Tensile Microstrain Research Articles

Behavior of Microstrain in Nd3+-Sensitized Near-Infrared Upconverting Core-Shell Nanocrystals for Defect-Induced Tailoring of Luminescence Intensity.

In an attempt to optimize the upconversion luminescence (UCL) output of a Nd3+-sensitized near-infrared (808 nm) upconverting core-shell (CS) nanocrystal through deliberate incorporation of lattice defects, a comprehensive analysis of microstrain both at the CS interface and within the core layer was performed using integral breadth calculation of high-energy synchrotron X-ray (λ = 0.568551 Å) diffraction. An atomic level interpretation of such microstrain was performed using pair distribution function analysis of the high-energy total scattering. The core NC developed compressive microstrain, which gradually transformed into tensile microstrain with the growth of the epitaxial shell. Such a reversal was rationalized in terms of a consistent negative lattice mismatch. Upon introduction of lattice defects into the CS systems upon incorporation of Li+, the corresponding UCL intensity was maximized at some specific Li+ incorporation, where the tensile microstrain of CS, compressive microstrain of the core, and atomic level disorders exhibited their respective extreme values irrespective of the activator ions.

Investigations of the structure and tunable magnetic properties of Cu doped cobalt chromite nanoparticles

This article reports the synthesis, microstructural, magnetic and optical properties of copper ions substituted cobalt chromite nanoparticles. We have prepared four nanosized chromite samples with a general composition of CuxCo1-xCr2O4 (x = 0.0, 0.1, 0.2 and 0.3) using conventional wet chemical co-precipitation method. The x-ray diffraction profiles verified the presence of pure spinel crystal structure of the samples. Using the Williamson-Hall (W-H) method, the average crystallite size of all the samples were calculated to be between 11 nm and 16 nm. A tensile microstrain in all the samples was noticed. Surface morphology and average particle size of doped cobalt chromite nanocrystals was examined using HRTEM images. A moderate increment in the optical band gap was detected with increasing Cu ions in cobalt chromite nanoparticles which is attributed to the nanosize effect of the samples. The presence of all five distinctive Raman active modes in the chromite samples ensured phase purity and a decrease in crystal symmetry was also observed as the amount of Cu dopants was increased. Due to low magnetic moment of Cu2+ ions when compared with Co2+ ions, incorporation of copper ions reduces the coercive field of the host chromite system. With increasing Cu percentage in chromite especially for 30 % Cu doped sample, the spin-spiral transition TS vanishes which indicates TS is affected by the dopant concentrations.

Tensile Microstrain Fluctuations in the BaPbO Units in Superconducting BaPb1−xBixO3 by Scanning Dispersive Micro-XANES

BaPb1−xBixO3 (BPBO) bismuthate, showing high TC superconductivity for 0.05 < x < 0.35, is an archetypal system for studying the complex inhomogeneity of perovskite lattice favoring the emergence of quantum coherence, called the superstripes phase. Local lattice fluctuations, detected by EXAFS; nanoscale stripes, detected by electron microscopy; and two competing crystalline structures, detected by diffraction, are known to characterize the superconducting phase. At nanoscale [BaBiO3] centered nanoscale units (BBO) coexist with BaPbO3 centered (BPO) units in the BPBO perovskite; therefore, we expect a tensile microstrain in BPO units due the misfit strain between the two different lattices. Here, we report the measurement of the spatial micro-fluctuations of the local tensile microstrain ε in the BaPO units in superconducting Ba(Pb1−xBix)O3 crystals with x1 = 0.19 an x2 = 0.28. We show here the feasibility of applying the scanning dispersive micro-X-ray absorption near edge structure (SdμXANES) technique, using focused synchrotron radiation, to probe the microscale spatial fluctuations of the microstrain in BPO units. This unconventional real-space SdμXANES microscopy at the Pb L3 edge has been collected in the dispersive mode. Our experimental method allows us to measure either the local Bi chemical concentration x and the local lattice microstrain of local BBO and BPO units. The 5 × 5 micron-size spots from the focused X-ray beam allowed us to obtain maps of 1600 points covering an area of 200 × 200 microns. The mapping shows a substantial difference between the spatial fluctuations of the microstrain ε and the chemical inhomogeneity x. Moreover, we show the different relations ε(x) in samples with lower (x1 = 0.19) and higher (x2 = 0.28) doping respect to the optimum doping (x = 0.25).

Synthesis, Electron Spin Resonance and Photoluminescence properties of Sm3+ ion doped Zn-Mn nanoferrites synthesized by glycol-thermal method

Nanocrystalline Zn0.5Mn0.5SmxFe2-xO4 (0 ≤ x ≤ 0.05) with average crystallite sizes varying between 12 and 17 nm were synthesized by the glycol-thermal process. X-ray diffraction (XRD) analysis confirmed a single-phase cubic spinel structure in all the compounds. Substituting a smaller Fe3+ ion with a larger rare-earth (RE) Sm3+ ion has affected the distribution of metal ions on tetrahedral (A) and octahedral (B) sites. In this work, a comprehensive study has been carried out on nanocrystalline particles of RE Sm3+ ion doped into Zn-Mn ferrite to estimate intrinsic strain through Williamson-Hall (W–H) analysis. The results were compared with those obtained from the Debye Scherrer equation. Tensile microstrain within the nanocrystals were detected from W-H plots for x = 0, 0.01,0.02 and 0,05 samples, while compressive microstrain was observed for x = 0.02 and 0.05 samples. A scanning electron microscope (SEM) has been used to study the morphology of nanoparticles and it revealed spherical-shaped nanoparticles. Energy dispersive X-rays (EDX) confirmed the phase purity and the elemental composition with no impurity elements were observed. Crystallite sizes affect electron spin resonance (ESR) signal intensity and the line width. The g-values fluctuated ranging from 2.31 to 2.51 due to fluctuating crystallite sizes. Photoluminescence (PL) displayed a blue-violet emission with maxima centred at 418 nm and 438 nm under the excitation wavelength of 320 nm. The electron spin resonance and photoluminescence results show that the Sm doped Zn-Mn ferrites are promising candidates for applications in blue LEDs.

In-situ XRD study on the effects of stress relaxation and phase transformation heat treatments on mechanical and microstructural behaviour of additively manufactured Ti-6Al-4V

Additively Manufactured (AM) titanium (Ti) components are routinely post-thermal heat treated (HT), to reduce internal stresses, as well as to obtain more desirable microstructural features, yielding improved mechanical performance. Currently, there is no consensus on the optimum HT method for AM Ti-6Al-4V, as the mechanism for the main phase transformation (α′ (martensite) → α + β (equilibrium)) is still ambiguous. In this study, stress relaxation and phase transformation in the alloy are investigated in detail, via isothermal heat treatments and in situ high temperature X-ray Diffraction (XRD). The latter was carried out at heating rates of 5 and 200 °C/min. The relationship between crystallographic evolution during isothermal treatments and mechanical behaviour was determined. Isothermal holding at 400 °C resulted in an increase in ultimate tensile strength (UTS) and yield strength (YS) by 3.4% and 2.1%, respectively, due to the relief of tensile microstrain. It was found that isothermal treatment conducted between 550 and 700 °C promotes martensitic decomposition, resulting in the formation of a transitional - αtr phase, which has an asymmetrical hexagonal crystal lattice. The formation of this αtr phase was determined to be the main factor contributing to a major decrease in ductility.

Unary doping effect of A2+ (A = Zn, Co, Ni) on the structural, electrical and magnetic properties of substituted iron oxide nanostructures

Pure and unary doped iron oxide nanostructures (NSs) were synthesized by hexamethylenetetramine (HMTA)-assisted hydrothermal method. The presence of micro-strain was well analysed and estimated by Williamson–Hall (uniform deformation model) and size–strain analysis using X-ray diffraction peak broadening. The analysis confirmed that all prepared samples exhibited a positive slope which enumerated the presence of tensile micro-strain in all samples. The conductivity of the sample depicted an increasing trend with temperature in all samples which indicated their semiconducting behaviour. Further, It was observed that ZnFe2O4 NSs exhibited super-paramagnetic behaviour, while CoFe2O4 NSs exhibited ferromagnetic behaviour with a high coercivity of 1890 Oe and magnetic anisotropy constant approximately 1.35 × 105 emu Oe/g. High saturation magnetization, high dielectric constant, low electrical conductivity and low dielectric loss depicted the potential usage of synthesized ferrite nanostructures (FNSs) for microwave devices.

Effect of tungsten doping on structural and optical properties of rutile TiO2 and band gap narrowing

Pure and W doped nanocrystalline rutile TiO2 samples were synthesized using high energy ball milling process. Rietveld refinement results of X-ray diffraction data confirmed that pure sample exhibited rutile TiO2 phase whereas doped samples contained both rutile TiO2 and a secondary Ti0.54W0.46O2 phase. Different models of Williamson–Hall method were employed to evaluate crystallite size and strain in the samples. The crystallite size was found to decrease from 50 to 47 nm with increase in the dopant concentration. The pure TiO2 exhibited tensile microstrain which became compressive and increased upon doping. A blue shift in A1g Raman mode with doping of W also indicated the increase in the compressive strain. The HR-TEM images also confirmed the presence of higher strain in doped samples compared to un-doped sample. The observed decrease in band gap from 3 to 2.83 eV with dopant concentration, as calculated from UV–vis spectroscopy data, may be attributed to the increased strain. The decrease in the intensity of photoluminescence emission indicated the increase in number of defects and oxygen vacancies with increasing dopant concentration. This is further, supported by the rise in Urbach energy, a signature of increased number of defects in doped samples. This study shows that the dopant induced strain plays significant role in band gap narrowing.

The Microstrain-Doping Phase Diagram of the Iron Pnictides: Heterostructures at Atomic Limit

The 3D phase diagram of iron pnictides where the critical temperature depends on charge density and microstrain in the active FeAs layers is proposed. The iron pnictides superconductors are shown to be a practical realization of a heterostructure at the atomic limit made of a superlattice of FeAs layers intercalated by spacer layers. We have focussed our interest on the A1−xBxFe2As2 (122) families and we show that FeAs layers have a tensile microstrain due to the misfit strain between the active layers and the spacers. We have identified the critical range of doping and microstrain where the critical temperature gets amplified to its maximum value.

Effect of strain on bone nodule formation by rat osteogenic cells in vitro

The purpose of this study was to assess in vitro bone nodule formation by cells exposed to a range of microstrain, at a sub-optimal oscillation frequency for bone formation. Fetal rat calvarial cells experienced a Flexercell™ regimen within either FLEX I™ (deformable) or FLEX II™ (non-deformable) substrates. Cells in FLEX I™ plates were exposed to growth medium only; those in FLEX II™ plates were exposed to either growth medium only, or growth medium+10 −7 M IGF-1. Cell numbers were assessed from 1 to 6 days. Other cells were exposed to the Flexercell™ regimen (−2 kPa, 0.05 Hz) for 1–3 (Group 1), 3–6 (Group 2), 1–9 (Group 3) or 10–15 (Group 4) days and were maintained, at other times, under standard conditions. After 21 days, nodules were counted within each well and within the compression, <999, 1000–4900, 5000–9999, 10,000–14,999 and 15,000–25,000 microstrain regions of the FLEX I™ membrane. Cyclic deformation inhibited cell numbers from 1 to 6 days, compared to control or IGF-1 groups ( P<0.001). The number of nodules in Groups 2 and 4 were greater than Groups 1 or 3 ( P<0.001), but not different from control or IGF-1 groups. Compression or tensile microstrain significantly affected nodule formation in all groups, with Group 4 producing more nodules than other groups in most microstrain regions. Thus, the number of bone nodules produced by osteogenic cell cultures exposed to cyclic deformation was significantly affected by the timing of initiation and the characteristics and magnitude of the deformation regimen.

ANISOTROPIC THERMAL EXPANSION IN DIBORIDES AS A FUNCTION OF MICRO-STRAIN

Thermal expansion of diborides ( AB 2), with different intercalated atoms (A) is studied as a function of temperature in the range of 100-370 K by high-resolution x-ray powder diffraction. The results indicate a well defined relationship between the anisotropy of the thermal expansion and the micro-strain of the boron layers, ε a = (a-a0)/a0 (where a0 = c/1.08 is the equilibrium a-axis for an unstrained AB2 system), determined by the atomic radius of the intercalated atoms. The thermal expansion is isotropic at εa = 0 (i.e., near c/a = 1.08) while the AB 2 system is unstrained, and it gets anisotropic away from the equilibrium. The anisotropy increases with increasing micro-strain in both directions (positive or negative, i.e. tensile or compressive) suggesting that the micro-strain is a key variable to define the state of diborides. As a matter of fact, the MgB 2 with the highest T c shows a tensile micro-strain, εa = 6% and a large thermal expansion anisotropy.

Scaling of the critical temperature with the Fermi temperature in diborides

The experimental determination of the scaling of the superconducting critical temperature ${(T}_{c})$ vs the Fermi temperature ${(T}_{f})$ of the holes in the boron \ensuremath{\sigma} subband is presented. The Fermi level has been tuned near the ``shape resonance,'' i.e., the two- to three-dimensional crossover of the Fermi surface of the boron \ensuremath{\sigma} subband by changing the Al/Mg content in ${\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Mg}}_{x}{\mathrm{B}}_{2}.$ The product ${k}_{f}{\ensuremath{\xi}}_{0}$ of the Fermi wave vector ${(k}_{f})$ times the superconducting Pippard coherence length $({\ensuremath{\xi}}_{0}),$ that is a measure of the pairing strength, remains constant, ${k}_{f}{\ensuremath{\xi}}_{0}=90$ for $x&gt;0.66.$ This high-${T}_{c}$ phase occurs in the boron superlattice under a tensile microstrain in the range $3%&lt;\ensuremath{\varepsilon}&lt;6%.$

Tensile microstrain properties of vapour quenched and rolled Al-alloys

Al-alloy deposits produced by quenching from the vapour phase were rolled into sheet and tensile stress-strain curves were obtained in the microstrain region (<10−4 strain). Two binary alloys (Al-5% Cr and Al-11% Cr) and two ternary alloys (Al-8% Cr-1.2% Fe and Al-6% Cr-1.0% Fe) were tested (compositions in wt%). The corresponding tensile strengths were 375 and 590 MPa for the binary alloys, and 679 and 662 MPa for the ternary alloys. The microyield stresses (the stress to produce a residual plastic strain of 2×10−6) for the vapour quenched alloys were less than 26 MPa compared with 100 to 260 MPa for commercial aluminium alloys. When the vapour quenched alloys were retested immediately after prestrain, the values were much greater (166 to 254 MPa), but after resting at room temperature for 7 to 106 days low values were again obtained. The low microyield stresses were attributed to the high density of dislocations present in the rolled sheet and the behaviour observed may be characteristic of high strength dispersion hardened Al-alloys produced by rapid solidification and rolling.

Hysteresis behaviour in CFRP

Hysteresis behaviour during tensile microstrain and constant amplitude load cycling has been studied with CFRP of approximately 50% fibre volume fraction. This hysteresis is explained in terms of the residual strain in the composite caused by the different thermal expansion coefficients of the fibre and matrix.The energy loss during cyclic deformation presented in terms of specific damping capacity was virtually constant after a rapid decrease during the first few cycles. Simultaneous measurement of the acoustic emission energy released showed similar trends.The mode of failure after cyclic loading was markedly different from that obtained by direct tensile loading.

Flow behavior of nylon-epoxide adhesive

Tensile microstrain and creep tests were made on a nylon-epoxide adhesive in a metal/metal joint, as a function of temperature, strain rate and applied load. High sensitivity extensometers were used to record the deformation of the adhesive material. The classic three stages of creep were observed at elevated temperatures. The stress threshold for creep was about the same as the precision elastic limit. Transient creep was found to obey the logarithmic creep law. The creep strain was greatly enhanced above 120°F (322°K) and the applied stress had a greater effect at the higher temperatures. Activation volumes were calculated and showed three distinct stages. Molecular deformation mechanisms have been proposed for each stage.