Czochralski growth of Lu1‐xScxBO3:Ce solid solution crystals

Single crystals of Lu_1‐xSc_xBO₃:Ce (x=0.2, 0.3, 0.5, 0.7) were grown by Czochralski method. Continuous solid solution with calcite structure and a linear compositional dependency of crystal lattice parameter in the system Lu_1‐xSc_xBO₃:Ce are formed and their symmetry belong to hexagonal system with R3c space group checked by X‐ray powder diffraction. The electron probe micro‐analysis measurements show that the main inclusions in Lu_1‐xSc_xBO₃:Ce crystals are in the form of Sc rich oxide and Ce rich oxide. The ICP‐AES tests show that the more Sc ion content in Lu_1‐xSc_xBO₃:Ce, the smaller effective segregation coefficient of Ce in crystal will be. The X‐ray excited luminescence spectra of Lu_1‐xSc_xBO₃:Ce crystals all present a double peaked emission band with maxima round 370 and 400 nm corresponding to Ce³⁺ emission and a self trapped excitons (STE) band peaking at 269 nm. In addition, due to high density, high relative light yield, fast decay time and no‐hygroscopic property, Lu_0.8Sc_0.2BO₃:1 at%Ce crystal could be a good candidate material for scintillation application by improving the crystal quality and cerium concentration. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth of rare-earth orthovanadate (RVO4) by the floating-zone method

Single crystals of rare-earth orthovanadate, RVO₄ where R=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, with the cross-sectional size of about 7×7 mm² and 20–50 mm length have been successfully grown by the floating-zone method. Fluorescence properties at room temperature and dielectric and elastic properties along the c-axis of some grown crystals have been reported.     

Crystal growth and luminescent properties of Pr-doped K(Y,Lu)3F10 single crystal for scintillator application

Pr1%:K(Y_1−xLu_x)₃F₁₀ (x=0, 0.2, 0.4) single crystals were grown by the μ-PD method. All the grown crystals were greenish and perfectly transparent without any inclusions or cracks. Radioluminescence spectra and decay kinetics of the Pr1%:K(Y,Lu)₃F₁₀ crystals were measured. Emission from the Pr³⁺ 5d–4f transition, peaking around 260 nm and of the decay time of around 22 ns were observed. The 5d–4f emission intensities of the Pr1%:K(Y,Lu)₃F₁₀ crystals were higher than that of the standard BGO scintillator.     

Crystal growth and optical properties of LuYAG:Ce single crystal

Crystals of Ce³⁺-doped (Lu_xY_1?x)₃Al₅O₁₂ (LuYAG) have been grown and studied by X-ray powder diffraction, emission spectroscopy, excitation spectroscopy and X-ray excited fluorescence spectroscopy. The X-ray powder diffraction pattern revealed that the as-grown LuYAG:Ce crystal possessed the garnet structure. Compared with Ce³⁺-doped Y₃Al₅O₁₂ (YAG), the absorption bands associated with the 4f–5d transition shifted to shorter wavelengths, the emission band that originated from a transition from the lowest 5d level to the ²F ground state of the Ce³⁺ ions shifted to the blue, which was probably due to a larger Stokes shift of the emission, and the reduction of relative intensity of antisite defect emission in the X-ray excited fluorescence spectra revealed that introducing Lu ions into YAG could reduce the antisite defect.     

Coupled substitution of gallium by magnesium and zirconium in single crystals of gadolinium gallium garnet

Single crystals of gadolinium gallium garnet in which the gallium ions on the octahedral sites were partially substituted by coupled substitution of magnesium and zirconium have been grown using the Czochralski technique. Single crystals of 36 mm in diameter and 100 mm in length corresponding to the formula Gd₃Ga_5-x-yMg_xZr_yO₁₂ have been obtained from melt compositions in which 0.1 ? x = y ? 0.7. The dislocation and inclusion densities of the single crystals are below 5 cm^-2. The lattice parameters increase linearly from 12.382 Å for gadolinium gallium garnet to 12.489 Å for x = y ≈ 0.54. The distribution coefficient increases in this concentration range from K_eff = 0.58 to K_eff = 0.89. Boules grown from melt compositions in which x = y ? 0.7 appear cloudy through precipitation of Gd₂Zr₂O₇ as a second phase.     

Nanostructured crystals of Sr1?xRxF2+x fluorite phases and their ordering: 6. Microindentation analysis of crystals

Hardness, crack resistance, brittleness, and effective fracture energy have been studied for crystals of 24 fluorite phases Sr_{1 − x} R _x F_{2 + x} (R are 14 rare earth elements (REEs); 0 < x ≤ 0.5) and SrF2 grown by the Bridgman method from a melt. These characteristics change nonlinearly with an increase in the REE content for Sr_{1 − x} R _x F_{2 + x} (0 < x ≤ 0.5) with R = La, Nd, Sm, Gd, and Lu; it is maximum in the range x < 0.1 for all REEs. The changes in a number of REEs have been traced for an isoconcentration series of Sr_0.90 R _0.10F_2.10 crystals (R = La, Nd, Sm, Gd, Ho, Er-Lu, or Y) and crystals (similar in composition) with R = Tb and Dy. The hardness of Sr_{1 − x} R _x F_{2 + x} crystals is higher by a factor of ∼2–3 than that of SrF2. The effect of decrease in microstresses in SrF₂ crystals is confirmed by the isomorphic introduction of R ³⁺ ions into this crystalline matrix.     

Investigation of the crystallization features,atomic structure,and microstructure of chromium-doped monticellite

A series of Cr⁴⁺:CaMgSiO₄ single crystals is grown using floating zone melting, and their microstructure, composition, and crystal structure are investigated. It is shown that regions with inclusions of second phases, such as forsterite, akermanite, MgO, and Ca₄Mg₂Si₃O₁₂, can form over the length of the sample. The composition of the single-phase regions of the single crystals varies from the stoichiometric monticellite CaMgSiO₄ to the solid solution Ca_{(1 ? x)}Mg_{(1 + x)}SiO₄(x = 0.22). The Cr:(Ca_0.88Mg_0.12)MgSiO₄ crystal is studied using X-ray diffraction. It is revealed that, in this case, the olivine-like orthorhombic crystal lattice is distorted to the monoclinic lattice with the parameters a = 6.3574(5) Å, b = 4.8164(4) Å, c = 11.0387(8) Å, β = 90.30(1)^o, Z = 4, V = 337.98 ų, and space group P2₁/c. In the monoclinic lattice, the M(1) position of the initial olivine structure is split into two nonequivalent positions with the center of symmetry, which are occupied only by Mg²⁺ cations with the average length of the Mg-O bond R _av = 2.128 Å. The overstoichiometric Mg²⁺ cations partially replace Ca²⁺ cations (in the M(2) position of the orthorhombic prastructure) with the average bond length of 2.347 Å in the [(Ca,Mg)-O₆] octahedron. The average distance in SiO₄ distorted tetrahedra is 1.541 Å.     

Crystallisation of a simulated borosilicate high-level waste glass produced on a full-scale vitrification line

A simulated (inactive) borosilicate high-level waste (HLW) glass was produced on a full-scale vitrification line with composition simulating vitrified oxide fuel (UO₂) reprocessing waste. As-cast samples were compositionally homogeneous (Type I microstructure) and/or compositionally inhomogeneous displaying compositional ‘banding’ and frequently containing ‘reprecipitated calcine’ (Type II microstructure). Crystal phases identified in as-cast samples were: tetragonal RuO₂, cubic Pd-Te alloy, cubic (Cr,Fe,Ni,Ru)₃O₄, trigonal Na₃Li(MoO₄)₂·6H₂O, ostensibly cubic Zr_{1 − x − y}Ce_xGd_yO_2 − 0.5y and a lanthanoid (Nd,Gd,La,Ce) silicate. Zr_{1 − x − y}Ce_xGd_yO_2 − 0.5y and lanthanoid (Nd,Gd,La,Ce) silicate were found exclusively in the Type II microstructure as component crystal phases of ‘reprecipitated calcine’. Heat treated samples (simulating the retarded cooling experienced by actual (active) borosilicate HLW glasses after pouring) displayed extensive crystallisation and cracking (Type A microstructure) and/or ‘banded’ crystallisation (Type B microstructure) depending on their parent (as-cast) microstructure (Type I and/or Type II respectively). Crystal phases identified in heat treated samples were: tetragonal SiO₂ (α-cristobalite), tetragonal (Na,Sr,Nd,La)MoO₄, cubic Ce_{1 − x − y}Zr_xGd_yO_2 − 0.5y, a Ni-rich phase, a lanthanoid (Nd,Gd,La,Ce) silicate and orthorhombic LiNaZrSi₆O₁₅ (zektzerite). α-cristobalite was found exclusively in the Type A microstructure, while lanthanoid (Nd,Gd,La,Ce) silicate and zektzerite were only found in the Type B microstructure. Potential host phases for HLW radionuclides are: Pd-Te alloy (¹⁰⁷Pd and ⁷⁹Se), (Cr,Fe,Ni,Ru)₃O₄ (⁶³Ni), Zr_{1 − x − y}Ce_xGd_yO_2 − 0.5y (⁹³Zr, Pu and U), both lanthanoid (Nd,Gd,La,Ce) silicates (Am and Cm), (Na,Sr,Nd,La)MoO₄ (⁹⁰Sr, Am and Cm), Ce_{1 − x − y}Zr_xGd_yO_2 − 0.5y (⁹³Zr, Pu and U), the Ni-rich phase (⁶³Ni) and zektzerite (⁹³Zr, ¹²⁶Sn and U). Cracking in samples was attributed to thermal expansion mismatch between the borosilicate HLW glass matrix and RuO₂, cristobalite (both α and β), (Na,Sr,Nd,La)MoO₄ and zektzerite on cooling. There was also a contribution from the cristobalite α-β phase transition.     

Study of the effects of Ga3+ co-doping on the Lu0.8Sc0.2BO3:Ce scintillation crystals

Transparent Lu_0.8Sc_0.2BO₃ crystals doped with 1 at%Ce³⁺ and co-doped with 1 at% and 3 at%Ga³⁺ were grown by the Czochralski method. We applied absorption spectrum, luminescence spectra under UV and X-ray excitation, fluorescence decay curve, three dimensional thermoluminescene and X-ray absorption near edge spectroscopy to study the effect of Ga³⁺ co-doping on the Lu_0.8Sc_0.2BO₃:Ce scintillation crystals. Experimental results indicated that no positive contribution of the Ga³⁺ ion doping on the scintillation efficiency was found. The causes for the deterioration of scintillation efficiency by co-doping Ga³⁺ were revealed. The decrease of practical cerium content and the Ce³⁺/Ce⁴⁺ ratio in crystals, and the increase of the trap concentrations, although the corresponding trap types still maintained the same, played a joint influence on the degrading of scintillation efficiency of Lu_0.8Sc_0.2BO₃:Ce crystals.     

Nonstoichiometry in inorganic fluorides: I. Nonstoichiometry in MF m -RF n (m < n ≤ 4) systems

The manifestation of gross nonstoichiometry in MF _m -RF _n systems (m < n ?? 4) has been studied. Fluorides of 34 elements, in the systems of which phases of practical interest are formed, are chosen. To search for new phases of complex composition, a program for studying the phase diagrams of the condensed state (??200 systems) has been carried out at the Institute of Crystallography, Russian Academy of Sciences. The main products of high-temperature interactions of the fluorides of elements with different valences (m ?? n) are grossly nonstoichiometric phases of two structural types: fluorite (CaF₂) and tysonite (LaF₃). Systems of fluorides of 27 elements (M ¹⁺ = Na, K; M ²⁺ = Ca, Sr, Ba, Cd, Pb; R ³⁺ = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; R ⁴⁺ = Zr, Hf, Th, U) are selected; nonstoichiometric M _{1 ? x} R _x F _{m(1 ? x) + nx} phases, which are of greatest practical interest, are formed in these systems. The gross nonstoichiometry in inorganic fluorides is most pronounced in 80 MF₂ ? RF₃ systems (M = Ca, Sr, Ba, Cd, Pb; R are rare earth elements). The problems related to the growth of single crystals of nonstoichiometric phases and basic fields of their application as new fluoride multicomponent materials, the properties of which are controlled by the defect structure, are considered.     

Synthesis,crystal growth and second harmonic generation properties of trivalent rare-earth-doped non-linear tungsten–bronze-type structure Ba2Na1−3xRExNb5O15 (RE=Sc,Y, La,Gd, Yb and Lu)

A new compound filled tungsten–bronze-type structure Ba₂Na_1−3xRE_xNb₅O₁₅ (trivalent rare-earth ions: RE³⁺=Sc³⁺, Y³⁺, La³⁺, Gd³⁺, Yb³⁺ and Lu³⁺, with x=0.02) has been prepared by selecting RE³⁺ ions without any absorption in the visible range. The effect of rare-earth addition on micro-twin formation, that is to say, tetragonal–orthorhombic ferroelastic phase transition in barium sodium niobate was investigated and micro-twin formation could be suppressed by doping of smaller RE³⁺ ions such as Yb³⁺ and Lu³⁺. All the samples exhibit an intense second harmonic generation signal under tunable IR pumping laser source, due to both the high values of the non-linear optical coefficients and the absence of absorption of additional RE ions in the visible range.     

ESR and optical absorption of Cu2+ in Na2OSiO2 glasses

ESR and optical absorption spectra of Cu²⁺ in xNa₂O(100?x)SiO₂ glasses were measured, where x ranges from 12 to 70 mol% Na₂O. This glass system was divided into three composition regions, 12 ? x ? 37, 37 ? x ? 55 and 55 ? x, from the composition dependence of the ligand field transition energy and spin hamiltonian parameters of Cu²⁺. Two boundary compositions (37 and 55 mol%) between the two adjacent regions agreed with the eutectics in the equilibrium phase diagram. Two types of Cu²⁺-complexes, with less basic ligands (HFS-1) and much more basic ones (HFS-2), were detected in ESR for ultra-high soda glasses (x ? 55). The distribution of the ESR parameters due to the fluctuation of ligand fields was negligible for HFS-2 compared with that for other glasses. The Cu²⁺ ion responsible for HFS-2 was considered to distribute in the microphase of orthosilicate. Imagawa's basicity, the covalency of the bondings between Cu²⁺ and ligands, was calculated by using Maki and McGarvey's analysis. The basicity of σ-type symmetry remained constant, irrespective of the glass composition, and the value was identical with those for other oxyanionic glasses. The π-type basicity was also constant for the glasses of x ? 55. Two different basicities, each corresponding to HFS-1 or 2, were obtained for the glasses of x ? 55. The value derived from HFS-1 was identical with those for x < 55 glasses, whereas that derived from HFS-2 suggested the formation of much more basic ligands.     

Investigation on defects in Lu2SiO5:Ce crystals grown by Czochralski method

Cerium‐doped lutetium oxyorthosilicate crystals (Lu₂SiO₅:Ce) with dimension of ∅︁50 × 60 mm were grown by Czochralski method from an inductively heated iridium crucible. The vaporized substance during growth was examined with XRD and proved to be SiO₂. The vertical and the screw strips existing on the surface of the boule were observed with optical microscope and tested with electron microprobe. They are confirmed to be iridium from the crucible and harmful to the crystal growth. The cleavage orientation of LSO was proved to be (110) and it is one of factors to cause crystal cracking. The scattering particles in LSO crystals are analyzed to be mainly composed of Lu₂O₃ inclusions. Two possible origins on these inclusions are proposed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The growth and defect structure of CdF2 and nonstoichiometric Cd1 ? xRxF2 + x phases (R are rare earth elements or in): Part VI. The optical properties of Cd0.9R0.1F2.1 crystals

The optical properties of the isoconcentration series of Cd_0.9 R _0.1F_2.1 crystals (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu) grown from a melt by the Bridgman method have been investigated. The crystals have an anomalous birefringence (∼10⁻⁶) nonuniformly distributed over the sample diameter; the dichroism in them does not exceed 10⁻⁹. Scanning using a spectral modulator showed the nonuniform distribution of rare earth elements over the crystal diameter. The refractive indices n have been measured at wave-lengths of 0.436, 0.546, and 0.589 μm. The character of change in n along the rare-earth series is nonuniform and similar to the change in n in Sr_0.9 R _0.1F_2.1 crystals. It is shown that the refractive indices in Cd_{1 − x} R _x F_{2 + x} crystals, depending on the RF₃ content, can be estimated using the method of molecular refraction additivity. Original Russian Text ? A.F. Konstantinova, T.M. Glushkova, I.I. Buchinskaya, E.A. Krivandina, B.P. Sobolev, 2009, published in Kristallografiya, 2009, Vol. 54, No. 4, pp. 648–651.     

Magnetic resonance study of the crystallization behavior of InF3-based glasses doped with Cu2+, Mn2+ and Gd3+

The crystallization of fluoroindate glasses doped with Gd³⁺, Mn²⁺ and Cu²⁺ heat treated at different temperatures, ranging from the glass transition temperature (T_g) to the crystallization temperature (T_c), are investigated by electron paramagnetic resonance (EPR) and ¹⁹F nuclear magnetic resonance (NMR). The EPR spectra indicate that the Cu²⁺ ions in the glass are located in axially distorted octahedral sites. In the crystallized glass, the g-values agreed with those reported for Ba₂ZnF₆, which correspond to Cu²⁺ in a tetragonal compressed F⁻ octahedron and to Cu²⁺ on interstitial sites with a square-planar F⁻ co-ordination. The EPR spectra of the Mn²⁺ doped glasses exhibit a sextet structure due to the Mn²⁺ hyperfine interaction. These spectra suggest a highly ordered environment for the Mn²⁺ ions (close to octahedral symmetry) in the glass. The EPR spectra of the recrystallized sample exhibit resonances at the same position, suggesting that the Mn²⁺ ions are located in sites of highly symmetric crystalline field. The increase of the line intensity of the sextet and the decrease of the background line in the thermal treated samples suggest that the Mn²⁺ ions move to the highly ordered sites which contribute to the sextet structure. The EPR spectra of the Gd³⁺ doped glasses exhibit the typical U-spectrum of a s-state ion in a low symmetry site in disordered systems. The EPR of the crystallized glasses, in contrast, have shown a strong resonance in g ≈ 2.0, suggesting Gd³⁺ ions in environment close to cubic symmetry. The ¹⁹F NMR spin–lattice relaxation rates were also strongly influenced by the crystallization process that takes over in samples annealed above T_c. For the glass samples (doped or undoped) the ¹⁹F magnetization recoveries were found to be adjusted by an exponential function and the spin–lattice relaxation was characterized by a single relaxation time. In contrast, for the samples treated above T_c, the ¹⁹F magnetization-recovery becomes non-exponential. A remarkable feature of our results is that the changes in the Cu²⁺, Mn²⁺, Gd³⁺ EPR spectra and NMR relaxation, are always observed for the samples annealed above T_c.     

The investigation of the magnetic interaction between Cu2+ and V4+ ions in x(CuO·2V2O5)(1 − x)[2B2O3·K2O] glasses

EPR and magnetic susceptibility measurements have been performed on (CuO·2V₂O₅)(1?x)[2B₂O₃·K_2O] glasses with 0 ? x ? 40 mol. %.For x < 10 mol.%, both Cu²⁺ and V⁴⁺ ions are present mostly as the isolated species. The values of MO coefficients indicate a high covalent degree of the transition metal (TM)-oxygen bonds. Also, the EPR parameters suggest the presence of strong (TM)-oxygen bonds along the 0_z axis, which lead to an octahedral (Oh) symmetry component at TM ions sites.In the case of 10 ? x ? 40 mol.%, the dipole-dipole and superexchange interactions occur between transition metal ions, which determine a broad resonance line at $\text{g ? 2}$. The strong interactions between Cu²⁺ and V⁴⁺ ions give rise to the exchange coupled Cu²⁺ V⁴⁺ pairs in the studied glasses with x > 10 mol.% (y > 3.9 mol.%).     

Growth and characterization of Fe1 ? x M x VO4 single crystals (M = Al, Cr, Co, Ga)

Triclinic Fe_{1 ? x} M _x VO₄ single crystals (M = Al, Ga, Co, Cr) have been grown by the flux method from systems based on PbO-V₂O₅. Their crystallographic parameters are determined by powder X-ray diffraction. Fe_{1 ? x} Ga _x VO₄ single crystals (x = 0?C0.3) with a volume more than 1cm³ are grown using the seeding technique. The temperature and field dependences of magnetization and magnetic susceptibility of the grown Fe_{1 ? x} Ga _x VO₄ and Fe_{1 ? x} Al _x VO₄ single crystals (x = 0.3 in the solution-melt) are reported. It is shown that the magnetizations of these crystals exceed that of FeVO₄, and both of their antiferromagnetic phase transitions are shifted to lower temperatures.     

Gd3Ga5O12:Nd3+ crystals for a continuous-wave diode-pumped laser operating in 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 channels

Garnet crystals of the composition Gd₃Ga₅O₁₂:Nd³⁺ (concentration series C_Nd = 1–10 at. %) were grown from flux. In terms of spectroscopy, these crystals, unlike those grown from melts, form medium with a single activator center. For the first time, continuous-wave lasing was excited by diode pumping with the use of Gd₃Ga₅O₁₂:Nd³⁺ crystals at the wavelengths λ₃ = 1.3315 and λ₄ = 1.3370 μm of the ⁴F_3/2 → ⁴I_13/2 channel and also the simultaneous generation at two wavelengths, λ₁ = 1.0621 and λ₂ = 1.0600 μm, of the ⁴F_3/2 → ⁴I_11/2 channel.     

Glass formation and crystallization behavior in Mg65Cu25Y10−xGdx (x=0, 5 and 10) alloys

The glass forming ability and crystallization behavior of Mg₆₅Cu₂₅Y_10−xGd_x (x=0, 5 and 10) alloys have been investigated. The glass forming ability (GFA) is significantly improved when Y in Mg₆₅Cu₂₅Y₁₀ is substituted with Gd. Ternary Mg₆₅Cu₂₅Gd₁₀ bulk metallic glass (BMG) with diameter of at least 8 mm was successfully fabricated by conventional Cu-mold casting method in air atmosphere. Mg₂(Y, Gd) is the first competing crystalline phase against the glass formation in the Mg₆₅Cu₂₅Y_10−xGd_x (x=0, 5) alloys, while Mg₂Cu and Cu₂Gd are the competing crystalline phases in the Mg₆₅Cu₂₅Gd₁₀ alloy. Therefore, the suppression of the formation of Mg₂(Y, Gd) during cooling from the liquid improves the GFA significantly.     

Growth and magnetic‐optical properties of Sr3Gd(BO3)3 and Sr3TbxGd1‐x(BO3)3 single crystals

Single crystals of Sr₃Gd(BO₃)₃ (SGB) and Sr₃Tb_xGd_1‐x(BO₃)₃ (TSGB) with dimension Ø 20 mm×20 mm have been grown by Czochralski method. The grown crystals were characterized by X‐ray powder diffraction analysis which showed the crystals belong to hexagonal structure with lattice parameters of a=b=1.254 nm, c=0.926 nm (SGB) and a=b=1.253 nm, c=0.925 nm (TSGB). In TSGB, x=17.7% was obtained by X‐ray fluorometry which showed the segregation coefficient of Tb is closed to 1. The transmission spectrum was measured, which indicated the crystals have high transmittance in 400‐1100 nm region. The Faraday rotation of single crystals at 532 nm wavelength was measured at room temperature. Finally, the Verdet constants were investigated, (SGB) V=17.9 degcm^‐1T^‐1 and (TSGB) V=21.3 degcm^‐1T^‐1. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)