Floating Zone Technique Research Articles

Crystal growth and scintillation properties of Eu:BaAl2O4 crystals

A series of Eu-doped BaAl2O4 crystals with different doping concentrations were grown by the floating zone technique, and the photoluminescence (PL) and scintillation properties were investigated. The samples exhibit PL and scintillation having a broad emission feature peaking around 500 nm, regardless of the concentration. From the spectral and decay time features, we confirm that the origin of the emission is the 5d-4f transitions of Eu2+. Determined by the pulse height analyses under 137Cs γ-ray irradiation, the scintillation light yields of the 0.1, 0.3, 1 and 3% Eu:BaAl2O4 crystals are 19,000, 22,000, 23,000 and 28,000 photons/MeV, respectively.

Modulation of Jahn-Teller Mn3+ ion on anisotropy and high field magnetic diagram of Sm(Fe, Mn)O3

SmFeO3 and SmFe0.9Mn0.1O3 single crystal samples grown with a floating zone technique have been investigated under static and pulsed high magnetic fields along all principal crystallographic axes. Comprehensive investigation on magnetization (behavior) show that the spin switch transition and spin reorientation transition among the Sm3+ and Fe3+/Mn3+ sublattices is highly anisotropic. Especially, with the applied magnetic field along a-axis, a field induced multi-step transition was observed in SmFeO3 around compensation temperature (TComp1 ~ 3.9 K), which was not observed in Mn doped SmFe0.9Mn0.1O3 (TComp2 ~ 9.3 K). The experimental results show that the Jahn-Teller (J-T) Mn3+ ions has an important effect on anisotropy and affects the spin-reorientation and high field magnetization behavior. The study provides a clear picture to show the dominate effects between rare earth ions and transition metal ions on the complicated magnetization behavior.

Crystal growth of the Ca2RuO4–Ru metal system by the floating-zone technique

Abstract In the last few decades there has been growing interest in studying Mott insulators due to their ability to host novel quantum phenomena when the system is perturbed by various stimuli. Recently the antiferromagnetic Mott insulator Ca2RuO4 has received considerable attention due to superconductivity and metal-insulator transition induced by pressure and electric field respectively. Here we report the details of the synthesis of a novel systems made by Ca2RuO4 and Ru metal inclusions. Samples with lamellae, rods and globules of Ru embedded in Ca2RuO4 single crystals were successfully synthesized by floating zone technique with an excess of Ru in the starting material. The morphology and structural studies revealed a randomly orientated distribution of the shining Ru inclusions with an average size of few microns. Magnetic and electrical properties showed a behavior similar to the one observed in single crystals with the only Ca2RuO4 phase. We also measured the current-voltage characteristics of the whole Ca2RuO4–Ru system and of a single Ru rod by electric micro-contacts estimating the room temperature resistivity of the Ru embedded inclusions. This study shows that physical properties of Ca2RuO4–Ru metal system are related to the properties of the constituent phases, similarly to the case of Sr2RuO4–Ru metal.

Rietveld refinement of Sm0.55Sr0.45Mn0.4Fe0.6O3

Single crystals of Sm0.55Sr0.45Mn0.4Fe0.6O3were grown by an optical floating zone technique in an oxygen atmosphere. The powder X-ray diffraction pattern for the grown crystal revealed single-crystalline nature. The lattice parameters and atomic structure were refined and indexed using a General Structure Analysis System (GSAS) to an orthorhombic structure with lattice parametersa= 5.4415 (32) Å,b= 7.6994 (27) Å,c= 5.43868 (28) Å, and space group Pnma.

Torque magnetometry study of the spin reorientation transition and temperature-dependent magnetocrystalline anisotropy in NdCo5

We present the results of torque magnetometry and magnetic susceptibility measurements to study in detail the spin reorientation transition (SRT) and magnetic anisotropy in the permanent magnet NdCo5. We further show simulations of the measurements using first-principles calculations based on density-functional theory and the disordered local moment picture of magnetism at finite temperatures. The good agreement between theory and experimental data leads to a detailed description of the physics underpinning the SRT. In particular we are able to resolve the magnetization of, and to reveal a canting between, the Nd and Co sublattices. The torque measurements carried out in the ac and ab planes near the easy direction allow us to estimate the anisotropy constants, K1, K2 and K4 and their temperature dependences. Torque curves, τ(γ) recorded by varying the direction of a constant magnetic field in the crystallographic ac plane show a reversal in the polarity as the temperature is changed across the SRT (240 < T < 285 K). Within this domain, τ(γ) exhibits unusual features different to those observed above and below the transition. The single crystals of NdCo5 were grown using the optical floating zone technique.

Optical floating-zone growth of single crystals of Li-ion battery material LiCoO2

Large, high quality single crystals of Li-ion battery cathode material LiCoO2 have been grown using the optical floating zone technique employing a four-mirror furnace. Several growth experiments reveal that the calcination temperature, quantity of excess Li in the starting feed rod, the atmosphere in the growth chamber, and the growth speed are crucial parameters that govern the stability of the molten zone and in turn the phase purity, stoichiometry and crystallinity of the grown crystal. It is observed that high-quality, phase pure single crystals can only be grown in an Ar-atmosphere of 9 bar and using slow growth speeds of 1–2 mm/h, using feed rods containing 15% excess Li content. The structural refinement of the powder x-ray diffraction data along with the Laue diffraction patterns confirms a rhombohedral crystal structure (space group R3¯m) and the presence of a single grain along the length (~2.5 cm) of the grown crystal. Atomic emission spectrometry (ICP-AES) ascertained the uniformity in stoichiometry along the length of the grown crystals. The x-ray rocking curve of the crystal has a resolution limited full-width at half-maximum (FWHM) of 0.22°, confirming the high single crystalline quality of the sample.

Laser processing as a tool for designing donor-substituted calcium manganite-based thermoelectrics

In this work, the laser floating zone technique (LFZ) for donor-substituted calcium manganite-based thermoelectrics were assessed using Ca1-xPrxMnO3 (x = 0.03, 0.06, 0.1) as a model system. Fibres were grown by LFZ with pulling rates of 25, 100 and 200 mm h−1 in various atmospheres (air, vacuum and argon). Strongly non-equilibrium conditions imposed by LFZ promoted the formation of impurities in (Ca, Pr)MnO3 ceramic fibres, in several cases possessing dendritic structures. The results clearly indicate that careful optimization of the laser processing conditions is needed to produce the manganites with reasonable thermoelectric performance. Negative effects of the phase impurities, promoted by LFZ, on the transport properties can be minimized by additional heat treatment of the laser-processed fibres. The guidelines suggest that LFZ is a suitable technique for processing of thermoelectric perovskite-type manganites if optimized control over growth parameters and re-equilibration conditions is imposed.

Biocerámicas con composición desviada del eutéctico ternario CaSiO3-Ca3(PO4)2-CaMgSi2O6, obtenidas mediante solidificación direccional por láser

Ceramic materials are increasingly used in biomedical applications due to their ability to produce complete osseointegration in the human body. This is possible because, in contact with physiological systems, these materials undergo certain transformations that facilitate the formation of new bone around the ceramic implant. In this research is intended the bioactivity study of a material of the P2O5-CaO-SiO2-MgO system. For this reason the preparation, by zonal fusion by laser, the microstructural characterization and the study of the in vitro response of a material, both vitreous and crystalline, are proposed.Starting from the powdered material we have generated ceramic rods by cold isostatic pressing. After the sintering process of the rods at 1200˚C, we have achieved dense bars by laser floating zone technique (LFZ). An exploration of experimental conditions was performed, being able to obtain both, vitreous and crystalline structure. Samples obtained are bioactive in contact with simulated body fluid because they are able of generate an hydroxyapatite layer on the surface of the material whose function is to promote the union of the implant to the bone and the regeneration of damaged tissue.

Evolution of α phase in metastable β titanium alloys studied by small-angle X-ray scattering

Small-angle X-ray scattering (SAXS) is a technique which makes use of elastic scattering of X-ray radiation on inhomogeneities in electron density in the studied material In particular, a difference in chemical compositions between individual phases can be detected. In this research, SAXS was used to study the evolution of α particles in aged samples of a metastable β titanium alloy, Ti-6.8Mo-4.5Fe-1.5Al (LCB). In order to obtain scattering patterns for a known crystallographic orientation, the experiments were carried out on single crystals grown by a floating zone technique. Aged single-crystalline samples were measured in three different orientations, namely (001), (110) and (111) planes of the bcc β matrix oriented perpendicularly to the primary beam. Resulting scattering patterns exhibited symmetries which correlated with the orientation of the studied sample. A simple theoretical model was developed to interpret the shape and orientation of the observed scattering streaks. Good qualitative agreement between experimental data and simulation was found and the first results of the model are presented in this paper.

Vacancy-Phosphorus Complexes in Electron-Irradiated Floating-Zone n-Type Silicon: New Points in Annealing Studies

Annealing processes of vacancy-impurity atom pairs in moderately doped n-type silicon grown by the floating-zone technique and subjected to 0.9 MeV electron irradiation are investigated by means of Hall effect and conductivity measurements taking over a wide temperature range of 20 to 300 K. Changes in the total concentrations of shallow donors and compensating acceptors in samples prior to and after irradiation as well in the course of isochronal annealing in a temperature interval of 100 to 700°C are determined. It is demonstrated that the Fermi level at annealing stages between 100 and 260°C plays an important part in recovery of the electrical properties of irradiated samples. There is evidence that the first annealing stage between 100 and 160°C is associated with limited migration of vacancy-impurity atom pairs and their trapping by free phosphorus impurity atoms. As a consequence, complexes of vacancy-two impurity atoms appear. They are stable up to 600°C. The complete restoration of the electrical parameters of irradiated samples is observed at 700°C.

Laser floating zone growth of Yb, or Nd, doped (Lu0.3Gd0.7)2SiO5 oxyorthosilicate single-crystal rods with efficient laser performance

Laser quality single crystals of Yb- and Nd-doped oxyorthosilicates, (Lu0.3Gd0.7)2SiO5, have been grown by the laser floating zone technique.

Single crystal growth of GdB6 by the optical floating-zone technique

A high-quality and large-sized GdB6 single crystal was successfully prepared by using the optical floating zone method to accurately control the temperature and composition of the molten zone.

Spectroscopic insight into the interplay between structural disorder and oxidation degree in melt‐grown Ce0.5Zr0.5O2‐y compounds

AbstractThe oxygen storage capacity of CexZr1‐xO2‐y compounds arises from the mixed‐valent character of cerium, which makes the system sensitive to external factors such as temperature and oxygen partial pressure through their influence in the Ce valence, cation ordering and oxygen content. In this work, we analyze the phase relations in Ce0.5Zr0.5O2‐y compounds fabricated by the laser floating zone technique in either oxidising or reducing atmosphere. Chemical, structural, and microstructural properties are studied by X‐ray diffraction, thermogravimetry, scanning electron microscopy (energy dispersive X‐ray spectroscopy and electron backscatter diffraction), and Raman spectroscopy. The latter proves to be determinant to discriminate between phases arising from subtle variations of atomic distribution that are hardly distinguished by X‐ray diffraction or energy dispersive X‐ray analyses. Cation disordered, fluorite‐like phases are obtained when processing is performed in air, whereas cation‐ordered, pyrochlore‐related phases are formed when processing in Ar+5%H2 atmosphere. Processing in a low but non‐negligible pO2 yields, besides the pyrochlore and fluorite‐like phases, an intermediate state with partial disorder that may be relevant for catalysis applications. The vibrational Raman spectrum of the Ce2Zr2O7 pyrochlore has been fully interpreted through polarisation measurements at room and low temperature. Bands arising from crystal field transitions within the ground and first excited multiplets of Ce3+ ions are also identified. The electronic Raman spectrum is found to be a sensitive probe of the degree of cation and oxygen order in these compounds.

Growth of CuFeO2 single crystals by the optical floating-zone technique

CuFeO$_2$ single crystals up to 50 mm in length and up to 10 mm in diameter were grown by the optical floating-zone method. Stoichiometric polycrystalline rods with a diameter of 6-12 mm were used as feed materials to produce crystals of sufficient size to be used as substrates for the growth of thin films of delafossites. For stable growth along the $c$-axis, low growth rates of 0.4 mm/h are necessary. Due to the incongruent melting behavior of CuFeO$_2$, a stable melt zone requires adjustment of the lamp power during growth. The melting of CuFeO$_2$ is not simply incongruent because the thermodynamic equilibrium includes more than two solid phases and the melt; the gas phase is also involved. The crystals were characterized by X-ray diffraction and X-ray fluorescence measurements.

Effect of Rubidium Substitution on the Physical and Superconducting Properties of Textured High-Tc BSCCO Samples

In this research, the effects of rubidium (Rb) substitution on the microstructural, physical, and superconducting properties of Bi2Sr2Ca1-xRbxCu2O8 + y with x = 0.0, 0.025, 0.05, 0.075, 0.10, and 0.125 superconductor have, in detail, been studied. For this purpose, samples were prepared through the classical solid state reaction route, followed by directional grown using the laser floating zone technique and annealing. XRD measurements showed that all samples are composed of Bi-2212 phase as the dominant one, together with less amount of secondary phases. The crystal symmetries of samples were determined as pseudo tetragonal. SEM-EDX confirmed that Bi-2212 phase is the major one, with minor amounts of Bi2 + x(Sr,Ca)2O6 + d, (Sr,Ca)CuO2, CuO2, and CaO secondary phases. In magnetization versus temperature measurements, very sharp diamagnetic transition is observed. The critical onset temperatures, TC, for all samples are obtained around 90 K. From M-H measurement, it has been found that all samples have very large loop areas. By using the data from M-H measurements in the Bean model, the intragranular critical field, JC, has been determined. It has been found that the x = 0.05Rb sample shows the highest superconducting properties and the largest JC values (2.2 105 A/cm2 at 10 K). Moreover, the maximum pinning force, FPmax, at this temperature has also been obtained in x = 0.05Rb sample (8.5 108 Oe A/cm2).

Commensurate to incommensurate magnetic phase transition in honeycomb-lattice pyrovanadateMn2V2O7

We have synthesized single crystalline sample of Mn$_2$V$_2$O$_7$ using floating zone technique and investigated the ground state using magnetic susceptibility, heat capacity and neutron diffraction. Our magnetic susceptibility and heat capacity reveal two successive magnetic transitions at $T_{N1} =$ 19 K and $T_{N2} =$ 11.8 K indicating two distinct magnetically ordered phases. The single crystal neutron diffraction study shows that in the temperature ($T$) range 11.8 K $\le T \le$ 19 K the magnetic structure is commensurate with propagation vector $k_1 = (0, 0.5, 0)$, while upon lowering temperature below $T_{N2} =$ 11.8 K an incommensurate magnetic order emerges with $k_2 = (0.38, 0.48, 0.5)$ and the magnetic structure can be represented by cycloidal modulation of the Mn spin in $ac-$plane. We are reporting this commensurate to incommensurate transition for the first time. We discuss the role of the magnetic exchange interactions and spin-orbital coupling on the stability of the observed magnetic phase transitions.

Preparation, characterization and properties of La0.6Ce0.3Pr0.1B6-ZrB2 directionally solidified eutectic grown via the optical floating zone technique

La0.6Ce0.3Pr0.1B6-ZrB2 directionally solidified eutectic (DSE) with the [100] orientation of the La0.6Ce0.3Pr0.1B6 matrix is firstly fabricated via the optical floating zone technique using LaB6, CeB6, PrB6 and ZrB2 powders as raw materials. The microstructure, mechanical and thermionic emission properties of the as-grown La0.6Ce0.3Pr0.1B6-ZrB2 DSE were systematically investigated. The ZrB2 fibers, whose average diameter is 0.8–1.2 μm, are embedded in the [100] La0.6Ce0.3Pr0.1B6 matrix and uniformly distributed. The Vickers hardness does not vary apparently between the transverse and longitudinal sections of La0.6Ce0.3Pr0.1B6-ZrB2, while the fracture toughness is of highly anisotropy. The fracture toughness of 5.71 MPa m1/2 on the longitudinal section, flexural strength of 826.50 MPa and thermionic emission current density of 84.96 A/cm2, which are all higher than that of LaB6 or LaB6-ZrB2, indicate that the La0.6Ce0.3Pr0.1B6-ZrB2 DSE grown here will have great application prospects as a candidate for high-performance thermionic emitters.

Growth of Single-Crystalline RFe2O4−δ (R = Y, Tm, Yb) by the Floating Zone Melting Method in a Mixture of N2, H2, and CO2 Gases and Magnetic Properties of the Compounds

We have grown single crystals of RFe2O4−δ (R = Y, Tm, Yb), proposed to be electronic ferroelectrics, by using the floating-zone melting technique under rather moderate conditions. For the crystal g...

Effect of reduction on the optical properties of Sr0.61Ba0.39Nb2O6 single crystals grown by optical floating zone technique

The effect of thermal reduction during growth of strontium barium niobate Sr0.61Ba0.39Nb2O6 (SBN61) crystal on its optical and electrical properties has been investigated. Single crystals of SBN61 were grown by the Optical Floating Zone technique in air ambience. Growth challenges such as formation of core and crystal cracking were eradicated by optimizing the synthesis and growth process parameters. The evidence of reduction was observed in the grown crystals that resulted in a characteristic gray colour. Further, the crystal became colourless on annealing in oxygen ambiance at ∼1200 °C for 20 h. The as-grown crystal is therefore identified as reduced SBN crystals due to formation of oxygen vacancies and the accompanied colour centers and charge compensated defects e.g. Nb4+ polaron in the as-grown crystals. X-ray powder diffraction analysis confirmed the formation of the desired phase and no structural change in the reduced crystal. Also, the absorption spectra revealed a broad absorption band centred around 500 nm in the as-grown reduced crystals confirming the thermal reduction of the crystal. Reduced crystals depicted a slight decrease in the optical band gap energy due to defect induced band tailing. An increase in the pyroelectric coefficient (p3) was observed for reduced SBN61 crystal in comparison to the crystal annealed in oxygen. The impedance measurement revealed higher electrical conductivity with smaller activation energy for the reduced crystal in comparison to the annealed SBN61 crystal. It shows that the thermal reduction induced defects influence the electrical conduction processes, causing the materials to be more conducting, which is desirable for a relaxor ferroelectric materials to be used as a thermoelectric generator application.

Colossal dielectric behaviour of Sr2TiMnO6-δ single crystals

Single crystals of Sr2TiMnO6-δ were grown by optical floating zone technique. The single phase nature of the grown crystal was confirmed by powder X-ray diffraction studies. The permittivity of the grown crystal was about 104 at room temperature. The presence of Mn3+ and Mn4+ state resulted in the splitting of T2g mode which is evident from Raman spectrum. The mixed valence state of Mn for charge carrier hopping was determined by X-ray photoelectron spectroscopy.