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We focused on LaBGeO5 (LBGO) single crystal as a novel ferroelectric material for quasi-phase-matching (QPM) devices which are suitable for UV generation. In order to enhance the conversion efficiency of periodically poled LBGO (PP-LBGO), it is required to grow large diameter crystal to obtain PP-LBGO device with long interaction length. However, poly-crystallization were easily happened during LBGO single crystal growth process, and there were several difficulties to increase the diameter. In order to investigate the cause of poly-crystallization, a part of polycrystalline LBGO was characterized by powder X-ray diffractometer. As a result of the measurement, the polycrystalline parts slightly contained La2Ge2O7 phase. By considering the evaporation of B from the melt and optimizing growth conditions, LBGO single crystals with a diameter greater than 30 mm were successfully grown.

The effect of Ce doping on the dielectric relaxation in Sr 0.75 Ba 0.25 Nb 2 O 6 single crystal grown by double crucible Stepanov technique has been investigated. It has been observed that the incorporation of Ce ion in the lattice reduces the dielectric maxima. It further increases the degree of diffusiveness and lowers the temperature of dielectric maxima as a result of the introduction of additional random field via created point defects. Both the undoped and Ce doped crystals undergo a non-debye type relaxation. Vogel–Fulcher fitting reveals that the attempt frequency reduced by one order of magnitude on Ce doping.

Terahertz waves are generated using a femtosecond laser pulse in a periodically poled stoichiometric lithium tantalate crystal and simultaneously detected via a non-collinear optical parametric interaction inside the same crystal. Real time up-conversion signal between the generated THz and an optic probe pulses is measured depending on the beam overlapped conditions using a general silicon-photodiode for the THz detection. The non-collinear geometry is to facilitate manipulated property of the position-dependent bandwidth at narrow and broad bandwidths of 45 GHz and 3.3 THz, respectively at the one crystal. Furthermore, an aperture effect at the detection part is characterized as the function of size and position owing to the spatial distribution of the frequency conversion signal and it is applied in optimization of the in-situ detection scheme.

We grew Sc-doped near-stoichiometric LiTaO 3 (Sc:SLT) crystals from Li-rich (61 mol% Li) solutions with Sc concentrations of up to 1.0 mol% by using a top-seeded solution-growth method. We investigated the effect of the Sc-doping on the effective distribution coefficient, the optical damage (photorefractive damage), the OH − absorption peak position, the Curie temperature, the transmittance spectra, the UV absorption edge, the electric field for domain inversion, the ordinary and extraordinary refractive indices, and the thermal conductivity along the Z -axis. Crystals doped to an Sc concentration of at least 0.44 mol% showed no optical damage at a wavelength of 532 nm. This concentration is low compared to the 1.0 mol% Mg-doping concentration required to suppress optical damage in SLT crystals. The thermal conductivity of these Sc(0.44 mol%):SLT crystals was closer to that of pure SLT crystal than was that of Mg(1.0 mol%):SLT crystals. This means that Sc:SLT crystal is a promising candidate material for use in high-power lasers used for quasi-phase-matching frequency conversion.

We investigated the effect of subgrain boundaries on periodic domain-inverted structures with a period of 30 lm in near-stoichiometric LiTaO3 (SLT) crystals and found that they negligibly affected the structures. Using SLT crystals having subgrain boundaries and a quasi-phase matching technique, we fabricated a 2-mm-thick, 60-mm-long periodically poled SLT frequency converter with a domain-inverted structure with a 30.5-lm period and demonstrated optical parametric oscillation. 2008 Elsevier B.V. All rights reserved.

Dielectric behaviour of Sr0.61Ba0.39Nb2O6 (61SBN) and Sr0.75Ba0.25Nb2O6 (75SBN) single crystals has been studied. It is observed that 61SBN has relatively low diffuseness as well as smaller relaxation compared to 75SBN. Increase in the configurational entropy imposed by the change in defect structure is suggested to be the origin of this behaviour. Analysis using Vogel–Fulcher expression and modified Curie–Weiss law give a signature of long-range polar order in 61SBN. The value of γ for 61SBN is closer to unity (1.14), where as for 75SBN it is 1.52. The fluctuation (in the orientation) of dipoles near dielectric maxima in SBN system is mediated by a paraelectric state.

Static and dynamic domain behavior of ferroelectric fluoride BaMgF4 single crystal was investigated using high-resolution piezoresponse force microscopy. High domain wall anisotropy was found in the as-grown BaMgF4 crystal. Antiparallel domain wall strain phenomena due to defects across the domain boundary were directly observed. The lateral domain growth in the inhomogeneous AFM tip field revealed the activation mechanism of the domain wall motion.

Piezoresponse mode atomic force microscopy was used to induce a dynamic polarization reversal process and to characterize domain configuration behavior in BaMgF4 single crystal. Triangular reversed domains observed on the polar and non-polar surface demonstrate a sideways domain wall motion mechanism prevailing in the switching process of the bulk BaMgF4 crystal. The domain wall bowing phenomenon due to the strong pinning of the crystal defects was first visualized in the piezoresponse image of the engineering domain pattern in BaMgF4 crystal.

Low-frequency (below 100 kHz, even down to several kHz) near-field acoustic probe microscopy for imaging ferroelectric microstructure was successfully developed based on the commercial atomic force microscope, which provides a subsurface depth profile information and as well as nanoscale spatial resolution up to 10 nm. The domain configurations of ferroelectric material were clearly visualized by this newly, non-destructive, low-frequency acoustic mode scanning probe microscopy technique with high resolution. The acoustic imaging origin is discussed in terms of interaction between the excited acoustic wave and ferroelectric domains. It is expected that the combination of the acoustic and piezoresponse mode probe microscopy in application to imaging domain structures undoubtedly enrich our understanding the nature of elasticity, piezoelectricity and ferroelectricity at submicro-, even nano-meter scale.

The isolated, six-side polygonal domain structures are observed in the orthorhombic as-grown BaMgF4 single crystal by optical microscope and atomic force microscope. The domain configurations demonstrate highly domain wall anisotropy along one principal crystal axis and polar–surface inhomogeneity. The anisotropic behaviour is due to the anisotropy of domain wall energy density in the thermodynamic equilibrium process, and the asymmetric domain surface phenomena is ascribed to the combined contribution from the local electric fields and structure defects-induced mechanical stress during the domain evolution process.

Ferroelectric domain phenomena and periodic domain patterning of orthorhombic as-grown BaMgF4 single crystal were investigated in the present study. An isolated ferroelectric domain shows a hexagonal form and exhibits a high domain-wall anisotropy. Periodic domain patterning was demonstrated on the polar surface by a periodic macropoling technique. In-plane polarization switching-induced microdomain patterning was tailored by the lateral component of the inhomogeneous electric field through a biased atomic force microscope tip. Such in-plane domain switching behavior exhibits potential promise for periodic domain engineered phonon devices.

Pure and MgO (0.5. 0.7 and 1 mol%)-doped near-stoichiometric lithium tantalate (near-SLT) crystals of 4-in diameter have been grown from off-stoichiometric melt using a double crucible. The grown crystals are free from cracks and twins. The addition of MgO increases the Curie temperature. SLT crystals with 0.7 mol% or more MgO doping concentrations showed enhanced optical damage resistance. The ordinary ray refractive indices in MgO-doped SLT crystals are slightly lower than the corresponding index of non-doped crystal. On the other hand, the extraordinary ray index of SLT is unaffected upon MgO doping. Periodically poled structures of 8 μm period have been fabricated over a length of 40 mm for 532 nm green generation through quasi phase matching.

Nd, Mg co-doped near-stoichiometric LiNbO 3 (Nd:Mg:SLN) crystals were grown from Li-rich solutions by a top-seeded solution-growth (TSSG) method. Doping of Mg 1 mol% was used to suppress photorefractive damage and the Nd nominal concentration added to the solution was either 0.1, 0.2, 0.5, 0.9, or 1.8 mol%. From the analyzed Nd concentration in the Nd:Mg:SLN crystals and nominal Nd concentration in the solutions, the effective distribution coefficient k eff for Nd was calculated to be 0.12. The thermal conductivity of these crystals was found to be sensitive to non-stoichiometric defects (Nb anti-site defects)—the thermal conductivity of the Nd:Mg:SLN crystal was found to be about 1.3 times as large as that of the Nd, Mg co-doped congruent LiNbO 3 (Nd:Mg:CLN) crystal. From the viewpoint of laser materials, this increased thermal conductivity is advantageous even if other laser properties are almost the same. The optical absorption and emission spectra of Nd:Mg:SLN crystals were found to be almost the same as those of the Nd:Mg:CLN crystal.

Pure and Mn doped single domain near stoichiometric lithium niobate crystals have been grown by top seeded solution growth from 55 mol% Li solution. A uniform segregation of Mn throughout the crystal was obtained. Doping concentration decreases the Curie temperature while the absorption edge shift towards the longer wavelength region. Two color holographic recording was examined in Mn doped samples. Improved sensitivity, dynamic range and lifetime of the hologram for the doped crystal have been determined. The effect of Mn doping on the switching properties has been analyzed.

Ti-diffused planer waveguides have been fabricated on pure and Mg-doped near stoichiometric lithium niobate (SLN). Secondary ion mass spectroscopy method was applied to study the Ti diffusion in 1 mol% Mg-doped Z-cut SLN crystal. 100 nm Ti film has been deposited on LN substrate by e-beam evaporation at room temperature. Diffusion constant value for Mg-doped SLN is lower (1.84×10 −13 cm −2 /s) than that of pure SLN. Mg-doped CLN also possesses low diffusion constant value of 1.27×10 −13 cm −2 /s due to higher doping concentration of Mg (5 mol%). AFM topographic observation reveals that Mg-doped SLN shows lower surface roughness than Mg-doped CLN. The roughness (peak to valley) of the Ti-diffused Mg:SLN is 20 nm compared to 62 nm for the congruent LN waveguide. These features make Mg:SLN highly attractive for the fabrication of efficient waveguides.

We present the aspects on the growth of 4-in diameter near-stoichiometric lithium tantalate (SLT) crystals, from lithium-enriched melt, employing double crucible Czochralski (DCCZ) technique. The difficulties encountered during growth such as crack and mechanical twin formation are discussed in detail and the same overcame by adopting suitable experimental parameters. The wafers sliced from the crystals are found to be compositionally homogeneous and free from sub-grains. The variation in the refractive indices across the wafer is of the order of 10 −5 . We could not observe any marked difference either in the absorption edge or poling field for domain inversion at different locations in the wafer.

Pure and MgO doped (up to 4 mol%) near-stoichiometric LiNbO 3 crystals are grown from Li rich (Li-55 mol%) melt. Significant improvement in the optical properties such as increase of optical damage resistance, accompanied by a shift in the –OH peak position in FTIR spectrum, and transparent range is observed at 1.75 mol% of MgO concentration in the crystal. Also the coercive field required for ferroelectric domain switching is minimum at 1.75 mol% MgO doping. Based on the results, the correlation between the defect structure and ferroelectric domain switching behavior in pure and MgO doped SLN is discussed.

Sc-doped near-stoichiometric LiNbO 3 (Sc:SLN) crystals were grown from Li-rich solutions with Sc concentrations of up to 1.3 mol% by a top-seeded solution-growth method. We investigated the Sc-doping effects on the effective distribution coefficient, photorefractive damage (optical damage), the OH-absorption peak position, transmittance spectra, the ordinary and extraordinary refractive indices ( n o and n e ), and the electric field needed for domain inversion. The Sc:SLN crystals doped with a Sc-doping concentration of 0.4 mol% or more showed no photorefractive damage. This critical Sc-doping concentration in the SLN crystal was one-fifth that in a congruent-melt composition LN (CLN) crystal which requires at least 2 mol% Sc (1 mol% Sc 2 O 3 ) to suppress photorefractive damage. The 0.4 mol% Sc doping needed to suppress photorefractive damage in the SLN crystal was also low compared to the 1 mol% required for Mg doping. Except for n o and n e , all of the measured properties were influenced by the Sc-doping effect.

For pure SLN and SLT crystals the coercive field measured from ferroelectric hysteresis loop was found to be independent of ramp rate. Decreased lithium concentration in pure SLN samples, the coercive field and internal field are strongly enhanced. Nb Li antisites are the major contribution to the internal field. Coercive field depends strongly on the ramp rate in case of MgSLN and MgSLT samples, because of domain pinning. The coercive field is considerably reduced in Mg doped SLN and SLT compared to pure samples, indicating that the switching fields are strongly dependent on the nonstoichiometry of the crystals. The coercive field values were found to be constant under multiple cycling in case of Mg (1 mol%) doped SLN crystal. A strong correlation is found to exist between coercive field value and the Curie temperature.

SrAlF 5 has recently become one of the most promising candidates for the realization of all-solid-state lasers in the ultraviolet wavelength region by the quasi-phase-matching technique. It has been shown that it is highly transparent down to the cutoff wavelength at about 150 nm, optically uniaxial and ferroelectric. The refractive index of SrAlF 5 from the ultraviolet to the near-infrared wavelength region is measured by the minimum deviation method. The Sellmeier and Cauchy coefficients are obtained from the fits to the curves of the ordinary and extraordinary refractive indices, and the grating period for the first-order quasi-phase-matching is estimated as a function of the wavelength. The effective nonlinear coefficient is similar to that of quartz, d eff ≈ 0.3 –0.4 pm/V, and the poling periodicity for 193 nm SHG from 386 nm is 4.1 μ m .

Bismuth silicon oxide (Bi 12 SiO 20 ) single crystals were grown from the melts with different SiO 2 mole percentages and with different dopants by Czhochralski technique. The absorption coefficient for these crystals depends on the stoichiometry of the melt composition. Photoluminescence emission spectra for the grown crystals were measured from 80 to 293 K. The spectra present a broad structureless peak at 80 K. The interband transitions for different stoichiometric crystals were analysed and the behavior seems to be independent of composition unlike the bismuth germanate crystals. The three level interband model proposed for the BGO crystals completely explains the interband transitions in BSO crystals also.

In this paper we consider the problem of thermal stress inhibition in double crucible Czochralski crystal growth by means of a thermal tube with linear temperature distribution computationally determined from solution with adiabatic boundary condition, which provides the formation of a stressless one-dimensional temperature distribution along the growing crystal. We study how this linear temperature distribution applied along the thermal tube is “transferred” into the growing crystal depending on the gap between crystal and inner tube surfaces, within which complex radiative–convective heat transfer takes place. Calculations presented in the paper suggest that linear temperature distribution along the thermal tube allows an order of magnitude stress reduction in 80–100 mm diameter crystals of LiNbO 3

Thermal analysis of the initial stage of crystal growth from melt reveals the specific temperature distributions which lead to the onset of compressive stress inside the crystal shoulder formed from the initial seed. This compressive stress increases with increase in the shoulder angle. The specific temperature distribution is also characterized by the significantly decreased temperature gradient at the growth interface which may lead to morphological destabilization. The initial stage of growth, i.e. crystal diameter increase from the seed, should be performed at significantly lower pulling rates as compared with the pulling rates applied to the constant diameter crystal.

Titanium-doped near-stoichiometric LiNbO3 (SLN) crystals were grown from lithium-rich solutions with a Ti concentration of up to approximately 20 mol% by a top-seeded solution-growth (TSSG) method. Ti-doped SLN (Ti:SLN) crystals with a Ti concentration of up to 9 mol% were free from inclusions, voids, cracks, or mechanical twins. The effective distribution coefficient keff for Ti in the Ti:SLN crystals was found to be approximately 0.45±0.05 for the Nb atom in the above composition range. The Ti-doping effects on Curie temperature, UV absorption edge, changes in the ordinary and extraordinary refractive indexes (Δno and Δne), and lattice constants were investigated. The Curie temperature for the Ti:SLN crystals linearly decreased with increasing Ti concentration up to 9 mol%. Both Δno and Δne linearly increased with increasing Ti concentration up to 9 mol%, and Δne was much larger than Δno over the entire wavelength range from 440 to 1550 nm. The UV absorption edge for the Ti:SLN crystals shifted to longer wavelengths with increasing Ti concentration. The a- and c-axes lattice constants in the Ti:SLN crystals decreased with increasing Ti concentration. In addition, a photoelastic effect on the refractive-index changes in the Ti:SLN crystal was estimated from the lattice-constant data.

The magnetooptical properties and magnetic-field-sensing properties of bulk Ce-substituted YIG (Ce x Y 3− x Fe 5 O 12 ) crystals were studied. There was an absorption edge at 1200 nm and a large negative Faraday rotation was obtained. Faraday rotation was increased to a greater extent by Ce substitution than by Bi substitution. The magnetic-field sensitivity of Ce 0.24 Y 2.76 Fe 5 O 12 was 0.0048% m/A which was larger than that of (BiGdLaY) 3 (FeGa) 5 O 12 . The optical current transformer (CT), using a Ce:YIG crystal as a sensor head, could measure the alternating steady state, faulting, breaking and reclosing currents. These results suggest that cerium-substituted yttrium iron garnet is a high-performance material suitable for magnetic-field (or electric-current) sensors.

The atomic structure of LiNbO 3 (0 0 0 1) surface was investigated by low-energy neutral scattering spectroscopy (LENS). Poled stoichiometric LiNbO 3 (SLN) samples were prepared for the measurements. The LENS was developed for surface structure and composition analysis particularly of highly insulating materials and was successfully applied to the structure analysis of the SLN(0 0 0 1) surface. The polar angle dependences of intensity of scattered He 0 from the poled SLN surfaces indicate obvious differences between the negatively and the positively charged surfaces. It is suggested that O atoms cover the surfaces, and the first metal layers underneath the O layer consist of Li and Nb for negatively and positively charged surfaces, respectively, parallel to the applied electric field.

We investigate two-color holography using Tb doped near-stoichiometric LiNbO 3 . We present the measurements of the hologram strength and sensitivity dependences on the wavelength and intensity of the writing near-IR laser light and on the gating UV light intensity. The diffraction efficiency of the holograms is satisfactory when the writing light wavelength is below 800 nm. The rapidly changing sensitivity around the photon energy of 1.6 eV is an indication that small polarons are involved in the recording mechanism. The recording speed mainly depends on the gating beam intensity, while the hologram strength is much more affected by the writing beam properties, both the intensity and wavelength. We show how to choose appropriate intensities to optimize the desired two-color performance that can be also applied to other two-color schemes.

We investigated the photoluminescence properties of near-stoichiometric LiNbO3 crystals doped with Tb only and double doped with Tb and Fe. Excitation spectra for the emission from the 5D4 state in both crystals have been studied in the range 200-500 nm. We observed two broad ultraviolet absorption bands and discussed their relations to Tb ions. Temperature dependence of the 5D4 emission intensity and lifetime showed strong quenching below room temperature.

Optical-quality near-stoichiometric lithium tantalate (SLT) crystals doped with Nb were grown by top seeded solution growth technique using induction-heating system. The crystalline wafers were subjected to optical transmittance studies and coercive field measurements. The optical transmittance spectra of doped crystals show a shift in the absorption edge towards longer wavelength side. A change in Curie temperatures with respect to doping concentrations of Nb has been observed. Hysteresis measurements reveal that the coercive field value increases for increasing niobium concentration. It has also been observed that there is a significant increase in the internal field value for Nb-doped SLT crystals.

We have investigated nanoscale ferroelectric-domain engineering of a Sr 0.61 Ba 0.39 Nb 2 O 6 (SBN) single crystal using a scanning force microscope (SFM). A high-quality single crystal of SBN was grown by a newly developed double-crucible Stepanov method. The SBN crystal fixed on metal substrate was polished to a thickness of approximately 55 μm. Artificial nanoscale patterns of domain structures such as inverted-domain dot and inverted-domain mesh patterns were fabricated in the SBN samples, in which polarization directions of the domains were locally switched by scanning a SFM conductive cantilever along the sample surfaces under applied voltages. These results demonstrate that nanoscale domain patterning of ferroelectric single crystals, such as the SBN crystal, by using SFM is promising for creating novel functional devices.

Photorefractive damage at u =532 nm and green-light-induced infrared absorption (GRIIRA) of near-stoichiometric LiTaO 3 (SLT) single crystals were investigated. The SLT crystal even without MgO doping showed high photorefractive damage resistance and suppressed GRIIRA. In addition, a small amount of MgO doped into the SLT crystal almost eliminated the photorefractive damage and GRIIRA. A 3-mm-thick periodically poled SLT (PPSLT) and a 1-mm-thick periodically poled MgO-doped SLT (PPMgSLT) were successfully fabricated and their optical parametric oscillation (OPO) performances were investigated.

Single crystals of strontium barium niobate (SBN) solid solution, (Sr x Ba 1− x ) 1− y (Nb 2 O 5 ) y , 0.75⩾ x ⩾0.40, 0.5050⩾ y ⩾0.4975, were grown by the floating zone method. There are two series of the crystals. x varies and y is fixed at 0.5 in the first series of crystals. x is fixed at 0.61 and y varies in the second series. The typical size of the grown crystal is 5 mm in diameter and 70 mm in length. All crystals, regardless of the compositions, revealed the facet parallel to the c -plane and the clear striations. A part around the crystal can be easily broken due to hoop stress. The spontaneous growth-direction of SBN is 〈0 0 1〉. The congruent melting composition of SBN is revealed by employing a zone-melting method at the final stage of growth experiments. It is (Sr 0.61 Ba 0.39 ) 0.5015 (Nb 2 O 5 ) 0.4985 . The absorption edges of the crystals in both series are around 360 nm and are shifted by 10 nm toward blue in comparison with those of the crystals grown by CZ method.

Lithium tantalate (LiTaO 3 ) single crystals having different Li/Ta ratios were grown by using conventional and double crucible Czochralski method. The grown crystals appeared to have mole percent of Li 2 O ranging from 45.5 to 50 mol%. We analyzed the real composition with ICP method and measured the Curie temperatures (T c ) with DTA method. The relationship between T c and the mole percent of Li 2 O in LiTaO 3 crystals was derived. The transmission spectra and refractive indices were measured. The refractive indices measured by prism coupler were analyzed in terms of single-term Sellmeir parameters.

Strontium barium niobate (SBN, (Sr 0.61 Ba 0.39 ) 0.5015 (Nb 2 O 5 ) 0.4985 ) was grown by using Stepanov technique (ST) or double crucible Stepanov technique (DCST). DCST is a modified Stepanov technique in which the inner crucible is introduced to reduce the temperature fluctuation inside the die. The change of refractive indices was estimated from the interference fringe of the grown crystal. In addition, the change in Sr concentration was estimated by using the relationship between the composition and the extraordinary refractive index. The local variation in the refractive index of the crystal grown by DCST is less than or equal to 3×10 −5 and is 1/3 of the value of the crystal grown by ST. The corresponding fluctuation in Sr concentration for the crystal grown by DCST is 0.0003, which is 1/3 of the value of the crystal grown by ST.

Codoped lithium niobate of congruent and stoichiometric compositions had been successfully grown specifically for holographic data storage applications. The dopants we have selected are Mn and Ce and their role in the recording process is described. Growth methods, sample preparation, doping level measurements, holographic recording data as well as the results of optical characterization and photorefractive properties of the two-photon sensitivity are discussed. Compared to the previously grown crystals, the codoped LiNbO 3 shows a higher sensitivity and dynamic range for recording in red ( λ=632 nm ).

Photorefractive damage, photoconductivity, and photogalvanic currents of stoichiometry controlled LiNbO3 and LiTaO3 have been investigated. A nearly stoichiometric LiNbO3 single crystal shows a lower photorefractive damage resistance than congruent LiNbO3, however, crystals doped with a small amount of MgO (> 0.78 mol.%) exhibit no measurable photorefractive damage at 532 nm up to intensities of 2 MW/cm2. In the case of LiTaO3, it turned out that nearly stoichiometric crystals exhibit considerably high damage resistivity even without MgO doping. Green-induced infrared absorption (GRIIRA) in the crystals was also investigated by a photothermal technique. The GRIIRA in nearly stoichiometric LiNbO3 is found to be remarkably decreased by a small amount of MgO. GRIIRA in nearly stoichiometric LiTaO3 was strongly suppressed even without MgO doping.

We report the dielectric anomaries at the phase transitions of Lu(Fe 2+ Fe 3+ )O 4 , which is considered as a charge and spin frustrated system. Dielectric constant shows a hump, just above the transition from the high temperature two-dimensional to the low temperature three-dimensional charge ordering. A few glassy behaviors were observed at this transition. The presence of spontaneous polarization in the low temperature phase was confirmed by the measurement of pyroelectricity. A step-wise increase of the dielectric constant with increasing temperature was observed between 150 K and 250 K as in other RFe 2 O 4 . These phenomena are explained by the presence of the polar domains with the ordering of Fe 2+ and Fe 3+ and the motions of the antiphase boundaries between them.

Undoped and MgO-doped LiNbO 3 single crystals with near-stoichiometric compositions were grown from K 2 O-doped melts and Li-rich melts by two different growth techniques. Near-stoichiometric LiNbO 3 single crystals, having large [Li]/[Nb] ratios of 0.988–0.993, showed smaller threshold concentrations of MgO than congruent crystals for the behavior of Curie temperature, OH absorption band and optical damage properties. We discuss the ideal defect structure models, and find that the Li-site vacancy model is consistent with the experimental results for MgO-doped near-stoichiometric LiNbO 3 single crystals.

Nondoped and MgO-doped LiNbO 3 single crystals of 30 mm in diameter and 25–30 mm in length were grown by the top-seeded solution growth method. The solution with [Li]/[Nb] ratio of 1 contained K 2 O component of 10.6 mol% (7 wt%). MgO of different concentrations was used to dope the solution. As-grown crystals were transparent, void-free and almost free from potassium contamination. The crystal grown without MgO-doping exhibited a Curie temperature of 1193°C, indicating that the crystal composition was considerably close to stoichiometry. The MgO-doped crystals grown from the above solution showed larger [Li]/[Nb] ratios (that is, closer to stoichiometry) than the crystals grown from the congruent composition melt doped with MgO of the same doping levels. The MgO-doped crystals with near stoichiometric composition showed a shift in absorption edge towards shorter wavelength, an increase in Curie temperature, and four orders of magnitude increase in photorefractive damage resistance compared to nondoped crystals grown from the congruent melt by the conventional Czochralski method.

With the aim of finding an optimum crucible for growth of Pr2−xCexCuO4 crystal, reactions between CuO flux and various crucible materials were studied. Among six different crucible materials, Pt, Al2O3, ZrO2, Y2O3, CeO2 and MgO, Pt crucible was suitable for using Ce free solution. For Ce doped solution, MgO crucible was better than other materials. The reactant between Pt crucible and CuO flux was identified as Pt2Cu. In the case of MgO crucible, Mg2CuOx and (Mg,Cu)Ox were produced as reactants. We found a method to restrain the reaction between the crucible and the solution. Using this method for growth of Ce doped crystal, we grew a crystal of size 30 mm∅×1.5 mm.

We have carried out electron tunnelling spectroscopy on single crystals with the use of a scanning tunnelling microscope at 4.2 K. A conductance peak structure was observed near zero bias voltage for the tunnelling along the Cu-O bonding direction. A clear superconducting gap was observed for the tunnelling along the Cu-Cu direction. Curves along the Cu-O and Cu-Cu directions are consistent with the -wave pairing symmetry which has line-nodes along the Cu-Cu direction, taking into account the periodic arrangement of surface oxygen atoms.

The ferroelectric domain wall thickness of a fluoride BaMgF4 single crystal was investigated by piezoresponse force microscopy. It was found that the domain wall thickness shows a strong spatial variation in the as-grown crystal and the polarization reversal process. The original wall thickness is greater (about two to seven times) than that switched by the tip fields of the atomic force microscope. A significantly narrower domain wall was obtained in the higher tip-field. The trapped defects at the domain wall play an important role in the spatial variation of the polarization width of 180° domain wall in the BaMgF4 single crystal. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ferroelectric domain structures of (001)-oriented Pb(Zn1/3Nb2/3)O3–7%PbTiO3 (PZN-7%PT) single crystals were visualized and characterized by piezoresponse force microscopy (PFM). Locally regular domain configurations are found to be possibly related to the stable macroscopic properties in the PZN-7%PT single crystals. Nanoscale piezoresponse hysteresis loops measured by PFM tip revealed no evidence of local domain switching behavior in the PZN-7%PT single crystal. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical quality near stoichiometric lithium niobate (SLN) and Mn-doped SLN crystals have been grown by top-seeded solution growth from 55 mol% Li-rich solution. A uniform segregation of Mn throughout the crystal was obtained. Doping of Mn decreases the Curie temperature while the absorption edge shifts towards the longer wavelength region. The effect of Mn doping on the switching properties has been analyzed.

On the idea of material designing, we have succeeded in synthesizing Y 3 Ni 4 B 4 C 3 with a new crystal structure and Y 1 Ni 1 B 1 C 1 phases through phase search experiments. The Y 3 Ni 4 B 4 C 3 phase is a tetragonal layer-like structure that is built up of one half Y 1 Ni 2 B 2 C 1 unit and one full Y 1 Ni 1 B 1 C 1 unit stacked along the c -axis. For the Y 3 Ni 4 B 4 C 3 phase, the possible space group is I4 (No. 79), lattice parameters are a =0.355190(7) nm and c =2.56454(7) nm. For the Y 1 Ni 1 B 1 C 1 phase with a CeFeSi type structure, lattice parameters are a =0.35660(5) nm and c =0.75625(12) nm. The crystal structure of Y 3 Ni 4 B 4 C 3 corresponds to the T * phase of the cuprate high T c superconducting materials and m =3, n =2 in the homologous series (LnC) m (B–Ni 2 –B) n . By magnetic susceptibility measurements, superconducting transitions were observed at around 11.0 and 3.0 K. Although the Y 1 Ni 2 B 2 C 1 phase was included in the sample and the single phase was not obtained yet, it is considered that the Y 3 Ni 4 B 4 C 3 or the Y 1 Ni 1 B 1 C 1 phase show a superconducting transition.

Changes of the dimensionality and Tc through iodine intercalation and oxidation have been studied in Bi2Sr2CaCu2O8+δ single crystals. Both intercalation and oxidation change the dimensionality of the physical properties from pseudo-two-dimensional to three-dimensional and decrease Tc. These effects are explained by the multilayer model, where a high-Tc cuprate is regarded as an alternating stack of CuO2 layers (superconducting layers) and block layers (normal layers), taking into account the proximity effect. The Tc-suppression by Cu-site substitution has also been studied for iodine-intercalated and pristine Bi2Sr2Ca(Cu1−zCoz)2O8+δ polycrystals with different δ-values.

Velocities and attenuations of longitudinal sound waves were measured at 100 MHz for a single crystal of non-stoichiometric ErFe 2 O 4-δ , along the and axes in the hexagonal frame, below 300 K. At room temperature, velocities were 5.22× 10 3 and 5.49×10 3 m/s along the and axes, respectively. These values correspond to the elastic constants of C 11 =1.94×10 12 dyne/cm 2 and C 33 =1.75×10 12 dyne/cm 2 . Slight softening was disclosed along the axis at around 240 K. Correspondingly, a large peak was observed in the attenuation. These anomalies are attributed to the emergence of two-dimensional spin ordering in this crystal at this temperature. On the contrary, no anomaly was detected along the axis at around 240 K, with rather high attenuation level almost independent of temperature. This absence of anomalies was discussed on the existence of three kinds of magnetic domains. Development of the correlation of Er spins was suggested below 30 K.