Optical properties of non‐centrosymmetric mixed crystals K2(La1‐x Cex)(NO3)5 · 2 H2O (x = 0.0 – 1.0)

Large single crystals of optical quality of the non‐centrosymmetric orthorhombic potassium rare earth nitrate mixed crystals K₂(La_1–x Ce_x)(NO₃)₅ · 2 H₂O were grown at 38 °C from diluted HNO₃. For crystals with x = 0.0, 0.19, 0.38 and 0.66 refractive indices and their dispersion were determined with an error less than 1 · 10^–4 in the wavelength range 0.404 – 1.083 μm by the prism method. Phase matching conditions for collinear SHG frequency conversion were analysed in detail, including calculation of the effective nonlinear optical susceptibility. By an appropriate choice of the fraction x of cerium the mixed crystals K₂(La_1–x Ce_x)(NO₃)₅ · 2 H₂O allow an adjustment of non‐critical type I phase matching conditions to a desired wavelength of the fundamental wave within the range 1.055(4) – 1.107(6) μm. Non‐critical type II phase matching can be tuned in the wavelength range 0.949(2) – 0.931(2) μm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared optical properties of (CuGe2P3)1−x(6 Ge)x solid solutions

Infrared reflectivity spectra of (CuGe₂P₃)_1−x(6 Ge)_x mixed crystals with compositions in the range x = 0.07–0.33 are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. An analysis of the spectra reveals six vibrational modes. The composition dependence of the mode frequencies and of the free carrier concentration and mobility is given and compared with infrared optical data for CuGe₂P₃.     

Growth and thermal studies on pure ADP,KDP and mixed K1‐x(NH4)xH2PO4 crystals

The investigations on the formation of mixed crystals of ammonium dihydrogen orthophosphate (ADP) and potassium dihydrogen orthophosphate (KDP) i.e. potassium ammonium dihydrogen phosphate, K_1‐x(NH₄)_xH₂PO₄ have been presented in this paper. Pure and mixed crystals of ADP and KDP have been grown by slow evaporation technique from the supersaturated solution at an ambient temperature 26±1 °C for ammonium concentration x in the range 0.0 ≤ x ≤ 1.0 in the case of mixed crystals. Crystal compositions were determined by flame atomic absorption spectroscopy and chemical analysis. The results of the X‐ray analysis of the grown crystals are also reported. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the kinetic process of dehydration and the high temperature phase behaviour. DTA showed the distinct thermal events attributed to dehydration of ADP, KDP and K_1‐x(NH₄)_xH₂PO₄. The results of thermal analysis and chemical analysis are consistent with each other. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multimode phonon structure of Be‐containing II ‐ VI mixed crystals determined by IR spectroscopic ellipsometry

Spectroscopic ellipsometry in the infrared spectral range 250‐5000 cm^‐1 is used for analysis of the dielectric response of Zn_1‐x‐yBe_xMg_ySe and Zn_1‐x‐yBe_xMn_ySe crystals grown by a high‐pressure Bridgman method. Ellipsometric spectra display features in the spectral range 390‐500 cm^‐1 associated with BeSe‐type phonon modes. In the optical spectra of Zn_1‐x‐yBe_xMg_ySe crystals both BeSe‐type and MgSe‐type lattice absorption bands are detected. The MgSe‐like modes are located at approximately 300 cm^‐1. The complex dielectric functions can be reproduced using a model with two or three and one or two classical damped oscillators corresponding to the BeSe‐like and the MgSe‐like transverse‐optical phonon modes, respectively. The frequencies of longitudinal‐optical phonons have been derived from the dielectric loss functions. A red‐shift of the BeSe‐like phonons frequencies with a mean rate 0.42 cm^‐1 (0.50 cm^‐1) per mole percent of Mg (Mn) incorporated to the alloy has been found for examined concentration range x, y ≤ 0.25. A noticeable damping the intensities of BeSe‐type modes with increasing fraction of Mg and Mn dopant is observed in comparison to the strengths of BeSe‐type modes in Zn_1‐xBe_xSe crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical absorption of Fe3+ Ion in LiF crystals

The absorption spectrum of LiF—Fe³⁺ single crystals was investigated at liquid nitrogen temperature. Six new absorption bands, unobserved earlier in other works, were found, which were located at 11 200, 16 000, 22 700, 27300, 30 500, and 41 900 cm⁻¹. The spectrum was interpreted in the cubic cristalline field approximation with D_q = 1397 cm⁻¹, B = 657 cm⁻¹, C = 3226 cm⁻¹. Above mentioned bands were assigned to the transitions from a ground state ⁶A_1g to the levels ⁴T_1g(G), ⁴T_2g(G), ⁴A_1g(G) (⁴E_g), ⁴E_g(D), ²T_1g(F), and ⁴T_1g(F), respectively.     

Germanium Incorporation in Ga1–xInxAs LPE Layers and GaAs Bulk Crystals

Atomic absorption spectroscopy (AAS) is used to determine the Ge concentration in Ga_1–xIn_xAs and GaAs. The orientation dependence of Ge incorporation in (111)A-and (111)B oriented samples has been studied. The distribution coefficients for both the orientations were determined to be k_Ge^(111)A = 2.6 · 10⁻² and k_Ge^(111B = 1.4 · 10⁻² for Ga_1–xIn_xAs with 0 ≦ x ≦ 0.13. The differences between the two orientations are explained with the aid of the band bending model. Doping gradients in thick epitaxial layers and along crystal length of polycristalline TGS-grown GaAs ingots have been investigated too. In Ga_1–xIn_xAs layers any Ge concentration gradient couldn't be observed, but in TGS compact crystals Ge concentration increases with crystal length because the melt composition changes significantly during solidification. The results are compared with those of electrical measurements.     

Elastic and elasto‐optical properties of Rb1–x(NH4)xH2AsO4 mixed crystals studied by Brillouin spectroscopy

The elastic and elasto‐optical properties of Rb_1–x (NH₄)_x H₂AsO₄ mixed crystals were studied by Brillouin spectroscopy at room temperature. The measurements were made on single crystals obtained from the aqueous solution by slow evaporation. The behaviour of bulk phonons propagating in investigated crystals was studied for different polarisations of incident and scattered beam. The components of the tensors of elasto‐optical and elastic properties of the crystals studied were determined. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,optical and dielectric studies on K1‐x(NH4)xH2PO4 mixed crystals grown from z‐cut seeds

Mixed crystals of K_1‐x(NH₄)_xH₂PO₄(KADP) were grown from KDP (KH₂PO₄) dominated mixed solutions with varying molar proportion of ADP (NH₄H₂PO₄) addition. It was found that, as the increase of ADP molar concentration, the growth rate along z‐axis of KADP crystal decreased rapidly. The structure of KADP crystals was investigated by powder XRD and the lattice parameter was calculated. The results showed that the lattice parameter c of KADP crystal increased with the molar concentration of ADP. The optical homogeneity of grown KADP crystals was determined with a differential phase‐shifting interferometry. Frequency dependences of the dielectric constant and dielectric loss of KADP crystals were measured at room temperature (290 K). The dielectric constants of KADP crystals were almost invariant with the increase of frequency. In the region of 10²∼10⁴Hz, the values of the dielectric loss reduced with the increase of frequency. The piezo‐resonance coupling effect still exists in KADP crystals at room temperature, but shifted to low frequency band. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and features of the surface morphology of <Emphasis Type="Italic">A</Emphasis><Superscript>4</Superscript><Emphasis Type="Italic">B</Emphasis><Superscript>6</Superscript> chalcogenide epitaxial films

The structure and features of the surface morphology of Pb_{1 − x} Mn _x Se (x = 0.03) epitaxial films grown on freshly cleaved BaF₂(111) faces and PbSe_{1 − x} S _x (100) (x = 0.12) single-crystal wafers were investigated by molecular beam condensation and the hot-wall method. It is shown that the epitaxial films, in accordance with the data in the literature for other chalcogenides, grow in the (111) and (100) planes, repeating the substrate orientation. Black aggregates are observed on the film surface of the films grown. The results obtained are compared with the data in the literature and generalized for other chalcogenides: A ⁴ B ⁶:Pb (S, Se, Te); Pb_{1 − x} Sn _x (S, Se, Te); and Pb_{1 − x} Mn (Se, Te). It is established that the formation of black aggregates, which are second-phase inclusions on the surface of epitaxial films obtained by vacuum thermal deposition, is characteristic of narrow-gap A ⁴ B ⁶ chalcogenides.     

Hyperfine structure of EPR spectra of Cr5+ ions in irradiated sodium dichromate crystals

EPR spectra are studied of X-irradiated sodium dichromate crystals grown from an aqueous solution by evaporation at 31°C. Doublet lines of EPR-absorption are attributed to the Cr⁵⁺ ions in the CrO₄³⁻ and CrO₃⁻ radicals resulting from radiation decomposition of Cr₂O₇²⁻ and being in the lattice in two unequivalent positions. Hyperfine structure caused by interaction of an unpaired electron with Cr⁵³ nucleus were observed both at liquid nitrogen and room temperatures. For the line, caused by CrO₄³⁻ radical, g_y and A_y directions coincide and angles both between A_x, g_x and A_z, g_z make up ∼ 25°. The spectrum is described by usual spin Hamiltonian for S = 1/2 with following parameters (T = 77 K): for CrO: g_z = 1.984, g_y = 1.970, g_x = 1.961, |A_z| = 8.2 · 10⁻⁴ cm⁻¹, |A_y| = 13.7 × 10⁻⁴ cm⁻¹, |A_x| = 36.1 · 10⁻⁴ cm⁻¹; for CrO₃⁻: g_z = 1.915, g_y = 1.975, g_x = 1.985, |A_z| = 32.2 · 10⁻⁴ cm⁻¹.     

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)     

Effect of change of state of aggregation of impurity on tl and microhardness of KClxBr1–x mixed crystals doped with Ca2+

Microhardness and Thermoluminescence (TL) measurements have been made in KCl_xBr_1–x mixed crystals doped with Ca²⁺ impurity. The variation of hardness in undoped and Ca²⁺ doped KCl_xBr_1–x crystals with quenching temperature is investigated. TL studied of KCl_xBr_1–x crystals doped with Ca²⁺, both in as-grown state and after quenching them from various elevated temperatures indicate that the positions of the glow peak which has been attributed to F-centers is found to depend upon the state of dispersion of impurity.     

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.     

The Investigation of Relation Between the Transition Temperature and the Unit Cell Volume in (K1-xCsx)2ZnCl4 Mixed Crystals

The relation between the phase transition temperature and unit cell volume in the (K_1-xCs_x)₂ZnCl₄ mixed crystals was studied. The phase transition temperature of A₂BX₄ family is dependent on the size of cation and anion (FABRY and PEREZ-MATO). That is, the transition temperature of crystal decreases with increasing unit cell volume. In this study we investigated this property of mixed crystals with the increasing mixture ratio. From the current study, we obtained the result that in the mixed crystals (K_1-xCs_x)₂ZnCl₄, the increase of x induces the increase of unit cell volume, so that T_I decreases with increasing unit cell volume. In order to determine the distribution of the substituted Cs⁺, using the near IR and UV spectrophotometer, we investigated both the band gap energy and the type of transition.     

Composition Dependency of Lattice Anisotropy of TlBX2‐type Chain Mixed Crystals

Variation of the lattice parameters of TlTl_1‐xIn_xSe₂ chain mixed crystals with composition have been studied by X‐ray diffraction technique. The lattice anisotropy ( c/a ) of the TlBX₂‐type mixed crystals changes linearly with substitution of the atoms located both at the center and at the vertices of the BX4 tetrahedra. A brief survey of the important features of the effect of isomorphic atom substitution on the lattice anisotropy of TlBX₂‐type mixed crystals with chain structure has been presented.     

Dynamic and static orientational disorder in mixed K1 − x (NH4)xI crystals

Earlier, we have shown that, at low temperatures, the mixed K_{1 ? x} (NH₄)_xI crystals show two low-energy resonance modes in the dynamically orientationally disordered region of the α-phase and statically orientationally disordered phase of the orientational glass, absent in the orientationally ordered γ-phase. Below, we report the results of the experimental study of the low-energy resonance and local modes in K_{1 ? x} (NH₄)_xI crystals obtained by the method of inelastic incoherent neutron scattering (IINS) over the wide temperature range.     

Spin‐Hamiltonian parameters for Dy3+ ion at the trigonal 12‐fold coordinated La3+ site of La2Mg3(NO3)12·24H2O

The spin‐Hamiltonian parameters (g factors g_‖, g_⊥ and hyperfine structure constants ¹⁶¹A_‖, ¹⁶¹A_⊥, ¹⁶³A_‖, ¹⁶³A_⊥) for ¹⁶¹Dy³⁺ and ¹⁶¹Dy³⁺ isotopes in the trigonal 12‐fold coordinated La³⁺ site of La₂Mg₃(NO₃)₁₂·24H₂O crystal are calculated from a diagonalization (of energy matrix) method. In the method, the Zeeman and hyperfine interaction terms are added to the conventional Hamiltonian used in the studies of crystal‐field energy levels, and a 66×66 energy matrix concerning the ground multiplet ⁶H_15/2 and the first to fifth excited multiplets ⁶H_13/2, ⁶H_11/2, ⁶H_9/2, ⁶H_7/2 and ⁶H_5/2 are applied. The calculated results are discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Raman scattering study on Ga1–x Mnx As prepared by Mn ions implantation,deposition and post‐annealing

Raman scattering measurements have been performed in Ga_1–x Mn_x As crystals prepared by Mn ions implantation, deposition, and post‐annealing. The Raman spectrum measured from the implanted surface of the sample shows some weak phonon modes in addition to GaAs‐like phonon modes, where the GaAs‐like LO and TO phonons are found to be shifted by approximately 4 and 2 cm^‐1, respectively, in the lower frequency direction compared to those observed from the unimplanted surface of the sample. The weak vibrational modes observed are assigned to hausmannite Mn₃O₄ like. The coupled LO‐phonon plasmon mode (CLOPM), and defects and As related vibrational modes caused by Mn ions implantation, deposition, and post‐annealing are also observed. The compositional dependence of GaAs‐like LO phonon frequency is developed for strained and unstrained conditions and then using the observed LO_GaAs peak, the Mn composition is evaluated to be 0.034. Furthermore, by analyzing the intensity of CLOPM and unscreened LO_GaAs phonon mode, the hole density is evaluated to be 1.84×10¹⁸ cm^‐3. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of doping and heat treatment on the mechanical parameters of ZnSe<Subscript>(1 − <Emphasis Type="Italic">x</Emphasis>)</Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> crystals grown from the melt

The mechanical properties of crystals of ZnSe_{(1 − x)}Te _x (0 < x < 1.3 wt %) solid solutions are investigated using the indentation method. The breaking points of doped and undoped crystals are measured by the uniaxial compression method. It is revealed that the microhardness anisotropy coefficient for crystals with a tellurium dopant content of ∼0.3 wt % is equal to unity. A change in the tellurium content in the solid solutions from 0.2 to 1.3 wt % leads to a linear increase in the microhardness by 23%. The brittle strength of the ZnSe and ZnSe_{(1 − x)}Te _x crystals varies in a similar manner. It is demonstrated that heat treatment and the presence of interblock boundaries affect the ultimate strength and the cracking resistance of the ZnSe_{(1 − x)}Te _x crystals. This is an important factor which should be taken into account in mechanical treatment of the materials under investigation.     

Preparation and investigation of (CuInSe2)x(2ZnSe)1‐x and (CuInTe2)x(2ZnTe)1‐x solid solution crystals

The (CuInSe₂)_x(2ZnSe)_1‐x and (CuInTe₂)_x(2ZnTe)_1‐x solid solution crystals prepared by Bridgman method and chemical vapor transport have been studied. The nature of the crystalline phases, the local structure homogeneity and composition of these materials have been investigated by X‐ray diffraction (XRD) and Electron Probe Microanalysis (EPMA) methods. The analysis revealed the presence of chalcopyrite‐sphalerite phase transition between 0.6 ≤ X ≤ 0.7. Lattice constants, value of σ position parameter and bond length between atoms were also calculated. It was found that the lattice parameters exhibit a linear dependence versus composition. The transmission spectra of solid solution crystals in the region of the main absorption edge were studied. It was established that the optical band gap of these materials changes non‐linearly with the X composition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)