Interrelationship between Interphase Boundaries and Phase Contents near the Critical Compositions of Lead-Free Ferroelectric (Na0.5Bi0.5)TiO3-BaTiO3

Heterophase structures in lead-free perovskite-type ferroelectric solid solutions of (1 - z)(Na0.5Bi0.5)TiO3 - zBaTiO(3) are analysed for a few critical compositions near the morphotropic phase boundary (z = 0.05-0.07). Examples of the phase coexistence and elastic matching of the phases from different symmetry groups are considered to find optimum volume fractions of specific domain types and coexisting phases at the complete stress relief in two-phase samples. Some interrelations between these volume fractions are described using variants of the domain arrangement at changes in the composition and unit-cell parameters. The evaluated room-temperature volume fractions of the ferroelectric monoclinic (Cm symmetry) and tetragonal (P4mm symmetry) phases near the morphotropic phase boundary are in agreement with experimental data.

Crystal chemistry and photomechanical behavior of 3,4-dimethoxycinnamic acid: correlation between maximum yield in the solid-state topochemical reaction and cooperative molecular motion

A new monoclinic polymorph, form II (P2(1)/c, Z = 4), has been isolated for 3,4-dimethoxycinnamic acid (DMCA). Its solid-state 2 + 2 photoreaction to the corresponding alpha-truxillic acid is different from that of the first polymorph, the triclinic form I (P (1) over bar, Z = 4) that was reported in 1984. The crystal structures of the two forms are rather different. The two polymorphs also exhibit different photomechanical properties. Form I exhibits photosalient behavior but this effect is absent in form II. These properties can be explained on the basis of the crystal packing in the two forms. The nanoindentation technique is used to shed further insights into these structure-property relationships. A faster photoreaction in form I and a higher yield in form II are rationalized on the basis of the mechanical properties of the individual crystal forms. It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction. Form I of DMCA is more plastic and seems to react under Kaupp-type conditions with maximum molecular movements. Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

Mechanism of improvement in the strength and volume change behavior of lime stabilized soil

An attempt has been made to bring out the influence on strength and volume change behavior of fabric changes and new cementitious compound formation in a soil upon addition of various lime contents and with curing periods. The effects of changes in fabric of treatment with various lime contents (0, 2,4 and 6%) and with curing periods (0, 7, 14 and 28 days) have been evaluated by one-dimensional consolidation tests, in terms of void ratio changes and compressibility. The strength of soil treated with different lime contents with curing periods up to 28 days, and with the optimum lime content of 6% up to one year has been determined by unconfined compression tests. Comparison of effects of lime on the strength and volume change behavior of the soil brings out that the formation of flocculated fabric and cation exchange significantly reduces the compressibility of soil but marginally increases the strength. Cementation of soil particles and filling with cementitious compounds of the voids of flocculated fabric in the soil marginally reduces the compressibility but significantly increases the strength. Thus, the mechanism of volume change behavior of soil treated with lower lime content at short curing periods is distinctly different from that of the soil treated with optimum lime content at longer curing periods. This is consistent with the increase in the permeability caused by the addition from 2 to 4% lime and the decrease following the addition of 6% lime. Changes consistent with mechanical behavior have been determined by scanning electron microscope, X-ray diffraction and thermal analyses, energy dispersive X-ray spectrometer and pH value in microstructure, mineralogy, chemical composition and alkalinity, respectively. (C) 2015 Published by Elsevier B.V.

Temperature dependent compressive behavior of graphene mediated three-dimensional cellular assembly

Mechanical behavior of three-dimensional cellular assembly of graphene foam (GF) presented temperature dependent characteristics evaluated at both low temperature and room temperature conditions. Cellular structure of GF comprised of polydimethyl siloxane polymer as a flexible supporting material demonstrated 94% enhancement in the storage modulus as compared to polymer foam alone. Evaluation of frequency dependence revealed an increase in both storage modulus and tan delta with the increase in frequency. Moreover, strain rate independent highly reversible behavior is measured up to several compression cycles at larger strains. It is elucidated that the interaction between graphene and polymer plays a crucial role in thermo-mechanical stability of the cellular structure. (C) 2015 Elsevier Ltd. All rights reserved.

Volume change behavior of lime treated gypseous soil - influence of mineralogy and microstructure

Series of oedometer tests and micro-analytical studies (XRD, SEM and EDAX) have been carried out to investigate the influence of varying gypsum content on swell, compressibility and permeability of lime treated montmorillonitic soil after curing for different period. Immediate swell is observed on inundation of compacted samples with water and continuously increased with gypsum content. However, changes in swell are found to be marginal with curing. This is attributed to the formation and growth of ettringite crystals by ionic reactions of aluminum calcium-sulfate in the presence of water which is confirmed through detailed micro-analysis. The higher swell in uncured specimens and gradual reduction in swell with increase in curing periods are due to relative dominance of formation and growth of ettringite and cementitious compounds, respectively. Also, the ionic reaction products are found to bear a significant influence on the compressibility and permeability behavior. (C) 2015 Elsevier B.V. All rights reserved.

Synthesis of Hollow Nanotubes of Zn2SiO4 or SiO2: Mechanistic Understanding and Uranium Adsorption Behavior

We report a facile synthesis of Zn2SiO4 nanotubes using a two-step process consisting of a wet-chemical synthesis of core-shell ZnO@SiO2 nanorods followed by thermal annealing. While annealing in air leads to the formation of hollow Zn2SiO4, annealing under reducing atmosphere leads to the formation of SiO2 nanotubes. We rationalize the formation of the silicate phase at temperatures much lower than the temperatures reported in the literature based on the porous nature of the silica shell on the ZnO nanorods. We present results from in situ transmission electron microscopy experiments to clearly show void nucleation at the interface between ZnO and the silica shell and the growth of the silicate phase by the Kirkendall effect. The porous nature of the silica shell is also responsible for the etching of the ZnO leading to the formation of silica nanotubes under reducing conditions. Both the hollow silica and silicate nanotubes exhibit good uranium sorption at different ranges of pH making them possible candidates for nuclear waste management.

Thermal, magnetic and electrical properties of Tb1-xDyxMnO3 multiferroics

A series of multiferroic materials with the compositional formula, Tb1 - xDyxMnO3 (where x=0, 0.1, 0.2, 0.3 and 0.4) were prepared by the sol gel method. After characterizing the samples structurally, a systematic investigation of specific heat, magnetization and dielectric properties over the temperature range, 4-300 K, was undertaken. Based on these studies, it was found that all the samples exhibit a transition at 40 K and the observed behavior may be attributed to the ordering of Mn3+ ions. Further, all the five samples are found to exhibit a ferroelectric transition in the temperature range 20-24 K. Finally, yet another transition was also exhibited by all the samples at temperatures below 10 K and is attributed to the antiferromagnetic (AF) ordering of rare-earth ionic moments. The magnetic entropy of all the samples was also computed with the help of their heat capacity data. (C) 2015 Elsevier B.V. All rights reserved.

Role of Si modification on the compressive flow behavior of Al-Si based alloy

The flow characteristics of a near-eutectic heat-treated Al-Si based cast alloy have been examined in compression at strain rates varying from 3 x 10(-4) to 10(2) s(-1) and at three different temperatures, i.e., room temperature (RT), 100 degrees C and 200 degrees C. The dependence of flow behavior on modification is examined by testing the alloy in both the unmodified and modified conditions. Modification has strong influence on strain rate sensitivity (SRS), strength and work hardening behavior of the alloy. The strength of the alloy is found to increase with increase in strain rate for both the conditions. The increase is more rapid above the strain rate of 10(-1) s(-1) for the unmodified alloy at all the temperatures. This rapid increase is observed at 1 s(-1) at RT and 100 degrees C, and at 10(-2) s(-1) at 200 degrees C for the modified alloy. The thermally dependent process of the Al matrix is rate controlling in the unmodified alloy. On the other hand, the thermally dependent process of both Al matrix and Si particles are rate controlling, which is responsible for the higher strain rate sensitivity (SRS) in the modified alloy. The unmodified alloy exhibits a larger work hardening rate than the modified alloy during the initial stages of straining due to fiber loading of unmodified Si particles. However, the hardening rate decreases sharply at higher strains for the unmodified alloy due to a higher rate of Si particle fracture. Thermal softening is observed for both alloys at 200 degrees C due to precipitate coarsening, which leads to a decrease in SRS at higher temperatures. Stress simulations by microstructure based finite element method support the experimentally observed particle and matrix fracture behavior. Negative SRS and serrated flow are observed at lower strain rate regime (3 x 10(-4) to 10(-2) s(-1)) at RT and 100 degrees C, in both alloys. The critical onset strain is found to be lower and the magnitude of serration is found to be higher for the modified alloy, which suggests that, in addition to dynamic strain aging, Si particle size and morphology also play a role in serrated flow. (C) 2015 Elsevier Inc All rights reserved.

Size Effects on Strength in the Transition from Single-to-Polycrystalline Behavior

During the transition from single crystalline to polycrystalline behavior, the available data show the strength increasing or decreasing as the number of grains in a cross section is reduced. Tensile experiments were conducted on polycrystalline Ni with grain sizes (d) between 16 and 140 mu m and varying specimen thickness (t), covering a range of lambda (-t/d) between similar to 0.5 and 20. With a decrease in lambda, the data revealed a consistent trend of strength being independent of lambda at large lambda, an increase in strength, and then a decrease in strength. Microstructural studies revealed that lower constraints enabled easier rotation of the surface grains and texture evolution, independent of the specimen thickness. In specimen interiors, there was a greater ease of rotation in thinner samples. Measurements of misorientation deviations within grains revealed important differences in the specimen interiors. A simple model is developed taking into account the additional geometrically necessary dislocations due to variations in the behavior of surface and interior grains, leading to additional strengthening. A suitable combination of this strengthening and surface weakening can give rise to wide range of possibilities with a decrease in lambda, including weakening, strengthening, and strengthening and weakening.

Origin of giant dielectric constant and conductivity behavior in Zn1-xMgxO (0 <= x <= 0.1) ceramics

Zn1-xMgxO ( <= x <= 0.1) ceramics were fabricated by conventional solid-state reaction of co-precipitated zinc oxide and magnesium hydroxide nanoparticles. Structural and morphological properties of the fabricated ceramics were studied using X-ray diffraction and scanning electron microscopic analysis. The dielectric measurements of the ceramics were carried out as a function of frequency and temperature respectively. Interestingly, Mg doped ZnO (MZO) samples exhibited colossal dielectric response (similar to 1 x 10(4) at 1 kHz) with Debye like relaxation. The detailed dielectric studies and thermal analyses showed that the unusual dielectric response of the samples were originated from the defected grain and grain boundary (GB) conductivity relaxations due to the absorbed atmospheric water vapor (moisture). Impedance spectroscopy was employed to determine the defected grain and GB resistances, capacitances and which supported Maxwell-Wagner type relaxation phenomena. (C) 2015 Elsevier Ltd. All rights reserved.

Electric field and temperature dependence of the local structural disorder in the lead-free ferroelectric Na0.5Bi0.5TiO3: An EXAFS study

The complex nature of the structural disorder in the lead-free ferroelectric Na1/2Bi1/2TiO3 has a profound impact on the perceived global structure and polar properties. In this paper, we have investigated the effect of electric field and temperature on the local structure around theBi and Ti atoms using extended x-ray absorption fine structure. Detailed analysis revealed that poling brings about a noticeable change in the bond distances associated with the Bi-coordination sphere, whereas the Ti coordination remains unaffected. We also observed discontinuity in the Bi-O bond lengths across the depolarization temperature of the poled specimen. These results establish that the disappearance of the monoclinic-like (Cc) global distortion, along with the drastic suppression of the short-ranged in-phase octahedral tilt after poling B. N. Rao et al., Phys. Rev. B 88, 224103 (2013)] is a result of the readjustment of theA-O bonds by the electric field, so as to be in conformity with the rhombohedral R3c structure.

Ferroelectric origin in one-dimensional undoped ZnO towards high electromechanical response

Ferroelectricity in ZnO is an unlikely physical phenomenon. Here, we show ferroelectricity in undoped 001] ZnO nanorods due to zinc vacancies. Generation of ferroelectricity in a ZnO nanorod effectively increases its piezoelectricity and turns the ZnO nanorod into an ultrahigh-piezoelectric material. Here using piezoelectric force microscopy (PFM), it is observed that increasing the frequency of the AC excitation electric field decreases the effective d(33). Subsequently, the existence of a reversible permanent electric dipole is also found from the P-E hysteresis loop of the ZnO nanorods. Under a high resolution transmission electron microscope (HRTEM), we observe a zinc blende stacking in the wurtzite stacking of a single nanorod along the growth axis. The zinc blende nature of this defect is also supported by the X-ray diffraction (XRD) and Raman spectra. The presence of zinc vacancies in this basal stacking fault modulates p-d hybridization of the ZnO nanorod and produces a magnetic moment through the adjacent oxygen ions. This in turn induces a reversible electric dipole in the non-centrosymmetric nanostructure and is responsible for the ultrahigh-piezoelectric response in these undoped ZnO nanorods. We reveal that this defect engineered ZnO can be considered to be in the competitive class of ultrahigh-piezoelectric nanomaterials for energy harvesting and electromechanical device fabrication.

Behavior of Brick-Mortar Interfaces in FRP-Strengthened Masonry Assemblages under Normal Loading and Shear Loading

Determination of shear strength of brick-mortar bed joint is critical to overcome the sliding-shear or joint-shear failure in masonry. In the recent past, researchers have attempted to enhance the shear strength and deformation capacity of brick-mortar bed joints by gluing fiber-reinforced polymer (FRP) composite across the bed joint. FRP composites offer several advantages like high strength-to-weight ratio, and ease of application in terms of labor, time, and reduced curing period. Furthermore, FRP composites are desirable for strengthening old masonry buildings having heritage value because of its minimal interference with the existing architecture. A majority of earlier studies on shear strengthening of masonry available in the literature adopted masonry having the ratio of modulus of elasticity of masonry unit (Emu) to modulus of elasticity of mortar (Em) greater than one. Information related to shear behavior of FRP glued masonry composed of masonry units having Young's modulus lower than mortar is limited. Hence the present study is focused on characterizing the interfacial behavior of brick-mortar bed joint of masonry assemblages composed of solid burnt clay bricks and cement-sand mortar (E-mu/E-m ratio less than one), strengthened with FRP composites. Masonry triplets and prisms with bed joint inclined to loading axis (0 degrees, 30 degrees, 45 degrees, 60 degrees and 90 degrees) are employed in this study. Glass and carbon FRP composites composed of bidirectional FRP fabric with equal density in both directions are used for strengthening masonry. Masonry triplets are glued with glass and carbon FRP composites in two configurations: (1) both faces of the triplet specimens are fully glued with GFRP composites; and (2) both faces of the triplet specimens are glued with GFRP and CFRP composites in strip form. The performance of masonry assemblages strengthened with FRP composites is assessed in terms of gain in shear strength, shear displacement, and postpeak behavior for various configurations and types of FRP composites considered. A semianalytical model is proposed for the prediction of shear strength of masonry bed joints glued with FRP composites. A composite failure envelope consisting of a Coulomb friction model and a compression cap is obtained for unreinforced masonry and GFRP-strengthened masonry based on the test results of masonry triplets and masonry prisms with bed joints having various inclinations to the loading (C) 2015 American Society of Civil Engineers.

High temperature deformation behavior of Nb-1 wt.%Zr alloy

The hot deformation behavior of Nb-1 wt.%Zr alloy was studied using uniaxial compression tests carried out in vacuum to a true strain of 0.6 in the temperature range of 900 to 1700 degrees C and the strain rate range of 3 x 10(-3) to 10 s(-1). The optimum regime of hot workability of Nb-1Zr alloy was determined from the strain rate sensitivity (m) contour plots. A high m of about 02 was obtained in the temperature and strain rate range of 1200-1500 degrees C and 10(-3) to 10(-1) s(-1) and 1600-1700 degrees C and 10(-1) to 1 s(-1). Microstructure of the deformed samples showed features of dynamic recrystallization within the high strain rate sensitivity domain. Compared to the study on Nb-1Zr-0.1C alloy, Nb-1Zr showed a lower flow stress and an optimum hot working domain at lower temperatures. In the 1500 to 1700 degrees C range the apparent activation energy of deformation for Nb-1Zr was 259 kJ mol(-1), the stress exponent 5, and the activation volume about 200 to 700 b(3). (C) 2015 Elsevier Ltd. All rights reserved.

On variant distribution and coarsening behavior of the a phase in a metastable beta titanium alloy

The stereology, variant distribution and coarsening behavior of semicoherent alpha(hcp) precipitates in a beta(bcc) matrix of a Ti5553 alloy has been analyzed, and a dominant 3-variant cluster has been observed in which the variants are related to each other by an axis-angle pair <<11(2)over bar> 0 >/60 degrees. Shape and spatial distribution independent elastic self and interaction energies for all pairwise and triplet combinations of a have been calculated and it is found that the 3-cluster combination that is experimentally observed most frequently has the lowest energy for the semicoherent state. The coarsening behavior of the delta distribution follows LSW kinetics after an initial transient, and has been modeled by phase field methods. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.