As-grown Crystals Research Articles

Effects of different annealing atmospheres on magnetic properties in La2CoMnO6 single crystals

We have successfully synthesized the high-quality single crystals of double perovskite La2CoMnO6 by flux method and investigated the effects of different annealing conditions on the magnetic properties. In an as-grown crystal, ferromagnetic order along the c axis arises below 204 K, and the spin-glass-type behavior inherent from ionic disorders is also observed. Upon annealing in different gas environments, the reconstructed magnetic states induce a metamagnetic transition (after Ar annealing), and increase Curie temperature (after O2 annealing). After quenching, the magnetic transition temperature decreases significantly, comprising lots of defects and disorders. Our results provide adequate procedures to control magnetic properties of double-perovskite compounds.

Flux growth, structure, and physical characterization of new disordered laser crystal LiNd(MoO4)2

A millimeter-sized LiNd(MoO4)2 crystal has been grown using the flux method. LiNd(MoO4)2 crystallizes in the scheelite-type structure with space group I41/a, lattice parameters: a=5.26090(10) Å, c=11.5395(3) Å, V=319.379(15) Å3, and Z=2. The full-matrix, least-squares refinement with R=1.64 % and Rw=4.34 % shows that the Li and Nd atoms are completely disordered at jointly occupied sites. The theoretical growth morphology with indexed (hkl) planes was developed from the Bravais–Friedel–Donnay–Harker (BFDH) theory and it is in good agreement with the morphology of the as-grown crystals. The chemical composition was analyzed using an inductively coupled plasma emission spectrometer. The full set of thermal properties, including specific heat, thermal expansion, thermal diffusivity, and thermal conductivity of LiNd(MoO4)2 are reported. The UV–visible diffuse reflectance spectrum contains many strong and broad Nd3+ absorption lines over the spectral range from 300 to 1000nm. Three transition emission bands located at 890, 1064 and 1335nm are observed in the fluorescence spectrum. The fluorescence lifetime is measured to be 2μs at room temperature. LiNd(MoO4)2 possesses a large absorption cross section of 1.04×10−20cm2 at 804nm and an emission cross section of 4.8×10−20cm2 at 1064nm.

Crystal Growth, Thermal, and Optical Studies: Thiourea Glycyl-L-Alanine Single Crystals

Single crystals of pure and thiourea substituted Glycyl-L-Alanine (TU-GLA) were successfully grown by the slow evaporation solution growth method at constant temperature of 35℃. The effect of thiourea dopant on the crystal properties has been studied. Single crystal XRD analysis confirms the structure and change in the lattice parameter values for the doped crystals. The crystals were characterized by the FTIR and UV-Vis-NIR techniques. The presence of all the elements was confirmed by EDAX analysis. Thermal stability of the grown crystals was tested by TGA/DTA. Hardness studies on the as-grown crystals of GLA and TU-GLA were carried out by a static indentation test at room temperature using a Leitz Wetzlar Vickers microhardness tester. The dielectric response of the crystals was also investigated and reported.

Czochralski growth, magnetic and magneto-optical properties of Na2Tb4(MoO4)7 crystal

Na2Tb4(MoO4)7 crystals have been grown by the Czochralski technique for the first time for magneto-optical applications. Structure refinement of XRD data confirms that the compound crystallizes in the tetragonal system I41/a, with scheelite structure. The as-grown crystal exhibits moderate thermal stability and weak thermal expansion anisotropy (αc/αa≈1.08), and the hardness is about 4.7Moh. Transmittance spectra indicated that the Na2Tb4(MoO4)7 crystal presents a high transparency from 600nm to 1500nm after annealing in O2 atmosphere at 973K for 20h. The Faraday effect and the temperature dependence of the magnetic susceptibility have been investigated, which demonstrate that the Na2Tb4(MoO4)7 crystal exhibits paramagnetic behavior over the experimental temperature-range 2–300K and yields a Faraday rotation which is about 1.6 times as large as that of Tb3Ga5O12 crystal. Na2Tb4(MoO4)7 crystal is therefore a promising Faraday material in particular for new magneto-optical applications in the visible–near IR wavelength region.

Large electrocaloric strength in the (100)-oriented relaxor ferroelectric Pb[(Ni1/3Nb2/3)0.6Ti0.4]O3 single crystal at near morphotropic phase boundary

Relaxor ferroelectric Pb[(Ni1/3Nb2/3)0.6Ti0.4]O3 (PNNT) single crystal with composition close to the morphotropic phase boundary (MPB) was successfully prepared using the molten salt method. The analysis results of XRD and TEM indicated that the as-grown crystal is of almost pure perovskite phase with coexistence of tetragonal and rhombohedral. Typical relaxor behavior was observed when the crystal was aged. Large electrocaloric strength (ΔT/ΔE) of 44.97mKcm/kV was obtained near the phase transition temperature of paraelectric to ferroelectric, indicating that PNNT is a promising material for application in cooling system. Moreover, it is found that the aging of point defects may make an important contribution to the electrocaloric performance of the single crystal, in addition to the contribution of the transition of phases induced by the electric field.

THM growth of (Cd, Mn)Te single crystal with the source ingot synthesized by VB method

The (Cd0.9, Mn0.1)Te crystal was grown by the Traveling Heater method (THM) from the indium-doped source ingot (Cd0.9, Mn0.1)Te which had been synthesized by the Vertical Bridgman (VB) method. The indium-doped (Cd0.9, Mn0.1)Te single crystal with the diameter of 31mm and length of 130mm was obtained. The variation of the Mn content was about ±1% along the length of (Cd, Mn)Te: In ingot, and the concentration of Te inclusions in the crystal was ~104cm−3 with the average diameter of 8–12μm. Te solvent showed purifying effects during the THM crystal growth, and the indium dopant distributed along the crystal with the concentration of 6.8–10ppm. IR transmittance and PL spectrum measurements revealed that the as-grown (Cd, Mn)Te crystal possessed high crystalline quality, and its resistivity was up to 6.2×109Ωcm. Under the 59.5keV 241Am irradiation, the planar (Cd, Mn)Te detector showed an energy resolution of 12.7%.

Characteristic electrical properties of Pb(Sc1/2Nb1/2)O3–PbTiO3 ferroelectric crystals

Perovskite-type Pb(Sc1/2Nb1/2)O3–PbTiO3 single crystals have been obtained by the top-seeded solution growth technique. The structure type and phase purity were verified by X-ray diffraction analyses. Crystals with morphotropic phase boundary compositions can be grown from nominal material with PT content in the range of 0.50–0.53. The dielectric spectra of the as-grown crystals present normal ferroelectric behavior. The temperature of the maximum dielectric constant of PSN–PT crystals is determined to be 500.15–562.15 K. And the depolarization temperature is in the range of 478.15–415.15 K, which is higher than Pb(Mg1/3Nb2/3)O3–PbTiO3 and Pb(Zn1/3Nb2/3)O3–PbTiO3 crystals. At room temperature, the hysteresis loops of the (001)-oriented Pb(Sc1/2Nb1/2)O3–PbTiO3 crystals are well developed. The maximum remanent polarization is detected for x = 0.52, and it is 37 µC cm−2 with the coercive field and being 5 kV cm−1. The piezoelectric coefficients of Pb(Sc1/2Nb1/2)O3–PbTiO3 crystals at room temperature were obtained with the maximum value of 1420 pC N−1 for the composition with PT content 0.515, which is the maximum among the reported results.

Synthesis, Crystal Growth, Characterization, and Theoretical Studies of 3-(4-fluorophenyl)-1-(4-methylphenyl)prop-2-en-1-one

Single crystals of 3-(4-fluorophenyl)-1-(4-methylphenyl)prop-2-en-1-one (FMPP) have been grown by mixed solvent system ethanol and chloroform 2:1 (v/v) at room temperature. Single crystal X–ray diffraction reveals that FMPP belongs to monoclinic system with four molecules in the unit cell. The structure and the crystallinity of the material were further confirmed by FT-IR, FT-Raman, and powder X–ray diffraction analyses. The band gap energy is estimated by Kubelka–Munk algorithm using DRS data. Theoretical calculations were performed to derive the optimized geometry and the first-order molecular hyperpolarizability (β) values. The as-grown crystal is further characterized by GC-Mass, SEM, and thermal analyses.

Synthesis, Growth and Characterization of Benzophenone-4-methoxybenzoylhydrazone Single Crystals

Structural analysis of single crystals of benzophenone-4-methoxybenzoylhydrazone, grown by conventional slow evaporation solution growth technique from ethanol at room temperature, belong to monoclinic system with the space group P21/c and the cell parameters are, a = 8.8380(4) Å, b = 10.0767(4) Å, c = 19.8146(9) Å and V = 1736.88(13) Å3. The functional groups present in the molecule are confirmed by FT-IR and FT-Raman spectral analyses. The 1H and 13C signals are confirmed by nuclear magnetic resonance spectroscopy. The powder X-ray diffraction study reveals the crystallinity of the as-grown crystal and it is compared with that of the simulated one. Mass spectrometry provides information pertaining to the structure and molecular weight of the compound. Good transmittance in the visible region is observed and the band gap energy is estimated using diffuse reflectance data by the application of Kubelka–Munk algorithm. Thermal analysis reveals the purity of the crystal. The scanning electron microscopy (SEM) studies reveal the surface morphology of the as-grown crystal. Theoretical calculations were performed using density functional theory (DFT) employing B3LYP functional and 6-31G(d,p) level as the basis set for to derive the optimized geometry, dipole moment, Mulliken charge population, HOMO–LUMO energies and first-order molecular hyperpolarizality (β) values. The optimized geometry closely resembles the ORTEP.

Growth and characterization of ferroelectric Pb(Sc1/2Nb1/2)O3 single crystals

Single crystals of Pb(Sc1/2Nb1/2)O3 were grown by the high-temperature solution method using PbO + B2O3 as flux. The size of the as-grown crystals varies from 1 to 2 mm. X-ray diffraction indicates a pure perovskite phase without B-site ordering. Polarized light microscopy shows that the crystals are of rhombohedral symmetry at room temperature and become cubic at TC = 112 °C on heating. A ferroelectric-to-relaxor phase transition is verified at TC by dielectric spectroscopy. Frequency-dependent permittivity is observed in dielectric measurements, revealing relaxor behavior above TC. Poling the crystal at room temperature does not change TC, but suppresses the permittivity. Typical ferroelectric hysteresis loop is displayed at room temperature, indicating the ferroelectric nature of the rhombohedral phase.

Recharging processes of Ce3+ in gamma-irradiated YAG:Ce single crystals

The influence of γ-irradiation on the spectral properties of YAG and YAG:Ce (∼0.12 and ∼0.2 at %) single crystals is studied. The interrelation between the changes of γ-induced absorption of Ce3+ and of some color centers in the crystals is established. It is shown that the analysis of radiative behavior of Ce3+ in YAG:Ce crystals gives the opportunity: to evaluate a quantity of electron-hole traps influencing on cerium ions in as-grown crystals and involving in radiation processes of cerium ions recharging; to predict the concentration changes of Ce3+ in the crystals irradiated by doses (1.13–5.5) × 107 rad of γ-rays. The reasons of the activator ions concentration impact on the various radiation behaviors of γ-induced absorption and optical quality of these crystals are discussed.

Van Vleck paramagnetism of europium oxyhydroxide

Europium oxyhydroxide crystals were synthesized by the flux method. The as-grown crystals were transparent and had a plate-like shape with natural flat surfaces. The powder XRD data were refined by assuming a monoclinic structure of the space group P21/m and lattice parameters of a=0.4346 nm, b=0.3744 nm, c=0.6107 nm, and β=108.62°. The magnetic susceptibility of the EuOOH crystals exhibited typical Van Vleck temperature-independent paramagnetism below 120 K. The calculated susceptibility, based on Van Vleck's theory, agreed with the experimental data to some extent, with the coupling constant λ=458±10 K. The experimental results were in close agreement with the results calculated using a modified formula with λ=505±2 K and a constant term C=4.6×10−4 emu/(mol·Oe).

MgGa2 O4 as a new wide bandgap transparent semiconducting oxide: growth and properties of bulk single crystals

Bulk MgGa2O4 single crystals with inverse spinel structure were grown from the melt by different methods. The degree of inversion could be changed by suitable annealing, which was confirmed by differential scanning calorimetry analysis and corresponding changes of the specific heat capacity. MgGa2O4 is thermally much more stable at high temperatures than β-Ga2O3 despite of a higher melting point of about 1930 °C and could be grown under a neutral atmosphere. Melt-grown MgGa2O4 crystals were found to be either electrical insulators or n-type semiconductors depending on the presence of oxygen in the growth atmosphere and the growth method applied. Growing the crystals in the presence of oxygen resulted in electrically insulating crystals. For as-grown and intentionally undoped semiconducting crystals, the free electron concentration was in the range of 1017–1018 cm−3, but the electron mobility was relatively low, just a few cm2V−1s−1. The free electron concentration remained at a level of 1018 cm−3 after annealing in a hydrogen-containing atmosphere at 600–900 °C for 10 h. On the other hand, annealing in an oxygen-containing atmosphere above 600 °C for 10–40 h turns the crystals from the semiconducting to the insulating state. The optical bandgap at room temperature amounts to about 4.9 eV. It decreases with temperature at a rate of 1.35 meV/K. Cathodoluminescence spectra of as-grown crystals show a dominant band at 362 nm. The melt-grown crystals have sufficient size and structural quality to be used as substrates for epitaxy.

Vapor growth of typical II-VI wide-gap semiconductor crystals directly from the constituent elements

Three ZnE (E=Se, Te) single crystals were successfully grown directly from Zn-E (E=Se, Te) system with the assistance of I2 or NH4Cl as the transport agents via a modified chemical vapor transport (CVT) method by avoiding the kinetics limitations of the congruent sublimation of ZnE compound. As-grown ZnE crystals exhibit different crystalline appearance due to various growth conditions. The structure, growth habit and morphologies of as-grown ZnE crystals are investigated by XRD, RO-XRD, SEM and optic microscope. ZnE crystals with NH4Cl transport agent look like the platelets with an interesting growth habit, while ZnE crystal with I2 transport agent has high crystalline quality with a conical shape. Contrasting investigation between different growth results offers us an opportunity to understand the vapor-free-growth mechanism of ZnE crystals in closed-space CVT system, indicating that the free-growth habit of ZnE crystals depends on the growth parameters, which can be essentially attributed to their growth mechanism and the main vapor–solid reactions on the interfaces.

Revealing the Preferred Interlayer Orientations and Stackings of Two‐Dimensional Bilayer Gallium Selenide Crystals

Characterizing and controlling the interlayer orientations and stacking orders of two-dimensional (2D) bilayer crystals and van der Waals (vdW) heterostructures is crucial to optimize their electrical and optoelectronic properties. The four polymorphs of layered gallium selenide (GaSe) crystals that result from different layer stackings provide an ideal platform to study the stacking configurations in 2D bilayer crystals. Through a controllable vapor-phase deposition method, bilayer GaSe crystals were selectively grown and their two preferred 0° or 60° interlayer rotations were investigated. The commensurate stacking configurations (AA' and AB stacking) in as-grown bilayer GaSe crystals are clearly observed at the atomic scale, and the Ga-terminated edge structure was identified using scanning transmission electron microscopy. Theoretical analysis reveals that the energies of the interlayer coupling are responsible for the preferred orientations among the bilayer GaSe crystals.

Growth and characterization of R(O,F)BiS2 (R = La, Ce, Pr, Nd) superconducting single crystals

AbstractR(O,F)BiS2 (R: La, Ce, Pr, Nd) superconducting single crystals with different F concentrations are grown using a CsCl/KCl flux. The obtained 1-2 mm-sized single crystals have a plate-like shape and are cleavable along the ab-plane. The crystal structure is tetragonal of space group P4/nmm (#129). The as-grown single crystals exhibit superconductivity at around 3–5 K. The superconducting transition temperature increases with decreasing the ionic radius of the R element. The superconducting anisotropies of the R(O,F)BiS2 single crystals are estimated to be 30–60 according to the effective mass model, whereas the anisotropies for Ce(O,F)BiS2 single crystals are 13–21. The c-axis transport measurements of a single crystal of Pr(O,F)BiS2 under a magnetic field parallel to the ab-plane reveal a “lock-in” state attributed to the Josephson vortex flow. Furthermore, the Ce(O,F)BiS2 single crystals exhibit a magnetic order at the temperature range of 5–7 K that apparently coexist with superconductivity below approximately 3 K.

Crystal growth and thermal properties of the laser crystal Yb3+:Gd3(AlxGa1−x)5O12

Bulk single crystals of Yb3+:Gd3(AlxGa1−x)5O12 (Yb:GAGG) with dimensions of Φ26mm×30mm were successfully grown using the Czochralski method. The nominal Yb and Al contents in the raw materials were 5.0 and 10.0at%, respectively. The effective segregation coefficients of Yb3+ and Al3+ ions were measured, and the doping concentrations of Yb3+ and Al3+ ions in the crystal were calculated to be 6.25–6.03at% and 12.0–11.67at% along the crystal growth direction, respectively. The crystalline perfection of the as-grown crystal was evaluated by high-resolution X-ray diffraction (HRXRD). The thermal properties, including thermal expansion, specific heat and thermal conductivity, have been studied in detail. In addition, the thermal-optical coefficient and the thermal shock resistance parameters were also calculated. Our results show that Yb:GAGG crystal has potential application in the field of high power solid state laser.

Synthesis and Growth of Ce,Pr:YLuAG Crystal for LED Application

Ce,Pr:YLuAG pure phase powder was synthesized by co-precipitation method and calcined at 1450°C, which had a garnet structure. The feed rod was prepared by press forming and solid state sintering. TEM showed that the sintered rod had good crystallinity and density. Ce,Pr:YLuAG single crystal was grown by the floating zone method. The as-grown crystal was transparent with a pale yellow color, and small cracks were observed in the shoulder. The transmittance of the crystal is 81.8%, which is close to the theoretical value 84.2%. Under 460 nm excitation, Ce,Pr:YLuAG crystal shows the emission band of Ce at 530 nm and peak of Pr at 610 nm, which shows that Ce can transfer the energy to Pr. However, only Pr emission peak appears when it is excitated at 487 nm. The color coordinate is located at (0.474, 0.495) which shifts to red zone compared with commercial Ce:YAG yellow phosphor. As a result, Ce,Pr:YLuAG crystal is more suitable to fabricate white LED.

Color centers in YAG

Yttrium aluminum garnet (Y 3 Al 5 O 12 , YAG) is one of the most important optical materials with many existing and potential future applications in laser, illumination, and scintillation. X-rays, g-rays, and UV light can induce ionization and significant changes in the valency of impurities and defects in YAG single crystals which may lead to the formation of color centers. In fact, the use of YAG crystals in laser and scintillation devices involves significant formation of color centers and requires full understanding for their characteristics and effects on the material properties. In this work, the formation and characteristics of color centers in undoped and rare-earth doped YAG single crystals was investigated mainly through optical absorption spectroscopy. An increase in the absorption over a broad range of wavelengths was observed in the as-grown sample after UV irradiation. F-centers and iron impurities in the as-grown undoped crystals were found to be responsible for the formation of color centers. However, air- or oxygen-anneal seems to be effective in suppressing most color centers in the crystals.

Growth and optical properties of the novel nonlinear optical crystal NaSr3Be3B3O9F4

The new UV nonlinear optical crystal NaSr3Be3B3O9F4 with dimensions up to 13 × 14 × 20 mm3 was successfully grown by the top-seeded solution growth method from LiF–NaF–B2O3 flux for the first time. The crystalline morphological faces are mainly (101), while (021) or (32) faces may occur depending on the direction of the seed applied. The crystalline quality of the as-grown crystal was evaluated by the X-ray rocking curve with the full-width at half-maximum being 0.013°. By a minimum deviation method, the refractive indices are measured from 235 to 2325 nm and fitted by the Sellmeier equations. Furthermore, the hardness, density and chemical stability of the crystal were also reported.