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A three-dimensional-micro-pulling-down (3D-μ-PD) method was developed for the growth of 3D shaped single crystals, and spring-shaped sapphire single crystals were grown by the 3D-μ-PD method using Mo crucibles with different dies. The shape of the die significantly affected the growth stability and shape control of the spring-shaped single crystals. Spring-shaped sapphire single crystals with a smaller helical pitch and larger helical radius were obtained easily using a Mo crucible with a sharp conical die compared to that with a blunt conical die. However, spring-shaped sapphire single crystals grown using a Mo crucible with an inverse conical die can be obtained with smaller helical pitches, and the shape of the cross-sectional plane is a horizontally extended elliptical shape. The difference in the shape of the cross-sectional plane for spring-shaped sapphire single crystals affects the crystallinity and mechanical properties. Furthermore, crystals grown using the Mo crucible with the inverse conical die exhibited a larger shrinkage rate in the compression test. [ABSTRACT FROM AUTHOR]

• La-doped SrTiO 3 /TiO 2 eutectic crystals were grown by a micro-pulling-down method. • Grown crystals were composed of the TiO 2 rod phase in the SrTiO 3 matrix phase. • Diameter of TiO 2 rods systematically decreased as the growth rate was increased. • Grown crystal exhibited a lower thermal conductivity than the SrTiO 3 single crystal. • ZT s of crystals grown at 0.02 and 0.5 mm/min were 0.015 and 0.025, respectively. La-doped SrTiO 3 /TiO 2 (La:STO/TO) eutectic crystals were grown by a micro-pulling-down method at various growth rates to control the eutectic morphology and thermoelectric properties. The La:STO/TO eutectic crystals were composed of a TiO 2 (TO) rod phase in the SrTiO 3 (STO) matrix phase for all growth rates. The diameter of the TO rod phase systematically decreased as the growth rate was increased, according to the Jackson–Hunt model, and the diameter reached approximately 1 μm at a growth rate of 1 mm/min. The La:STO/TO eutectic crystal exhibited a lower thermal conductivity than the Nb:STO single crystal, owing to the decrease in the lattice thermal conductivity by phonon scattering at boundaries in the eutectic morphology. The figures of merit, ZT s, of the La:STO/TO eutectic crystals grown at 0.02 and 0.5 mm/min growth rates were 0.015 and 0.025, respectively. The faster growth rate led to an increased ZT, owing to the decrease in electrical resistivity. [ABSTRACT FROM AUTHOR]

• La 2 Hf 2 O 7 crystals (m.p.: 2418 °C) were grown by the µ-PD method using a W crucible. • The La 2 Hf 2 O 7 grown at a rate of 2.00 mm/min had some cracks. • The La 2 Hf 2 O 7 grown at a rate of 0.07 mm/min was transparent without any cracks. • The LHO[0.07 mm/min] had a transmittance of over 70% in the range of 450–800 nm. • The XRC of the LHO[0.07 mm/min] showed a sharp peak with a FWHM of 138 arcsec. La 2 Hf 2 O 7 crystals with a melting point of ∼2418 °C were grown by the micro-pulling-down method using a W crucible and deoxygenated ZrO 2 insulators. A La 2 Hf 2 O 7 crystal grown at a rate of 0.07 mm/min (LHO[0.07 mm/min]) showed a high transparency without any visible cracks and inclusions, while a La 2 Hf 2 O 7 crystal grown at a rate of 2.00 mm/min had some cracks. The LHO[0.07 mm/min] crystal had a transmittance of over 70% in the wavelength range of 450–800 nm. The X-ray rocking curve of the LHO[0.07 mm/min] crystal showed a symmetric sharp peak with a full width at half maximum of 138 arcsec. The Laue image revealed that the grown crystals were single crystals. [ABSTRACT FROM AUTHOR]

• La 2 Zr 2 O 7 crystals were grown by micro-pulling-down method using Mo & W crucibles. • Grown crystals under Ar + 3%H 2 were composed of La 2 Zr 2 O 7 phase including Mo and W. • A grown crystal under Ar using W crucible & deoxygenated insulator was La 2 Zr 2 O 7. • The La 2 Zr 2 O 7 crystal indicated a transmittance exceeding 70% after post-annealing. La 2 Zr 2 O 7 crystals with a melting point of 2283 °C are grown via the micro-pulling-down (μ-PD) method using Mo and W crucibles to expand the possibility of material research of functional single crystals with high melting points by the μ-PD method. La 2 Zr 2 O 7 crystals grown using Mo and W crucibles under an Ar + 3% H 2 atmosphere are composed of a La 2 Zr 2 O 7 main phase, which includes Mo and W. However, a La 2 Zr 2 O 7 crystal without W can be grown under an Ar atmosphere using the μ-PD method using a W crucible and deoxygenated ZrO 2 insulators. After post-annealing in air at 1000 °C, the La 2 Zr 2 O 7 crystal without W becomes colorless and transparent, indicating a transmittance exceeding 70% in wavelengths ranging from 450 to 800 nm. [ABSTRACT FROM AUTHOR]

Scintillators are used not only as single crystals in radiation detection systems but also as arrays, columns, and fibers. In this study, a novel optical-guiding crystal scintillator (OCS) was fabricated using an Eu:SrI 2 crystal as the core and borosilicate glass as the cladding. The OCS has an elongated shape and can be flexibly processed like an optical fiber. Furthermore, because inorganic scintillator crystals are used as the core, the OCS has high sensitivity to high-energy radiation, such as γ- and X-ray radiation, unlike plastic scintillators. In this study, by observing the cross section of the fabricated OCS, identifying the crystal structure, and investigating the radioluminescence spectrum under X-ray irradiation, OCS fabrication in accordance with the OCS design specifications was confirmed, and the SrI 2 crystal structure and Eu2+ 5d–4f luminescence were maintained. The γ-ray responses, such as light yield and decay time, were also investigated. [ABSTRACT FROM AUTHOR]

• (Gd 1-x Ce x) 3 (Ga 0.995 Cr 0.005) 5 O 12 single crystals were grown by micro-pulling down method. • The emission wavelengths of these crystals were approximately 730 nm. • Cr was segregated in the center part of the crystals. • The relationship between Cr segregation and emission intensity was investigated. • The correlation coefficients of thoes relationships were around 0.9. For the decommissioning of Fukushima Daiichi Nuclear Plants, a novel real-time dose-rate monitor consisting of a scintillator, 100-m long optical fiber and CCD spectrometer has been proposed, and this scintillation material is required to have an emission wavelength of longer than approximately 650 nm. In this paper, as a candidate material for the system, we focused on Ce/Cr co-doped Gd 3 Ga 5 O 12 (Ce/Cr:GGG) single crystals grown by the micro-pulling down method. Since the light output of this material was expected to depend on the Cr3+ concentration, we investigated the relationship between Cr segregation and luminescence properties in Ce/Cr:GGG crystal. Generally, a single photon counting method is not available to evaluate its light output accurately due to the long decay time, we used a novel technique "emission-intensity two-dimensional- mapping method" (2D-image method) to verify the light intensity at each point of the sample. This method realized estimation of the light intensity within the sample, though segregation of Cr3+ is observed. The results showed that Cr was concentrated in the center part along the radial direction in the grown crystals, while all parts had an emission wavelength of approximately 730 nm excited by X-ray. Using the 2D-image method, emission intensity was found to correspond to the Cr concentration, and its correlation coefficients between emission intensity and Cr concentration were over 0.8. We found that our material is available for the monitoring system when the Cr dense part of the crystal is cut and used. [ABSTRACT FROM AUTHOR]