Dielectric Properties of Superionic System AgBr—PbI2—Ag2O—B2O3

Dielectric properties of the system AgBr—PbI₂—Ag₂O—B₂O₃ has been studied for various temperatures and frequencies. Conductivity of the sample has also been measured and it is found that at 160 °C it attains the value 5.9 × 10^—3 (Ohms cm)^—1 and the activation energy calculated from the Arrhenius is found to be 0.16 eV.     

On the Structural and Electronic Characteristics of Titanium Sulphide (Tis1.7) Crystals

TiS_1.7 crystals have been grown by vapour transport technique employing a two-zone furnace with the temperatures of reaction and growth zone maintained at 1073 K and 973 K, respectively. We have measured the variation of electrical conductivity (s̀) with temperature (T) of TiS_1.7 single crystals. It has been found that the conductivity increases at temperatures T > 433 K, which provides convincing evidence that the TiS_1.7 crystal is a semiconductor. Another electronic characteristic of TiS_1.7 crystals observed in the present investigation is the occurrence of voltage controlled negative resistance (VCNR) at a field of 32.1 V cm^-1 to 35.7 V cm^-1. All the polytypes of TiS_1.7 were found to exhibit VCNR nearly at the same field which indicates that the VCNR is polytype independent property. The occurrence of VCNR has been explained on the intervally transfer of electrons in the conduction band.     

Thermal expansion and structural properties of (CuAlTe2)1–x(CuAlSe2)x solid solutions

Investigations of the thermal expansion of (CuAlTe₂)_1–x(CuAlSe₂)_x solid solutions in the temperature range from 100 to 800 K have been carried out for the first time. It has been demonstrated that the thermal expansion coefficient α_L grows considerably in the temperature range from 100 to 300 K, whereas the temperature dependence above 300 K is rather weak. The isotherms of composition dependence of the thermal expansion coefficient α_L for 100, 293, 500 and 800 K were constructed, and it was found that linear relations could express them. The Debye temperatures θ_D , the average mean‐square dynamic displacements , the average root‐mean‐square amplitudes of thermal vibration RMS , the anion position parameter u using S. C. Abrahams & J. L. Bernstein (u_AB ) and J. E. Jaffe & A. Zunger (u_JZ ) models were calculated. The composition dependence of microhardness H using the phenomenological theory was also calculated, and it was discovered that this dependence has a non‐linear character with a maximum of 383 kg/mm² at x=0.67. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Heat Capacity and Thermodynamic Properties of p'-Substituted p-n-Hexyloxybenzylideneaniline. I. p-n-Hexyloxybenzylideneamno-p'-Benzonitrile (HBAB)

Abstract

The heat capacity of the nematogenic liquid crystal, HBAB, has been measured between 15 K and 385 K by using an adiabatic calorimeter. The crystal-crystal phase transition has been discovered at 27 K below the crystal-nematic phase transition temperature. The transition temperatures, the enthalpies and the entropies of the three phase transitions have been determined: T ₁ = 306.98 K, ΔH _t = 5.11 kJ mol^?1, ΔS _t = 16.7 JK^?l; T _m = 334.05 K, ΔH _m = 23.77 kJ mol^?1, ΔS_m = 71.2 J K^?l mol^?1; and T _c = 375.10 K, ΔH _c = 1.75 kJ mol^?1, ΔS _c = 3.2 J K^?1 mol^?1, respectively. The thermodynamic functions of HBAB from 0 K to 385 K have been determined from the heat capacity data and the enthalpies of the transitions. Two crystal modifications, one yellow and granular form and the other white and needle-like form, have been obtained during the course of the preparation of the sample. It turned out that the yellow form was the stable crystal and the white the metastable modification. The crystal-crystal phase transition has been discussed as an onset of partial melting from the entropy consideration. In this connection the total entropies of the transitions, 91.1 J K^?1 mol^?1 has been proposed to be an important measure of melting.     

A neutron diffraction study of the phase transition of fully deuterated triglycine sulphate (ND2CD2COOD)3.D2SO4

Using neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND₂CD₂COOD)₃.D₂SO₄ is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below T_C using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range — from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H‐bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long‐range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS – no low temperature anomalies were observed in the crystal structure.     

Morphology of F8T2/PC71BM Blend Film as Investigated by Scanning Transmission X-ray Microscope (STXM)

Clarification of the morphology of bulk heterojunction (BHJ) is indispensable for true comprehension of the organic solar cells. Here, we performed scanning transmission X-ray microscopy (STXM) for a poly-(9,9-dioctylfluorene-co-bithiophene) (F8T2)/[6,6]-phenyl C71-butyric acid methyl ester (PC₇₁BM) blend film annealed at various temperatures (T_an). We found that the fullerene concentration within the polymer-rich domain decreases with T_an while the domain size (～230 nm) is essentially unchanged. We will discuss the interrelation between the film morphology and the photovoltaic performance.     

High-field conductivity in SnO2 glazes

The conductivity of glazes consisting of SnO₂ in Sb-doped BaAl-borate and BaAl-borosilicate glasses has been studied for fields in the range 10²–10⁵ V/cm at temperatures 4.2 K ? T ? 470 K. The glazes were free of mobile ions such as K, Na, Li and Pb. Conduction takes place between Sb-doped SnO₂ particles concentrated in the fused contact region between the much larger glass particles. At high temperatures (300–470 K), the conductivity is thermally activated of the Frenkel-Poole type. At 77 K, both tunneling and thermally activated conductivity appear to be present.     

Unusual Glassy Smectic-G Liquid Crystal: Heat Capacity of N-p-n-Pentyloxybenzylidene-p'-n-butylaniline between 11 and 393 K

Abstract

The heat capacities of the title compound (C₃H₁₁,O—C₆H₄,- CH=N—C₆H₄,—C₄H₉, abbreviation 5O ? 4) with a purity of 99.92 mole percent have been measured with an adiabatic-type calorimeter between 11 and 393 K. The transition temperature and the enthalpy and entropy of phase transition for stable crystal → S_G, S_G → N and N → isotropic liquid were T _c = 299.69 K/ΔH = 22.68 kJ mol^?1/ΔS = 75.70 JK^?1 mol^?1, 325.72/7.11/21.79 and 342.48/1.78/5.22, respectively. The crystal which melts at 285.5 K is a metastable modification. The S_A phase hitherto reported in between S_G and N does not exist. The glassy So state was realized by rapid cooling of the specimen from the So phase. The molar enthalpy of the glassy S_G state at 0 K was by (10.1±0.1) kJ mol^?1 higher than that of the stable crystalline state and the residual entropy of the glassy state was (9.40±0.83) JK^?1 mol^?1. The relaxational heat-capacity anomaly was observed from as low as 100 K and double glass transition phenomenon occurred around 200 K; a quite unusual phenomenon which has never been observed for the glassy states of nematic and cholesteric liquid crystals. The present results give a fair evidence that the unusual glass transition phenomenon previously found for the S_G state of 6O?4 (a homologous compound) is not exceptional at all but common to the smectic glasses; at least common to the glassy S_G states. Two possible origins responsible for the double glass transitions have been discussed.     

Structural and electrical properties of CuIn0.7Ga0.3Se2 epitaxial layers on GaAs substrates

Epitaxial layers of CuIn_0.7Ga_0.3Se₂ could be prepared by flash evaporation onto (111)A-oriented GaAs substrates in the substrate temperature range T_sub = 745 … 870 K. At T_sub = 745 … 820 K the films had the chalcopyrite structure, at T_sub = 820 … 845 K an additional pseudohexagonal phase was found. Indications to the presence of a sphalerite phase were found at high substrate temperatures. Films grown at T_sub ≦ 750 K were always n-type conducting and showed a largely pronounced impurity band conduction effect. At T_sub ≧ 860 K the films were always p-type conducting and two acceptor states with ionization energies of some 10⁻³ eV and of 125 … 140 meV were found.     

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.     

Strontium-based Mercury Cuprates with Perovskite-like Crystal Structures

Conditions of synthesis, structure, and temperatures of superconducting transitions of strontium-based mercury cuprates Hg—Sr—Me—Cu—O (Me = Ca, La, Ce, Sm, Ho) with perovskite-like crystal structure are described. The samples belong to two homological series: HgSr₂ (Ln, Ce)_n–1CunO_2n + _{2 + δ} with the Hg—O bond directed along <110> and (Hg, Cu) Sr₂Ln_n–1Cu_nO_{2n + 2 + δ} with the (Hg, Cu)—O bond directed along <100>. The variation of composition leads to rotation of the Hg—O bond along the hk0 direction and consequently to the increase of T_c from 28 K to 81 K. An anomaly of the resistivity was observed around 200 K for most of the investigated samples, independent of their content and phase composition.     

On the strengthening of Magnesium Single Crystals by Cadmium

Solid solution hardening in single crystals of magnesium containing cadmium (up to 2.4 at.%) has been investigated in the temperature range 77 K to 295 K. A strong temperature dependence of the critical resolved shear stress, τ₀, is observed below 230 K, while above this temperature τ₀ is temperature independent. At all temperatures τ₀ is found to increase linearly with c^2/3, where c is the concentration (in atomic fractions) of cadmium as solute. The concentration dependence of τ₀ can be explained by the theory of LABUSCH .     

Structural Phase Transition of an Intercalation Compound Mn1/4NbS2

Abstract

A structural phase transition of an intercalation compound Mn_1/4NbS₂ has been investigated by X-ray diffraction at high temperatures. The lattice parameter c exhibited a discontinuous change at 640K. The superlattice reflections observed below 640K disappeared suddenly above 640K. The phase transition at 640K took an aspect of the first-order phase transition. The precise structure analyses were performed at various temperatures above and below the phase-transition temperature. It was revealed that Mn atoms were arranged in disorder in the high-temperature phase, while the Mn atoms were ordered forming the 2a ₀ × 2a ₀ × c ₀ superlattice in the low-temperature phase. The Nb and S atoms around the ordered Mn atoms slightly shifted from the high-symmetry position in the low-temperature phase. The order parameters were the degree of order of the Mn atoms and the degree of displacement of the Nb and S atoms.     

Structural and Electrical Characterization of Ag3Ga5Te9 and Ag3In5Se9 Crystals

X-ray powder diffraction studies revealed that Ag₃Ga₅Te₉ and Ag₃In₅Se₉ crystallize in orthorhombic and tetragonal systems, respectively. The temperature dependent conductivity and Hall effect measurements have been carried out between 65—480 K. Ag₃Ga₅Te₉ exhibits p-type conduction with a room temperature conductivity of 4.3 × 10^—4 (Ω · cm)^—1 and mobility less than 1 cm²/V · s. Ag₃In₅Se₉ was identified to be n-type with room temperature conductivity 7.2 × 10^—5 (Ω · cm)^—1 and mobility 20 cm²/V · s. From temperature dependence of the conductivity three different impurity ionization energies were obtained for both compounds. The anomalous behavior observed in the temperature dependence of mobility was attributed to the different features of the microstructure.     

Crystal structure of a nucleoside analog: 1-(R)-[6-(R)-hydroxymethyl-1,4-dioxan-2-yl] uracil

The title compound (C₉H₁₂N₂O₅,M _r =228.2) crystallizes in the trigonal space groupP3₁,21 witha=b=9.438(3) andc=19.775(3) Å,V=1525.5 ų,D _x =1.490 gm cm^–3,Z=6,=0.12 mm^–1,F(000)=720.0,T=293 K. The structure was solved by direct methods and refined by full-matrix least-squares calculations to anR value of 0.044 on 843 unique observed reflections. The dioxane ring adopts a chair conformation. The crystal structure is stabilized by N-HO hydrogen bonds and C-HO close contacts.     

Thermoelectric Power of Polycrystalline Sb2Te3 Films

Polycrystalline stochiometric films of Sb₂Te₃ with different thickness were prepared on glass substrates by a flash evaporation technique at constant substrate temperature of 423 K. The thermoelectric power of these films was determined by measuring integrally the developed thermo — e.m.f. at different temperature differences between the hot and cold ends. The thermoelectric power of Sb₂Te₃ films was determined as a function of the temperature and thickness of the films. It was found that the Fermi level becomes pinned at higher temperatures. The values of γ, E₀, and A parameters were determined as functions of the thickness of the films. The dependence of the thermoelectric power on the reciprocal thickness of the films was explained on the basis of the grain size effect.     

EPR and pulsed NMR study of (NH4)2ZnBr4:Mn2+

The EPR and pulsed NMR measurements of (NH₄)₂ZnBr₄:Mn²⁺ have been carried out in the temperature range 110–473 K and 83–284 K, respectively. EPR spectra from three different paramagnetic entities have been observed. Intensity changes of certain lines in the EPR spectrum observed at ≈ 430 K indicate the occurrence of a phase transition. Another phase transition at ≈ 235 K is indicated as a change of slope in the T₁ vs 1/T curve.     

Interfacial stability and grain diameter of the metal phase of directionally solidified Al-Si-type eutectics

The morphology of the solid-liquid interface and the metal phase grain diameter of Al—Si-type eutectics (Al—Si, Ag—Si, Ag—Ge, Zn—Ge) were investigated in the range of a growth rate R = 0.2 … 20 mm/h and of a temperature gradient at the solid-liquid interface G = 2 … 25 K/mm. Three types of interfacial morphologies depending on the G/R ratios were found out. The G/R ratio of the transition from a planar to a nonplanar solid-liquid interface corresponds to the critical G/R|_c ratio, which can be calculated by the criterion of the constitutional undercooling. The grain diameter of the metal phase depends on growth parameters as follows: d_K ∼ R^—rG^—g with r = 0.33 … 0.43 and g = −0.37 … 0.03.     

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)     

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.