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.     

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.     

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.     

Effect of temperature and isomorphic atom substitution on optical absorption edge of TlInS2xSe2(1‐x) mixed crystals (0.25 ≤ x ≤ 1)

The optical properties of the TlInS_2xSe_2(1‐x)mixed crystals (0.25 ≤ x ≤ 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400–1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS_2xSe_2(1‐x)mixed crystals. The transmission measurements carried out in the temperature range of 10–300 K revealed that the rates of change of the indirect band gaps with temperature are γ = –9.2×10^–4 eV/K, –6.1×10^–4 eV/K, –4.7×10^–4 eV/K and –5.6×10^–4 eV/K for TlInS₂, TlInS_1.5Se_0.5, TlInSSe and TlInS_0.5Se_1.5 crystals, respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electric Characterization of Indium Sesquiselenide Single Crystals

Conductivity, Hall-effect measurements were performed on δ-phase In₂Se₃ single crystals, grown by the Bridgman method over the temperature range 150–428 K, in the directions perpendicular and parallel to the c-axis. The anisotropy of the electrical conductivity and of the Hall coefficient of n-type In₂Se₃ had been investigated. The values of the Hall coefficient and electrical conductivity at room temperature spreads from an order of R_H11 = 1.36 × 10⁴ cm³/coul, σ₁₁ = 4.138 × 10⁻³ Ω⁻¹ cm⁻¹ and R_H = 66.55 × 10⁴ cm³/coul, σ = 0.799 × 10⁻³ Ω⁻¹ cm⁻¹ for parallel and perpendicular to c-axis, respectively. The temperature dependence of Hall mobility and carrier concentration are also studied.     

Dynamics of twin layer widening in In-Pb crystals

The authors studied mobility of boundaries of plane-parallel twin layers in In-0.2 wt.% Pb and In-2 wt.% Pb crystals in the temperature range 290–373 K when stresses are applied τ/G = (1.35 – 7) × 10⁻⁶ (G is the shear modulus). They found that lead concentration increase as well as dislocation structure deterioration result in lower boundary velocity for a constant stress. In In-2 wt.% Pb crystals, the boundary velocity is well describable as V_n = V₀(τ) × × exp [ − ΔH (τ)/kT] where V₀(τ) = Ae^ατ/G (A = 10⁻³ cm/s, α = 1.1 × 10⁶) τ ΔH(τ) is the activation energy depending on the stress, ranging under these circumstances from 0.33 to 0.43 eV. At present it is difficult to interpret the results at hand. The analysis allows only to assume that the change in the boundary movement activation energy for impure crystals as against that for pure ones can be associated with the impurity effect on the structure of the intermediate zone between the twin and the matrix. The dependence of the pre-exponential factor on the stress is probably due to the effect of the internal long-range stress field on sources of twinning dislocations. Comparison with data for calcite and pure indium shows that twin boundary mobility parameters and their dependence on the stress are governed by the crystal type and defect structure.     

An EPR Study of Scapolite

In single crystals of scapolite from two different localities, three paramagnetic centres are detected by electron paramagnetic resonance (EPR): 1. One isotropic singlet with g_iso = 2.005; 2. One triclinic singlet with g‖ = 2.005 ± 0.001 and g⟂= 2.009; 3. One triclinic sextet with g‖= 2.005 ± 0.001, g⟂ = 2.011; A‖ = 85.4 × 10⁻⁴ cm⁻⁴, A⟂ = 85.3 × 10⁻⁴ cm⁻¹. Centres 1 and 2 can be attributed to colour centres as they are bleached after annealing. Centre 3 can be due to Mn²⁺ (only the central M_s = ± 1/2 transition is observable) most likely substituting for Ca²⁺ The site symmetry must be triclinic but due to Al, Si disorder and mixed Na, Ca composition the different components from magnetically non-equivalent sites are averaged out for many orientations.     

Growth,thermophysical and electrical properties of the nonlinear optical crystal BPO4

Bulk BPO₄ crystals have been successfully grown from high temperature solution of BPO₄, Li₂O, and MoO₃ in the molar ratio of 2.3:1:1.3 by the top‐seeded solution growth (TSSG) method using [101]^c orientation seeds. There are no visible scattering centers and impurity of Mo in the as‐grown BPO₄ crystals, whose optical homogeneity reaches up to 1.6×10^–5/cm. BPO₄ possesses a specific heat of 0.50–1.00 J·g^–1·K^–1 in the temperature range from 298 to 698 K and exhibits strong anisotropic thermal expansion behavior with α_a = 14.2 × 10^–6 K^–1 and α_c = ‐4.0 × 10^–7 K^–1. Moreover, the thermal conductivity coefficients are calculated to be κ_a = 62.4 W·m^–1·K^–1 and κ_c = 51.5 W·m^–1·K^–1, which are remarkably larger than those of some commonly used borates. The measured dielectric constants, ε_a and ε_c, are 4.8 and 6.1, respectively, and the ionic conductivity coefficients, σ_a = 4.3 × 10^–8 S/cm and σ_c = 9.5 × 10^–8 S/cm, are several orders of magnitude lower than that of LiB₃O₅ (LBO). (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron Spin Resonance of Mn2+ in Hemimorphite

The Electron Spin Resonance of Mn²⁺ in natural crystals of hemimorphite was studied at RT, X-band. No fine structure other than the central M = | + 1/2 〉 ⇆ | −1/2 > transition with allowed (Δm = 0) and forbidden (Δm = ±1) hyperfine transitions were observed. The spectrum was fitted with the spin Hamiltonian parameters g = 2.001, A = −84.6 × 10⁻⁴ cm⁻¹. The crystal field parameter D was estimated equal to (8 ± 2) × 10⁻³ cm⁻¹. The most striking result is the size of the hyperfine splitting constant favoring occupancy of sixfold coordinated sites.     

Thermoelectric power of indium sesquisulphide single crystals

The investigation covers a temperature range from 200 to 450 K. Thermoelectric power measurements of In₂S₃ crystals showed that all samples under investigation have a positive TEP in all temperature ranges, indicating n-type conductivity for In₂S₃ crystals. The ratio of the electron and hole mobilities is μ_n/μ_p = 4.71. The effective mass of electrons m is found to be 0.00008 × 10⁻³¹ kg. The obtained effective masses of holes m = 1.893 × 10⁻³¹ kg. The diffusion coefficient for both carriers (electrons and holes) is evaluated to be 84.71 cm²/s and 17.985 cm²/s respectively. The mean free time between collision is estimated to be τ_n = 1.7 × 10⁻²⁰s, and τ_p = 8.5 × 10⁻¹⁷s. The estimated diffusion length for electrons is found to be L_n = 1.2 × 10⁻⁹ cm and L_p = 3.9 × 10⁻⁸ cm.     

Comparison of lead solubility in NaCl crystals from data obtained by different methods

The solvus of the NaCl: Pb²⁺ system was found in the concentration range from 1.5 × 10⁻³ to 1.9 × 10⁻² mol% at temperatures ranging from 375 to 430 °C from the data of flotation measurements of the crystal density. The heat of impurity dissolution equal to 2.0 ± ± 0.6 eV and the change in the vibrational entropy in the formation of the solid solution S_v/K= 20 ± 10 were determined. Reasons for a difference in the estimates of lead solubility in NaCl, obtained from temperature dependences of light scattering and by other methods: measurement of the density, electric conductivity, and the electron-microscopic decoration of the same crystals are discussed.     

Growth,structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)2Sr2Ca2Cu3O10‐y crystals

Large and high‐quality single crystals of both Pb‐free and Pb‐doped high temperature superconducting compounds (Bi_1‐xPb_x)₂Sr₂Ca₂Cu₃O_10‐y (x = 0 and 0.3) were grown by means of a newly developed “Vapour‐Assisted Travelling Floating Zone” technique (VA‐TSFZ). This modified zone‐melting technique was realised in an image furnace and allowed for the first time to grow Pb‐doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm³ were successfully grown. Post‐annealing under high pressure of O₂ (up to 10 MPa at T = 500°C) was undertaken to enhance T_c and improve the homogeneity of the crystals. Structural characterisation was performed by single‐crystal X‐ray diffraction (XRD) and the structure of the 3‐layer Bi‐based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb‐free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔT_c ≤ 1 K). In optimally doped Pb‐free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�10⁵ A/cm² were measured at T = 30 K and μ₀H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40‐50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1‐5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d‐wave superconductivity in Bi‐2223. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature‐tuned band gap energy and oscillator parameters of Tl2InGaSe4 semiconducting layered single crystals

The optical properties of Tl₂InGaSe₄ layered single crystals have been studied through the transmission and reflection measurements in the wavelength range of 500‐1100 nm. The analysis of room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.86 and 2.05 eV, respectively. Transmission measurements carried out in the temperature range of 10‐300 K revealed that the rate of change of the indirect band gap with temperature is γ = – 4.4 × 10^‐4 eV/K. The absolute zero value of the band gap energy was obtained as E_gi(0) = 1.95 eV. The dispersion of the refractive index is discussed in terms of the single oscillator model. The refractive index dispersion parameters: oscillator wavelength and strength were found to be 2.53 × 10^–7 m and 9.64 × 10¹³ m^–2, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature dependences of the optical characteristics of ZnMgSe single crystals

The temperature dependences of the refractive index of wide-gap Zn_{1 − x} Mg _x Se (x ∼ 0.5) single crystals are measured. It is established that, in the temperature range 300–530 K, the value of dn/dT for such crystals grown by the vertical Bridgman method is 9.31 × 10⁻⁵ at λ = 0.63 μm and 5.29 × 10⁻⁵ at λ = 10.6 μm. The obtained values of the coefficients dn/dT for hexagonal Zn_{1 − x} Mg _x Se single crystals are close to the corresponding values for cubic ZnSe single crystals and are much lower than those for hexagonal CdS. Examples of practical application of single crystals of the ZnMgSe substitutional solid solution as a thermostable material for polarization optical elements in the IR range are given.     

Effect of monovalent salts on morphology of calcium carbonate crystallized in Couette‐Taylor reactor

Monovalent ionic additives, Na⁺, K⁺ and NHequation/tex2gif-stack-1.gif impact on the morphology and agglomeration of CaCO₃ crystals. As increasing the additive concentration, the regular shaped crystals such as rhombohedron and spindle are changed to irregular one due to the inclusion of Na⁺ and K⁺ into the crystal structure. The inclusion of Na⁺ and K⁺ is detected using ICP‐AES. The partition of coefficients of Na⁺ and K⁺ are estimated as 9.74 × 10^–4, 9.73×10^–4, respectively and the amount of inclusion in the crystals is about 2×10³ ppm. However, the inclusion of ions does not modify a crystal structure of calcite. Since NH₄⁺ is large in radius, it is not included in crystal but shifts the spindle shape of crystal to the rhombohedral one. It is interesting to find that such modification of crystal morphology begins to appear at high additive concentration (0.05 M). In addition, the crystal agglomeration is promoted because the electric repulsive charge is reduced as increasing the additive concentration. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Investigations for Sn diffusion in Pb1−xSnxTe and PbTe

By annealing Pb_1−xSn_xTe and PbTe isothermally in a quartz ampoule Sn diffused from Pb_1−xSn_xTe into PbTe. The profiles obtained have been investigated by means of an electron beam microanalyser, and the coefficients of diffusion have been determined at various temperatures. The diffusion of Sn can be explained by the expressions: D_PbSnTe = 1.5 · 10⁻¹ exp (−1.8 eV/kT) cm² s⁻¹ (0,14 < x < 0,18) D_PbTe = 5,5 · 10⁻⁴ exp (−1.5 eV/kT) cm² s⁻¹. N-type layers are observed at the surface of Pb_1−xSn_xTe specimens.     

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.     

Electrical Characterization of Irradiation plus Annealing – induced VAsZnGa Pairs in p-type GaAs (Zn) Crystals

Effect of fast electron irradiation (E =2.2 Mev, ϕ_c = 1 × 10¹⁶ el/cm²) and subsequent annealings (T = 150 to 350 °C, t = 10 to 600 min) of zinc-doped p-type GaAs crystals on the formation and dissociation of V_AsZn_Ga, pairs is studied. An analysis of the formation and dissociation kinetics of V_AsZn_Ga pairs permitted to find the diffusion coefficient of radiation-induced arsenic vacancies D(D = 1.5 × 10⁻¹⁸, 1 × 10⁻¹⁷ and 5 × 10⁻¹⁷ cm²/s at 150, 175 and 200 °C accordingly), their migration energy ϵ_m(ϵ_m = 1.1 eV), the binding energy of V_AsZn_Ga, pairs ϵ_b(ϵ_b = 0.5 eV), and also their dissociation energy ϵ_d(ϵ_d = 1.6 eV).     

Growth of congruently melting Ca0.59Sr0.41F2 crystals and study of their properties

Homogeneous crystals of Ca_0.59Sr_0.41F₂ alloy (sp. gr., Fm $ \bar 3 $ \bar 3 m, a = 0.56057 nm), corresponding to the point of minimum in the melting curve in the CaF₂-SrF₂ phase diagram, have been grown by the vertical Bridgman method. The optical, mechanical, electrical, and thermophysical properties of Ca_0.59Sr_0.41F₂ and MF₂ crystals (M = Ca, Sr) have been studied and comparatively analyzed. Ca_0.59Sr_0.41F₂ crystals are transparent in the range of 0.133–11.5 μm, have refractive index n _D = 1.436, microhardness H _μ = 2.63 ± 0.10 GPa, ion conductivity σ = 5 × 10⁻⁵ S/cm at 825 K, and thermal conductivity k = 4.0 W m⁻¹ K⁻¹ at 300 K. It is shown that the optical properties of Ca_0.59Sr_0.41F₂ crystals are intermediate between those of CaF₂ and SrF₂, whereas their mechanical and electrical characteristics are better than the latter compounds.