scholarly journals Phonon anomalies in optical spectra of LnNbO3 single crystals

2004 ◽  
Vol 69 (6) ◽  
pp. 493-502 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Rados Gajic ◽  
Ivana Hinic ◽  
Andreja Valcic
Keyword(s):  
Single Crystals ◽  
Published Data ◽  
Czochralski Technique ◽  
Phonon Modes ◽  
Critical Rate ◽  
Air Atmosphere ◽  
Domain Structures ◽  
Infrared And Raman Spectroscopy ◽  
Crystal Diameter ◽  
Domain Inversion

LiNbO3 single crystals were grown by the Czochralski technique in an air atmosphere. The critical crystal diameter Dc = 1.5 cm and the critical rate of rotation ?c=35 rpm were calculated by equations from the hydrodynamics of the melt. The domain inversion was carried out at 1430 K using a 3.75 V/cm electric field for 10 min. The obtained crystals were cut, polished and etched to determine the presence of dislocations and single domain structures. The optical properties were studied by infrared and Raman spectroscopy as a function of temperature. With decreasing temperature, an atypical behaviour of the phonon modes could be seen in the ferroelectrics LiNbO3. The obtained results are discussed and compared with published data.

scholarly journals The crystallization and optical properties of LiNbO3 single crystals

2000 ◽  
Vol 65 (5-6) ◽  
pp. 391-397 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Rados Gajic ◽  
Slobodanka Nikolic ◽  
Stevan Djuric ◽  
Andreja Valcic
Keyword(s):  
Optical Properties ◽  
Single Crystals ◽  
Ferroelectric Properties ◽  
Wave Number ◽  
Published Data ◽  
Phonon Modes ◽  
Number Range ◽  
Air Atmosphere ◽  
Domain Structures ◽  
Crystal Diameter

LiNbO3 single crystals were grown by the Czochralski technique in an air atmosphere. The critical crystal diameter Dc = 1.5 cm and the critical rate of rotation wc = 35 rpm were calculated from the dynamic of fluids equations for buoyancy-driven and forced convections under which the shape of the melt/crystal interface changed. The domain inversion was carried out at 1473 K using a 10 min 3.75 V/cm electric field. The obtained crystals were cut, polished and etched to determine the presence of dislocations and single domain structures. The lattice parameters a = 0.51494 nm, c = 1.38620 nm and V = 0.3186 nm 3 were determined by X-ray powder diffraction. The optical properties were studied by infrared spectroscopy in the wave number range 20. 5000 cm -1. With decreasing temperature, an atypical behaviour of the phonon modes, due to the ferroelectric properties of LiNbO3 single crystal, could be seen. The optical constants were calculated by Kramers-Kronig analysis and the value of the critical temperature was estimated. The obtained results are discussed and compared with published data.

scholarly journals The growth of sapphire single crystals

2001 ◽  
Vol 66 (6) ◽  
pp. 411-418 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Slobodanka Nikolic ◽  
Stevan Djuric ◽  
Andreja Valcic
Keyword(s):  
Crystal Growth ◽  
Single Crystals ◽  
Powder Diffraction ◽  
Chemical Polishing ◽  
Published Data ◽  
Czochralski Technique ◽  
Critical Rate ◽  
Etching Solution ◽  
X Ray ◽  
Crystal Diameter

Sapphire (Al2O3) single crystals were grown by the Czochralski technique both in air and argon atmospheres. The conditions for growing sapphire single crystals were calculated by using a combination of Reynolds and Grash of numbers. Acritical crystal diameter dc = 20 mm and the critical rate of rotation c = 20 rpm were calculated from the hydrodynamics of the melt. The value of the rate of crystal growth was experimentally found to be 3.5 mm/h. According to our previous experiments, it was confirmed that three hours exposures to conc. H3PO4 at 593 K was suitable for chemical polishing. Also, three hours exposure to conc.H3PO4 at 523Kwas found to be a suitable etching solution. The lattice parameters a = 0.47573 nm and c = 1.29893 nm were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

scholarly journals The growth of Nd: YAG single crystals

2002 ◽  
Vol 67 (4) ◽  
pp. 291-300 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Slobodanka Nikolic ◽  
Rados Gajic ◽  
Stevan Djuric ◽  
Andreja Valcic
Keyword(s):  
Crystal Growth ◽  
Single Crystals ◽  
Powder Diffraction ◽  
Lattice Parameter ◽  
Argon Atmosphere ◽  
Published Data ◽  
Czochralski Technique ◽  
Critical Rate ◽  
X Ray ◽  
Crystal Diameter

Y3Al5O12 doped with 0.8%wt.Nd (Nd:YAG) single crystals were grown by the Czochralski technique under an argon atmosphere. The conditions for growing the Nd:YAG single crystals were calculated by using a combination of Reynolds and Grashof numbers. The critical crystal diameter and the critical rate of rotation were calculated from the hydrodynamics of the melt. The crystal diameter Dc=1.5 cm remained constant during the crystal growth while the critical rate of rotation changed from ?c=38 rpm after necking to ?c=13 rpm at the end of the crystal. The value of the rate of crystal growth was experimentally found to be 0.8?1.0 mm/h. According to our previous experiments, it was confirmed that 20 min exposure to conc. H3PO4 at 603 K was suitable for chemical polishing. Also, one-hour exposure to conc. H3PO4 at 493 K was found to be suitable for etching. The lattice parameter a=1.201 (1) nm was determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

scholarly journals The growth and optical properties of Bi12SiO20 single crystals

2002 ◽  
Vol 67 (4) ◽  
pp. 279-289 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Slobodanka Nikolic ◽  
Rados Gajic ◽  
Stevan Djuric ◽  
Andreja Valcic
Keyword(s):  
Crystal Growth ◽  
Single Crystals ◽  
Lattice Parameter ◽  
Published Data ◽  
Czochralski Technique ◽  
Critical Rate ◽  
X Ray ◽  
Wave Numbers ◽  
Different Temperatures ◽  
Crystal Diameter

Single crystals of Bi12SiO20 were grown from the melt by the Czochralski technique. The critical crystal diameter dc=10 mm and the critical rate of rotation ?c=20 rpm were calculated by equations from the hydrodynamics of a melt. The rate of crystal growth was experimentally obtained to be 5 mm/h. The crystal growth was in the [111] direction. The lattice parameter a=1.0096nm was determined by X-ray powder diffraction. The reflectance spectra were recorded in the wave numbers range 20?5000 cm-1 at different temperatures. For all the recorded spectra the values of the vibrational TO and LO modes were found using the Kramers-Kronig analysis (KKA). Twentyfive TO and LO modes were found at 70 K, and eighteen at 295 K. The obtained results are discussed and compared with published data.

scholarly journals The growth of ruby single crystals

2005 ◽  
Vol 70 (1) ◽  
pp. 87-95 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Slobodanka Nikolic ◽  
Stevan Djuric ◽  
Andreja Valcic
Keyword(s):  
Crystal Growth ◽  
Single Crystals ◽  
Powder Diffraction ◽  
Argon Atmosphere ◽  
Published Data ◽  
Czochralski Technique ◽  
Critical Rate ◽  
Etching Solution ◽  
X Ray ◽  
Crystal Diameter

Ruby (Cr:Al2O3) single crystals were grown by the Czochralski technique in an argon atmosphere. The critical crystal diameter dc = 1.0 cm and the critical rate of rotation ?c = 20 rpm were calculated by equations of the hydrodynamics of the melt. The rate of crystal growth was experimentally obtained to be 2.7 mm/h. For chemical polishing, conc. H3PO4 at 593 K for an exposure of 3 hours was determined. Conc. H3PO4 at 523 K for an exposure of 3 h was found to be a suitable etching solution. The lattice parameters a = 0.47627(6) nm and c = 1.301(1) nm were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

scholarly journals The growth of Nd:CaWO4 single crystals

2003 ◽  
Vol 68 (12) ◽  
pp. 1001-1009 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Slobodanka Nikolic ◽  
Rados Gajic ◽  
Stevan Djuric ◽  
Andreja Valcic
Keyword(s):  
Single Crystals ◽  
Room Temperature ◽  
Chromic Acid ◽  
Critical Diameter ◽  
Published Data ◽  
Hydrodynamic Equations ◽  
Czochralski Technique ◽  
Critical Rate ◽  
X Ray ◽  
C 30

CaWO4 doped with 0.8 % at. Nd (Nd:CaWO4) single crystals were grown from the melt in air by the Czochralski technique. The critical diameter dc = 1.0 cm and the critical rate of rotation ?c = 30 rpm were calculated from hydrodynamic equations for buoyancy-driven and forced convection. The rate of crystal growth was experimentally obtained to be 6.7 mm/h. For chemical polishing, a solution of 1 part saturated chromic acid (CrO3 in water) and 3 parts conc. H3PO4 (85 %) at 433 K with an exposure time of 2 h was found to be adequate. A mixture of 1 part concentrated HF and 2 parts chromic acid at room temperature after exposure for 30 min was found to be a suitable etching solution. The lattice parameters a = 0.52404 (6) nm, c = 1.1362 (6) nm and V0 = 0.312 (2) nm3 were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

scholarly journals Single crystals of bismuth silicon oxide grown by the czochralski technique and their characterisation

1999 ◽  
Vol 64 (9) ◽  
pp. 553-561 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Slobodanka Nikolic ◽  
Rados Gajic ◽  
Stevan Djuric ◽  
Andreja Valcic
Keyword(s):  
Optical Properties ◽  
Single Crystals ◽  
Silicon Oxide ◽  
Critical Diameter ◽  
Lattice Parameters ◽  
Published Data ◽  
Czochralski Technique ◽  
Critical Rate ◽  
Bismuth Silicon Oxide ◽  
X Ray

Single crystals of Bi12SiO20 were grown by the Czochralski technique. The critical diameter and the critical rate of rotation were calculated. Suitable polishing and etching solutions were determined. X-Ray measurements were performed on powdered samples to obtain the lattice parameters. The optical properties of the bismuth silicon oxide single crystals were investigated. The obtained results are discussed and compared with published data.

scholarly journals The optical properties of LiNbO3 single crystals obtained in air atmosphere

1999 ◽  
Vol 64 (10) ◽  
pp. 637-646 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Slobodanka Nikolic ◽  
Rados Gajic ◽  
Stevan Djuric ◽  
Aleksandar Jelisijevic ◽  
...  
Keyword(s):  
Optical Properties ◽  
Single Crystals ◽  
Optical Constants ◽  
High Temperature Superconductor ◽  
Critical Diameter ◽  
Published Data ◽  
Critical Rate ◽  
X Ray ◽  
Air Atmosphere ◽  
Reflectance Data

Single crystals of LiNbO3 were grown by the Czochralski technique in an air atmosphere. The critical diameter and the critical rate of rotation were calculated. X-Ray measurements of the powder were carried out to obtain the lattice parameters.The optical constants were calculated by Kramers-Kronig analysis of reflectance data. The optical properties of LiNbO3 single crystals were studied for samples grown in an air atmosphere to investigate the influence of air on the optical properties of the formed crystals. A peak due to OH. gtroups appears in the transmission spectrum at 3385 cm -1. It was still present after annealing in an air atmosphere at temperature up to 873 K, but it was no longer detectable after annealing at 1473 K in an electric field. Thick films of the high-temperature superconductor YBa2Cu3O7 (Ag) were obtained on plates of LiNbO3 single crystals. The obtained results are discussed and compared with published data.

scholarly journals The optical properties of bismuth germanium oxide single crystals

2000 ◽  
Vol 65 (9) ◽  
pp. 611-618 ◽  
Author(s):  
Aleksandar Golubovic ◽  
Rados Gajic ◽  
Changkang Chen ◽  
Andreja Valcic
Keyword(s):  
Optical Properties ◽  
Single Crystals ◽  
Optical Constants ◽  
Published Data ◽  
Germanium Oxide ◽  
Reflection Spectra ◽  
Czochralski Technique ◽  
Phonon Modes ◽  
Bismuth Germanium Oxide ◽  
Wave Numbers

Bi12GeO20 single crystals were grown by the Czochralski technique. Suitable polishing and etching solutions were determined. Reflection spectra were recorded in the wave numbers range 20-5000 cm-1, and compared with the spectra of Bi12SiO20 single crystals to study the position of the phonon modes. The optical constants of the Bi12GeO20 single crystals were obtained using Kramers-Kronig analysis. The obtained results are dicussed and compared with published data.

scholarly journals Numerical Analysis of Difficulties of Growing Large-Size Bulk β-Ga2O3 Single Crystals with the Czochralski Method

Crystals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 25
Author(s):  
Xia Tang ◽  
Botao Liu ◽  
Yue Yu ◽  
Sheng Liu ◽  
Bing Gao
Keyword(s):  
Crystal Growth ◽  
Single Crystals ◽  
Czochralski Method ◽  
Liquid Interface ◽  
Spiral Growth ◽  
Growth Time ◽  
Large Size ◽  
Crystal Diameter ◽  
Solid Liquid Interface ◽  
Solid Liquid

The difficulties in growing large-size bulk β-Ga2O3 single crystals with the Czochralski method were numerically analyzed. The flow and temperature fields for crystals that were four and six inches in diameter were studied. When the crystal diameter is large and the crucible space becomes small, the flow field near the crystal edge becomes poorly controlled, which results in an unreasonable temperature field, which makes the interface velocity very sensitive to the phase boundary shape. The effect of seed rotation with increasing crystal diameter was also studied. With the increase in crystal diameter, the effect of seed rotation causes more uneven temperature distribution. The difficulty of growing large-size bulk β-Ga2O3 single crystals with the Czochralski method is caused by spiral growth. By using dynamic mesh technology to update the crystal growth interface, the calculation results show that the solid–liquid interface of the four-inch crystal is slightly convex and the center is slightly concave. With the increase of crystal growth time, the symmetry of cylindrical crystal will be broken, which will lead to spiral growth. The numerical results of the six-inch crystal show that the whole solid–liquid interface is concave and unstable, which is not conducive to crystal growth.

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