Papers by Takumi Fujiwara
Philosophical Magazine A-physics of Condensed Matter Structure Defects and Mechanical Properties, 1990
Polysynthetically twinned crystals of TiAl with a nearly stoichiometric composition have been gro... more Polysynthetically twinned crystals of TiAl with a nearly stoichiometric composition have been grown and deformed in compression at room temperature. The yield stress and deformation behaviour depend strongly on the angle between the twin boundaries and the compression axis rather than on the crystallographic orientation of the compression axis. The yield stress is high when compression is perpendicular or parallel
Solid State Communications, 2005
Nanosecond (∼100ns) pulsed (10Hz) Nd:YAG laser operating at the wavelength (λ) of 1064nm with pul... more Nanosecond (∼100ns) pulsed (10Hz) Nd:YAG laser operating at the wavelength (λ) of 1064nm with pulse energies of 0.16–1.24mJ/cm2 has irradiated 10Sm2O3·40BaO·50B2O3 glass. It is demonstrated for the first time that the structural modification resulting the large decease (∼3.5%) in the refractive index is induced by the irradiation of YAG laser with λ=1064nm. The lines with refractive index changes are written
Optical Materials, 2002
... The second harmonic (SH) generation from the crystalline phases at the surface layers has bee... more ... The second harmonic (SH) generation from the crystalline phases at the surface layers has been confirmed from Maker fringe measurements. ... 5. Considerably clear and fine (narrow)Maker fringe patterns are observed in Gd 2 O 3 -containing sample. ...
Journal of Non-crystalline Solids, 2003
The formation mechanism of ferroelastic Ba 2 TiGe 2 O 8 crystals in 30BaO Á 15TiO 2 Á 55GeO 2 gla... more The formation mechanism of ferroelastic Ba 2 TiGe 2 O 8 crystals in 30BaO Á 15TiO 2 Á 55GeO 2 glass and second order optical non-linearity of transparent crystallized glasses have been examined. It has been confirmed that the BaTiGe 3 O 9 crystalline phase is initially precipitated and acts as a nucleation site for the formation of the Ba 2 TiGe 2 O 8 crystalline phase. Transparent surface crystallized glasses consisting of grain-oriented Ba 2 TiGe 2 O 8 crystals have been successfully fabricated by means of heat-treatments (690-750°C, 3 h) for the first time, and second harmonic (SH) generation has been clearly observed, demonstrating that Ba 2 TiGe 2 O 8 is a non-linear optical crystalline phase. The SH intensity of transparent crystallized glasses (bulk state) with crystalline layers of $10 lm thickness is comparable to that of Z-cut a-quartz single crystal with a thickness of 0.6 mm. The SH intensity of Ba 2 TiGe 2 O 8 crystals (powdered state) prepared through solid-state reaction is about 130 times as large as that of pulverized a-quartz.
Solid State Communications, 2004
ABSTRACT
Journal of The Ceramic Society of Japan, 2005
The optical absorbance, refractive index and absorption edge of vapour deposited amorphous Sb2S 3... more The optical absorbance, refractive index and absorption edge of vapour deposited amorphous Sb2S 3 films are studied systematically as a function of annealing temperature in the range 160°C > T > 23°C. As deposited films continuously loose sulphur above 60°C as determined by ESCA and this loss affects their measured optical properties. Modification of optical properties upon heating to T = 160°C opens the possibility of a WORM (write once read many times) kind of optical storage as demonstrated in laser irradiation experiment.
Journal of Non-crystalline Solids, 2001
A CW YAG laser with a wavelength of 1064 nm and with a power of 1 W has been used to irradiate sa... more A CW YAG laser with a wavelength of 1064 nm and with a power of 1 W has been used to irradiate samarium tellurite glasses with the compositions of 10RO Á 10Sm 2 O 3 Á 80TeO 2 (R Mg, Ba) at room temperature for 30±60 s. It is found from polarized optical microscopy and from X-ray diraction (XRD) analyses that crystalline dot patterns with sharp refractive index changes are formed by laser irradiation. The diameters of the spherical dots in the glasses with BaO and MgO are about 50 and 150 lm, respectively. It has been proposed that the crystallization of a nanocrystalline Sm 2 Te 6 O 15 phase is induced through the absorption of irradiated YAG laser by the Sm 3 ions. This is the ®rst ®nding of crystalline dot patterning induced by infrared CW YAG laser irradiation in glass. Ó
Optical Materials, 2004
Crystalline phases and second-order optical nonlinearities in crystallized glasses of (Na,K)NbGeO... more Crystalline phases and second-order optical nonlinearities in crystallized glasses of (Na,K)NbGeO 5 (i.e., xNa 2 O AE (25 À x)K 2 O AE 25Nb 2 O 5 AE 50GeO 2 ) are examined. The molar volume of the glasses decreases with increasing Na 2 O content, indicating that the glass structure of NaNbGeO 5 glass is more compact compared with KNbGeO 5 glass. The optical basicity of the glasses is 0.94-0.95, implying that chemical bonds among constituents ions are basically very ionic. (Na,K)NbGeO 5 glasses exhibit a unique crystallization depending on the Na 2 O/K 2 O ratio. The main crystalline phase in crystallized NaNbGeO 5 glass is the NaNbGeO 5 phase. KNbGeO 5 glass shows a prominent bulk nanocrystallization giving nanocrystals of the K 3:8 Nb 5 Ge 3 O 20:4 phase. A glass with the composition of K 3:8 Nb 5 Ge 3 O 20:4 also shows a bulk nanocrystallization. The crystallized glasses with K 3:8 Nb 5 Ge 3 O 20:4 and NaNbGeO 5 crystalline phases do not show a second harmonic generation (SHG) at room temperature. The nonlinear optical (Na,K)NbO 3 phases showing a SHG are formed at the surface ($5 lm) of crystallized glasses with x ¼ 15 and 20, giving an orientation of the (1 1 0) plane. The present study suggests the presence of mixed-alkali effect in the crystallization behavior of (Na,K)NbGeO 5 glasses.
Journal of The American Ceramic Society, 2007
This paper reports recent progress in the patterning of non-linear optical crystals on the glass ... more This paper reports recent progress in the patterning of non-linear optical crystals on the glass surface by laser irradiation. Two techniques for the writing of crystal lines have been developed, i.e., rare-earth (samarium) atom heat processing and transition metal atom heat processing, in which a continuous wave Nd:YAG laser (wavelength: k 5 1064 nm) is irradiated to the glasses containing rare-earth (RE: Sm 31 , Dy 31 ) ions or transition metal (TM: Ni 21 , Fe 21 , V 41 ) ions. The writing of crystal lines such as b-BaB 2 O 4 , Sm x Bi 1Àx BO 3 , and Ba 2 TiGe 2 O 8 showing second harmonic generations has been successful. It is clarified from the azimuthal dependence of second harmonic intensity and polarized micro-Raman scattering spectra that crystal lines consist of highly oriented crystals along the crystal line growth direction. It is also possible to write two-dimensional crystal bending or curved lines by just changing the laser scanning direction. The mechanism of the laser-induced crystallization has been proposed.
Physica C-superconductivity and Its Applications, 2005
A high magnetic field of 10 T was applied to the crystallization process of Bi 2 Sr 2 CaCu 2 O x ... more A high magnetic field of 10 T was applied to the crystallization process of Bi 2 Sr 2 CaCu 2 O x superconducting precursor glasses, and the effect of high magnetic field on crystal grain orientations and superconducting properties were examined from electrical resistivity measurements, X-ray diffraction analyses and scanning electron microscope observations. The glass-ceramics prepared in a high magnetic field show better superconducting properties (higher critical temperature, larger critical current density, and smaller normal-state resistivity) compared with the samples crystallized in a normal heat-treatment with no magnetic field. It was found that Bi2212 crystal grains with a plate-like shape tend to stack to the direction of the magnetic field, i.e., the orientation of the c-axis of the Bi2212 phase to the direction of the magnetic field.
Optics Communications, 2003
A transparent TeO 2 -based nanocrystallized (crystalline particle size: $40 nm) glass (composition:
Journal of Solid State Chemistry, 2005
New glasses giving the crystallization of Sm3+-doped SrxBa1−xNb2O6 (SBN) ferroelectrics have been... more New glasses giving the crystallization of Sm3+-doped SrxBa1−xNb2O6 (SBN) ferroelectrics have been developed in the Sm2O3−SrO−BaO−Nb2O5−B2O3 system, and the formation of SBN crystal dots and lines by continuous wave Nd:YAG laser (wavelength:1064nm, power: 1W) irradiations, i.e., samarium atom heat processing, has been examined. The formation of Sm3+-doped SBN non-linear optical crystals is confirmed from X-ray diffraction analyses, micro-Raman scattering spectra,
Journal of Non-crystalline Solids, 2007
The glasses with the compositions of 21.25RE 2 O 3 -63.75MoO 3 -15B 2 O 3 (RE: Sm, Gd, Dy) were p... more The glasses with the compositions of 21.25RE 2 O 3 -63.75MoO 3 -15B 2 O 3 (RE: Sm, Gd, Dy) were prepared and the formation of b 0 -RE 2 (MoO 4 ) 3 ferroelectrics was confirmed in the crystallized glasses obtained through a conventional crystallization in an electric furnace. The features of the glass structure and crystallization behavior were clarified from measurements of Raman scattering spectra. Continuous-wave Nd:YAG laser with a wavelength of 1064 nm (laser power: 0.6-0.9 W, laser scanning speed: S = 1-16 lm/s) was irradiated to 10.625Sm 2 O 3 -10.625Gd 2 O 3 (or Dy 2 O 3 )-63.75MoO 3 -15B 2 O 3 glasses, and the structural modification was induced at the glass surface. At the scanning speed of S = 10 lm/s, crystal lines consisting of b 0 -Gd 2Àx Sm x (MoO 4 ) 3 or b 0 -Dy 2Àx Sm x (MoO 4 ) 3 crystals were patterned on the glass surface. It was found that those crystal lines have the surface morphology with periodic bumps. At S = 1 lm/s, it was found that crystal lines consist of the mixture of paraelectric a-Gd 2Àx Sm x (MoO 4 ) 3 and ferroelectric b 0 -Gd 2Àx Sm x (MoO 4 ) 3 crystals, indicating the phase transformation from the b 0 phase to the a phase during laser irradiation. Homogeneous crystal lines with b 0 -RE 2 (MoO 4 ) 3 ferroelectrics have not been written in this study, but further research is continuing.
Solid State Communications, 2005
Two-dimensional crystal curved lines consisting of the nonlinear optical Sm x Bi 1Kx BO 3 phase a... more Two-dimensional crystal curved lines consisting of the nonlinear optical Sm x Bi 1Kx BO 3 phase are fabricated at the surface of 8Sm 2 O 3 $37Bi 2 O 3 $55B 2 O 3 glass by continuous wave Nd:YAG laser (wavelength: 1064 nm) irradiation (samarium atom heat processing) with a power of w0.9 W and a laser scanning speed of 5 mm/s. The curved lines with bending angles of 0-908 or with sine-shapes are written by just changing the laser scanning direction. The polarized micro-Raman scattering spectra for the line after bending are the same as those for the line before bending, indicating that the crystal plane of Sm x Bi 1Kx BO 3 crystals to the crystal growth direction might be maintained even after the change in the laser scanning direction. It is found from laser scanning microscope observations that the crystal lines at the surface are swelled out smoothly, giving a height of about 10 mm. q
Journal of Non-crystalline Solids, 2003
Transparent nanocrystallized glasses consisting of Er 2 Te 5 O 13 nanocrystals ($100 nm size) hav... more Transparent nanocrystallized glasses consisting of Er 2 Te 5 O 13 nanocrystals ($100 nm size) have been prepared in 10BaO Á 10Er 2 O 3 Á 80TeO 2 , and load/unload displacement curves at room temperature (humidity 53%) have been measured in the penetration depth of h t ¼ 200-600 nm using a Vickers nanoindentation technique. The values (4.0-9:4 AE 0:1 GPa) of universal (dynamic) hardness ðH u Þ in the nanocrystallized glasses are larger than those (H u ¼ 2:7-6:5 AE 0:1 GPa) in the precursor glass and are slightly smaller than those (H u ¼ 4:4-9:7 AE 0:1 GPa) in the opaque crystallized glass consisting of Er 2 TeO 6 crystals. The elastic recoveries during unloading are 0.53-0.61, being almost the same as those in the precursor and opaque crystallized glasses. The elastic U e and plastic U p deformation energies at h t ¼ 500 nm in the nanocrystallized glasses are estimated to be U e ¼ 106 and U p ¼ 91 AE 3 kJ mol À1 , respectively. These values are larger than those of the precursor glass (U e ¼ 83 and U p ¼ 57 AE 3 kJ mol À1 ), suggesting that the deformation energy during loading in TeO 2 -based glasses is largely increased due to nanocrystallization. The main origin of plastic deformation at h t < 600 nm is considered to be densification.
Journal of The American Ceramic Society, 2004
Load/unload displacement curves at room temperature (humidity 49%) for silica glass have been mea... more Load/unload displacement curves at room temperature (humidity 49%) for silica glass have been measured in the penetration range of 0.5–1.2 μm using a Vickers nanoindentation technique (load/unload speed 50 mN/s). Deformation energies have been estimated for the first time. The universal (dynamic) hardness, Hu, and elastic recovery, ER, at the penetration depth, ht, of 1.0 μm are Hu= 4.1 GPa and ER= 0.7. The following energies for total deformation, Ut, elastic deformation, Ue, and plastic deformation (i.e., densification during loading), Up, are obtained: Ut=190, Ue=135 and Up= 55 kJ/mol at ht= 0.5 μm and Ut= 139, Ue= 96 and Up= 43 kJ/mol at ht=1.0 μm. All these deformation energies increase with decreasing penetration depth. It is found that plastic deformation energies of 38–55 kJ/mol for 0.5 < ht < 1.2 μm are very close to the activation energy (46–54 kJ/mol) for the recovery of densification in silica glass, but are very small compared with the single bond strength (443 kJ/mol for Si—O bond) of SiO2.
Optical Materials, 2004
Metastable BiBO 3 and rare-earth (RE)-doped RE x Bi 1Àx BO 3 crystals were prepared through the c... more Metastable BiBO 3 and rare-earth (RE)-doped RE x Bi 1Àx BO 3 crystals were prepared through the crystallization of 50Bi 2 O 3 AE 50B 2 O 3 and xRE 2 O 3 AE (50Àx)Bi 2 O 3 AE 50B 2 O 3 glasses (RE = Y, La, Gd, Yb), and their second harmonic (SH) intensities were examined using the Kurtz powder method. It was confirmed that BiBO 3 has two different crystalline forms, i.e., BiBO 3 (I) and BiBO 3 (II), and that BiBO 3 (I) transforms into BiBO 3 (II) at temperatures around 500°C. Both phases were found to be nonlinear optical crystals with a phase matchable character, and the SH intensity of BiBO 3 (II) powders was approximately 110 times as large as a-quartz powders. The incorporation of RE 3+ into BiBO 3 (II) was confirmed from X-ray diffraction analysis, and in particular, Gd x Bi 1Àx BO 3 (II) showed an enhanced SH intensity of approximately 145 times as large as a-quartz.
Journal of The American Ceramic Society, 2005
ABSTRACT
Journal of Physics and Chemistry of Solids, 2003
A continuous-wave (CW) YAG laser (power: 0.75 -0.9 J/s, irradiation time: 15 s -15 min) with a wa... more A continuous-wave (CW) YAG laser (power: 0.75 -0.9 J/s, irradiation time: 15 s -15 min) with a wavelength of 1064 nm is irradiated to 11.1Sm 2 O 3 ·44.4BaO·44.4B 2 O 3 glass, and the formation of b-BaB 2 O 4 (b-BBO) crystalline dots with a diameter of 30 -150 mm is confirmed from micro-Raman spectra. b-BBO crystals with around 200 mm length grow towards the interior of the glass. The incorporation of Sm 3þ into b-BBO crystalline dots is suggested from micro-Raman and fluorescence spectra. The second harmonic generation is detected from the array (10 £ 10 ¼ 100 dots) of b-BBO crystalline dots, indicating that each crystalline dot formed by YAG laser irradiation is a nonlinear optical crystal. CW YAG laser irradiation to glass with Sm 3þ ions is a nice technique for a spatially controlled crystal growth. q
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Papers by Takumi Fujiwara