Traveling Solvent Floating Zone Method Research Articles

Quantum paramagnetism in a non-Kramers rare-earth oxide: Monoclinic Pr2Ti2O7

Little is so far known about the magnetism of the ${A}_{2}{B}_{2}{\mathrm{O}}_{7}$ monoclinic layered perovskites that replace the spin-ice supporting pyrochlore structure for ${r}_{A}/{r}_{B}>1.78$. We show that high quality monoclinic ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ single crystals with a three-dimensional network of non-Kramers ${\mathrm{Pr}}^{3+}$ ions that interact through edge-sharing superexchange interactions, form a singlet ground-state quantum paramagnet that does not undergo any magnetic phase transitions down to, at least, 1.8 K. The chemical phase stability, structure, and magnetic properties of the layered perovskite ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ were investigated using x-ray diffraction, transmission electron microscopy, and magnetization measurements. Synthesis of polycrystalline samples with the nominal compositions of ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2+x}{\mathrm{O}}_{7}$ ($\ensuremath{-}0.16\ensuremath{\le}x\ensuremath{\le}0.16$) showed that deviations from the ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ stoichiometry lead to secondary phases of related structures including the perovskite phase ${\mathrm{Pr}}_{2/3}{\mathrm{TiO}}_{3}$ and the orthorhombic phases ${\mathrm{Pr}}_{4}{\mathrm{Ti}}_{9}{\mathrm{O}}_{24}$ and ${\mathrm{Pr}}_{2}{\mathrm{TiO}}_{5}$. No indications of site disordering (stuffing and antistuffing) or vacancy defects were observed in the ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ majority phase. A procedure for growth of high-structural-quality stoichiometric single crystals of ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ by the traveling solvent floating zone method is reported. Thermomagnetic measurements of single-crystalline ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ reveal an isolated singlet ground state that we associate with the low-symmetry crystal electric-field environments that split the ($2J+1=9$)-fold degenerate spin-orbital multiplets of the four differently coordinated ${\mathrm{Pr}}^{3+}$ ions into 36 isolated singlets resulting in an anisotropic temperature-independent van Vleck susceptibility at low $T$. A small isotropic Curie term is associated with 0.96(2)% noninteracting ${\mathrm{Pr}}^{4+}$ impurities.

Growth and phase transition of Sr3Zr2O7 single crystals

The melting behavior of Ruddlesden-Popper type hybrid improper ferroelectric Sr3Zr2O7 phase in the ZrO2–SrO pseudo-binary system was investigated, and its single crystals were successfully grown. A series of the slow-cooling floating zone experiments revealed that Sr3Zr2O7 melts incongruently into SrZrO3 phase and a liquid and that the compositional range where Sr3Zr2O7 and a liquid coexist is located around 70 mol% SrO composition. Based on the results, we attempted to grow Sr3Zr2O7 single crystals by the traveling solvent floating zone method using SrO-excess solvent and feed. Consequently, many small single crystals of Sr3Zr2O7 phase with several millimeters in size were discovered in the as-grown boules covered with SrO phase. The phase transition behavior of the grown crystals was investigated by differential thermal analysis with polarizing optical microscopy as well as by optical second harmonic generation measurements. We directly observed a reconstruction of orthorhombic twin domains in Sr3Zr2O7 single crystals accompanied by the first-order ferroelectric transition at about 410 °C.

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.

Stable growth of (Ce,Gd)3Ga2Al3O12 crystal scintillators by the traveling solvent floating zone method

Ce:GGAG is promising as scintillators. We present a traveling solvent floating zone method (TSFZ) to stabilize the molten zone. The obtained Ce:GGAG crystals demonstrate a fast decay (64 ns) with higher ratio of fast component (85%).

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 and Characterization of LixLa(1–x)/3NbO3 by the Traveling Solvent Floating Zone Method

Single crystals of LixLa(1–x)/3NbO3 were grown successfully using the traveling solvent floating zone method with LaNbO4-poor and Li-rich solvents. Crack- and inclusion-free single crystals with a ...

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.

Control of the solid-liquid interface during growth of a Ce-doped Gd2Si2O7 crystal by the traveling solvent floating zone method

The growth conditions of Ce-doped Gd2Si2O7 crystals, using the infrared convergent heating floating zone method, were optimized to make the shape of the crystal-melt interface flat or convex. The shape of the crystal-melt interface, meaning the interface between the molten zone and the grown crystal, was evaluated quantitatively using the convexity (h/r) as a parameter. The h/r value was found to be systematically dependent on the crystal diameter, the focus position of the ellipsoidal mirror for infrared convergent heating, and the lamp power used during crystal growth. For an 8.2-mm-diameter crystal grown using conventional conditions, the h/r value was −0.8, which indicates that the crystal-melt interface had a concave shape. The h/r value increased with the position of the ellipsoidal mirror, going from −0.8 for the −8mm mirror position, to −0.5 for the +6mm mirror position. Lastly, when the lamp power increased from 5.8 to 7.0kW, the h/r value increased from −0.6 to −0.3, which was the maximum value observed, indicating that a flat or convex crystal-melt interface was not obtained.

Single crystal growth of spin-ladder compound La8Cu7O19 by the travelling-solvent floating zone method

Large single crystals of La8Cu7O19 have been grown using the travelling-solvent floating zone method. A rather high oxygen pressure of 9 bar in the growth chamber and a slow growth speed of 0.5mm/h were among the most important parameters in stabilizing the growth of this incongruently melting compound. Interestingly, a novel growth scenario has been witnessed. The crystal structure of the grown La8Cu7O19 crystal has been analyzed using single crystal diffractometry to extract important structural parameters of this compound. We find that La8Cu7O19 crystallizes in a monoclinic structure with space group C2/c and has the lattice parameters a≈13.83Å, b≈3.75Å, c≈34.59Å, and β≈99.33°, in good agreement with the data obtained on polycrystalline samples in the literature. The magnetization shows a highly anisotropic behavior, and an anomaly at T ≈103K.

Self-Adjusted Traveling Solvent Floating Zone Growth of Single Crystal CaFe2O4

Single crystals of high-quality CaFe2O4 have been grown successfully using a self-adjusted traveling solvent floating zone method with a four-mirror optical furnace in oxygen atmosphere. Although CaFe2O4 has been reported to melt incongruently, the optimal molten zone has been achieved through a self-adjusted cooling following the liquidus line directly using the stoichiometric CaFe2O4 as both the feed and flux rods in the beginning. Details regarding long-term stability of the molten zone and lamp power optimization to obtain the bubble-free molten zone are discussed. The obtained large single crystal of a few centimeters long and ∼0.5 cm in diameter shows homogeneous stoichiometry and crystallinity as verified by the optical microscopy and synchrotron X-ray diffraction structure refinement. Long range ferrimagnetic spin ordering of TN ≈ 180 K is confirmed from the measurement of magnetization as a function of temperature, which shows significant thermal hysteresis and field dependence. Curie–Weiss law f...

Crystal Growth of Spin Chain Compound Sr2CuO3 Doped with Quantum Defects: Zn, Co, Ni, and Mn

Single crystals of spin chain compound Sr2CuO3 and its doped variants consisting of Zn (1%), Co (1 and 2.5%), Ni (1 and 10%), and Mn (0.25%) at the Cu site were grown using the traveling solvent floating zone method. The floating zone at the end of each growth experiment was analyzed in detail to investigate the melt composition, the shape of the crystal–melt interface, the region of the feed adjacent to the melt, and the dopant concentration of the melt. The composition of the molten zone was found to be in good agreement with the peritectic point associated with the incongruent decomposition of Sr2CuO3. The floating zones in each case were found to be extended deeply into the feed where its composition varied in accordance with the binary SrO–CuO phase diagram. Analysis of the dopant concentration revealed significant accumulation of Zn and Co in the floating zones, suggesting that the actual Zn/Co concentration in the grown crystals is less than the nominal value. No such accumulation was observed with Ni and Mn doping. Magnetic susceptibility of all the grown crystals was measured under two field orientations: parallel and perpendicular to the chains. We show that upon inclusion of a quantum defect in a spin 1/2 chain the magnetic ground state evolves in a manner that is characteristic of the quantum defect.

Floating zone growth of Ba-substituted ruthenate Sr2−xBaxRuO4

We report on the exploration to synthesize Sr2−xBaxRuO4, the large volume variant of the unconventional superconductor Sr2RuO4. We have succeeded in growing single crystals for x-values up to 0.4 by making use of the traveling solvent floating zone method. The quality of the obtained crystals is confirmed by X-ray and neutron diffraction measurements and the properties of these Ba-substituted ruthenates were studied with magnetic and electrical transport measurements.

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.

Growth of single crystalline delafossite LaCuO2 by the travelling-solvent floating zone method

Single crystals of LaCuO2 have been grown for the first time using the travelling-solvent floating zone method. The crystal was grown in an Ar-atmosphere by reduction of La2Cu2O5, which was used as the feed rod composition for the growth. The grown crystal has been characterized with regard to phase purity and single crystallinity using powder X-ray diffraction, energy dispersive X-ray analysis, Laue diffraction and scanning electron microscopy.

Growth, characterization, and magnetic properties of a Li(Mn,Ni)PO4 single crystal

LiMn0.95Ni0.05PO4 single crystals have been grown for the first time by the travelling-solvent floating-zone method at low argon pressure. The grown sample exhibits large single crystalline grains as revealed by means of polarization microscopy, X-ray Laue back scattering, and single-crystal X-ray diffraction. The composition of the crystal was determined by Energy-dispersive X-ray (EDX) spectroscopy. LiMn0.95Ni0.05PO4 orders in an orthorhombic olivine-like structure as expected and phase purity was confirmed by powder X-ray diffraction. An oriented cuboid with size of 2.4×2.5×2.7mm3 along a, b, and c crystalline directions, respectively, was used for anisotropic magnetic measurements.

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.

Effect of rotation of feed and seed rods on the quality of Na 0.75CoO 2 single crystal grown by traveling solvent floating zone method

High purity Na 0.75CoO 2 single crystals have been grown by floating zone method. We found the rotation of feed and seed rods play a crucial role in growing high quality single crystal. Systematic investigations suggest the occurrence of a phase separation at microscopic level, such as the separation into Na-rich and Na-poor domains during the growth, and formation of impurity phase(s) depending on growth conditions. Na x CoO 2 ( x = 0.30, 0.60) crystals have been prepared by sodium deintercalation from Na 0.75CoO 2. Powder X-ray and energy dispersive X-ray analyses have confirmed the phase purity and homogeneity of the samples. Magnetic susceptibility measurements of x = 0.60 and 0.75 crystals indicate a bulk phase transition at 22 K and an anomaly around 339 K and 334 K respectively which are attributed to structural transition. In addition some unique features related to Na 0.60CoO 2 were observed.

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.

Control of carrier concentration in Bi-2212

We realized highly underdoped Bi-2212 crystals by using a Bi substitution into a Sr site (x), together with the excess oxygen (δ) control. The samples with x=0–0.3 were grown by a traveling solvent floating zone method. For each x, δ was varied using the precision annealing method [1]. Under several assumptions, the effective Bi valence was evaluated to be +2.2, which is much lower than the formal valence +3. This indicates that the Bi substitution accompanies additional uptake in excess oxygen. The x dependent δ-doping level p relation and the observed shrink in the c-axis length are consistent with this assumption. Based on the decomposition phase diagram obtained in this study, Tc of 22K was realized by careful annealing treatments. The samples showed a superconducting volume fraction of over 50%.