Unusual effect of tellurium doping on the electrical-properties of bulk amorphous selenium

Abstract is not available.

Analysis Of Curved Laminated Beams Of Bimodulus Composite-Materials

Composite materials exhibiting different moduli in tension and in compression, commonly called as bimodular composites are being used in many engineering fields. A finite element analysis is carried out for small deflection static behavior of laminated curved beams of bi modulus materials for both solid and hollow circular cross-sections using an iterative procedure. The finite element has 16 d.o.f. and uses the displacement field in terms of first order Hermite in terpolation polynomials. The neutral surface, i.e. the locus of points having zero axial strain is found to vary drastically depending on the loading, lay up schemes and radius of curvature. As il lustrations, plots of the cross-sections of the ruled neutral-surface are presented for some of the investigated cases. Using this element a few problems of curved laminated beams of bimodulus materials are solved for both solid and hollow circular cross-sections.

Bismuth-doped amorphous-germanium sulfidesemiconductors

A study of the effect of bismuth dopant on the electronic transport properties of the amorphous semiconductors Ge20S80-xBix under high pressure (up to 140 kbar) has been carried out down to liquid-nitrogen temperature. The experiments reveal that the electronic conduction is strongly composition dependent and is thermally activated with a single activation energy at all pressures and for all compositions. A remarkable resemblance between the electronic conduction process, x-ray diffraction studies, and differential thermal analysis results is revealed. It is proposed that the n-type conduction in germanium chalcogenides doped with a large Bi concentration is due to the effect of Bi dopants on the positive correlation energy defects present in germanium chalcogenides. The impurity-induced chemical modification of the network creates a favorable environment for such an interaction.

Pressure-Induced transitions in amorphous TlxSe100-x alloys

The electrical resistivity of bulk semiconducting amorphous TlxSe100-x alloys with 0 ≤ x ≤ 25 has been investigated up to a pressure of 14 GPa and down to liquidnitrogen temperature by use of a Bridgman anvil device. All the glasses undergo a discontinuous pressure-induced semiconducting-to-metal transition. X-ray diffraction studies on the pressure-recovered samples show that the high-pressure phase is the crystalline phase. The pressure-induced crystalline products are identified to be a mixture of Se having a hexagonal structure with a = 4·37 Aring and c = 4·95 Aring and TlSe having a tetragonal structure with a = 8·0 Aring and c = 7·0 Aring

Phase relations and dielectric properties of BaTi03 ceramics heavily substituted with neodymium

Investigations on the phase relations and dielectric properties of (1 -x)BaTiO3 + xNd2/3TiO 3 (BNT) ceramics sintered in air below 1650 K have been carried out. X-ray powder diffraction studies indicate apparent phase singularity for compositions with x < 0.3. Nd2Ti207 is detected at higher neodymium concentrations. The unit cell parameter changes continuously with neodymium content, and BaTiO3 is completely cubic at room temperature with x -- 0.0525, whereas electron diffraction studies indicate that the air-sintered BNT ceramics with x > 0.08 contain additional phases that are partly amorphous even to an electron beam. SEM observations reveal that BaTiO3 grains are mostly covered by a molten intergranular phase, and show the presence of randomly distributed Nd2Ti207 grains. Energy dispersive X-ray analysis shows the Ba-Nd-Ti ternary composition of the intergranular phase. Differential thermal analysis studies support the formation of a partial melt involving dissolution-precipitation of boundary layers of BaTiO3 grains. These complex phase relations are accounted for in terms of the phase instability of BaTiO3 with large cation-vacancy concentration as a result of heavy Nd 3+ substitution. The absence of structural intergrowth in (1 - x)BaTiO3 + xNd2/3TiO3 under oxidative conditions leads to a separation of phases wherein the new phases undergo melting and remain X-ray amorphous. BNT ceramics with 0.1 < x < 0.3 have ~eff >~ 104 with tan 6 < 0.1 and nearly flat temperature capacitance characteristics. The grain-size dependence of ee,, variations of ~eff and tan 6 with the measuring frequency, the non-ohmic resistivities, and the non-linear leakage currents at higher field-strengths which are accompanied by the decrease in eeff and rise in tan 3, are explained on the basis of an intergranular (internal boundary layer) dielectric characteristic of these ceramics.

Studies in Nonlinear Optical Materials: Structure of 3-Menthyl 2-[Bis(dimethylarnino)methylene]-3-oxobutyrate Hemihydrate

C 19Ha4N203.~xH 2 O, Mr= 347.5, monoclinic, C2, a = 15.473 (3), b = 6.963 (2), c = 20.708 (4) ]1, //=108.2(2) ° , V=2119(2)A 3, Z=4, Ox= 1.089 Mg m -3, ,~(Cu Ktx) = 1.5418 ]1, p = 0.523 mm -~, F(000) = 760.0, T= 293 K, R = 0.068 for 1967 unique reflections. The C=C bond length is 1-447 (6)]1, significantly longer than in ethylene, 1.336 (2)]1. The crystal structure is stabilized by O-H...O hydrogen bonding. Explanation for the observed low second-harmonic-generation efficiency (0.5 times that of urea) is provided.

Dielectric Relaxation in SrLiB9O15 Glasses

Transparent SrLiB9O15 (SLBO) glasses were fabricated via the conventional melt-quenching technique. X-ray powder diffraction and differential thermal analysis carried out on the as-quenched samples confirmed their amorphous and glassy nature, respectively. The dielectric constants in the 100 Hz to 10 MHz frequency range for SLBO glasses were measured as a function of temperature (300–1023 K). The dielectric relaxation characteristics were rationalized using the electric modulus formalism. The electrode polarization effect was subtracted from the low-frequency dielectric constant to have an insight into the intrinsic dielectric behavior of SLBO glasses. The imaginary part of electric modulus spectra was modeled using an approximate solution of Kohlrausch–Williams–Watts relation. The dielectric constant for the as-quenched glass increased with increasing temperature and exhibited anomalies in the vicinity of the glass transition and crystallization temperatures.

Crystallization behaviour of Metglas 2826 MB (Fe40Ni38Mo4B18)

Differential scanning calorimetry, x-ray diffraction and transmission electron microscopy have been employed to determine the thermal stability and identify the crystalline phases on devitrification of Metglas 2826 MB. The glass crystallizes intoγ-FeNiMo and fcc (FeNi)23B6 with activation energies of 270 and 375 kJ mol−1 respectively. The reactions are primary and polymorphic in nature. The influence of Mo towards crystallization of Fe40Ni40B20 has been to enhance the formation of the fcc (FeNi)23B6 phase in preference to orthorhombic (FeNi)3B phase and to raise the thermal stability of the amorphous state.

Studies in Nonlinear Optical Materials: Structure of Methyl 2-(4-Ethyl-5-methyl- 2-thioxo-2,3-dihydro-l,3-thiazol- 3-yl) propionate

CIoH15NO282, Mr=245"0, orthorhombic, P21212 ~, a = 6.639 (2), b = 8.205 (2), c = 22.528(6)A, V= I227.2(6)A 3, z=4, Dm= 1.315, Dx= 1.326gem -3, MoKa, 2=0.7107A, 12= 3.63 cm -1, F(000) = 520, T= 293 K, R = 0.037 for 1115 significant reflections. The second-harmonicgeneration (SHG) efficiency of this compound is only 1/10th of the urea standard. The observed low second-order nonlinear response may be attributed to the unfavourable packing of the molecules in the crystal lattice.

Unusual stress and grain size dependence for creep in nanocrystalline materials

Analyses of diffusion and dislocation creep in nanocrystals needs to take into account the generally utilized low temperatures, high stresses and very fine grain sizes. In nanocrystals, diffusion creep may be associated with a nonlinear stress dependence and dislocation creep may involve a grain size dependence.

Chemical bond approach to determining conductivity band gaps in amorphous chalcogenides and pnictides

The minimum energy required for the formation of conjugate pair of charged defects is found to be approximately equal to the experimental activation energy for d.c. conductivity in a number of amorphous chalcoganides and pnictides. This observation implies that the defect pair formation energy represents an intrinsic gap for transport in amorphous chalcogenides.

Influence of seeding on crystallization behaviour of BaNaB9O15 glasses

Transparent BaNaB9O15 (BNBO) glasses were fabricated via the conventional melt-quenching technique. X-ray powder diffraction (XRD) followed by differential scanning calorimetric (DSC) studies confirmed the amorphous and glassy nature of the as-quenched samples, respectively. The effect of seeding on the crystallization of BNBO glasses was studied by non-isothermal DSC method and was modeled using the Johnson-Mehl-Avrami and Ozawa equations. The activation energy for seeded glasses decreased with the increase in fraction of crystallization. The values for the onset of crystallization and Avrami exponent were found to be lower for seeded samples which were associated with the heterogeneous nucleation and epitaxial processes.

On the structural features of doped amorphous chalcogenide semiconductors

A study of Bi-doped amorphous (Ge42S58)100−xBix and Ge20S80−xBix has been carried out by differential thermal analysis (DTA) and X-ray diffraction methods so as to elucidate the impurity-induced modifications in the semiconductors. Thermal analysis reveals the presence of complex structural units in the modified material. An interesting feature of this study is the existence of a double glass transition in Ge20S80−xBix, which is reported for the first time in this system.

Dipole ordering in dilute solutions of ferroelectrics in antiferroelectric materials

The coefficients of thermal expansion reported by Worlton et al. [6] in the case of zircon are given in Table II along with the present data. Although Oql > or• in both cases, the anisotropy is more marked in the case of DyV04. From Table II, it is clear that the coefficient of volume expansion (,6) is almost the same for both compounds.

Role of free volume in strain softening of as-cast and annealed bulk metallic glass

Plasticity in amorphous alloys is associated with strain softening, induced by the creation of additional free volume during deformation. In this paper, the role of free volume, which was a priori in the material, on work softening was investigated. For this, an as-cast Zr-based bulk metallic glass (BMG) was systematically annealed below its glass transition temperature, so as to reduce the free volume content. The bonded-interface indentation technique is used to generate extensively deformed and well defined plastic zones. Nanoindentation was utilized to estimate the hardness of the deformed as well as undeformed regions. The results show that the structural relaxation annealing enhances the hardness and that both the subsurface shear band number density and the plastic zone size decrease with annealing time. The serrations in the nanoindentation load-displacement curves become smoother with structural relaxation. Regardless of the annealing condition, the nanohardness of the deformed regions is similar to 12-15% lower, implying that the prior free volume only changes the yield stress (or hardness) but not the relative flow stress (or the extent of strain softening). Statistical distributions of the nanohardness obtained from deformed and undeformed regions have no overlap, suggesting that shear band number density has no influence on the plastic characteristics of the deformed region.