Effect of Yb3+ content on purity and crystal growth of Ba2NaNb5O15 (original) (raw)
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Effect of gadolinium (Gd3+) addition on the monophased field and crystal growth of Ba2NaNb5O15 (BNN)
Journal of Crystal Growth, 2001
Ba 2 Na 1À3x Gd x Nb 5 O 15 compounds with (0.024x40.2) have been prepared. The limit of the monophased composition field was determined as a function of Gd substitution. The effect of Gd on barium sodium niobate (BNN) was examined by X-ray powder diffraction at room temperature as a function of temperature. The melt behavior was studied by DTA. The homogeneity of single-crystal fibers doped with Gd and grown by micro-pulling down technique was investigated by EPMA. No cracks or other inhomogeneities could be detected, as already shown for Yb-and Nd-doped BNN. In this study, Gd addition was effective for growth of bulk crystals by Czochralski technique. #
Ba3Yb(BO3)3 single crystals: Growth and spectroscopic characterization
Journal of Materials Research, 2008
We obtained Ba3Yb(BO3)3 single crystals by the flux method with solutions of the BaB2O4–Na2O–Yb2O3 system. The evolution of the cell parameters with temperature shows a slope change at temperatures near 873 K, which may indicate a phase transition that is not observed by changes appearing in the x-ray powder patterns or by differential thermal analysis (DTA). The evolution of the diffraction patterns with the temperature shows incongruent melting at temperatures higher than 1473 K. DTA indicates that there is incongruent melting and this process is irreversible. Ba3Yb(BO3)3 has a wide transparency window from 247 to 3900 nm. We recorded optical absorption and emission spectra at room and low temperature, and we determined the splitting of Yb3+ ions. We used the reciprocity method to calculate the maximum emission cross section of 0.28 × 10−20 cm2 at 966 nm. The calculated lifetime of Yb3+ in Ba3Yb(BO3)3 is τrad = 2.62 ms, while the measured lifetime is τ = 3.80 ms.
Single crystal growth of the tetragonal tungsten bronze CaxBa1−xNb2O6 (x=0.28; CBN-28)
Journal of Crystal Growth, 2002
The material group of the tetragonal tungsten bronzes (TTBs) is very attractive due to its outstanding ferroelectric properties. Herein we report attempts to grow single crystals of calcium barium niobate (CBN) that until now was only known as ceramic samples. The single crystal growth of CBN could be realized in two different ways. In a first step a high-temperature tetraborate flux was applied to prepare small crystals for phase analysis. Then, for the first time large single crystals of Ca 0.28 Ba 0.72 Nb 2 O 6 (CBN-28) with dimensions up to 5 cm length were grown by using the Czochralski method. CBN-28 shows a ferroelectric phase transition at about 2801C (detected by dielectric and thermal expansion measurements) that is about 2001C higher than the transition temperature of the widely investigated TTB Sr 0.60 Ba 0.40 Nb 2 O 6 (SBN-60).
Materials Research Bulletin, 2009
Single crystals of (1 − x)BaTiO3 + xNaNbO3 (BTNN) for x = 0.84 were obtained by high temperature solution growth using Na2B4O7 as solvent. The room temperature crystal structure of BTNN 16/84-phase was determined from X-ray single crystal diffraction data, in the tetragonal system with space group P4bm. The refinement from 246 independent reflections led to the following parameters: a = b = 5.5845(3) Å, c = 3.9453(2) Å, V = 123.041(11) Å3, Z = 2, with final cRwp = 0.150 and RB = 0.041. The structure of BTNN 16/84-phase can be described as a three-dimensional framework built up from (Nb–Ti)O6 octahedra with Na and Ba in the dodecahedral site of perovskite-like type. Some mm3-sized crystals have been selected and various dielectric measurements (ferroelectric, pyroelectric, and piezoelectric) have been performed. Transition from paraelectric to ferroelectric state at around 460 K has been observed to be in good agreement with ceramics of closer composition. Dielectric, piezoelectric and pyroelectric measurements on crystal confirm the ferroelectric behaviour of BTNN 16/84.
Optical Materials, 2007
Beta barium borate (b-BaB 2 O 4 ; BBO) single crystals have been grown from Na 2 O flux by the TSSG technique and the observed growth rate anisotropy is reported. The symmetrical conoscopic interference pattern on the c-cut plate confirmed strain-free and optical homogeneity of the crystals. The observed growth habits of as-grown crystals are explained using crystal growth theories. The relative growth rate along different crystallographic directions of BBO can be described by R [100] = R [010] > R [001] . The absorption measurements show a nearly 9 nm shift in fundamental absorption edges in X and Z cut samples. Band gap energies measured were 6.45 and 6.2 eV along the X and Z directions, respectively. The absorption spectra near the fundamental absorption edges (AE) follow Urbach's rule.
Laser heated pedestal growth and spectroscopic properties of K2NdNb5O15 and Ba2NdNbO6 crystals
Chemical Physics Letters, 1997
Single crystals of mixed niobates K2NdNb5OI5 and Ba2NdNbO 6 have been grown by the laser heated pedestal growth (LHPG) technique. The mini-crystals grown by this method were characterized by X-ray diffraction, optical absorption and photoluminescence techniques. The optical absorption spectra (400-950 nm) and emission spectra 4F3/2 ~ 419/2 (~ 900 nm), 4111/2 (~ 1070 rim) are strongly broadened by intrinsic crystalline disorder in both materials.
Evolution of nanocrystalline BaBi2Nb2O9 in Li2B4O7 BaO Bi2O3 Nb2O5 glass system
Journal of Non-crystalline Solids, 2007
Transparent glasses and glass nano crystal composites (GNCs) of various compositions in the system (100 À x)Li 2 B 4 O 7 -x(BaO-Bi 2 O 3 -Nb 2 O 5 ) (where x = 10, 20, and 30 in molar ratio) were fabricated via splat-quenching technique. The glassy nature of the asquenched samples was established by differential thermal analyses. X-ray powder diffraction and transmission electron microscopic (TEM) studies confirmed the formation of layered perovskite BBN via a fluorite like phase. TEM studies revealed the presence of 10 nm sized spherical crystallites of fluorite like BaBi 2 Nb 2 O 9 phase in the glassy matrix of Li 2 B 4 O 7 (LBO). The influence of composition on the dielectric and the optical properties (transmission, optical band gap) of these samples has been investigated.
Effect of processing method on physical properties of Nb2O5
Journal of the European Ceramic Society, 2011
Samples of Nb 2 O 5 were prepared by laser floating zone (LFZ) technique and by solid-state reaction in order to study some of their physical properties as a function of synthesis conditions. Single crystals fibres were obtained by LFZ, while a structural orthorhombic to monoclinic phase transition was observed in samples sintered at temperature higher than 800 • C. Transmission optical spectroscopy and photoconductivity measurements allowed identifying a ∼3.2 eV bandgap energy for the H-Nb 2 O 5 monoclinic crystalline phase. Band gap shrinkage of ∼100 meV was observed from 14 K to RT. For the orthorhombic phase (T-Nb 2 O 5 ), the photoconductivity measurements evidence a higher energy bandgap. The sintered samples have shown a broad recombination luminescence band at the orange/red spectral region while no luminescence was detected from the LFZ grown fibres. A dielectric constant of ∼40 was found for the 800 • C and 1200 • C sintered pellets while that of 1000 • C reached four times that value.