><sub>x</sub></i><sub>)/3</sub>TaO<sub>3</sub> single crystals

In this study, single crystals of double-perovskite-type oxide LixLa(1−x)/3TaO3 (LLTaO) were successfully grown using the traveling solvent floating zone (TSFZ) method. The Ta-rich phase, which was precipitated in the crystals, was grown via the conventional floating zone (FZ) growth process, indicating that LLTaO behaved as an incongruent melt. For the TSFZ growth for solvents with a LiTa3O8 composition of 8 %, which is less than the LLTaO (x = 0.18) stoichiometric composition, the black grown crystals were homogeneous and crack-free, with a typical size of approximately 20 mm in length and 5 mm in diameter. The grown crystals turned colorless and transparent after being left overnight in the air at room temperature (about 25 °C). The Li concentration in the grown crystals was determined to be x = 0.086(1). This value is lower than the nominal composition (x = 0.18) of the feed owing to Li evaporation during the crystal growth. The ionic conductivities of the grown crystals along [110] and [001] were 2.8 × 10−5 and 1.8 × 10−5 S·cm−1, respectively. The anisotropic parameter was determined to be 1.56 indicating that the ionic conductivity along the ab-plane is higher than that along the c-axis. Furthermore, the calculated activation energies along [110] and [001] were 0.29 and 0.34 eV, respectively.

A homogeneity study on (Ce,Gd)3Ga2Al3O12 crystal scintillators grown by an optical floating zone method and a traveling solvent floating zone method

1 at% Ce3+-doped Gd3Ga2Al3O12 (GGAG) single crystals were grown by an optical floating zone (OFZ) method and a traveling solvent floating zone (TSFZ) method.

TSFZ Growth of Eu-Substituted Large-Size LSCO Crystals

The travelling solvent floating zone (TSFZ) growth of Eu-substituted LSCO (La1.81−xEuxSr0.19CuO4, with nominal x = 0 ÷ 0.4) single crystals was systematically explored for the first time. The substitution of La with Eu considerably decreased the decomposition temperature. Optimal growth parameters were found to be: oxygen pressure 9.0–9.5 bars; Eu-free CuO-poor solvent (66 mol% CuO) with a molar ratio of La2O3:SrCO3:CuO = 4:4.5:16.5 and growth rate 0.6 mm/hour. The obtained single crystals were characterized with optical polarized microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy analysis. The solubility of Eu in LSCO appeared to be limited to x~0.36–0.38 under the used conditions. The substitution of La3+ with smaller Eu3+ ions led to a structural transition from tetragonal with space group I4/mmm for La1.81Sr0.19CuO4 (x = 0) to orthorhombic with space group Fmmm for La1.81−xSr0.19EuxCuO4 (x = 0.2, 0.3, 0.4), and to a substantial shrinking of the c-axis from 13.2446 Å (x = 0.0) to 13.1257 Å (x = 0.4). Such structural changes were accompanied by a dramatic decrease in the superconducting critical temperature, Tc, from 29.5 K for x = 0 to 13.8 K for 0.2. For x ≥ 0.3, no superconductivity was detected down to 4 K.

Magnetic properties of a highly ordered single crystal of the layered perovskite YBaCuFe0.95Mn0.05O5

The layered perovskite YBaCuFeO5 (YBCFO) is able to adopt chiral magnetic order up to unexpectedly high temperatures, paving the way to strong magnetoelectric coupling at room temperature. In this perovskite A-site cations are fully ordered whereas the occupancy of the B-sites strongly depend on the preparation process. Though the structure is not geometrically frustrated, the presence of partial Fe3+/Cu2+ disorder at the B-sites produces magnetic frustration. In an effort to increase the spin–orbit coupling in the system, we have synthesized and studied YBaCuFe0.95Mn0.05O5 in single crystal form, where the highly symmetric Fe3+ ions (3d5) are partially substituted with Jahn-Teller active 3d4 Mn3+ ions. We report the structural and magnetic properties of a highly ordered single crystal of this layered perovskite, which are presented in comparison with a polycrystalline specimen (three times more disordered). Single crystal neutron diffraction measurements reveal two collinear magnetic phases and the lack of incommensurate spiral order. The magnetic phases and transitions found in the crystal grown by the traveling solvent floating zone (TSFZ) method are fully described and analyzed in the light of its high level of Fe/Cu cationic order (∼90%).

Crystal growth, characterization, and phase transition of PbCuTe2O6

Single crystals of the three-dimensional frustrated magnet and spin liquid candidate compound PbCuTe$_2$O$_6$ were grown using both the Travelling Solvent Floating Zone (TSFZ) and the Top-Seeded Solution Growth (TSSG) techniques. The growth conditions were optimized by investigating the thermal properties. The quality of the crystals was checked by polarized optical microscopy, X-ray Laue and X-ray powder diffraction, and compared to the polycrystalline samples. Excellent quality crystals were obtained by the TSSG method. Magnetic measurements of these crystals revealed a small anisotropy for different crystallographic directions in comparison with the previously reported data. The heat capacity of both single crystal and powder samples reveal a transition anomaly around 1 K. Curiously the position and magnitude of the transition are strongly dependent on the crystallite size and it is almost entirely absent for the smallest crystallites. A structural transition is suggested which accompanies the reported ferroelectric transition, and a scenario whereby it becomes energetically unfavourable in small crystallites is proposed.

Synthesis and study the influence of yttrium doping on band structure, optical, non-linear optical and dielectric results for Ca12Al14O33 (C12A7) single crystals grown using traveling-solvent floating zone (TSFZ) method

Ca12Al14O33 (C12A7) and Y0.02Ca11.98Al14O33 (Y-C12A7) single crystals were grown by using the traveling-solvent floating zone (TSFZ) method. The temperature was increased to avoid the bubbles and cracks which may be formed during the preparation of the ingot material. We have started with the flux higher than the normal to avoid the bubbles and make good treatment for the solid-liquid interface. The structures of both Ca12Al14O33 (C12A7) and Y0.02Ca11.98Al14O33 (Y-C12A7) were studied by using x-ray diffraction (XRD). Optical properties for C12A7 and Y-C12A7 single crystals have been studied in order to determine the optical parameters such as optical energy gap (E g), refractive index n, oscillating energy (E o), dispersion energy (E d), volume energy loss function (VELF), and surface energy loss function (SELF). Finally, a new result for these samples is that the third-order nonlinear optical susceptibility (χ (3)) was determined. The results have been discussed with effect of Y-doping on the C12A7 single crystals for optical and industrial applications.

Enhanced stability of floating-zone by modifying its liquid wetting ability and fluidity for YBa2Cu3O7-δ crystal growth

As an ideal material platform for deep investigations on superconductivity, high purity YBa2Cu3O7-δ (Y123) single crystals have been highly concerned and requested recently. However, it is very difficult to grow such crystals by the conventional travelling-solvent floating-zone (TSFZ) process due to the intrinsic instability of floating zone caused by the liquid loss. To overcome this obstacle, the feed rod with modified precursor powder (MPP) of 0.5Y2O3+ Ba2Cu3O5 was adopted, instead of the conventional one (Y123). Our experimental results proved that less Ba3Cu7Oy solvent penetrated to the MPP-rod due to its low wettability. Furthermore, it was also observed that less melt dropped down from the floating zone owning to its low fluidity, caused by low dimension of bubbles and Y211 particles generated from the MPP-rod. Consequently, the molten zone was remarkably stabilized and the Y123 single crystal was successful grown. The effective size of the grown boule was about 5 mm (Ø) × 30 mm. This new conception of altering precursor components for continuous TSFZ growth is universally worth of producing other functional materials.

Lithium-ionic conductivity of LixLa(1−x)/3NbO3 single crystals grown by the TSFZ method

LixLa(1−x)/3NbO3 single crystals with various Li compositions (x = 0.05–0.15) were grown via the travelling solvent floating zone (TSFZ) method. The electron probe microanalysis (EPMA) and inductively couple plasma (ICP) analyses revealed that there is Li evaporation from the molten zone during crystal growth due to high temperature treatment. However, the Li concentration in the grown crystals increased as the nominal composition in the feeds increased. Additionally, the grown crystal of LixLa(1−x)/3NbO3 (x = 0.05–0.15) showed uniform composition measured by EPMA X-ray intensity distribution except when x = 0.15. The experimental result confirmed that the ionic conductivity of LixLa(1−x)/3NbO3 (x = 0.05–0.15) showed a maximum of σ = 1.2 × 10−4 S cm−1 with x = 0.07 composition in the grown crystal. The anisotropy of ionic conductivity was measured along the [100] and [001] directions of the solid electrolyte of the LixLa(1−x)/3NbO3 (x = 0.05–0.15) single crystal. The maximum anisotropic ionic conductivity of the crystals annealed in oxygen was σ[100]/σ[001] ≈ 1.6.

Crystal growth of La2/3-x Li3x TiO3 by the TSFZ method.

Double-perovskite-type La2/3-xLi3xTiO3 (LLT) crystals were grown by the travelling solvent floating zone (TSFZ) method. When the floating zone (FZ) crystal growth method was applied, the La2Ti2O7 phase was deposited as an inclusion in the initial growth region. Using the TSFZ crystal growth method, however, inclusion-free LLT crystals were obtained for a 10 mol% La2Ti2O7-poor composition solvent relative to the stoichiometric LLT crystals. The molten zone was initially unstable as a result of habit plane formation during the crystal growth; however, the molten zone was stably maintained for a long period of time by decreasing the feed rate compared with the growth rate. Hence, LLT crystals of approximately 5 mmφ and 37 mm in length were obtained. The anisotropic ionic conductivity of the crystals annealed in air was σ[110]/σ[001] ≈ 3, with σ[110] = 1.64 × 10−3 S cm−1 and σ[001] = 5.26 × 10−4 S cm−1. LLT single crystals are candidates for high-performance solid-state electrolytes in all-solid-state Li ion batteries.

Growth of LiCoO2 Single Crystals by the TSFZ Method

We have grown LiCoO2 single crystals by the traveling solvent floating zone (TSFZ) growth with Li-rich solvent, having observed the incongruent melting behavior of LiCoO2 between 1100 and 1300 °C. The optimum growth conditions in terms of atmosphere and solvent composition were determined to be Ar flow and an atomic ratio Li/Co 85:15, respectively. The crystals grown using a conventional-mirror-type furnace contained periodic inclusions of a Co–O phase due to the influence of Co–O phase segregation on the stability of the molten zone during growth. By using a tilted-mirror FZ furnace, inclusion-free LiCoO2 crystals of about 5 mm in diameter and 70 mm long were obtained at a tilting angle θ = 10°. The grown crystals were confirmed to be single-domain by neutron Laue diffraction.

The pyrochlore Ho2Ti2O7: Synthesis, crystal growth, and stoichiometry

We have investigated the effect of synthesis and growth conditions on the magnetic, structural, and compositional properties of the pyrochlore oxide holmium titanate and demonstrate a method for growing high quality stoichiometric single crystals. A series of polycrystalline samples with various contents of Ti (−0.08 ≤ x ≤ 0.08, and nominal compositions of Ho2Ti2+xO7) were synthesized at different temperatures, and characterized using powder X-ray diffraction. The results show that synthesizing powders at a higher temperature of 1500 °C yields single phase compounds. Ti deficient powders showed an increase of lattice constant due to stuffing (Ho into Ti positions), while Ti rich powders showed a decrease in lattice constant due to anti-stuffing (Ti into Ho positions). A post-reaction annealing in O2 was found to be necessary to accomplish the anti-stuffing process. Use of the conventional floating zone (FZ) technique introduced Ti deficiency, stuffing, and oxygen vacancies in the grown crystal. Growth of high structural quality and stoichiometric single crystals of Ho2Ti2O7 by the traveling solvent floating zone (TSFZ) method is reported. AC susceptibility measurements revealed that the stoichiometric crystal shows a higher spin ice freezing temperature, indicating that crystal quality and stoichiometry play a key role on low temperature spin ice properties of this compound.

Protected Vacuum Annealing Effect on Single Crystals of Pr1-xLaCexCuO4 in the Overdoped Regime

We report the effect of protected vacuum annealing on the superconducting (SC) and magnetic properties of Pr1-xLaCexCuO4 (PLCCO) single crystals in the overdoped regime (x = 0.13 – 0.20). The powders and single crystals of PLCCO with all x were synthesized by the solid state reaction and grown by the travelling solvent floating zone (TSFZ) method, respectively. The powder x-ray diffraction (XRD) results analyzed by the Rietveld method have shown that there is a systematic decrease in the c-axis length with increasing x, suggesting the proper substitution of Ce for Pr in overdoped PLCCO up to x = 0.20. The so-called two-step annealing performed in the overdoped regime was essential for increasing the SC volume fraction estimated from the magnetic susceptibility measurements. Furthermore, the temperature dependence of the normal-state magnetic susceptibility for reduced crystals of PLCCO with all x has exhibited a Curie-Weiss-like behavior regardless of various steps of the protected vacuum annealing process.

Travelling-solvent floating-zone growth of the dilutely Co-doped spin-ladder compound Sr14(Cu, Co)24O41

We present here crystal growth of dilutely Co-doped spin-ladder compounds Sr14(Cu 1−x, Cox)24O41 (x = 0, 0.01, 0.03, 0.05, 0.1) using the Travelling Solvent Floating Zone (TSFZ) technique associated with an image furnace. We carried out detailed microstructure and compositional analysis. The microstructure of the frozen-in FZ revealed two bands: a lower band consisting of well-aligned single-crystalline stripes of the phase Sr14(Cu, Co)24O41 embedded in the eutectic mixture of composition SrO 18% and (Cu, Co)O 82%; and an upper band consisting of a criss-crossed pattern of these stripes. These analyses were also employed to determine the distribution coefficient of the dopants in Sr14Cu24O41. The distribution coefficient turned out to be close to 1, different from Sr2CuO3 reported previously where Co tend to accumulate in the molten zone. Direct access to the composition of the frozen-in zone eliminated any previous ambiguities associated with the composition of the peritectic point of Sr14Cu24O41; and also the eutectic point in the binary SrO–CuO phase diagram. The lattice parameters show an anisotropic variation upon Co-doping with parameters a and b increasing, c decreasing; and with an overall decrease of the unit cell volume. Magnetic susceptibility measurements were carried out on the pristine and the Co-doped crystals along the principal crystallographic axes. The spin susceptibility of the x = 0.01 crystal exhibits a strong anisotropy, which is in stark contrast with the isotropic behaviour of the pristine crystal. This anisotropy seems to arise from the intradimer exchange interaction as inferred from the anisotropy of the dimer contribution to the susceptibility of the Co-doped crystal. The Curie-tail in the magnetic susceptibility of Sr14(Cu 1−x, Cox)24O41 (x = 0, 0.01, 0.03, 0.05, 0.1) crystals (field applied parallel to the ladder) was found to scale with Co-doping – the scaling is employed to confirm a homogeneous distribution of Co in a x = 0.1 crystal boule.

Self-adjusted flux for the traveling solvent floating zone growth of YBaCuFeO5 crystal

A modified traveling solvent floating zone (TSFZ) technique was used to successfully grow a large size and high quality single crystal of multiferroic material YBaCuFeO5. This modified TSFZ growth uses a stoichiometric feed rod and pure copper oxide as the initial flux without prior knowledge of the complex phase diagram involving four elements, and the optimal flux for the growth of incongruently melt crystal is self-adjusted after a prolonged stable pulling. The wetting of the feed rod edge that often perturbs the molten zone stability was avoided by adding 2wt% B2O3. The optimal flux concentration for the YBaCuFeO5 growth can be extracted to be near YBaCuFeO5:CuO=13:87 in molar ratio. The crystal quality was confirmed by the satisfactory refinement of crystal structure of space group P4mm and the two consecutive anisotropic antiferromagnetic phase transitions near 455K and 170K.

Crystal Growth of the Nonmagnetic Zn2+ and Magnetic Co2+ Doped Quasi-One-Dimensional Spin Chain Compound SrCuO2 Using the Traveling Solvent Floating Zone Method

We report on the crystal growth of the quasi-one-dimensional quantum spin chain compound SrCuO2 and its doped variants containing magnetic cobalt (0.25%, 0.5%, 1%, and 2.5%) and nonmagnetic zinc (0.5% and 1%) impurities. Crystals are grown using the traveling solvent floating zone (TSFZ) method in a four-mirror optical furnace. Some crucial factors, key to the stability of a TSFZ process, including the choice of solvent composition and its associated melting behavior, are discussed in detail. The grown crystals were characterized using X-ray powder diffraction, scanning electron microscopy, optical microscopy, neutron single crystal diffraction and magnetic susceptibility measurements. Co-doping induces magnetic anisotropy and a corresponding change of magnetic behavior characterized by the presence of a sharp peak in the magnetic susceptibility at low-temperatures (T = 5 K), which is not seen for the pristine compound. The peak position is shown to scale linearly with Co-concentration for low doping levels up to 2.5%.

Crystal growth and thermoelectric properties of CaMn0.98Nb0.02O3−δ

Thermoelectric CaMn0.98Nb0.02O3−δ single crystals were grown from sintered polycrystalline material using the traveling-solvent floating zone (TSFZ) method. The floating-zone furnace was operated at over-pressure using an Ar/O2 mixture to prevent evaporation during the growth process. Six twin-domain variants were detected with single-crystal X-ray diffraction (XRD) and confirmed by electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM). The Seebeck coefficient (S) of the single-crystalline material indicates n-type semiconducting behavior. Within 10K<T<125K a negative peak in S is observed, known to be characteristic of antiferromagnetic ordering. The ferromagnetic long-range ordering, expected on the basis of double exchange between Mn4+ and doped Mn3+ species, thus appears to remain suppressed in the single-crystalline material.

Growth and magnetic properties of stoichiometric and site-disordered single crystalline MgV2O4

We have grown several single crystals of the highly frustrated $S$ = 1 spinel MgV${}_{2}$O${}_{4}$ using different starting compositions and growth conditions. From our study of their physical properties by magnetic susceptibility, heat capacity, and single-crystal neutron and powder-diffraction measurements, we observe that a minute amount of disorder suppresses the structural and magnetic phase transitions. As little as 3$%$ disorder in the octahedral site introduced random strain, which was enough to completely suppress the transitions and induce a spin-glass phase at low temperatures. We believe that the reason is spin-exchange disorder rather than disorder in the weakly diluted magnetic lattice. Our results also show that the MgO-V${}_{2}$O${}_{3}$ system is a solid solution that melts slightly incongruently, and we demonstrate that by using an optimized solvent in the traveling-solvent floating-zone configuration a large single crystal ($l$ = 25 mm, $d$ = 6 mm) with a homogeneous composition, free of site disorders can be grown.

Anisotropic thermoelectric properties associated with dimensional crossover in quasi-one-dimensional SrNbO3.4+d(d∼0.03)

We have grown large single crystals of SrNbO${}_{3.4+d}$ ($d\ensuremath{\sim}0.03$) with $n=5$ in the homologous series Sr${}_{n}$Nb${}_{n}$O${}_{3n+2}$ by using a traveling solvent floating-zone method and measured resistivity, thermopower, and thermal conductivity along all crystallographic axes. The thermoelectric properties are found to be highly anisotropic, which reflects a quasi-one-dimensional electronic structure. In particular, the thermopower along the $b$ axis is $\ensuremath{-}170$ $\ensuremath{\mu}$V/K at 300 K, which is 1 order of magnitude higher than the $\ensuremath{-}15$ $\ensuremath{\mu}$V/K along the $a$ axis and $\ensuremath{-}25$ $\ensuremath{\mu}$V/K along the $c$ axis. A possible origin of the high anisotropy in the thermopower is discussed in terms of dimensional crossover associated with a structural modification.

Unconventional Growth Mechanism in Optical Traveling Solvent Floating Zone Growth of Large β-CuNb2O6 Single Crystals

A large single crystal (5mm x 4 mm x 15 mm) of CuNb 2 O 6 has been grown in a four-mirror-type optical floating-zone furnace by the traveling solvent floating zone (TSFZ) method using a composition having excess CuO as flux. The as-grown single crystal was found to be phase-pure orthorhombic β-CuNb 2 O 6 , excellent in quality and with a spontaneous growth direction along the crystallographic b-axis. A novel growth mechanism as observed for β-CuNb 2 O 6 in the floating-zone machine is illustrated, and characteristics of the magnetic susceptibility and magnetization along different crystallographic axes are also shown.

Crystal growth and characterization of the dilutable frustrated spin-ladder compound Bi(Cu 1− xZn x) 2PO 6

High quality centimeter size single crystals of Bi(Cu 1− x Zn x ) 2PO 6 ( x=0%, 1%, 5%) have been successfully grown by the Travelling Solvent Floating Zone (TSFZ) technique. The crystals were grown with a rate of 1 mm/h in a gas mixture of 20% O 2 in Ar. Characterization of the single crystal samples by means of optical microscopy, X-ray powder diffraction, X-ray Laue diffraction, neutron diffraction and magnetization measurement are reported. The magnetic susceptibility χ spin ( T ) , measured from 2 to 300 K, passes a broad maximum around 60 K, followed by an exponential decrease towards lower T, and confirm the formation of a spin singlet ground state at low temperature. At low-temperature a paramagnetic Curie-like upturn quantitatively reflect the increasing Zn-doping level.