Crystal growth of PbTe and (Pb,Sn)Te by the bridgman method and by THM

Synthesis and growth of PbTe and (Pb, Sn)Te single crystals by the Bridgman method and by the Travelling Heater Method (THM) from Te-rich solutions are described. It is to be seen from comparative investigations that seeded THM growth reproducibly provides oriented single-crystalline ingots free of low-angle grain boundaries and with etch pit densities of 8–12 × 10⁴ cm⁻². All the materials were p-type with carrier concentrations from 1 to 2 × 10¹⁸ cm⁻³.     

Doping of GaSb single crystals with volatile elements

The Czochralski technique without encapsulant in a flowing atmosphere of hydrogen was used for the growth of GaSb single crystals doped with either sulphur or nitrogen. It has been shown that this method is not suitable for the prepartion of GaSb doped with volatile elements because they evaporate during the growth procedure and impair the single crystalline growth. The highest concentration of sulphur in the single crystals has been found to be < 1.2 × 10¹⁷ atoms · cm⁻³. At higher concentrations, GaSb became either polycrystalline or twinned. The growth of N-doped single crystals was similar to that of S-doped GaSb.     

Investigation of structural perfection and faceting in highly Er‐doped Yb3Al5O12 crystals

The undoped Yb₃Al₅O₁₂ (YbAG) single crystals and doped with 1.5, 10 and 30 at% erbium were grown by the Czochralski method. The YbAG crystals offer efficient emission of laser beam of 2.94 µm and 1.55 µm important for practical applications in communication and medicine. The crystals were investigated by various synchrotron X‐ray diffraction methods including white beam topographic methods, monochromatic beam topography and recording of the rocking curves. The experiments were performed at E2 and F1 experimental stations in HASYLAB. The investigations proved a good crystallographic perfection of the crystals, in most cases revealing only segregation fringes and growth facets. The crystallographic identification of the facets was performed together with direct evaluation of growth front radius from the transmission section topographs. Relative lattice parameter changes connected with erbium segregation were found to be less than 2 × 10^‐5 inside the segregation fringes and 8 × 10^‐5 in the facets. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of ferroelectric magnesium hydrogen phosphate single crystals

Ferroelectric Magnesium Hydrogen Phosphate MgHPO₄ (MHP) single crystals are grown by slow diffusion of magnesium chloride in sodium metasilicate gels impregnated with orthophosphoric acid. Bright and transparent prismatic, tabular, and isometric habit MHP crystals upto 3 × 2 × 1 mm³ are obtained. Results of chemical, X-ray diffraction, EDAX, microhardness and magnetic analysis are reported. The average etch pit density is determined by chemical etching to be 7 × 10³ cm⁻². Microtopographic investigations revealed the mechanism of crystal growth.     

Effect of rhodium incorporation in KTiOPO4 single crystals grown from self‐flux

The presence of an impurity like rhodium in the platinum crucible used for the growth of KTiOPO₄ (KTP) single crystals can have severe consequences in the performance of devices made from these crystals. In the present study the effect of rhodium incorporation has been investigated. Rhodium‐incorporated KTP crystals have a lower ionic conductivity (1.3 × 10^–7 S/cm at 100 kHz) than pure KTP crystals (3.5 × 10^–6 S/cm at 100 kHz) along the c‐axis. And the optical absorption in the green‐wavelength regime leads to a detrimental effect on their SHG performance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study on rapid growth of KH2PO4 and its characterization

Large size crystals of KH₂PO₄ (KDP) were grown by adopting rapid growth technique from point seeds in a 1500‐liter crystallizer which is used to grow KDP crystals by conventional method. The grown KDP crystal size can reach to 310 × 310 × 320 mm³ and the average growth rate was 8mm/day. The optic properties of the rapidly grown KDP crystals were characterized comparing with the KDP crystals grown by the traditional temperature reduction method. We found it that the optical quality of the KDP crystals we grown rapidly are not significantly different from those of KDP crystals grown by traditional method. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural Conditionality of the Ionic Conductivity of MTiORO<Subscript>4</Subscript> (M = K,Rb; R = P,As) Single Crystals

The ionic conductivity σ_||c along the crystallographic axis c and the structural imperfection of the lattices of KTiOPO₄, RbTiOPO₄, and RbTiOAsO₄ single crystals with low defect concentration, grown by the high temperature solution growth technique, have been investigated by impedance spectroscopy and X-ray diffraction analysis. Isomorphic substitutions of Rb⁺ ions for conduction K⁺ cations in MTiOPO₄ crystals decreases the σ_||c value, whereas the substitution of As⁵⁺ ions for framework P⁵⁺ cations in RbTiORO₄ crystals increases the σ_||c value. The σ_||c values at 573 K are found to be 1.0 × 10^–5, 5.7 × 10^–6, 2.0 × 10^–6, and 3.3 × 10^–5 S/cm for the KTiOPO₄, RbTiOPO₄ {100}, RbTiOPO₄ {201}, and RbTiOAsO₄ crystals, respectively (the growth zone of the crystalline boule from which the samples were cut is indicated in braces).     

Influence of <Emphasis Type="Italic">in situ</Emphasis> photoexcitation on structure of damaged layer in GaAs (001) substrates implanted with Ar<Superscript>3+</Superscript> ions

The influence of photoexcitation on the formation of the defect structure in GaAs crystals implanted with 200 keV Ar⁺ ions at doses of 1 × 10¹³, 3 × 10¹³, and 5 × 10¹³ cm^?2 has been studied by high-resolution Xray diffractometry. It was found that photoexcitation gives rise to annihilation of radiation-induced Frenkel pairs, and, thus, decreases the residual concentration of radiation-induced point defects. It is established that amorphization of the damaged layer proceeds via the formation and growth of clusters of radiation-induced point defects. The vacancy-and interstitial-type clusters are spatially separated—the former are located closer to the crystal surface than the latter. Photoexcitation hinders cluster growth and stimulates diffusion of interstitial defects into the substrate depth.     

Growth of large KDP single crystals for UV spectrum range

The influence of various technological parameters of crystallization (acidity of growth solutions, crystallization temperature, growth rate, degree of solution purification) on the optical absorption of large KDP single crystals has been studied in the UV range of the spectrum. It is shown that the method of solvent recirculation with the use of the starting material with the microimpurity content not exceeding 5 × 10^?5 wt % and solution ultrafiltration under the optimum crystallization conditions (t_cr = 80°C, V_cr ～ (0.8–1.6) × 10^?6 cm/s, pH 4) enables one to grow KDP single crystals with cross sections up to 300 × 300 mm² and the transmission in the vicinity of the fundamental absorption edge λ = 200 nm) equal to 86%.     

Crystal growth and dislocation structure of gallium antimonide

Single crystals of GaSb have been grown by the Czochralski method under reducing conditions. Crystals were grown in the 〈100〉, 〈111〉, and 〈112〉 directions. The 〈111〉 growth direction was found to be the most suitable for the successful and reliable crystal growth. Dislocation densities in 〈111〉 oriented crystals were examined by chemical etching. The etch pits density in these crystals didn't exceed the value of 1 × 10² cm⁻².     

Growth of Nd:Sr3Ga2Ge4O14 crystals by a modified Bridgman method

Bridgman growth of Nd:SGG (Sr₃Ga₂Ge₄O₁₄) crystals has been investigated for the first time. Pt crucible of ∅︁25mm×250mm with a seed well of ∅︁10mm×80 mm is used, and seed is SGG crystal of ∅︁10mm×50mm grown by Bridgman method in advance. The growth parameters are optimized as the furnace temperature is set to 1450∼1500°C, temperature gradient in the crystal‐melt interface is less than 25 K/cm and growth rate is less than 0.5mm/h. The Nd:SGG crystals with 25mm in diameter and 60mm in length are grown successfully from 1.5 to 8at% Nd³⁺ doped stoichiometric Sr₃Ga₂Ge₄O₁₄ melt. The distribution coefficient and concentration of Nd³⁺ in Nd:SGG crystals are obviously higher than those of Nd:YAG crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of bismuth tri‐iodide platelets by the physical vapor deposition method

The work reports the growth of single BI₃ crystals with platelets habit. Platelets were grown by physical vapor deposition (PVD) in a high vacuum atmosphere and with argon, polymer or iodine as additives. Crystals grew in the zone of maximum temperature gradient, perpendicular to the ampoule wall. Crystals grown with argon as additive show a very shining surface, have hexagonal (0 0 l) faces, sizes up to 20 x 10 mm² and thicknesses up to 100 μm. They were characterized by optical microscopy and scanning electron microscopy (SEM). Dendritic‐like structures were found to be their main surface defect. SEM indicates that they grow from the staking of hexagonal unities. Electrical properties of the crystals grown under different growth conditions were determined. Resistivities up to 2 x 10¹² Ωcm (the best reported value for monocrystals of this material) were obtained. X‐ray response was measured by irradiation of the platelets with a ²⁴¹Am source of 3.5 mR/h. A comparison of results according to the growth conditions was made. Properties of the crystals grown by this method are compared with the ones measured for others previously grown from the melt. Also, results for bismuth tri‐iodide platelets are compared with the ones obtained for mercuric and lead iodide platelets. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

KTiOPO4(KTP) crystal growth from high-temperature solutions containing WO3

The process of seed growth of KTiOPO₄ crystals from three different high-temperature solutions containing WO₃, with definite compositions is reported. The low viscosity and relatively slight change of the solubility of the KTP with the variation of the temperature allow the growth of adequately large crystals, free from inclusions, in the case of two tested techniques – slow cooling and temperature gradient. Conditions to avoid defects in the seed region have been found. The relatively high growth rates allow the production of crystals in a 5-day growth run, that can be cut into samples oriented along synchronism for the second harmonic generation(SHG) with dimensions 8 × 8 × 7 mm³. SHG measurements reveal that the quality of the samples considered is comparable with KTP crystals grown from high-temperature nonstoichiometric solutions.     

Synthesis,crystal growth and properties of the charge transfer complex adduct of 2‐nitro aniline with picric acid – An organic non‐linear optical material

The organic NLO material 2‐nitro aniline and picric acid (2NAP) was synthesized, needle shaped single crystals of dimension 10 × 1 × 0.8 mm^‐3 were grown by slow evaporation solution growth technique from the saturated solution of the title compound in chloroform at ambient temperature. The material was characterized through elemental analysis, powder XRD, ¹H NMR, ¹³C NMR and FTIR techniques. The various planes of reflection have been identified from the XRD powder pattern. The formation of the charge transfer complex was confirmed by UV‐VIS spectroscopy. The thermal stability of the crystals was investigated using TG/DTA analyses techniques. The second harmonic generation (SHG) efficiency of the material was estimated using Nd: YAG laser as source. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of Vanadyl Pyrophosphate Single Crystals

The present work communicates about the first successful attempt at growing of sizeable single crystals of vanadyl pyrophosphate (VO)₂P₂O₇ (VOPO) — a low dimensional antiferromagnet. The growth of VOPO is complicated by two features of this compound. The first is a strong sensitivity of the oxydation state of vanadium (and stability of VOPO) to the oxygen content in the growth atmosphere. The second is a tendency of the VOPO-melt to glass formation during the cooling due to its high viscosity. Therefore the growth has to be carried out with a very low growth rate and in an atmosphere with exactly controllable oxygen content. The best results were achieved with a combination of Czochralski and Kyropoulos techniques, i.e. pulling of crystals with simultaneous cooling of the melt. Crystals of VOPO with sizes up to 10 × 5 × 3 mm³ have been grown. The growth from the melt is accompanied by growth from gaseous phase also (sublimation). Since the VOPO phase has a homogeneity range in oxygen content, attention was paid to the composition of the grown crystals. Growth experiments combined with TGA and XRD measurements show, that the oxygen content and thus the oxidation state of vanadium in the crystals can be adjusted accurately.     

Influence of purity of NdF3 single crystals on their ionic conductivity

Single crystals of the NdF₃ superionic conductor have been grown by the Bridgman method from a melt in a helium atmosphere using a fluorinating PbF₂ agent. Commercial NdF₃ reagents of special purity grade, reagent grade, and pure grade are used. It is found that the ionic conductivity ?? of the crystals depends considerably on the purity grade of the starting substances: at 200°C ?? = 1.4 × 10^?, 3 × 10^?4, and 8 × 10^?4 S/cm for reagents of special purity grade, reagent grade, and pure grade, respectively.     

Enhancement of thermoelectric efficiency in vapor deposited Sb2Te3 and Sb1.8In0.2Te3 crystals

Pure and indium doped antimony telluride (Sb₂Te₃) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb_1.8In_0.2Te₃ crystals (155 μVK⁻¹, 2.669 × 10⁻³ W/mK²) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10⁻³ K⁻¹ for vapour grown Sb_1.8In_0.2Te₃ platelets indicates that it could be used as a potential thermoelectric candidate.     

Kinetics of growth of calcite crystals in presence of ammonium ions

The growth of calcite crystals from an aqueous supersaturated solution of initial concentration 0.15 mol m⁻³ containing 10 mol m⁻³ of (NH₄)₂CO₃ has been studied at 298 K. The progress of growth has been followed through determining the composition of the solution by chemical analysis. The crystal growth is controlled by the surface reaction mechanism and satisfies a kinetic equation of the second order with the rate constant 3.7 × 10⁻⁶ m⁴ mol⁻¹ s⁻¹ that is independent on the surface area of the present solid. NH₄⁺ ions do not change the crystal growth mechanism but decrease the growth rate of calcite crystals.     

Microstructures of gel-grown ammonium hydrogen tartrate single crystals

Single crystals of ammonium hydrogen tartrate (AHT) have been grown in silica gels by employing the controlled reaction between ammonium chloride and tartaric acid. Transparent AHT crystals upto 24 × 4 × 3 mm³ in size have been grown at room temperature. Optical and electron-optical studies have been made on the various surface structures of {010} faces of the grown crystals. A variety of growth striations and growth hillocks have been observed. Growth layers modified by the presence of misaligned microcrystals have been illustrated. It has been suggested that two-dimensional nucleation, spreading and pilling up of growth layers is mainly responsible for the growth of these crystals and the implications are discussed.