On the scandium distribution in indium arsenide crystals grown by the Czochralski method

In this paper the behaviour of scandium in n-type monocrystalline indium arsenide grown by Czochralski method in sealed ampoule is studied. The crystals have been grown in [111] direction under different conditions: crystallization rate, As-partial pressure and scandium initial concentration in the melt. The effect of the above factors on the scandium distribution along the crystals have been investigated. Using these results and by means of the equation of normal freezing the effective Sc distribution coefficient (k) in InAs under different technological conditions has been determined. It has been found that k < 1 in all experiments. In order to find the equilibrium coefficient (k₀) at fixed growth conditions the Burton-Prim-Slichter model has been used. On the basis of Hall measurements and atomic absorption analysis of Sc-doped InAs it is concluded that connected with Sc electrically active centers behave as shallow donors, most probably monovalent ones.     

Agglomeration of potash alum crystals

Crystals of potash alum, crystallized in suspension at higher supersaturations, are partially agglomerated. Two sets of experiments have been chosen: batch experiments with precipitation of potash alum from its components and continuous crystallization by cooling. Using three different ways described in the preceding paper the size distribution of potash alum crystals was analyzed and the effect of agglomeration on calculated kinetic data demonstrated.     

Dissolution and growth of spinel crystals in a borosilicate glass

The rate of dissolution and growth of settling crystals of spinel was measured optically in a borosilicate melt that was pre-heated at a temperature above liquidus to erase the effects of previous history. The Hixson-Crowell equation, which is based on Fick's first law, was used to determine mass-transfer coefficients (k_H) for dissolution and growth; both were found to fit the same Arrhenius function of temperature (T). An attempt was made to estimate the diffusion coefficient (D) and the concentration-boundary-layer thickness (δ). The calculated values of δ compared well with experimental results and observations. The D vs. T function was similar to a literature function obtained for the dissolution of magnetite in sodium disilicate glass.     

Investigation of the crystallization of the system KAl(Cr)(SO4)212 H2O under various conditions

The crystallization of the isomorphous system KAl(Cr)(SO₄)₂ · 12 H₂O under various conditions has been studied. It has been found that the rate of linear crystallization of the face (100) passes through a maximum on the interval of Cr³⁺ concentrations 0.02–0.08 g ions/l which is shifted to the right with increasing temperature. Under the same conditions, the equilibrium coefficient of distribution of the microcomponent D has been determined in single crystals. D decreases with the increase of the Cr³⁺ concentration and the crystallization temperature. These results can be explained with the formation of complexes of Cr³⁺ in the solution which decreases the active concentration of the ion and are selectively adsorbed on the face (100). At the same Cr³⁺ concentration (0.058 g ion/l), the temperature dependence of the rate of growth of the face (100), as well as the influence of supersaturation on the rate of growth of the faces (100) and (111), have been studied. The apparent activation energy of crystallization of the face (100) has been determined to be E = 11.2 Kcal. · mol⁻¹. The data obtained are compared with analogical results for pure KAl(SO₄)₂ 12 H₂O.     

Anisotropy of microhardness and fracture of (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Ni(SO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O (ANSH) crystals

The Vickers hardness of the (010) and (001) planes in (NH₄)₂Ni(SO₄)₂ · 6H₂O (ANSH) crystals has been measured. Anisotropy hardness of the first kind is revealed for the (010) plane in ANSH. The hardness anisotropy coefficient k ₂ was determined to be 1.5. The temperature dependence of the microhardness of the (001) face of ANSH crystals was investigated in the temperature range from 20 to 80°C. The character of fracture of the (100), (010), and (001) planes during indentation with a spherical indenter has been qualitatively determined.     

Strength of Crystals of Small Dimensions and their Triboluminescence

Stress-dependence of triboluminescence (TBL) in uranyl nitrate, tartaric acid and other nine crystals has been studied with the help of a new technique of crushing the crystals. As the appearance of TBL needs the creation of new surfaces in a crystal, the minimum stress at which TBL appears has been taken to be the fracture-strength of the crystal. The value of the fracture-strength and stress coefficient of binding energy determined from TBL measurements are found to be of correct order. It has been found that the rate of rise of TBL intensity with stress is higher for those crystals which have less value of the fracture-strength. The fracture strength (σ_f) is found to be higher for those crystals which have less value of stress coefficient of binding energy (β) and the product of σ_f and β is higher for those crystals which have higher melting point. It has been shown that the rate of rise of TBL intensity with stress decreases at higher values of stress due to strain hardening in the crystals.     

Absorption and electrical conductivity of CaMoO4 crystals

The electrical conductivity σ of CaMoO₄ crystals was investigated between room temperature and 850°C. The mobility v_v and the diffusion coefficient D_v of the O⁻ ion vacancies have been derived from σ: v_vT = 3300 exp (−1.52 eV/kT) cm² K/Vs, D_v = (0.1…1) × exp (−1.52 eV/kT) cm²/s. An absorption occuring in crystals which are reduced or X-irradiated at low temperatures is dichroitic and caused by Mo⁵⁺ ions. For measurement in c direction the oscillator strength of the 680 nm absorption band is found to be about 0.1.     

Kinetic investigations within the transition region from polyhedral to skeletal growth mode (I). Growth kinetics of the basal face of zinc single crystals under diffusion conditions

The effect of diffusion in the vapour phase on the kinetics of growth of zinc single crystals in the presence of argon has been studied. The shift of the basal face in normal direction as a function of the time has been measured at constant temperature and supersaturation and argon pressures varying within the range 5–250 Torr as well as in vacuum 1 × 10⁻⁶ Torr. It has been established that the crystal size R changes with the time t following a linear and a parabolic law in the kinetic and the diffusion regimes, respectively. The kinetic critical size R_k for the transition from a kinetic to a diffusion regime has been experimentally obtained. A relatively good agreement is found between the experimentally established and theoretically calculated values of the critical size. The problems related to the transition of the basal faces of zinc single crystals from a kinetic to a diffusion growth mode is discussed.     

Batch Precipitation of Potash Alum Crystals by Mixing Aqueous Solutions of the Component Salts

The effects of temperature, supersaturation, excess of reacting component salts and method of precipitation on the batchwise precipitation of potash alum crystals, by mixing aqueous solutions of potassium sulphate and aluminium sulphate, have been investigated. From the primary characteristics of the process (crystal size, size distribution and yield) relative crystal growth rates and relative nucleation rates are calculated and interrelation of these rates with the corresponding supersaturation leads to a value of the nucleation order. It is concluded that secondary nucleation plays an important role in the batch precipitation of potash alum crystals.     

Crystal Growth of Deuterated KDP and Determination of the Deuterium Content

The relation between the deuterium concentration in the solution and in the solid phase during the growth of K(H, D)₂PO₄ crystals at 30, 45, and 60°C has been examined. The solubility of K(H, D)₂PO₄ in deuterated water was measured. The concentration of D₂O in the solvent has been determined by means of the interferometric method with an accuracy of ± 0.4 mol%. The deuterium concentration in the crystals was measured with an accuracy better than ± 1.2 mol% by the same method after decomposing them thermally. The deuterium content in crystals is determined by the deuterium content in the solvent. It is practically not influenced by temperature.     

Rotational Striations and Diffusion in Barium Sodium Niobate Crystals

The possibility of inducing rotational growth striae with a small period in barium sodium niobate crystals (BSN) is examined. Crystals grown had a period stability up to 1 percent and were suitable material for anisotropic light diffraction by ferroelectric domains. However intense striae were produced only for periods λ > 5 m̈m. With the help of Bragg optical diffraction by growth striae the diffusion coefficient D in solid phase responsible for striae smoothing during annealing was measured. The magnitude D ≈ 10^-11 cm² s^-1 at the melting point was obtained. Such D value leads to the vanishing of striae with λ < 5 m̈m in BSN crystals during growth.     

Dislocation density in heteroepitaxial indium arsenide layers

In As layers have been grown by CVD on (111)B-oriented GaAs substrates. The dislocation density (N_D) distribution through the layer thickness has been studied. N_D is dependent on the mole fraction of AsCl₃ in the gaseous phase and, consequently, on the current carriers concentration. This results in the supposition that the decreasing of N_D in the layers after a “critical” thickness is due to the “pinning” of dislocations at impurity atoms which form stronger bonds with the host In or As atoms than the bond In–As, an effect which is known for bulk GaAs and InP crystals.     

Trioxatruxenes: A New Family of Disc-Like Mesogens with a Complex Polymorphism

A homologous series of hexa-n-alkanoyloxytrioxatruxenes has been prepared with n=7 t o n=15 in order to check the influence upon the mesomorphic properties exerted by the substitution of the three methylenes of the truxene core by oxygen atoms. Interphase transitions between solid, mesomorphic and isotropic phases were studied by hot stage microscopy and DSC. One of the homologs (R=C₁₃H₂₇CO-) was previously identified by X-Ray investigations and used as t h e reference substance to confirm the structure of the various mesophases by contact method. A new example of the socalled inverted sequence (crystal-N_D nematic-D columnar-isotropic) and several examples of the new oblique disordered columnar phase (Dobd) are reported. Trioxatruxenes can be quoted as able to exhibit the most complex polymorphism found in disc-like liquid crystals with the sequence: K - N_D - D_obd - D_rd - D_hd - I.     

Zur Bestimmung des effektiven Verteilungskoeffizienten von Te bei der Züchtung von GaP-Einkristallen aus nichtstöchiometrischen schmelzen

An equation for determining the effective distribution coefficient, k_eff, under the conditions of growing single crystals from non-stoichiometric melts is proposed. This equation is used for the calculation of k_eff at Te concentrations in the melt from 3.5 × 10⁻³ up to 9.1 × 10⁻² at.%. From numerous measurements a k_eff value of 0.070 with the 1 σ boundaries at 0.116 and 0.043 is found. The relatively wide spread is accounted for by the heterogeneous distribution of doping material which is due to the technique applied and to the polar properties of the GaP lattice.     

X-ray diffraction study of (TlInSe<Subscript>2</Subscript>)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(TlGaTe<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> crystal system

The crystallographic and dynamic characteristics of TlInSe₂ and TlGaTe₂ crystals have been studied by X-ray diffraction in the temperature range of 85–320 K. The temperature dependences of the unit-cell parameters a of TlInSe₂ and TlGaTe₂ crystals, as well as their coefficients of thermal expansion along the [100] direction, are determined. The concentration dependences of the unit-cell parameters a and c for (TlInSe₂)_{1 − x} (TlGaTe₂) _x crystals are measured. Anomalies are found in the temperature dependences of the unit-cell parameters a and, correspondingly, the coefficient of thermal expansion, indicating the existence of phase transitions in TlInSe₂ and TlGaTe₂ crystals.     

Single crystal growth of La2(SO4)3 · 9 D2O

Single crystals of La₂(SO₄)₃ · 9 D₂O were grown from saturated D₂O solutions. According to X-ray diffraction measurements, the crystals have a hexagonal structure with unit cell parameters a = 10.996 Å and c = 8.077 Å (space group C–P6₃/m). Several physical properties were also determined (density, refractive indices, dielectric constants, specific heat, coefficient of linear expansion, microhardness).     

Über den Einfluß von Wachstumsfluktuationen auf den effektiven Verteilungskoeffizienten beim Zonenschmelzen

The influence of growth rate fluctuations on the micro and macrodistribution of Ir during zone melting of Mo is investigated. The microdistribution is principally the same as that found for W in Mo, although the equilibrium-distribution-coefficient k₀ is now smaller than 1. A mean effective distribution coefficient k_eff describes the macrodistribution. Its dependence on the fluctuations is qualitatively quite different from that of W in Mo with k₀ > 1. With the occurence of fluctuations the value of k _eff is changed continually in the direction of one. Its dependence on the zone-melting rate is found in the region of fluctuations too.     

Kinetic investigations within the transition region from polyhedral to skeletal growth mode (III). Growth kinetics of the basal face of zinc single crystals and its edge under diffusion conditions

The growth kinetics of the basal face and its edge of zinc single crystals grown from zinc vapours in the presence of argon at pressures 5 – 250 Torr has been investigated simultaneously. The alterations of the crystal size R and the length of the basal edge a with time t have been measured at constant temperature and supersaturation. It is shown that the R²(t) and a²(t) dependences change their initial shape into linear at one and the same moment. It is established that the transition from a kinetic to a diffusion regime can be determined both by the kinetic critical size R_k and by the kinetic critical size a_k. It is found also that in the kinetic regime the lateral growth rate of the basal edge is higher than the normal growth rate of the {0001} face. During the growth in a diffusion regime the R²(t) and a²(t) curves of a given single crystal become parallel, due to the isotropic character of the transport processes of the material. The rate determining role of the diffusion in the parent phase on the growth of the basal face and its edge is demonstrated.     

Verteilungskoeffizienten und Konzentrationsanreicherungen an der Phasengrenzfläche bei ebenem und zellularem Erstarren von Zinn-Zink-Legierungen

The experimental results of KRUMNACKER on the effective distribution coefficient k_eff and the concentration-profil at the solidification interface were examined. On the basis of this examination and some new calculations the depencence of the segregation coefficient on the solidification rate R and on the concentration C₀ is studied in the cases of planar and cellular solidification. — In the case of planar interface the dependence of k_eff on the solidification rate is that of the Burton-Prim-Slichter-theorie. The interface distribution coefficient is not a function of R, or C₀. Thus, the result od BRICE , basing on the same experiments, is not correct. It is impossible, to improve the model of BRICE by these values. — In the case of cellular growth the distribution depends on the diffusion in the diffusion layer at the interface and on the segregation in the grooves of the cells. Under the applied experimental conditions of a large diffusion-boundary-layer the diffusion determines the dependence of k_eff on the solidification rate also under the condition of cellular growth.