Flux Growth Technique Research Articles

Flux growth of straw‐like rutile monocrystals

AbstractMillimetric straw‐like rutile monocrystals were grown by the flux growth technique. A suitable mixture of flux (MoO3, V2O5, Li2CO3) and amorphous TiO2 gel was slowly cooled down to 750°C from 1250°C or 1350°C. The best yields of straw‐like rutile were obtained with a nutrient/flux ratio and a cooling rate in the range 0.015‐0.006 and 1.8‐1.9 K h‐1, respectively. The hollowed crystals were characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy, microthermometry, and µ‐Raman spectroscopy. As for skeletal crystal, the formation of axial canals in rutile is attributed to a lack of nutrient due to the viscosity of the melt and the high growth rate along [001]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The magnetism and its pressure dependence of europium interlanthanide chalcogenides

Using a novel flux growth technique, we have synthesized polycrystalline samples of the ternary interlanthanide chalcogenide system EuLn2X4 (X=S and Se) for several heavy lanthanides, Ln. The magnetic properties of these materials, all of which are antiferromagnetic below a few Kelvin, are related to the complex crystal structure. In this paper, we describe the crystal structure of EuLn2X4 and measurements of their magnetic properties, mostly at low temperatures. For X=Se and Ln=Ho, Tm, and Lu, we present the hydrostatic pressure dependence of the antiferromagnetic ordering temperatures, TN, and the low temperature (∼2K) high field magnetization to 9T. Similar results are presented for the isomorphic sulfide EuLu2S4.

Inhomogeneity issues in the growth of Na 1/2Bi 1/2TiO 3–BaTiO 3 single crystals

Lead-free piezoelectric single crystals of Na 1/2Bi 1/2TiO 3–BaTiO 3 (NBT–BT) have been grown by flux and zone melting techniques. Growth was carried out by employing two flux systems: (a) Bi 2O 3 and (b) Bi 2O 3 and Na 2CO 3 fluxes. In order to avoid the serious problem of composition variations suffered in flux growth technique, metal strip heated zone melting (MSHZM) technique was employed for the growth of NBT–BT crystals. Inductively coupled plasma (ICP) analysis was carried out for the grown crystals and the composition variations in the crystals obtained from flux and MSHZM techniques were analyzed. Results reveal that the composition variations suffered in the flux-grown crystals have been avoided by adopting the zone melting technique.

Flux growth, structural studies and spectroscopy of K2NdNb5O15 and Nd:K2LaNb5O15 crystals

Single crystals of K 2 NdNb 5 O 15 (KNdN) and Nd 3+ -doped K 2 LaNb 5 O 15 (Nd:KLN) were grown by means of the flux growth technique. X-ray diffraction studies indicate that they belong to the tetragonal tungsten–bronze niobates family. The 10 and 298 K absorption and emission spectra and the luminescence decay curves were measured and discussed in the light of the structural properties. The room temperature absorption spectra were analyzed in the framework of the Judd–Ofelt Theory in order to obtain information about the probabilities of the radiative processes. The calculated lifetimes have been compared with the experimental decay times in order to estimate the efficiencies of the non-radiative processes in both crystals.

Structure, and magnetic and transport behavior of twinned Ce 2Rh 3(Pb,Bi) 5

Single crystals of a new compound, Ce 2Rh 3(Pb,Bi) 5, have been grown via a flux-growth technique using molten Pb as a solvent. The compound has been characterized by single crystal X-ray diffraction and found to be of the orthorhombic Y 2Rh 3Sn 5 structure type [ Cmc2 1 (No. 36), Z=4] with lattice parameters a=4.5980(2), b=27.1000(17) and c=7.4310(4) Å, with V=925.95(9) Å 3. Ce 2Rh 3(Pb,Bi) 5 has a complex crystal structure containing Ce atoms encased in Rh– X ( X=Pb/Bi) pentagonal and octagonal channels in [100], with polyanions similar to those found in Ce 2Au 3In 5 and Yb 2Pt 3Sn 5. Magnetization measurements find that Ce 2Rh 3(Pb,Bi) 5 is a quasi-two-dimensional system, where the Ce moments are spatially well-localized. Heat capacity measurements show a transition at the Néel temperature of 1.5 K. Evidence for Fermi surface nesting is found in electrical resistivity measurements, and we argue that Ce 2Rh 3(Pb,Bi) 5 is very near a metal–insulator transition in zero field.

Flux Growth and Optoelectronic Study of PbWO4 Single Crystals

Lead tungstate (PbWO4) single crystals have been obtained by the flux growth technique using strontium chloride (SrCl2) as flux. Optimum growth conditions are described for obtaining well-faceted transparent crystals. A thermogravimetric study shows that the compound is stable in the temperature range 25−1000 °C. Analysis of optical absorption normal to the ab-plane recorded at room temperature in the spectral range of 200−800 nm reveals the absorption edge, the type of transition being the allowed indirect one at 4.52 eV. The crystal has been characterized by determining useful optical and dielectric parameters.

Investigations on the growth of Zinc Oxide crystals from molten hydrous KOH solution and on the impedance analysis of Zinc Oxide crystals

Single crystals of Zinc Oxide (ZnO) were grown by flux growth technique. The conditions for the growth were optimized. The quality of the crystals has been evaluated using X-ray rocking curve studies. The grown crystals were confirmed to be of wurtzite structure using X-ray Diffraction. Surface morphology of ZnO crystals was analyzed using Scanning Electron Microscopy. A strong band-edge emission at 3.14 eV for ZnO crystals has been observed through Photoluminescence. The measurement of complex impedance response to small ac signals was carried out in the frequency range of 1 Hz to 1 MHz and in the temperature range of 300 to 473 K. The impedance plot shows a single semicircle in the measured frequency range. Dielectric analysis includes measuring dielectric constant as a function of frequency at different temperatures. Activation energy has been calculated using the Arrhenius plot of d.c conductivity as a function of temperature.

Magnetic and transport properties in the Ti doped cobaltite Ca3Co4−xTixO9 (⩽x⩽0.8) single crystals

Single crystals of Ca3Co4−xTixO9 (x=0, 0.2, 0.4, 0.6, and 0.8) are grown by flux growth technique. The effect of Ti doping at Co site on magnetic and transport properties is studied. All samples show Curie-Weiss behavior at temperatures above 50K except for the x=0.8 sample, and the effective magnetic moment μeff increases with increasing Ti content. The free-doped sample Ca3Co4O9 shows a ferrimagnetic transition at 19K. However, a spin-glass transition at Tf(∼20K) appears for the Ti doped samples and the transition temperature Tf shifts to higher temperature as the Ti content increases. The magnetic moment values M at Tf and 5K under the applied field of 4.5T increase with increasing Ti doping content. The variation of the magnetic properties may be related to the induced extra Co2+ ions in the CoO2 layer by substituting Ti4+ for Co3+. The resistivity ρ of the x=0, 0.2, 0.4, and 0.6 samples shows metalliclike behavior at high temperatures and a broad metal-insulator (M-I) transition appears as the temperature decreases to a certain value Tmin. The value of resistivity and the ratio of ρ5K∕ρ300K increase with increasing Ti content. The results are discussed according to the decrease of charge carrier concentration in the samples, which is confirmed by the Hall coefficient measurement. For the x=0.8 sample, there exists another M-I transition in the vicinity of 269K, which is suggested to originate from the spin-state transition of Co3+ or Co4+ ions.

Luminescence of lanthanide ions in strontium barium niobate

Single crystals of strontium barium niobate, Sr x Ba 1- x Nb 2O 6, doped with the lanthanide ions Pr 3+, Nd 3+, Eu 3+, Er 3+ and Yb 3+, were grown for x in the range 0.33–0.75 using the flux growth technique. Emission and excitation spectra were recorded in the visible and near infrared range at room and low temperatures. The spectral bands are strongly affected by inhomogeneous broadening due to the intrinsic disorder of the host. The 10 K optical spectra for the Eu 3+ ion are attributed to the occupation of a single class of sites, tentatively identified as the distorted octahedral Nb 5+ sites.

Flux growth and characterization of SrMo 0.93O 3 single crystal

Single crystals of SrMo 0.93O 3 have been grown by a flux-growth technique using MoO 3 as the flux. The growth process is divided into three stages. First, SrMoO 4 ceramics were sintered in a solid-state reaction. Then, good-quality SrMoO 4 single crystals have been successively grown from the high temperature solutions. Finally, the compound was reduced by hydrogen and argon to SrMo 0.93O 3 single crystal. Powder X-ray diffraction pattern indicated that the SrMo 0.93O 3 crystal has a cubic structure with a = 3.974 Å . ICP-AES analysis indicates that the Sr and Mo ratio is 1:0.93 in the crystal. The temperature dependence of resistivity, magnetization and specific heat of the crystal has also been studied.

Reentrant metal-insulator transition in the Cu-doped manganitesLa1−xPbxMnO3(x∼0.14)single crystals

Single crystals of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Pb}}_{x}{\mathrm{Mn}}_{1\ensuremath{-}y\ensuremath{-}z}{\mathrm{Cu}}_{y}{\mathrm{O}}_{3}$ ($x\ensuremath{\sim}0.14$; $y=0$,0.01,0.02,0.04,0.06; $z=0.02$,0.08,0.11,0.17,0.20) are grown by the flux growth technique. The effect of Cu doping at the Mn-site on magnetic and transport properties is studied. All studied samples undergo a paramagnetic-ferromagnetic transition. The Curie temperature ${T}_{C}$ decreases and the transition becomes broader with increasing Cu-doping level. The high-temperature insulator-metal (I-M) transition moves to lower temperature with increasing Cu-doping level. A reentrant M-I transition at the low temperature ${T}^{*}$ is observed for samples with $y\ensuremath{\geqslant}0.02$. In addition, ${T}^{*}$ increases with increasing Cu-doping level and is not affected by applied magnetic fields. Accompanying the appearance of ${T}^{*}$, there exists a large, almost constant magnetoresistance (MR) below ${T}^{*}$ except for a large MR peak near ${T}_{C}$. This reentrant M-I transition is ascribed to charge carrier localization due to lattice distortion caused by the Cu doping at Mn sites.

Effect of rare-earth-site cations on the physical properties ofLa0.7−yNdyPb0.3MnO3single crystals

Single crystals of $La_{0.7–-y}Nd_yPb_{0.3}MnO_3$ with different y are grown by flux growth technique. The influence of change in average cationic radius $(\langle r_A\rangle)$ and cation size disorder $(\sigma^2)$ on the transport and magnetic properties of these crystals due to the presence of different cations (La and Nd) on the rare-earth sRd site is studied. Curie temperature $T_C$ and metal-insulator transition temperature $T_M_I$ are sensitive to the R site occupation. The temperature dependence of magnetization of $La_{0.7}Nd_yPb_{0.3}MnO_3$ is consistent with spin wave excitations according to the Bloch $T^{3/2}$ law at zero magnetic field limit. The Nd-based systems follow $T^{3/2}$ law only in a certain range of temperature and deviate at low temperatures, which is ascribed to a probably canted ordering of Nd and Mn moments with an antiferromagnetic component at very low temperatures. The values of spin stiffness constants and saturation magnetization vary systematically with changing occupation on the R site. Specific heat measurements of Nd containing samples show a Schottky-like anomaly at low temperature (below 15 K), which increases with the concentration of Nd ions in the lattice. It is concluded that the magnetic properties of manganites with Nd are affected by a tendency for magnetic ordering of the Nd ions.

Luminescence of trivalent rare earth ions in the yttrium aluminium borate non-linear laser crystal

Single crystals of YAl3(BO3)4 doped with the rare earth ions Sm3+, Eu3+, Tb3+, Dy3+, Tm3+ and Yb3+ were grown using the flux growth technique. Luminescence spectra and decay curves were recorded in the visible range at room and low temperatures. The observed transitions were assigned and analysed on the basis of group theory for the D3 point symmetry. Evidence for the presence of non-equivalent centres has been found for Yb3+ and possibly for Sm3+ and Dy3+ doped crystals.

Plasticity of icosahedral Zn–Mg–Dy single quasicrystals

We present the results of first deformation experiments on Zn–Mg–Dy icosahedral single quasicrystals. The samples were produced by the flux growth technique. The plastic deformation experiments were performed at temperatures between 490 and 530°C at strain rates of 10−5 and 10−6s−1. The thermodynamic activation parameters of the deformation process were determined. The stress–strain curves show strong yielding followed by a steady state regime with a constant flow stress level up to strains of about 8%. Microstructural investigations by transmission electron microscopy on deformed samples indicate a deformation mechanism mediated by dislocations. We found a high density of planar defects which were interpreted as slip planes of moving dislocations.

Growth of large single-grain quasicrystals from high-temperature metallic solutions

Flux-growth techniques have been successfully applied to the preparation of several families of quasicrystals and related approximant phases. Large (up to 1cm3) single-grain samples have been obtained for icosahedral R–Mg–Zn (R=Y, Gd, Tb, Dy, Ho and Er), decagonal Al–Ni–Co, icosahedral Al–Pd–Mn, icosahedral Al–Ga–Pd–Mn, and the ξ′ Al–Pd–Mn approximant phase. The samples are obtained by slowly cooling ternary (or quaternary) melts of a composition that intersects the primary solidification surface of the desired phase in the equilibrium ternary alloy phase diagram (i.e. this is a self-flux technique). The technique clearly reveals the growth habit, and results in remarkably strain-free quasicrystals.

Chemical inhomogeneities of flux grown rare-earth aluminate RAlO 3 (R=La, Gd, Tb, Dy, Ho and Er) crystals

Results of scanning electron microscopy and energy dispersive X-ray analysis of the microstructures on the surfaces of flux-grown crystals of RAlO 3 (R=La, Gd, Tb, Dy, Ho and Er) are reported. The results of the microanalytical characterisation of these crystals grown from PbO–PbF 2 flux (with and without additives) suggest their chemical imperfections due to crystallisation or precipitation of secondary phases in the growth of the major phase of RAlO 3. The secondary phases include PbAl 12O 19 and Pb 2OF 2. Formation of other impurity phases mainly ROF, platinum free from or associated with flux components (i.e., Pb 2OF 2) and a secondary phase (i.e., PbAl 12O 19) in the growth of major phase RAlO 3 are evidenced and the deposition of the former on the growing crystals of the latter is explained to be taking place during eutectic solidification. The nucleation mechanism proposed by Wanklyn and Watts (Mater. Res. Bull. 19 (1984) 711) applies generally to the flux growth of RAlO 3 crystals. The crystallisation of minor phases in the growth of a major phase (viz., RAlO 3) and formation of other impurity phases in the multicomponent system and the containing crucible involved in flux growth technique, leading to inhomogeneity of crystal surfaces, are discussed.

Magnetic properties of RMn 6Sn 6 (R=Tb, Ho, Er, Tm, Lu) single crystals

Single crystals of the compounds RMn 6Sn 6 where R=Tb, Ho, Er, Tm, and Lu have been prepared by the flux growth technique. Their magnetic properties were studied in the temperature range from 4.5 to 500 K. TbMn 6Sn 6 and HoMn 6Sn 6 order ferrimagnetically at 450 and 410 K, respectively. Both of these compounds undergo a change in the easy axis, and this transition has been mapped as a function of field and temperature for TbMn 6Sn 6. The other compounds studied (R=Er, Tm, Lu) order antiferromagnetically in zero field. In an applied DC field, a ferrimagnetic structure is found in ErMn 6Sn 6 while TmMn 6Sn 6 exhibits at least two structures at high field, a ferrimagnetic structure and a structure that appears to be half- ferrimagnetic. In LuMn 6Sn 6, the moments are also partially flipped by an applied field.

Magneto-optical properties of RMn 6Sn 6 (R=Gd, Tb, Dy, Ho, Er, Tm, Lu) single crystals

Single crystals of compounds in the series RMn 6Sn 6 (R=Gd–Tm, Lu) have been prepared by the flux growth technique. The crystal structure was found to be isotypic with HfFe 6Ge 6 for all of the compounds, and the variation of the lattice parameters with the lanthanide element exhibit the lanthanide contraction. The polar Kerr effect has been measured between 1.3 and 5 eV, and the structure of the spectra are similar for all of the compounds of the series. The maximum Kerr rotation found was 0.225° in TbMn 6Sn 6, and the magnitude of the Kerr rotations scaled across the series as a function of the fraction saturation. This, combined with the temperature dependence, indicates that the Kerr rotation is primarily a function of the Mn moment and is independent of the lanthanide element present in the compound. The main features in the spectra shift to slightly higher energies as one moves from Gd to the end of the lanthanide series (i.e. Tm and Lu) which is related to the contraction in the lattice parameters.

Thermodynamic and transport properties of single-crystalYb14MnSb11

Relatively large (up to 250 mg) single crystals of the intermetallic compound ${\mathrm{Yb}}_{14}{\mathrm{MnSb}}_{11}$ have been prepared by a flux-growth technique. The results of thermodynamic and transport measurements of these samples are presented. The compound orders ferromagnetically at approximately ${T}_{C}=53\ifmmode\pm\else\textpm\fi{}1\mathrm{K},$ with a magnetization consistent with the assignment ${\mathrm{Mn}}^{3+}$ ${(3d}^{4})$ and ${\mathrm{Yb}}^{2+}$ ${(4f}^{14}).$ The Mn moments are local in nature, with the full effective and saturated moment of the Hund's rule spin-only ground state. The electrical resistivity has a metallic temperature dependence, with only a modest anisotropy. Room-temperature values of the resistivity are relatively high for an intermetallic compound: $1630\ifmmode\pm\else\textpm\fi{}160\ensuremath{\mu}\ensuremath{\Omega}\mathrm{cm}$ and $1250\ifmmode\pm\else\textpm\fi{}130\ensuremath{\mu}\ensuremath{\Omega}\mathrm{cm}$ for currents flowing approximately parallel and perpendicular to the c axis, respectively. There is a distinct loss of spin-disorder scattering in the resistivity at ${T}_{C}.$ From the heat capacity, a rough estimation of the magnetic entropy gives $\ensuremath{\Delta}{S}_{M}\ensuremath{\approx}12.1\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{K},$ the value in reasonable agreement with the expected $\ensuremath{\Delta}{S}_{M}\ensuremath{\approx}R\mathrm{ln}5$ from the assignment of these moments. All of these data are consistent with a picture of ${\mathrm{Mn}}^{3+}$ local moments being coupled via conduction electrons. To this end, ${\mathrm{Yb}}_{14}{\mathrm{MnSb}}_{11}$ appears to be analogous to local-moment rare-earth intermetallic compounds, and may point the way toward a class of $3d$ Kondo lattice compounds.

Spectroscopic analysis and laser parameters of Nd 3+ in Ca 3 Sc 2 Ge 3 O 12 garnet crystals

Sc2Ge3O12 (CaSGG) single crystals with the garnet structure have been grown by means of the flux growth technique. The doping with Nd3+ and Mg2+ (as charge compensator) yields samples suitable for optical spectroscopy experiments. The absorption and emission properties have been measured at temperatures ranging from 10 to 298 K. The emission spectra give evidence of the presence of non-equivalent Nd3+ sites. The decay time of the 1.06-μm emission band has been measured as a function of temperature and incident power. The intensities of the 298 K absorption transitions have been analyzed by means of the Judd–Ofelt theory. The radiative lifetimes, the branching ratios (β), and the spontaneous emission probabilities have been evaluated for the 4F3/2 excited state using the calculated intensity parameters. The stimulated-emission cross sections and the branching ratios have been estimated from the experimental data for the most important laser transitions indicating that this crystal can be considered an interesting material for solid-state laser applications.