Electrical characterization of strontium tartrate single crystals

The a.c. and d.c. conductivity of SrC₄H₄O₆·3H₂O are measured and are found to lie between usual conductivities of semiconductor and insulator. Temperature dependence of d.c. conductivity shows intrinsic conduction, which is confirmed by the slope of versus data. Due to application of thermal energy, noticeable conductivity peaks imply liberation of water molecules during dehydration and the formation of strontium oxalate. The conductivity plot has a nature similar to the intrinsic-to-extrinsic transition found in normal semiconductors. There occurs Efros hopping conduction in our samples.     

Optical, thermal, dielectric and ferroelectric behaviour of sodium acid phthalate (SAP) single crystals

Sodium acid phthalate (SAP), an efficient semi-organic crystal having dimensions 17×8×2 mm³ has been grown from aqueous solution by slow evaporation technique at room temperature within the period of 2 weeks. The lattice parameters of the grown crystals were determined using single-crystal X-ray diffraction analysis. The presence of functional groups was estimated qualitatively by Fourier transform infrared (FTIR) analysis. The band gap energy was determined using optical absorption studies. The TG/DTA analysis reveals that the SAP crystal is thermally stable up to 141.6 °C. The dielectric constant and dielectric loss was studied as a function of frequency and the corresponding activation energy (E_a) has been calculated for the grown crystal. Scanning electron microscope studies enunciate the ferroelectric domain patterns of the SAP crystal. Ferroelectric property of the grown crystal was confirmed by hysteresis loop studies.     

Mechanical behaviour and fracture mechanism of flux grown holmium orthoferrite single crystals

Results of indentation induced microhardness and fracture studies on (110) and (001) planes of flux grown HoFeO₃ single crystals using a Vicker's hardness tester, in the load range of 10-100 g are presented. The variation of microhardness with load is found to be non-linear and is explained by using Hays and Kendall's law. The hardness results and the indentation-induced cracking yields the values of the yield strength, fracture toughness and brittleness index for (110) and (001) planes of HoFeO₃ crystals. Transition from Palmqvist to median crack systems takes place at higher loads for (110) plane of the crystal whereas (001) plane is characterized by Palmqvist cracks only.     

Optical and magneto-optical spectra of europium-doped strontium tetraborate single crystals

Optical absorption, luminescence, magnetic circular dichroism and Faraday rotation spectra of Sr_0.95Eu_0.05B₄O₇ single crystals are studied. The crystal field parameter for europium ions is found to be equal to 790 cm⁻¹. Excitation spectrum of luminescence strongly differs from that of low-doped polycrystalline strontium tetraborate. The Verdet constant in the ultraviolet is comparable to that of terbium gallium garnet in the visible.     

Photoconductivity, dielectric and thermal investigations of pure, benzophenone- and iodine-doped benzoyl glycine NLO single crystals

Physical properties such as photoconductivity, dielectric and thermal stability have been investigated for pure benzoyl glycine (BG) crystals. In addition to this, the influence of dopants (benzophenone and iodine) of these properties on BG crystals has been studied. Photoconductivity studies on pure BG, benzophenone-and iodine-doped BG revealed the positive photoconducting nature. The dielectric responses of the samples have been studied in the frequency range 100 Hz-500 KHz at room temperature and the results are discussed in detail. The thermogravimetric studies of pure and doped BG crystals indicate that the presence of dopants has slightly increased the decomposition temperature of pure BG samples, thereby enhancing thermal stability to the doped ones.     

Effect of urea and thiourea on nonlinear optical hippuric acid crystals

Pure, urea and thiourea doped hippuric acid (HA) single crystals have been grown in acetone using slow evaporation technique at a constant temperature, with the vision to improve the properties of the crystals. The crystal systems and the unit cell parameters of the grown crystals were identified from single crystal X-ray diffraction. The crystalline nature of the grown crystals was confirmed by powder X-ray diffraction and the diffraction peaks were indexed. The variations in composition due to the addition of dopants were identified by CHNS analysis. FT-IR studies reveal the presence of different vibrational bands. The optical characteristics were assessed by UV–vis analysis and it indicates the transmission in the visible region. TGA and DSC studies indicate the thermal behavior of pure and doped crystals. The Second Harmonic Generation (SHG) has been tested using Kurtz Powder Technique for the pure and doped crystals. It is found that the thiourea doped hippuric acid crystals have SHG efficiency of 2.08 times higher than that of potassium dihydrogen phosphate (KDP) single crystal. The dielectric studies were carried out, and the variations of dielectric constant and dielectric loss with temperature have been studied.     

Effect of magnetic field in the microhardness studies on calcium hydrogen phosphate crystals

Calcium hydrogen phosphate dihydrate (CaHPO₄·2H₂O, brushite) crystals are grown in gel medium at physiological pH by single diffusion method in the presence of different magnetic field strengths, namely 0, 0.1 and 0.2 Tesla. The results indicate that in the presence of magnetic field, the number of brushite crystals formed at the gel-solution interface reduces and the average size of the crystals increases. This shows that the growth of brushite crystal was favored by magnetism. Vickers and Knoop microhardness studies were carried out on the crystals grown at various magnetic fields. The Vickers (H_V) and Knoop (H_K) microhardness numbers were found to increase with increasing load. The values of Meyer’s index number (n) decrease while the magnetic field strength increases. Nevertheless the n values are greater than 1.6, which shows that the brushite crystals grown under magnetic fields still fall in the soft material category. The brittle index (Bi), yield strength (σ_y) and elastic stiffness constant (c₁₁) were calculated. The Young’s Modulus was calculated using the Knoop hardness value and found to decrease in higher magnetic field strengths.     

Structural, dielectric, optical and ferroelectric property of urea succinic acid crystals grown in aqueous solution containing maleic acid

Urea-succinic acid crystals have been grown at room temperature from aqueous solution in the presence of maleic acid by a slow evaporation technique. The structural parameters were determined using powder X-ray diffraction (XRD) and found to have monoclinic symmetry (space group P2₁/m) with a=9.902, b=17.510, c=5.555 Å and α=γ=90°, β=96.46°. The transparency and optical analysis were carried out using UV-vis analysis. The optical band gap is found to be 4.71 eV. The presence of various functional groups was confirmed by FTIR analysis. The samples have shown piezoelectric behavior with a fairly good piezoelectric charge coefficient (d₃₃) of 5 pC/N, when it is poled at 7 kV/cm. The hysteresis loop was plotted and the remnant polarization and coercive field were found to be 2.8 μC/cm² and 4 kV/cm, respectively. The dielectric analysis was carried out as a function of temperature at various frequencies and the results were also discussed.     

Compositional behaviour of Urbach absorption edge and exciton-phonon interaction parameters in Cu6PS5I1−xBrx superionic mixed crystals

Temperature behaviour of optical absorption edge in Cu₆PS₅I_1−xBr_x mixed crystals is studied in the interval 77-325 K. It is shown that the absorption edge has Urbach shape in the 215-325 K temperature interval. The influence of temperature and compositional disorder on the Urbach absorption edge parameters is presented. The mechanism of the Urbach bundle formation and the effect of I→Br anionic substitution on the exciton-phonon interaction parameters is elucidated.     

Structure and thermal behaviors of organic crystals based on substituted 1,3,4-thiadiazoles

The crystalline structure of some compounds containing the 1,3,4-thiadiazole moiety, (1) 5-ethyl-2-amino-1,3,4- thiadiazole (EATZ), (2) 5-benzylsulfany-2-amino-1,3,4-thiadiazole (BSATZ) and (3) 2,5-bis-benzylsulfanyl-1,3,4-thiadiazole (BBSTZ) were determined. Both EATZ and BBSTZ show orthorhombic structures with space group Pbca and BSATZ a monoclinic system with space group C2/c. The lattice parameters: a=0.72280 (14), b=1.0811 (2), c=1.6210 (3) nm for 1, a=2.5282 (5), b=0.59083 (12), c=1.5390 (3) nm for 2 and a=0.87530 (18), b=1.0365 (2), c=3.6098 (7) nm for 3. To compare the intra- and intermolecular interactions in thiadiazole containing organic crystals, thermal analysis studies on each crystal is performed using DSC and TG in N₂ atmosphere to describe the thermal behaviors. Based on the results, the changing regularity of melting point and decomposition temperature of these compounds is educed     

Growth and optical properties of Eu/Li-co-doped SrB4O7 single crystals

This paper reports the growth and optical properties of Eu²⁺/Li⁺-co-doped SrB₄O₇ single crystals. High-quality Eu,Li:SrB₄O₇ crystals without macro-defects or cracks were grown using the top-seeded solution growth (TSSG) method. The absorption and luminescent properties were measured and different spectra were observed in the as-grown crystals. As the doping amount of lithium increases, the absorption peak at 300 nm becomes stronger and the emission peak shifts to a longer wavelength. This phenomenon could be attributed to the doping lithium ions, which might affect the electric field distribution in the lattice structure.     

Microhardness and fracture mechanics of flux grown samarium doped gadolinium vanadate (Sm:GdVO4) single crystal

Indentation induced hardness studies on flux grown samarium doped gadolinium vanadate (Sm:GdVO₄) crystals are reported. Mechanical characteristics including Vickers microhardness, fracture mechanics, crack propagation, brittleness index and yield strength are assessed. The mechanical behaviour of the crystal is explained using various theoretical models viz., Meyer’s law, proportional specimen resistance (PSR) and Hays and Kendall’s approach. Variation of microhardness with load is found to be non-linear and is best explained by the concept of Newtonian resistance pressure as proposed by Hays and Kendall’s law. Classification of cracks as median type is explained. The values of fracture toughness (K_c), brittleness index (B_i) and yield strength (σ_y) have also been calculated.     

Photoluminescence spectra of rare earth doped CaGa2S4 single crystals

Six kind CaGa₂S₄ single crystals doped with different rare earth (RE) elements are grown by the horizontal Bridgman method, and their photoluminescence (PL) spectra are measured in the temperature range from 10 to 300 K. The PL spectra of Ce or Eu doped crystals have broad line shapes due to the phonon assisted 4f-5d transitions. On the other hand, those of Pr³⁺, Tb³⁺, Er³⁺ or Tm³⁺ doped samples show narrow ones owing to the 4f-4f transitions. The assignments of the electronic levels are made in reference to the reported data of RE 4f multiplets observed in same materials.     

Effect of Ce co-doping on KY3F10:Pr crystals

A spectroscopic investigation on the effect of Ce³⁺ co-doping in fluoride KY₃F₁₀:Pr³⁺ crystals is presented. In particular spectroscopic measurements of three different samples of KY₃F₁₀ crystal doped with 0.3at% Pr³⁺ and co-doped with 0at%, 0.17at% and 0.3at% Ce³⁺ are discussed. Details on the growth of the crystals are also reported. Measurements were performed in the temperature range 10-300 K. Fluorescence and lifetime measurements have shown a cross relaxation between ³P₀-¹D₂ levels of Pr³⁺ and ²F_7/2-²F_5/2 of Ce³⁺. Data exhibit that this effect is strictly related to the Cerium concentration.     

Experimental and theoretical studies on bis(glycine) lithium nitrate (BGLiN): A physico-chemical approach

Good quality and bulk size single crystal (size: 20×13×8 mm³) of bis(glycine) lithium nitrate (BGLiN) was grown by a slow evaporation solution technique from the aqueous solutions at constant temperature i.e. 27 °C using synthesized materials. Crystal system and lattice parameters were determined by single crystals as well as powder X-ray diffraction analysis. The lattice parameters of the titled compound are a=10.0223 Å, b=5.0343 Å, c=17.0510 Å, and V=860.312 Å³ and it crystallized in an orthorhombic system with space group Pca2₁ obtained by single crystal XRD. Elemental composition was confirmed by energy dispersive X-ray spectroscopic analysis. Optical absorption spectrum was recorded and various optical parameters such as optical transmission (~60%), and optical band gap (4.998 eV) were calculated. Photoluminescence study shows that the grown crystal is free from major defects. Crystalline perfection of the grown crystal was assessed and found good. Ground state optimized geometry has been obtained by using DFT with 6-31G(d,p) basis set. HOMO and LUMO energy gap was found to be 6.01 eV and dipole moment was 1.65 D.     

Preparation of Ca(1−x)EuxGa2S4 crystals and their photoluminescence, absorption and excitation spectra

The single crystal of CaGa₂S₄:Eu is expected as a useful laser material with a high quantum efficiency of light emission. However, as far as our knowledge is concerned, the systematic study of the mixed compounds of Ca_(1−x)Eu_xGa₂S₄ as a function of x has not been reported up to now. Here, we have first constructed the phase diagram of the CaGa₂S₄ and EuGa₂S₄ pseudo binary system, and show that it forms the solid solution. Then we have grown single crystals of these compounds. The maximum photoluminescence efficiency is achieved at x=0.25. From the three peak energies observed in the photoluminescence excitation (PLE) and absorption spectra, the 5d excited states are suggested to consist of three levels arising from the multiplets of Eu²⁺ ions.     

Transport properties of MgB2 single crystals doped with electrons and holes

The thermoelectric power of C, Mn, C:Li, and Al:Li substituted MgB₂ single crystals has been investigated in the temperature range 10-300 K. Both the in-plane (S_ab) and the out-of-plane (S_c) thermopowers are positive for the non-substituted crystal and both S_ab and S_c change a sign for crystals doped with electrons where C is substituted for B in the amount larger than 5 at%. When Li is substituted for Mg, the π band rather than the σ band is doped with holes and the doping effects are much more subtle. The anisotropy ratio of the non-substituted crystal S_ab/S_c≈3 and this ratio is strongly reduced by the substitution of C. Isovalent magnetic Mn ions, which substitute for Mg with a drastic reduction of T_c, do not influence the values and temperature dependences of both S_ab and S_c.     

Time series of ac conductivities of terbium nitrate crystals at low temperatures

Time series of ac conductivities are measured at 2 kHz along three crystal directions in terbium nitrate crystal below 50 K. The anisotropy is found in the structure of the fluctuation observed in the time series of the conductivities. The bursts with non-periodic oscillations are found in only the measurements of the time series of the ac conductivities for one direction perpendicular to the c-axis (c2-axis). The anisotropy is seen in probability distribution functions and power spectral ones derived from the time series of the conductivities. The characteristic behaviors are found in the time series of the conductivity for the one crystal direction perpendicular to the c-axis. Asymmetric non-Gaussian line shape of the probability distribution function is seen for the c2-axis. Chaotic behavior is also found in the function of the correlation exponent to the embedding dimension derived from the time series of the conductivities.     

Growth and characterization of new transparent conductive oxides single crystals β-Ga2O3: Sn

Tin oxide doped β-Ga₂O₃ single crystals are recognized as transparent conductive oxides (TCOs) materials. They have a larger band gap (4.8 eV) than any other TCOs, thus can be transparent in UV region. This property shows that they have the potential to make the optoelectronic device used in even shorter wavelength than usual TCOs. β-Ga₂O₃ single crystals doped with different Sn⁴⁺ concentrations were grown by the floating zone technique. Their optical properties and electrical conductivities were systematically studied. It has been found that their conductivities and optical properties were influenced by the Sn⁴⁺ concentrations and annealing.     

A novel method for the assembly of nano-zeolite crystals on porous stainless steel microchannel and then zeolite film growth

A new method that is simple, efficient, and clean was developed for seeding surfaces with a monolayer of covalently bonded zeolite seeds. This method was used to seed the microchannels fabricated on porous stainless steel with NaA nano-zeolites enabling the deposition and growth of defect-free zeolite film. The NaA nano-zeolites were attached to the surface of the stainless steel via alkoxysilane linkers (e.g., 3-chloropropyltrimethoxysilane and 3-aminopropyltrimethoxysilane) grafted on the stainless steel. The NaA zeolite grown on the microchannel by hydrothermal synthesis consists of intergrown, (1 1 1)-oriented pyramidal NaA crystals that completely clad the stainless steel grains. The zeolite cladding the grains grew uniformly until the zeolite layers of neighboring grain impinges, then intergrew to fully bridge the gaps between the grains forming a defect-free film layer. A separation factor of 10,000 and a flux of 0.04 kg m⁻² h⁻¹ were obtained for water pervaporation from a 3 wt% water-benzaldehyde solution at room temperature.