Lattice disorder and optical absorption of PbTiO3 crystals

The electric conductivity and the optical absorption of PbTiO₃ crystals are explained by the existence of Pb³⁺ ions and free holes as electronic defects and of O^– vacancies and interstitials as ionic anti-Frenkel defects. The absorption band at 475 nm is caused by Pb³⁺ ions and produces the yellowish or brownish colour of the crystals. Using fluoridic fluxes instead of oxidic fluxes for the crystals growth a small part of O^– ions is replaced by F⁻ foreign ions. This substitution diminishes the Pb³⁺ ion content and causes an increased optical transmission of the PbTiO₃ crystals.     

Dislocations in magnetic garnet crystals

1. Dislocations in magnetic flux-grown garnet crystals (Y₃Fe₅O₁₂ and others) have been observed. As a rule, {110} growth pyramids have more defects than {211} ones. 2. The highest content of defects (dislocation density 10³–10⁴ cm⁻²) is observed in Y₃Fe₅O₁₂ that grows on crucible walls adjacent to the free surface of the solution where the flow of heat is not uniform to the greatest degree. Bottom grown crystals usually have less dislocations. Far fewer dislocations are in wall grown crystals, least of all dislocations are contained in crystals that grow inside the solution. The solution pouring off at the end of the crystallization period increases dislocation density by some dozens. 3. Heat treatment decreases dislocation density. The less dislocation content and the lower ordering are in the initial crystal, the higher heat treatment effectiveness.     

Investigation of radiation defects in electron irradiated Hg1−xCdxTe crystals using positron annihilation

The electron characteristics of defects in the initial and electron irradiated Hg_1−xCd_xTe (2–3 MeV, 10¹⁸ cm⁻², 300 K) crystals using the positron annihilation method have been investigated. The data of electric measurements are confirmed on connection of p-type conductivity with vacancy defects of metal sublattice initial crystals Hg_1−xCd_xTe. An analysis of correlation curves of irradiated crystals has shown a possibility of formation of associations of initial defects and radiation damages of vacancy type during radiation process. The presence of narrow component on correlation curves in the region of small angles is associated with formation of positronium states localized in the region of radiation defect complex of vacancy type. Identification of positron-sensitive defects with electrically active radiation induced ones has been carried out according to the results of isochronal annealing of irradiated crystals.     

Effect of γ-irradiation on mechanically activated and on non-activated LiF

By means of EPR spectroscopy lattice defects have been investigated, which had been produced in OH⁻ containing LiF by mechanical activation and subsequent irradiation (mainly γ-irradiation). The structure of irradiation-induced hydrogen centers shows characteristic differences dependent on the kind of LiF: H_s⁰ (hydrogen atoms in anion vacancies) are created in mechanically activated LiF powders, whereas H_i⁰ (hydrogen atoms in interstitial positions) in LiF single crystals. In both the cases also F centers are produced besides other paramagnetic defects. The observed defects can be used for an estimation of the degree of distortion in mechanically activated LiF.     

High-temperature Localization of Plastic Deformation in Lithium Fluoride Single Crystals

Experimental results on the superlocalization of plastic deformation at high strains and high temperatures in LiF single crystals are described. The physical conditions of transition to a localized plastic flow in the temperature range of 603 K to 1073 K T (0.53–0.94T_mp) using constant strain rate compression tests under strain rates from 10⁻³s⁻¹ to 10⁻²s⁻¹ are found. The results indicate that the deformation mechanism involves dislocation climb, controlled by diffusion. The connection of high temperature flow instability with an excessive concentration of point defects (strain vacancies) in zone of shear has been confirmed.     

Influence of proton implantation on the properties of CuInSe2 single crystals (I). Ion channeling study of lattice damage

The lattice damage of p-type CuInSe₂ single crystals implanted with 10 keV protons in the fluence range from 2.5 · 10¹⁴ to 8 · 10¹⁵ cm⁻² was investigated using the Rutherford backscattering/channeling technique. At proton fluences up to about 2 · 10¹⁵ cm⁻² radiation annealing of the defects is observed which is ascribed to very high defect concentrations in the unimplanted samples. At higher fluences radiation damage occurs but the concentration of radiation induced defects ramains low. There are indications that selenium interstitials or defect complexes with selenium interstitials involved are stable defects at room temperature.     

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.     

TSM-gewachsene Halbleiter-Einkristalle aus (Pb0,8Sn0,2)Te

By means of the Travelling Solvent Method (TSM) the authors succeeded in growing PbSnTe solid solution crystals using a simple working growing principle. Imperfections and constitution as well as electrical properties of the crystals have been investigated. The results lead to the conclusion that one can grow homogeneous, nearly perfect crystals having low carrier densities and high carrier mobilities in a relatively short time which seems to be the main advantage of the experimental techniques used. Representative values of electrical crystal parameters are p₇₇ ≦ 10¹⁷ cm⁻³, n₇₇ ≦ 10¹⁷ cm⁻³; pμ₇₇ ⋍ 1,6 × × 10⁴cm²/Vs; dimensions: 1 × 4 × 4 mm³.     

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.     

Dislocation etching in V3Si

Dislocations in as-grown and in plastically deformed V₃Si single crystals have been studied by chemical etching. In as-grown crystals dislocations are partly arranged in small-angle boundaries parallel to {001}, {011}, and {112} planes. The total dislocation density amounted to (10⁵−10⁶) cm⁻². After plastic deformation at elevated temperatures indications for slip and climb processes were observed. The dislocation density increased to 10⁷ cm⁻².     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

On the Inhomogeneity of Refractive Index of CaF2 Crystals for High Performance Optics

CaF₂-crystals belong to the standard materials, used in optical precision instruments. As well as the traditional optics for microscopy new developments in the field of DUV-lithography (projecting lenses made out of CaF₂ and quartz) need a homogeneity of the refractive index in the order of 10⁻⁶, but over much larger volumes (diameter of the projecting lenses for lithography >100mm). Some interesting physical connections between the real structure of the crystals and the homogeneity of refractive index are discussed.     

Complex study of the structural and optical homogeneity of lithium niobate crystals

Methods of Raman spectroscopy, laser conoscopy, optical microscopy, and electron spin resonance have been used to study the photorefractive properties and structural and optical homogeneity of the following lithium niobate (LiNbO₃) crystals: nominally pure crystals of congruent composition (LiNbO_3con); LiNbO₃:Cu[0.015 wt %] crystals grown from a melt of congruent composition and nominally pure crystals of stoichiometric composition grown from a melt with 58.6 mol % Li₂O (LiNbO_3st). A small deformation of optical indicatrix and regular microdomain structures of fractal type are revealed for the LiNbO₃:Cu[0.015 wt %]; the microdomain structures may be due to the nonuniform impurity incorporation into the structure. It is shown that oxygen octahedra in the LiNbO₃:Cu[0.015 wt %] crystal are deformed in comparison with the octahedra in LiNbO_3st and LiNbO_3con crystals and that the main and impurity cations are clusterized along the polar axis. It is established that the LiNbO₃:Cu[0.015 wt %] crystal exhibits photorefractive properties not only due to the presence of intrinsic defects with localized electrons, as in the case of LiNbO_3st, but also due to the charge exchange in copper cations (Cu²⁺ → Cu⁺) under illumination.     

Structural and mechanical properties of KН2PО4 single crystals with embedded nanoparticles and organic molecules

Single crystals of KDP crystals with embedded Urea molecules and TiO₂ nanoparticles have been grown from aqueous solution by the temperature lowering method. The effect of the organic molecules and nanoparticles on the structural and mechanical properties has been studied. It has been observed that addition of Urea molecules improves laser induced damage threshold and mechanical strength of the crystal, while TiO₂ nanoparticles have the opposite effect. The structure and composition of KDP:Urea crystal are studied by three‐crystal X‐ray diffraction analysis, which reveals the existence of a correlation between the increase of the microhardness value and the change of the crystal lattice parameter. The surface features of KDP:TiO₂ crystals are analyzed by scanning electron microscopy that reveals the presence of quasi‐equidistant growth bands caused by capture of the nanoparticles. It is shown that the rise of TiO₂ nanoparticles concentration up to 10⁻⁴ wt.% and higher resulted in 3‐fold reduction of the laser damage threshold of KDP:TiO₂ relative to pure KDP in [001] and [100] crystallographic directions. It is found that microhardness and fracture toughness decrease at the nanoparticles concentration of 10⁻³ wt.% due to crack formation at crystal lattice discontinuities. The grown crystals also have been subjected to dielectric studies.     

Plastische Verformung von Siliziumeinkristallen unterschiedlicher Ausgangsversetzungsdichte im Streckgrenzenbereich

Floating-zoned Silicon crystals orientated for single slip both dislocation-free and with grown-in dislocations (EPD₀ = 6,5 · 10⁴ cm⁻²) were dynamically deformed in compression in the temperature range 1120 … 1300 K up to the lower yield point. The dislocation structure of plastically deformed crystals (T = 1138 K; a₀ = 1,45 · 10⁻⁴ s⁻¹) was examined by etching and high-voltage electron microscopy. The crystals exhibit essential differences in deformation behaviour and in the resulting dislocation structure. Typical for the dislocation-free basic material are (i) an inhomogeneous deformation in the range of the upper yield point (ii) a greater portion of sessile lomer dislocations at the lower yield point in relation to the crystal with grown-in dislocations. The measured stresses were related to those values calculated from structure data by employing plasticity theory of diamond-like semiconductors.     

Growth mechanism of crystals from aqueous solutions

Microscopic processes occurring on the surface of a growing crystal or a dissolving one were observed by microcinematography. The crystals under observation were grown either in a drop of solution by evaporation or in a constant-temperature microscope stage at a chosen supersaturation. Small (approx. 0.1 mm) and large (approx. 10 mm) crystals of NaCl, Pb(NO₃)₂, NaNO₃, CdI₂, KDP and ADP were studied. It is concluded qualitatively that the layers, in general polygonal, originating in one or several active centres, are formed on the crystal face, never at the corners or edges. – The average velocity of layer motion was studied quantitatively in dependence on their thickness and supersaturation. The layer motion at constant supersaturation considerably fluctuated. – Surface patterns created by moving layers agree in most cases with predictions of the dislocation theory. Two categories of steps were found on the surface: ”︁real”︁ macrosteps and shock waves. – The velocity of layer motion for most compounds lies within (1–10) · 10⁻⁴ cm · s⁻¹.     

The growth of HgI2 crystals

The paper presents a system for αHgI₂ crystal growth by the temperature oscillation method. The system has a capability of crystal growing at an excess I₂ or Hg vapour pressure. Optimum conditions for producing crystals up to 2 cm³ by volume have been established. The crystals grown at an excess I₂ vapour pressure have higher resistivity and higher drift electron and hole mobilities — μ_e = 120 cm² V⁻¹ s⁻¹ and μ_h = 6 cm² V⁻¹ s⁻¹, respectively.     

EPR-spectrum of irradiated potassium dichromate single crystals

EPR-spectra of X-irradiated potassium dichromate crystals are studied at various temperatures from RT to LNT. The most intensive lines are interpreted as due to radicals CrO₄³⁻ (A-lines) and CrO₃⁻ (C-lines), resulting from Cr₂O₇ owing to X-irradiation. Hyperfine structure of C-line, due to interaction of unpaired electron with Cr⁵³ nucleus, occurs at low temperatures, and new unobserved earlier Q-lines appear near-by C-line. The spectrum may be described by usual spin Hamiltonian for S = 1/2 with following parameters: for A-line gz = 1.9841, gy = 1.9685, gx = 1.9592; for C-line gz = 1.9148, gy = 1.9671, gx = 1.9886, |Az| = 30.53 · 10⁻⁴ cm⁻¹, |Ax| = 10.62 · 10⁻⁴ cm⁻¹, |Ay| = 6.62 · 10⁻⁴ cm⁻¹.     

IR-spannungsoptische Ermittlung züchtungsbedingter Eigenspannungen in Silizium

The growth conditions and the resultant defect structure are the cause of residual stresses in silicon single crystals. The field of residual stress is nearly axial symmetrically; tensile stresses are in the centre and compressive stresses are at the periphery. The field of residual stress adapts itself to crystal symmetry by plastic deformation during the growth or annealing processes. The tangential compressive stresses at the periphery are 25 kp/cm² for Czochralski-grown crystals (diameter 36 mm, etch-pit density 5 · 10³ cm⁻²) and about 70 kp/cm² for crystals grown by the floating zone technique (diameter 28 mm, etch-pit density 3 · 10⁴ cm⁻²). Dislocation free crystals are almost free of residual stresses.     

Brown colour of ruby

The defects characteristic of brown pure ruby crystals coloured by specific growth conditions, annealing and irradiation are described. The comparsion of UV- and X-rayed crystals is given. Brown or yellow colour is attributed to the O⁻ centre which is formed by the electron transfer from O²⁻.