Dielectric properties of electron irradiated PbZrO3 thin films

The present paper deals with the study of the effects of electron (8 MeV) irradiation on the dielectric and ferroelectric properties of PbZrO3 thin films grown by sol-gel technique. The films were (0.62 mu m thick) subjected to electron irradiation using Microtron accelerator (delivered dose 80, 100, 120 kGy). The films were well crystallized prior to and after electron irradiation. However, local amorphization was observed after irradiation. There is an appreciable change in the dielectric constant after irradiation with different delivered doses. The dielectric loss showed significant frequency dispersion for both unirradiated and electron irradiated films. T (c) was found to shift towards higher temperature with increasing delivered dose. The effect of radiation induced increase of E >'(T) is related to an internal bias field, which is caused by radiation induced charges trapped at grain boundaries. The double butterfly loop is retained even after electron irradiation to the different delivered doses. The broader hysteresis loop seems to be related to radiation induced charges causing an enhanced space charge polarization. Radiation-induced oxygen vacancies do not change the general shape of the AFE hysteresis loop but they increase P (s) of the hysteresis at the electric field forced AFE to FE phase transition. We attribute the changes in the dielectric properties to the structural defects such as oxygen vacancies and radiation induced charges. The shift in T (C), increase in dielectric constant, broader hysteresis loop, and increase in P (r) can be related to radiation induced charges causing space charge polarization. Double butterfly and hysteresis loops were retained indicative of AFE nature of the films.

Anisotropic properties of the layered semiconductor in Te

Anisotropic properties of the Bridgman grown layered semiconductor p-InTe were studied by analyzing the temperature dependence of electrical conductivity and Hall mobility parallel and perpendicular to the layer planes. The mobilities were μamalgamation or coproduct = 50–60 cm2V−1 sec−1 and μperpendicular = 10–15 cm2V−1sec−1 and varied as μ ≈ Tn where n = 1.43 due to impurity scattering. Pressure-induced semiconductor-metal transition occurred at about 50 kbar. The pressure coefficient of resistance was 3 times larger in the direction perpendicular to the layer plane due to the difference between inter and intra-planar bonding.

Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm(-2). A single-crystal silicon 311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.

Nonlinear fracture properties of concrete-concrete interfaces

The fracture properties of different concrete-concrete interfaces are determined using the Bazant's size effect model. The size effect on fracture properties are analyzed using the boundary effect model proposed by Wittmann and his co-workers. The interface properties at micro-level are analyzed through depth sensing micro-indentation and scanning electron microscopy. Geometrically similar beam specimens of different sizes having a transverse interface between two different strengths of concrete are tested under three-point bending in a closed loop servo-controlled machine with crack mouth opening displacement control. The fracture properties such as, fracture energy (G(f)), length of process zone (c(f)), brittleness number (beta), critical mode I stress intensity factor (K-ic), critical crack tip opening displacement CTODc (delta(c)), transitional ligament length to free boundary (a(j)), crack growth resistance curve and micro-hardness are determined. It is seen that the above fracture properties decrease as the difference between the compressive strength of concrete on either side of the interface increases. (C) 2010 Elsevier Ltd. All rights reserved.

Thermodynamic properties of RhO2

A solid-state electrochemical cell, with yttria-stabilized zirconia as the electrolyte and pure O-2 gas at 0.1 MPa as the reference electrode, has been used to measure the oxygen chemical potential corresponding to the equilibrium between beta-Rh2O3 and RhO2 in the temperature range from 850 to 1050K. Using standard Gibbs energy of formation of beta-Rh2O3 available in the literature and the measured oxygen potential, the standard Gibbs free energy of formation of RhO2 is derived as a function of temperature: Delta G(f)degrees(RhO2)(+/- 71)/J mol(-1) = 238,418 + 179.89T Using an estimated value of Delta C-p degrees; for the formation reaction of RhO2 from its elements, the standard enthalpy of formation, standard entropy and isobaric heat capacity of RhO2 at 298.15 K are evaluated: Delta H-f degrees (298.15 K)(+/- 164)/kJ mol(-1) = -244.94, S degrees (298.15 K)(+/- 3.00)/J mol(-1) K-1 = 45.11 and C-p degrees(298.15 K)(+/- 2.6)1mol(-1) K-1 =64.28. (C) 2010 Elsevier B.V. All rights reserved.

Thermoelectric properties of electrostatically tunable antidot lattices

We report on the fabrication and characterization of a device which allows the formation of an antidot lattice (ADL) using only electrostatic gating. The antidot potential and Fermi energy of the system can be tuned independently. Well defined commensurability features in magnetoresistance as well as magnetothermopower are observed. We show that the thermopower can be used to efficiently map out the potential landscape of the ADL. (C) 2010 American Institute of Physics. doi: 10.1063/1.3493268]

Effect of pressure on the dielectric properties of DTAAP

Effect of pressure on the dielectric properties of ferroelectric DTAAP has been carried out upto about 4 Kbars. The dTc/dP value was found to be -1.65°C/Kbar. It was noted that the value of dTc/dP is 1.63 times smaller in DTAAP as compared to TAAP, where as Tc itself is 1.13 times larger.

Thermodynamic properties of the system toluene — 1, 1, 1-trichloroethane

Data on molar excess enthalpy on mixing at 298.15 K and 308.15 K, vapor-liquid equilibrium, latent heats of vaporization at 91.444 kPa and vapor pressures for the system toluene – 1, 1, 1-trichloroethane are presented. A simple adiabatic calorimeter designed for molar excess enthalpy measurements is described, tested and used. On présente, dans le cas du système toluène – 1, 1, 1-trichloréthane, des résultats relatifs aux grandeurs suivantes: a) enthalpie molaire d'excès à 298.15 K et 308.15 K; b) équilibre liquid-vapeur; c) chaleurs latentes de vaporisation à une pression absolue de 91.444 kP; d) pressions de vapeur. On décrit un calorimètre adiabatique simple, conçu pour mesurer l'enthalpie molaire d'excès, dont on a fait l'essai.

Thermodynamic properties of the systems benzene-chloroethanes

This paper presents the experimental data on vapor-liquid equilibrium and heats of mixing of mixtures of benzene with 1, e-dichloroethane, 1, l, 1 -trichloroethane, and lt1,2,2-tetrachloroethane.A literature survey revealed that the heats of mixing of benzene-l,2-dichloroethane have been studied and Table I shows the extent of study on this system.

Effect of amino acid substitutions at the subunit interface on the stabiity and aggregation properties of a dimeric protein: role of Arg 178 and Arg 218 at the dimer interface of thymidylate synthase

The significance of two interface arginine residues on the structural integrity of an obligatory dimeric enzyme thymidylate synthase (TS) from Lactobacillus casei was investigated by thermal and chemical denaturation. While the R178F mutant showed apparent stability to thermal denaturation by its decreased tendency to aggregate, the Tm of the R218K mutant was lowered by 5 degrees C. Equilibrium denaturation studies in guanidinium chloride (GdmCl) and urea indicate that in both the mutants, replacement of Arg residues results in more labile quaternary and tertiary interactions. Circular dichroism studies in aqueous buffer suggest that the protein interior in R218K may be less well-packed as compared to the wild type protein. The results emphasize that quaternary interactions may influence the stability of the tertiary fold of TS. The amino acid replacements also lead to notable alteration in the ability of the unfolding intermediate of TS to aggregate. The aggregated state of partially unfolded intermediate in the R178F mutant is stable over a narrower range of denaturant concentrations. In contrast, there is an exaggerated tendency on the part of R218K to aggregate in intermediate concentrations of the denaturant. The 3 A crystal structure of the R178F mutant reveals no major structural change as a consequence of amino acid substitution. The results may be rationalized in terms of mutational effects on both the folded and unfolded state of the protein. Site specific amino acid substitutions are useful in identifying specific regions of TS involved in association of non-native protein structures.

Conformational properties of hybrid peptides containing alpha and omega-amino acids

This review briefly surveys the conformational properties of guest omega-amino acid residues when incorporated into host alpha-peptide sequences. The results presented focus primarily on the use of beta- and gamma-residues in alphaomega sequences. The insertion of additional methylene groups into peptide backbones enhances the range of accessible conformations, introducing additional torsional variables. A nomenclature system, which permits ready comparisons between alpha-peptides and hybrid sequences, is defined. Crystal structure determination of hybrid peptides, which adopt helical and beta-hairpin conformations permits the characterization of backbone conformational parameters for beta- and gamma-residues inserted into regular alpha-polypeptide structures. Substituted beta- and gamma-residues are more limited in the range of accessible conformation than their unsubstituted counterparts. The achiral beta,beta-disubstituted gamma-amino acid, gabapentin, is an example of a stereochemically constrained residue in which the torsion angles about the C-beta-C-gamma (theta(1)) and C-alpha-C-beta (theta(2)) bonds are restricted to the gauche conformation. Hybrid sequences permit the design of novel hydrogen bonded rings in peptide structures.