Polytypes of monoclinic TlInS<Subscript>2</Subscript>

The polytypes of monoclinic TlInS₂ (c ～ 15, 60, 120 Å) and triclinic TlInS₂ (c ～ 30 Å) were prepared. The positions of edge excitons and the band gaps were determined by the optical and photoelectric measurements. It was found that the maxima in the temperature dependences of dielectric constants of pure polytypes are situated at different temperatures. The photoconductivity spectra and the capacitive measurements showed that pure polytypes are unstable and transform with time into a mixture of the monoclinic polytypes of TlInS₂. It is also established that all polytypes of monoclinic crystals tend to transform to the triclinic system.     

Preparation and properties of orthorhombic TlInS<Subscript>2</Subscript>

A procedure is described for crystal growth of orthorhombic TlInS₂. The lattice parameters of the grown crystals are a = 6.88 Å, b = 14.04 Å, and c = 4.02 Å (sp. gr. P222₁, Z = 4, _x = 6.59 g/cm³). The dielectric permittivity of the crystals is measured from 170 to 300 K. The spectral dependence of the 300-K photocurrent through the crystals indicates that orthorhombic TlInS₂ is a wide-gap semiconductor. Its band gap, E _g = 2.52 ± 0.01 eV, slightly exceeds that of monoclinic TlInS₂.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 138–142.Original Russian Text Copyright © 2005 by Nadjafov, Alekperov, Guseinov.     

Magnetic Features of Boron Doping on Hf<Subscript>2</Subscript>Co<Subscript>11</Subscript> Thin Films

The effect of boron (B) doping on the structural and magnetic properties is studied systematically in the Hf₂Co₁₁ thin films. The modified crystal microstructure and annealing process enhanced the coercive field up to 1754 Oe. In order to obtain superior magnetic properties, the optimum doping ratios should be properly controlled attentively. To identify the structure, B-doped Hf₂Co₁₁ thin films were investigated by temperature-dependent X-ray diffraction analysis for the first time. The hard magnetic phase of Hf₂Co₁₁ B _x thin films was formed to orthorhombic phase with some Co impurities and had a crystallization temperature around 823 K.     

Effect of Hydrogen on the Crystallization of Amorphous Ti<Subscript>50</Subscript>Ni<Subscript>25</Subscript>Cu<Subscript>25</Subscript> Titanium Alloy

We describe effects unknown earlier in the physics of interaction between hydrogen and amorphous metallic alloys: an increase in the crystallization temperature of hydrogen-containing Ti₅₀Ni₂₅Cu₂₅ alloy in the course of its heating and suppression of the inverse martensitic transformation B2 → B19 after crystallization. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 3, pp. 66 – 70, May – June, 2005.     

Dielectric anomalies in monoclinic TlInS<Subscript>2</Subscript> polytypes

Comparison of room-temperature x-ray diffraction data and temperature-dependent (190–220 K) permittivity data for different polytypes of monoclinic TlInS₂ demonstrates that the anomalies in (T) at the phase transition correlate with the c cell parameter of the polytypes. The (T) curve of single-phase crystals with c 15 Å shows a single, sharp peak at about 205 K. The peaks in the of the polytypes with c 30 and 60 Å occur at other temperatures, indicating that permittivity data near the phase transition can be used to identify the polytypes present in TlInS₂ crystals.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1423–1426.Original Russian Text Copyright © 2004 by Alekperov, Nadjafov     

Phase relations in the TlInS<Subscript>2</Subscript>-TlYbS<Subscript>2</Subscript> system and electrical properties of Tl<Subscript>2</Subscript>InYbS<Subscript>4</Subscript> crystals

We have studied phase relations in the TlInS₂-TlYbS₂ system and showed that it contains a congruently melting compound of composition Tl₂InYbS₄ (1: 1 ratio of the constituent sulfides). According to X-ray diffraction results, the compound Tl₂InYbS₄ crystallizes in tetragonal symmetry. Temperature-dependent electrical conductivity and Hall data for Tl₂InYbS₄ single crystals demonstrate that this compound is a p-type semiconductor with a band gap of 1.60 eV. The temperature variation of the carrier Hall mobility in Tl₂InYbS₄ corresponds to carrier scattering by acoustic phonons.     

Peculiarities of phase transitions in polytypes of monoclinic TlInS<Subscript>2</Subscript>

The existence of two polytypes at room temperatures, C-TlInS₂ and 2C-TlInS₂, with different monoclinic cell parameters, c and 2c, has been revealed. Significant differences in crystal lattice dynamics of these polytypes have been found. In particular, two phase transitions (PTs) have been detected for the polytype C-TlInS₂ as the temperature varies: a second-order PT from paraphase to incommensurate phase at T _i = 215 K and a first-order ferroelectric PT accompanied by a quadrupling of the parameter c at T _c = 197 K. No PT accompanied by an increase in unit cell parameter c has been found in the polytype 2C-TlInS₂, but a global temperature hysteresis characteristic of crystals with an incommensurately modulated structure has been detected at T = 180–230 K.     

Effect of Bi Doping on the Optical Properties of CdI<Subscript>2</Subscript>

The effect of Bi impurity on the optical absorption and roentgeno-, photo-, and thermoluminescence spectra of CdI₂ crystals grown by the Bridgman-Stockbarger method is studied. CdI₂ activation with BiI₃ produces a number of absorption bands related to electronic transitions of Bi³⁺. Bi produces no emission centers in CdI₂. The 550- to 560-nm luminescence of CdI₂ is due to the radiative recombination of self-trapped anion excitons. The observed changes in spectral distribution and the reduction in light yield upon CdI₂ activation with Bi³⁺ are mainly due to the reabsorption of emission from native centers by activator centers. Under x-ray excitation, CdI₂: Bi³⁺ accumulates a small light sum at shallow trap levels related to native defects.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 886–891.Original Russian Text Copyright © 2005 by Kravchuk, Novosad, Voitsekhovskaya.     

Electrical Properties of Amorphous S<Subscript>0.60</Subscript>Ge<Subscript>0.40</Subscript>:H<Subscript>x</Subscript> Films

Amorphous Si_0.60Ge_0.40:H_x films containing 1.7, 3.9, 7.1, 12.1, and 17.3 at % H are prepared by magnetron sputtering at different hydrogen partial pressures, and their electrical conductivity is measured from 80 to 350 K. The conductivity of the films exhibits Arrhenius behavior in the range 250–350 K and satisfies the relation log(σT ^1/2) ∼ T^−1/4 between 80 and 250 K. The conductivity data are used to evaluate the electron localization radius, hop distance, and activation energy of hopping conduction at 80 K; the electron mobility at the Fermi level and in the conduction band; and the 300-K activation energy of conduction.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 787–791.Original Russian Text Copyright © 2005 by Najafov, Isakov.     

Crystallization of amorphous Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> films

The crystallization kinetics of amorphous Bi₂S₃ films have been studied by kinematic electron diffraction. The results have been used to evaluate the activation energies for activation energy and crystal growth.     

Effect of Blocking and Superconducting Layer Doping on the Superconductivity and Magnetic Properties of Polycrystalline Sr<Subscript>2</Subscript>CaCu<Subscript>2</Subscript>O<Subscript>6</Subscript>

The possible difference in the properties upon doping the Sr₂CaCu₂O₆ superconducting or blocking layers with Fe and Eu respectively was investigated in this work. The homogeneous Sr_2?yEu_yCaCu₂O_6+δ and Sr₂CaCu_2?xFe_xO_6+δ (y = 0, 0.1, 0.5, x = 0, 0.05) compounds were produced by a high-pressure synthesis route. Judging by the magnetic susceptibility measurements, all samples exhibit a superconductivity transition and the Eu/Fe concentration dependencies on the diamagnetic moment and average T_c have been constructed using the experimental data. As a result, an unusual behavior of the T_c value was observed for the samples with doped Eu: a fivefold reduction in the europium concentration in the sample does not give a noticeable effect on the transition temperature value while the diamagnetic signal becomes more stronger. Complex superconducting dome was found for Eu-doped material: 0.1 ≤ y ≤ 0.5 region T_c vs. concentration data were approximated by inverted parabola-like curve with a maximum at y = 0.3. Difference in properties of the Eu and Fe-doped samples was also found in the behavior of the hysteresis loops showed the opposite orientations.     

Effect of Ni Doping at Pd Site in Nb<Subscript>2</Subscript>PdS<Subscript>5</Subscript> Superconductor

The superconducting properties of Nb₂PdS₅ superconductor have been investigated with Ni doping at Pd site All the bulk polycrystalline Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.10) samples are crystallized in singlephase monoclinic structure. The electrical resistivity and magnetic measurements of Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.15) were carried out to study the variation of superconducting critical parameters with Ni doping. Superconductivity in Nb₂PdS₅ sample completely disappears for x ≥ 0.15. We observed that the ratio of upper critical field to transition temperature decreases with increasing Ni concentration. Also, the magnetization study of Nb₂Pd_1?xNi_x S ₅ (0 = x ≤ 0.15) samples shows similar superconducting behaviour. In summary, the superconductivity in Nb₂PdS₅ sample is slightly varying with partial doping of Ni at Pd site in Nb₂PdS₅ superconductor.     

Crystallization from high-temperature solutions in the K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied general trends of crystallization from high-temperature solutions in the K₂O-P₂O₅-V₂O₅-Bi₂O₃ system at P/V = 0.5?2.0, K/(P + V) = 0.7?1.4, and Bi₂O₃ contents from 25 to 50 wt % and identified the stability regions of BiPO₄, K₃Bi₅(PO₄)₆, K₂Bi₃O(PO₄)₃, and K₃Bi₂(PO₄)_{3 ? x} (VO₄) _x (x = 0?3) solid solutions. The synthesized compounds have been characterized by X-ray powder diffraction and IR spectroscopy, and the structure of two solid solutions has been determined by single-crystal X-ray diffraction (sp. gr. C ₂/c): K₃Bi₂(PO₄)₂(VO₄), a = 13.8857(8), b = 13.5432(5), c = 6.8679(4) Å, β = 114.031(7)°; K₃Bi₂(PO₄)_1.25(VO₄)_1.75, a = 13.907(4), b = 13.615(2), c = 6.956(2) Å, β = 113.52(4)°.     

NMR-Study of the Crystalline and Amorphous CuB<Subscript>2</Subscript>O<Subscript>4</Subscript>

¹¹B nuclear magnetic resonance (NMR) spectroscopy was applied to study the crystalline, amorphous and crystallizing from an amorphous states of copper metaborate. The occurrence of trigonal BO₃ units at the expense of converting tetragonal BO₄ units was observed in amorphous CuB₂O₄. This fact explains the essential change of CuB₂O₄ magnetic properties under amorphization.     

Studies on Micro-Structure of Nano-ZrO<Subscript>2</Subscript> Films

In this paper, the micro-structure and laser damage threshold of nano-ZrO₂ thin films were investigated. High-purity nano-ZrO₂ particles as the coating materials of samples were prepared by electron beam evaporation. The crystallitic size and surfaces’ roughness of the samples were analyzed. The laser damage threshold test used a 1064 nm, 10 ns, 3 Hz Nd:YAG laser. The experimental results showed that oxygen partial pressure has an important influence on the micro-structure of nano-ZrO₂ films, and also we found that the laser damage threshold was dependent on the micro-structure.     

Effect of Heat Treatment on the Electrical Properties of Thin Yttrium-Doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> Films

Thin indium oxide films and In–Y–O films containing 0.7 to 3.6 at % Y have been grown by ionbeam sputtering of an indium target and a composite (indium + weighed amounts of yttrium) target in a mixture of argon and oxygen. The thin indium oxide films have a cubic crystal structure (sp. gr. Ia\(\bar 3\)). The incorporation of yttrium atoms into indium oxide leads to the formation of an amorphous structure in the as-grown films and an increase in their room-temperature electrical resistance by several orders of magnitude. Lowtemperature electrical resistance data indicate a change in conduction mechanism. High-temperature heat treatment of the thin In–Y–O films leads to the crystallization of their amorphous structure and an increase in their electrical resistance.     

Enhanced Critical Current Properties of MgB<Subscript>2</Subscript> Bulks by Doping Amorphous Carbon Containing Magnetic Impurity

The doping effect of amorphous carbon (C) containing magnetic impurity in MgB₂ bulk has been studied. Structural characterization by means of X-ray diffraction and the superconducting transition temperature, T _c , measurement indicate that little C effectively enters the MgB₂ structure. This should be due to the lower sintering temperature. The upper critical field, H _c2, and irreversibility field, H _irr, of samples show no systematic evolution with C doping. However, critical current density J _c (H) performance is greatly improved with C doping at 4, 15, and 28 K, respectively. Corresponding to this case, scanning electron microscope (SEM) image indicates that the grain size in samples becomes very small and grain boundary is developing roundness with the increasing of C content. This should be intimately related with the increase of magnetic impurity along with C doping. The result is discussed.      

The Effect of Substrate Temperature on Magnetic and Electrical Properties of (CeO<Subscript>2</Subscript>)<Subscript>14</Subscript>Fe<Subscript>86</Subscript> Films

(CeO₂)₁₄Fe₈₆ films were fabricated by a radio frequency magnetron sputtering method at different substrate temperature. The results reveal that the films deposited at substrate temperature lower than 773 K exhibit a strong perpendicular anisotropy, and the correlated dynamic permeability spectrum measured over the frequency range of 0.5–7 GHz shows a high resonance frequency. The study on the relation R～T shows that the resistivity of the thin film has a minimum near room temperature and tends to saturation as the temperature approaches zero, exhibiting a behavior reminiscent of Kondo scattering. However, as the substrate temperature increases to 973 K, the films possess an in-plane anisotropy and lower H _c. The resistivity exhibits a transition from metal to insulator characterized by a maximum of resistivity at 220 K.     

Crystallization kinetic studies of CaBi<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>7</Subscript> glasses by non-isothermal methods

Transparent glasses of CaBi₂B₂O₇ (CBBO) were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were, respectively, confirmed by X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC). The glass transition (T _g) and the crystallization parameters (crystallization activation energy (E _cr) and Avrami exponent (n)) were evaluated under non-isothermal conditions using DSC. The heating rate dependent glass transition and the crystallization temperatures were rationalized by Lasocka equation for the as-quenched CBBO glasses. There was a close agreement between the activation energies for the crystallization process determined by Augis and Bennet and Kissinger methods. The variation of local activation energy (E _c(x)) that was determined by Ozawa method increased with the fraction of crystallization (x). The Avrami exponent (n(x)) decreased with the increase in fraction of crystallization (x), suggesting that there was a changeover in the crystallization process from the bulk to the surface.     

Spontaneous Sn whisker formation on Ti<Subscript>2</Subscript>SnC

Spontaneous Sn whisker growth on Sn-containing substrates has resisted interpretation for several decades. In this paper, Ti₂SnC-Sn and Ti₂SnC samples were prepared and then cultivated in the same conditions. Many Sn whiskers had appeared on the ball milled Ti₂SnC-Sn sample after being stored in air for 40 days, while no whisker grew on the Ti₂SnC-Sn samples without ball milling although the cultivation time had been extended to more than half a year. Moreover, even though it was ball milled, the Sn-free Ti₂SnC sample did not grow any whisker. The whiskers formed on this system share typical features with the ones grown on Sn platings and solders, while they do not follow any of the existing growth models. A catalysis-based whisker formation model, in which the cleavage planes of Ti₂SnC grains act as heterogeneous nucleation sites, is proposed, which well interprets Sn whisker formation in the ball milled Ti₂SnC-Sn system.