Floating Zone Technique Research Articles

Enhanced electrical and thermoelectric properties from textured Bi1.6Pb0.4Ba2Co2Oy/Ag composites

Bi1.6Pb0.4Ba2Co2Oy/3 wt% Ag composites have been textured using the laser floating zone technique. Microstructural observations have shown the formation of relatively high amounts of secondary phases and cracks along the plate-like grains in the as-grown materials. In spite of these microstructural features, electrical properties have not been drastically decreased. Annealing of these as-grown rods has enhanced the grains connectivity, decreased the contents of the secondary phases, and healed the cracks, thereby increasing their electrical performances. It has been deduced that oxygen content in the thermoelectric phase has not been significantly modified through annealing, as demonstrated by the very similar Seebeck values at room temperature in the as-grown and annealed samples. As a consequence of the low electrical resistivity values in the annealed materials, they reached higher power factor values than the as-grown ones. The highest power factor at room temperature is in the range of those reported for single crystals, while at 650 °C, it is the highest reported in Bi–Ba–Co–O polycrystalline family so far.

Single crystal growth of Mn4Nb2O9 and its structure-magnetic coupling

A single crystal of Mn4Nb2O9 of about 8 mm in diameter and 30 mm in length was successfully grown by a newly designed one-step method based on the optical floating zone technique.

Single crystal growth, structure and magnetic properties of Pr2Hf2O7 pyrochlore

Large single crystals of pyrochlore were successfully grown by the floating zone technique using an optical furnace equipped with high power xenon arc lamps. Structural investigations were carried out via powder synchrotron x-ray and neutron diffraction to establish the crystallographic structure of the materials produced. The magnetic properties of the single crystals were determined for magnetic fields applied along different crystallographic axes. The results revealed that is an interesting material for further investigation as a frustrated magnet. The high quality of the crystals produced makes them ideal for detailed investigation, especially using neutron scattering techniques.

Floating Zone Growth and Characterization of (Ca1-x Nd x )12Al14O33+6x (x ∼ 0.001) Single Crystals.

Rare earth Nd3+ ion-doped Ca12Al14O33 single crystals were grown at a rate of 1 mm/h by the floating zone technique in an oxygen atmosphere. The Nd concentration in the central area of the as-grown crystals was higher than that in the peripheral area due to the highly concave growth interface shape. The average Nd concentration in the as-prepared parallelepiped slices of ∼6 × 3 × 2 mm3 for electride fabrication was ∼0.093 ± 0.011 atom % Nd in contrast to the nominal 0.1 atom % Nd concentration. The Nd-doped C12A7:Nd single crystalline electride prepared by thermal treatment with a Ti metal at 1100 °C for 48 h induced an insulator–metal transition with the highest conductivity of approximately 1165 S/cm. These annealing conditions provide an approach to completely remove clathrated oxide ions from the crystallographic cages, leading to the formation of C12A7:Nd(e–) and C12A7:e– electrides with high-density electrons (∼2.4 ± 0.2 × 1021 and ∼1.8 ± 0.1 × 1021 cm–3) localized in the cages. The carrier mobility at room temperature in C12A7:Nd(e–) was very similar to that in C12A7:e–, even though it was very high at temperatures below ∼150 K.

Floating zone growth of α-Na0.90MnO2 single crystals

Single crystal growth of α-NaxMnO2 (x=0.90) is reported via the floating zone technique. The conditions required for stable growth and intergrowth-free crystals are described along with the results of trials under alternate growth atmospheres. Chemical and structural characterizations of the resulting α-Na0.90MnO2 crystals are performed using ICP-AES NMR, XANES, XPS, and neutron diffraction measurements. As a layered transition metal oxide with large ionic mobility and strong correlation effects, α-NaxMnO2 is of interest to many communities, and the implications of large volume, high purity, single crystal growth are discussed.

Electrical-Transport, Magnetoresistance and Magnetic Properties of La1-xCaxMnO3 (x = 0.12 and 0.3) Single Crystals

We report the electrical-transport and magnetic properties of the hole doped La0.7Ca0.3MnO3 (LCMO-1) and La0.88Ca0.12MnO3 (LCMO-2) single crystals, prepared using floating zone technique. The metal to insulator transition (TMI) occurs at 211 K along c-axis and TMI = 185 K along ab-plane for LCMO-1 single crystal. No electronic transition was observed over the whole temperature range under the magnetic field up to 8 T for LCMO-2 single crystal. It is observed that the TMI is higher along c-axis as compared to that in the ab-plane, consequently signifying more favorable hoping of electrons is along c-axis in LCMO-1. The ac-susceptibility measurement shows that ferromagnetic to paramagnetic transition temperature (TC) at 206 K for LCMO-1 and TC = 118 K for LCMO-2 single crystals which is seemingly related to notable change of resistance at 120 K in LCMO-2 single crystal. The maximum MR of 98% for LCMO-1 and 59% for LCMO-2 single crystals up to 8 T applied magnetic field along c-axis and ab-plane, respectively are observed.

Ge distribution in Si0.9Ge0.1 alloy ingot grown from thin melt layer

We have studied experimentally and theoretically the possibility to obtain a uniform single crystal of SiGe alloy enriched at the Si side. The content of the second component in a crystal 15mm in diameter and 40mm in length grown by the modified floating zone technique from the charge of 79.8 at.% Si and 20 at.% Ge composition with 0.2% B admixture has been investigated using selected area X-ray analysis in different points and in line scanning mode along and across the crystal axis. The longitudinal changes in the germanium concentration proved to be well described by the analytical equation previously derived for conditions of Sb (Ga) doped Ge growth from a thin melt layer in the presence of a heater submerged into the melt. For a more accurate description of the experimental data we have made allowance for the change in the melt layer thickness between the growing crystal and the bottom of the submerged heater. The lateral distribution of the second component not exceeding 5% over the crystal diameter can be significantly improved by reducing the curvature of the phase interface during the growth.

Magnetic structures and excitations in a multiferroic Y-type hexaferrite BaSrCo2Fe11AlO22

Multiferroic hexaferrites have been extensively investigated because they exhibit ferroelectricity associated with noncollinear magnetic orders in relatively low magnetic field and high temperature regions. To understand the static and dynamical spin-polarization coupling in such systems, it is necessary to determine the magnetic structures and spin-wave modes. This is impossible for polycrystalline samples. Here, the authors have successfully grown single crystals of BaSrCo${}_{2}$Fe${}_{12}$AlO${}_{22}$ by means of a laser floating zone technique. They perform magnetization, electric polarization, and neutron diffraction measurements to establish the magnetic phase diagram. Several interesting features are seen and the new understanding should provide a useful guide for developing multiferroic-based functional devices working at room temperature.

Crystal growth of the triangular-lattice antiferromagnet Ba3CoSb2O9

We report growth of large single crystals of the triangular-lattice antiferromagnetic compound Ba3CoSb2O9 by the floating-zone technique in an image furnace. Evaporation of Sb due to its high volatility was controlled by high pressure and addition of excess Sb in the starting materials to compensate for the losses. The crystal quality was analysed using different X-ray techniques, and the magnetic transition temperature was confirmed by magnetization and heat capacity measurements.

Room-temperature tensile properties of float-zone processed β-stabilized γ-TiAl(Nb,Cr,Zr) intermetallic

We extend the study of Ti-44Al-5Nb-3Cr-1.5Zr (at%) β-stabilized intermetallic processed by high-gradient (300°Ccm−1) induction float zone (FZ) technique that reported in Mater. Lett.162 (2016)180. The alloy ingots possess unique phase microstructure consisting of (γ+α2) submicron-scaled strictly oriented lamellar matrix with incorporated minor γ-granular fraction, and the least intergranular quota of β(Ti)/B2 phase. The tensile tests of axially-oriented bars have shown high average yield strength (YS) value of 837MPa and ultimate strength (UTS) of 983MPa along with the rupture elongation of 1.45%. Judging by these values, FZ-processing could be proposed as the efficient alternative to complex multistage thermal treatments or HIPing of cast β-stabilized intermetallics. Advanced room-temperature (RT) tensile deformability of alloy with specific microstructure and composition is explained by the softening of chromium-alloyed B2 intergranular fraction due to mutually exclusive redistribution of Cr and Zr between the conjugate γ and B2 phases.

A simplified finite element model for numerical simulation of temperature field and optimization of parameters in single crystal growth by optical floating zone technique

Optical floating zone (OFZ) is one of the most extensively used techniques to grow a variety of bulk crystals, especially single crystals of metal oxides. Although the growth parameters have been identified to be the nature of feed rod, lamp power, rotation rate, growth atmosphere and gas pressure, etc., few studies revealed the effects of these parameters on temperature field during crystal growth in image furnaces. It is well known that the temperature gradient is the driving force for float zone crystal growth. Therefore, it is essential to obtain the major growth parameters affecting OFZ temperature field. In this work, a simplified finite element (FE) model was developed for numerical simulation of temperature field during OFZ crystal growth. The effects of major growth parameters (i.e. lamp power, lamp filament, and molten zone geometry) on temperature field during OFZ crystal growth were hence identified theoretically and validated experimentally. According to the numerical calculation, the growth parameters were optimized and high-quality TiO2 single crystal was grown in practice. Prospectively, the FE model presented in this work can be applied to optimize growth parameters for other crystals as well as opens up new opportunities to understand the physical process of OFZ crystal growth in a simple and scientific way.

Comparative Study on Multifunctional Behaviors of La<sub>0.7</sub>Ca<sub>0.3</sub>MnO<sub>3</sub> and La<sub>0.7</sub>Ca<sub>0.24</sub>Sr<sub>0.06</sub>MnO<sub>3</sub> Single Crystals

We report the electrical-transport, magneto-transport, and magnetic properties of the hole doped La0.7Ca0.3MnO3 (LCMO) and La0.7Ca0.24Sr0.06MnO3 (LCSMO) single crystals, prepared using floating zone technique. The resistivity data shows the metal to insulator transition (TMI) occurs at 211 K and 290 K for LCMO and LCSMO single crystals respectively. The electrical transport mechanisms of these crystals are investigated by using different theoretical models, for temperatures below and above TMI. The magnetization measurements show that these single crystals exhibit ferromagnetic to paramagnetic transition temperature (TC) at 208 K for LCMO and 273 K for LCSMO single crystals. From device application point of view, both samples show the maximum MR of 98% for LCMO and 80% for LCSMO at 8 T applied magnetic field, while for bolometer IR detectors application point of view the temperature coefficient of resistance (TCR) are found to ~17% K-1 and 28% K-1 for LCMO and LCSMO respectively.

Structural, optical, and electrical properties of SmNbO4

Rare-earth orthoniobates constitute a class of materials that has been exploited due to their interesting physical properties depending on the lanthanide element. Besides paramagnetism, ferroelasticity, and negative compressibility, these materials are known by their interesting optical properties and mixed types of conduction processes (protonic, ionic, and electronic). In this work, two types of SmNbO4 samples were studied: polycrystalline samples, prepared by a sol-gel route using the Pechini method, and single crystalline fibres grown by the Laser Floating Zone technique. These samples were structurally characterized based on powder and single-crystal X-ray diffraction studies. A metastable tetragonal phase, stabilized by grain size, was identified in the synthesized powders. After a sintering process of such powders, a single monoclinic phase was obtained. Complementarily, scanning electron microscopy and Raman spectroscopy analyses were performed to these samples. Photoluminescence and photoluminescence excitation spectroscopic studies allowed identifying more than one optically active centre of the trivalent samarium ion in the analysed material. Impedance spectroscopy measurements have shown a large variation of the ac conductivity as a function of temperature, assigned to a protonic conduction and to native ionic conduction mechanisms.

Microstructure, texture, and crystallography in Ni–GDC and Co–GDC porous cermets obtained from directionally solidified eutectic ceramics

Lamellar NiO–GDC (Gadolinium-doped Ceria) and CoO–GDC directionally solidified eutectic ceramics (DSECs) were produced by the laser floating-zone technique and subjected to reduction in order to obtain porous cermets of Ni–GDC and Co–GDC, which have potential applications as anodes in solid oxide fuel cells (SOFC). The reduction of these DSECs into porous cermets was studied at 650 °C in NiO–GDC and at 500 and 700 °C in CoO–GDC, all of them processed with similar reduction kinetics. In comparison to similar Ni–YSZ and Co–YSZ lamellar cermets previously studied, no sharp reduction front was observed. The interface between the reduced and nonreduced zones is broader, with pores homogenously distributed in wide areas. Afterwards, the microstructure, texture, and crystallography of the samples were studied by electron microscopy as well as by electron and X-ray diffraction when completely reduced. The single crystal NiO and CoO lamellae transformed into porous polycrystalline metallic lamellae. Moreover, microscopy observations revealed a porous nanostructure of Co particles obtained by reduction at low temperatures (500 °C). Many of the Co and Ni particles seemed to have roughly maintained the previous crystallographic orientation with respect to the GDC phase, although the disorder of the crystallographic orientation increased significantly. In addition, a significant amount of the Ni particles reoriented to form an epitaxial interface with the (100)–GDC surface.

Zirconate Pyrochlore Frustrated Magnets: Crystal Growth by the Floating Zone Technique

This article reviews recent achievements on the crystal growth of a new series of pyrochlore oxides—lanthanide zirconates, which are frustrated magnets with exotic magnetic properties. Oxides of the type A 2 B 2 O 7 (where A = Rare Earth, B = Ti, Mo) have been successfully synthesised in single crystal form using the floating zone method. The main difficulty of employing this technique for the growth of rare earth zirconium oxides A 2 Zr 2 O 7 arises from the high melting point of these materials. This drawback has been recently overcome by the use of a high power Xenon arc lamp furnace for the growth of single crystals of Pr 2 Zr 2 O 7 . Subsequently, large, high quality single crystals of several members of the zirconate family of pyrochlore oxides A 2 Zr 2 O 7 (with A = La → Gd) have been grown by the floating zone technique. In this work, the authors give an overview of the crystal growth of lanthanide zirconates. The optimum conditions used for the floating zone growth of A 2 Zr 2 O 7 crystals are reported. The characterisation of the crystal boules and their crystal quality is also presented.

On the control of optical transmission of aluminosilicate glasses manufactured by the laser floating zone technique

In this work, a detailed study of the properties of aluminosilicate glass rods manufactured by means of the laser floating zone (LFZ) technique is presented. Samples fabrication was carried out in controlled atmosphere using air, nitrogen, and oxygen. Transmission spectra showed that glasses manufactured in oxygen presented high optical transmission in the visible spectral range compared to those manufactured in other environments, thus allowing us to tune their optical behavior between transparent and nearly opaque through the control of the surrounding atmosphere. Microstructure and thermo-mechanical properties were also assessed, showing similar hardness, toughness, flexural strength and glass transition temperature values, and in the same range as other aluminosilicate glasses. Compositional and structural characterization in terms of energy dispersive X-ray spectroscopy (EDX) and electron paramagnetic resonance (EPR) allowed us to determine the origin of optical transmission dependence on the fabrication atmosphere.

Microstructural and multiferroic properties in layered perovskite-related Sm6Ti4Fe2O20

Layered perovskite-related Sm6Ti4Fe2O20 compound was successfully synthesized through the intercalation of bilayer SmFeO3 into the Sm2Ti2O7 with pyrochlore structure by means of floating-zone melting technique. The microstructural properties were characterized using aberration-corrected scanning transmission electron microscopy and X-ray diffraction. Electron energy-loss spectroscopy investigation reveals that the Fe3+ ions prefer to occupy the inner sites within the perovskite-like layers. This compound exhibits clearly the spin glass-like behavior as demonstrated by the magnetic properties measurement. Such complex magnetic behavior could be attributed to the partial chemical order of Ti/Fe over the B sites and the interactions between magnetic ions including Sm3+ and Fe3+. In addition, the multiferroic behavior with the coexistence of the ferroelectricity and ferromagnetism was well established by magnetic and piezoresponse measurements.

Single crystal growth, magnetic and thermal properties of perovskite YFe0.6Mn0.4O3 single crystal

High quality YFe0.6Mn0.4O3 single crystal was grown by floating zone technique using a four-mirror-image-furnace under flowing air. Powder X-ray diffraction gives well evidence that the specimen has an orthorhombic structure, with space group Pbnm. Temperature dependence of the magnetizations of YFe0.6Mn0.4O3 single crystal were studied under ZFC and FC modes in the temperature range from 5K to 400K. A clear spin reorientation transition behavior (Γ4→Γ1) is observed in the temperature range of 322–316K, due to the substitution of Mn at the Fe site of YFeO3. Its Néel temperature is around 385K. Moreover, the spin reorientation is verified by the change of magnetic hysteresis loops of the sample along [001] axis in the temperature range of 50–385K. The thermal properties of the sample were measured by the differential scanning calorimeter (DSC) from 300K to 500K, which also clearly appear anomaly in the spin reorientation region.

Si1−xGex crystal growth by the floating zone method starting from SPS sintered feed rods – A segregation study

The availability of suitable feed rods for Si–Ge bulk crystal growth is known to be a limiting factor in floating zone growth and other growth techniques. In this work, three Si-rich SiGe single crystals were crystallized by an optical floating zone technique in a double ellipsoid mirror furnace. The feed rods were prepared by pre-synthesis in the Spark Plasma Sintering (SPS) process starting with powders of different compositions. In a detailed section the preparation method of consolidation by mechanical alloyed powders to feed rods will be given. Results from two growth experiments starting with uniform compositions with 11at% and 20at% germanium as well as a zone leveling experiment with a segmented feed rod consisting of a starting zone with 32at% Ge will be discussed. The latter experiment resulted in a crystal with nearly no axial segregation.

Experimental and theoretical modelling of Vickers, Knoop microhardness and laser damage threshold studies on Ca0.9Nd0.1Ti0.9Al0.1O3 single crystals grown by optical floating zone technique

Vickers and Knoop microhardness studies were done on the (200) face of Ca0.9Nd0.1Ti0.9Al0.1O3 crystals grown by optical floating zone technique for various loads ranging from to 0.24–9.8 N. Various important mechanical properties such as Vickers hardness, Knoop hardness, Young's (elastic) modulus, yield strength, stiffness constant which accounts for various industrial applications were determined. The Indentation Size Effect (ISE) were observed for the grown crystal, four different models such as Meyer's law, Hays-Kendall (HK) model, proportional sample resistance (PSR) model, elastic/plastic deformation model (EPD) were used to determine the true hardness values. Among these four mechanical analysis models, HK approach seemed to be the best model to describe the mechanical properties of the grown crystal. The variation of microhardness number for different orientations showed the presence of microhardness anisotropy in the grown crystal. Laser damage threshold for the grown crystal was found to be 2.49 GWm−2.