Non-destructive Evaluations of Gallium Nitride Nanowires

We have calculated the second and third order elastic constants of GaN nanowires at room temperature validating the interaction potential model. The ultrasonic attenuation and velocity in the nanowires are determined using the non-linear elastic constants for different diameters (97 nm -160 nm) of the wires at the nanoscale. Where possible, the results are compared with the experiments. Finally we established the correlation between the size dependent thermal conductivity and the ultrasonic attenuation of the nanowires.     

Effect of electrical resistivity on ultrasonic attenuation in NpTe

Ultrasonic attenuation due to electron-phonon interaction (EPI) has been computed in semimetallic single crystal neptunium telluride (NpTe) in low temperatures 5-80 K. For the same evaluation, we have also evaluated ultrasonic velocity, electronic viscosity and second order elastic constants (SOEC). The SOEC of NpTe have been evaluated using the Born model of ionic solid. The behaviour of ultrasonic attenuation is quite similar to its inverse resistivity. The ultrasonic attenuation due to EPI is most significant at 40 K. Computed results of ultrasonic parameter have been compared and discussed.     

Mechanical and Thermophysical Properties of Cerium Monopnictides

The ultrasonic attenuation due to phonon–phonon interaction, thermoelastic relaxation and dislocation damping mechanisms has been investigated in cerium monopnictides CeX (X: N, P, As, Sb and Bi) for longitudinal and shear waves along \({\langle }100{\rangle }\), \({\langle }110{\rangle }\) and \({\langle }111{\rangle }\) directions. The second- and third-order elastic constants of CeX have also been computed in the temperature range 0 K to 500 K using Coulomb and Born–Mayer potential upto second nearest neighbours. The computed values of these elastic constants have been applied to find out Young’s moduli, bulk moduli, Breazeale’s non-linearity parameters, Zener anisotropy, ultrasonic velocity, ultrasonic Grüneisen parameter, thermal relaxation time, acoustic coupling constants and ultrasonic attenuation. The fracture/toughness ratio is less than 1.75, which shows that the chosen materials are brittle in nature as found for other monopnictides. The drag coefficient acting on the motion of screw and edge dislocations due to shear and compressional phonon viscosities of the lattice have also been evaluated for both the longitudinal and shear waves. The thermoelastic loss and dislocation damping loss are negligible in comparison to loss due to Akhieser damping (phonon–phonon interaction). The obtained results for CeX are in qualitative agreement with other semi-metallic monopnictides.     

Attenuation of ultrasonic waves in V, Nb and Ta at low temperatures

Variation of ultrasonic attenuation and velocities with temperature have been evaluated in the temperature range 5-50 K due to electron-phonon interaction mechanism in transition metals vanadium, niobium and tantalum for longitudinal and shear waves. For this evaluation, we have also computed the second order elastic constants using Morse potential. Behaviour of acoustical phonons in these bcc metals is different from other normal metals, intermetallics, semimetallics and alloys. Some characteristic features of these materials connected to ultrasonic parameters are discussed.     

Nondestructive Characterization and Evaluation of Embrittlement Kinetics and Elastic Constants of Duplex Stainless Steel SAF 2205 for Different Aging Times at 425°C and 475°C

In this work, an experimental study was carried out to evaluate the potential of the ultrasonic technique, with ultrasonic velocity and attenuation measurements, to assess the heat aging effects on duplex stainless steel SAF 2205, at temperatures of 425°C and 475°C for time periods of 12 h, 24 h, 50 h, 100 h and 200 h, as well as in the as received state of the material. Velocity measurements were calculated for both longitudinal and transversal waves. The elastic constants, Young’s modulus and shear modulus, of the material were computed from the relationship between longitudinal and transversal velocities. For the ultrasonic attenuation, only longitudinal waves were considered. Despite the large scatter measurements, both ultrasonic velocity and attenuation increased with the heat aging time, particularly at 475°C. Thus, it may be concluded that the technique used is promising and provides relevant contributions to an accurate characterization of materials and evaluation of their mechanical properties in a non-destructive manner.     

Evaluation of precipitation reaction in 2024 Al-Cu alloy through ultrasonic parameters

Non-destructive diagnosis of nano-scale pre-precipitation and precipitation events can provide valuable support in controlling the thermal treatment for achieving the peak aged or any alternate desired microstructural state. The aim of the present investigation is to study the effect of isothermal ageing on density and hardness of 2024 Al-Cu-Mg alloy, and also to search the ability of measured ultrasonic velocity and attenuation and calculated elastic constants for monitoring the variations in microstructure and precipitation events during ageing. The specimens aged at 463 K for various periods up to 32 h followed by a solution annealed at 766 K for 1 h and water quenched, have been used for the ultrasonic velocity and attenuation measurements and metallurgical studies. The initial sharp acceleration in the hardness and velocities is due to the depletion of Cu from solid solution associated with the formation and growth of Cu-Mg co-cluster (GPB zone) and other intermediate phases. The local maximum at 10 h ageing time is due to the presence of higher volume fraction of precipitates like S′ and S and the minimum at 32 h of ageing time is due to the existence of dissolution and coarsening of S′ and S precipitates by overaged effect.     

B3–B1 phase transition and pressure dependence of elastic properties of ZnS

We have performed the ab initio calculations based on density functional theory to investigate the B3–B1 phase transition and mechanical properties of ZnS. The elastic stiffness coefficients, C₁₁, C₁₂, C₄₄, bulk modulus, Kleinman parameter, Shear modulus, Reuss modulus, Voigt modulus and anisotropy factor are calculated for two polymorphs of ZnS: zincblende (B3) and rocksalt (B1). Our results for the structural parameters and elastic constants at equilibrium phase are in good agreement with the available theoretical and experimental values. Using the enthalpy–pressure data, we have observed the B3 to B1 structural phase transition at 18.5 GPa pressure. In addition to the elastic coefficients under normal conditions, we investigate the pressure dependence of mechanical properties of both phases: up to 65 GPa for B1-phase and 20 GPa for B3-phase.     

Ultrasonic studies on irradiated sodium borate glasses

The ultrasonic velocity and attenuation coefficient have been measured at the frequency 4 MHz and at room temperature using the pulse echo technique. The effect of γ-radiation (1–10 Gy) on the ultrasonic attenuation, the internal friction and elastic properties inside the modified sodium borate glasses was studied. The used modification oxides are CaO, ZnO, MgO, BaO, and CdO. The results indicate the possibility for using modified sodium borate glasses as γ-ray dosimeters in the low γ-radiation doses.     

Effect of pressure on the structural and elastic properties of ZnS and MgS alloys in the B3 and B1 phases

From the first-principles calculations, we have investigated the elastic stiffness coefficients C₁₁, C₁₂, C₄₄ and the bulk modulus B of the II-VI semiconductors ZnS and MgS under hydrostatic pressure. The calculations are based on the density functional theory within the generalized gradient approximation (GGA) for exchange-correlation interaction. For the structural properties we have shown that ZnS adopt the rocksalt (NaCl or B1) structure over 11.87 GPa pressure, the same character is adopted by MgS over 0.8 GPa. The elastic coefficients have the same behavior for the different structures of alloys; they increase with increasing pressure values. Our results for the structural parameters and equilibrium phase elastic constants are in good agreement with the available theoretical and experimental data.     

Acoustic wave propagation in Laves-phase compounds

We have studied the acoustic wave propagation in the hexagonal structured materials TiCr₂, ZrCr₂ and HfCr₂. In this paper, we have calculated the orientation dependence of three types of acoustic wave velocity and Debye average velocity using second order elastic constants. The six second order elastic constants are calculated for these materials at 300 K using Lenard-Jones Potential. An anomalous behaviour in orientation dependent acoustic wave velocity is obtained which is due to the combined effect of elastic constants and density. These velocity data are important for their structural information and to differentiate them from third group nitrides.     

Preparation and characterization of ZnS nanocrystalline thin films by low cost dip technique

Nanocrystalline ZnS semiconducting nanopowder and thin films have been deposited by simple low cost technique based on combination of dip coating and thermal reaction process. The deposited films and the prepared nanopowder have been characterized in the structurally, optically and electrically point of views. The effect of preparation conditions has been also optimized for good quality films. X-ray diffraction analysis performed the ZnS cubic phase in the reaction temperatures in the range 473–593 K. Above 593 K mixed cubic and hexagonal crystallographic phases have been resolved. Crystallite size and micro strain have been calculated to be 2.65 and 0.011 nm, respectively. The deposited film surface and cross section morphologies show that neither cracks nor peels have been observed and good film adhesion with the substrate was performed. Energy dispersive X-ray measurements of the film agree well with the calculated concentrations of the precursor components. Optical measurements confirm the optical characteristics of nanocrystalline ZnS film such as absorption and dispersion properties. Copper doped ZnS reduces the band gap while indium doped ZnS increases the band gap. Electrical characterization shows that copper doped ZnS increases the resistivity by one order of magnitude due to electron compensation process while indium doped ZnS decreases the resistivity three orders of magnitude due to increase of the carriers concentration. Hot probe thermoelectric quick test of ZnS:Cu and ZnS:In show opposite sign of thermoelectric voltage due to bipolar p and n types, respectively.     

Photoluminescent properties of ZnS:Mn nanoparticles with in-built surfactant

Mn-doped ZnS nanoparticles, having average diameter 3–5 nm, have been synthesized using chemical precipitation technique without using any external capping agent. Zinc blende crystal structure has been confirmed using the X-ray diffraction studies. The effect of various concentrations of Mn doping on the photoluminescent properties of ZnS nanoparticles has been studied. The time-resolved photoluminescence spectra of the ZnS:Mn quantum dots have been recorded and various parameters like lifetimes, trap depths, and decay constant have been calculated from the decay curves at room temperature. The band gap was calculated using UV–Visible absorption spectra.     

Substrate temperature influence on ZnS thin films prepared by ultrasonic spray

ZnS thin films were deposited by ultrasonic spray technique. The starting solution is a mixture of 0.1 M zinc chloride as source of Zn and 0.05 M thiourea as source of S. The glass substrate temperature was varied in the range of 250 °C-400 °C to investigate the influence of substrate temperature on the structure, chemical composition and optical properties of ZnS films. The DRX analyses indicated that ZnS films have nanocrystalline hexagonal structure with (002) preferential orientation and grain size varied from 20 to 50 nm, increasing with substrate temperature. The optical films characterization was carried out by the UV-visible transmission. The optical gap and films disorder were deduced from the absorption spectra and the refractive indices of the films were determined by ellipsometric measurements. It is shown that the obtained films are generally composed of ZnO and ZnS phases with varied proportion, while at deposition temperature of 400 °C, they are near stoichiometric ZnS.     

Acoustic study of nano-crystal embedded PbO-P2O5 glass

Nano-crystal embedded PbO-P₂O₅ glass has been prepared and characterized by XRD and TEM measurements. The ultrasonic velocity and attenuation measured within the temperature range 80–300 K show significant structure and interesting feature with the presence of nano-crystalline region. The glass samples were prepared by melt-quench method and nano-crystals of different sizes were produced by heat treatment of the glasses for different durations of heating. All the processes were carried out at or above glass transition temperature. A theoretical model that takes account of the effects of thermally activated relaxation, anharmonicity as well as microscopic elastic inhomogeneities arising out of fluctuations has been successfully applied to interpret the variation of ultrasonic velocity and attenuation data. An interesting outcome of this application has been to propose a method for the determination of the size of nano-crystals from the ultrasonic attenuation data.     

Electrical properties of ZnO/Au/ZnS/Au films deposited by ultrasonic spray pyrolysis

Polycrystalline ZnS semiconducting films have been prepared by ultrasonic spray pyrolysis technique in the form of planar and sandwich configurations using amorphous and ZnO coated glass substrates. Deposition of ZnS films by the spray pyrolysis has been studied extensively by several investigators and the process parameters have been optimized to obtain films with good characteristics. However we report for the first time the preparation of ZnS films sandwiched between top and bottom electrodes on the transparent conducting ZnO films that have been produced by the spray pyrolysis technique. The produced ZnS films have been crystallized in a wurtzite structure. The electrical properties of the samples having planar and sandwich structures have been measured in dark at room temperature by applying the voltage values between 0.01 and 100 V.     

Growth and properties of ZnS thin films by sulfidation of sputter deposited Zn

ZnS thin films with the hexagonal structure have been produced by sulfurizing sputter deposited Zn in sulfur vapor for 1 h. These films have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), synchrotron radiation photoelectron spectroscopy (SR-PES), Auger electron spectroscopy (AES) and UV-VIS transmission spectra. It is found that at the sulfidation temperature (T_S) of 400 °C a little and partial Zn can be transformed to ZnS. At T_S = 500 °C, the total conversion of Zn in sulfur vapor can take place and form ZnS with a c-axis preferred orientation. The Zn-to-ZnS conversion is kinetically a reactive diffusion process. Also the ZnS thin film has much greater size of grains than the as-deposited Zn film, due to ZnS recrystallization and growth in sulfur vapor. Residual sulfur existing on the surface of ZnS grains leads to the poor optical transparency and great broadening of absorbing edge in the optical transmittance. However, ZnS thin film prepared by gradient sulfidation exhibits the improved optical transmittance, with a band-gap energy of 3.64 eV.     

Influence of microstructure on macroscopic elastic properties and thermal expansion of nickel‐base superalloys ERBO/1 and LEK94

In the present work the thermal expansion and the elastic properties of second generation nickel‐base superalloy single crystals ERBO/1 (CMSX‐4 variation) and LEK94 have been studied between about 100 K and 1273 K using dilatometry and resonant ultrasound spectroscopy, respectively. Inhomogeneity related to the large scale microstructure of the samples can act as a potential source of scatter for the propagation of ultrasonic waves. This can be overcome by choosing samples of sufficient size so that they appear as homogeneous media at the scale of the elastic wave length. Our final results are in good agreement with data reported in literature for similar alloy systems. In particular, the elastic material properties are only weekly affected by moderate variations in chemical composition and microstructure. Taking into account literature data for other superalloys like CMSX‐4, we derive general polynomial functions which describe the temperature dependence of the elastic moduli E_〈100〉, E_〈110〉 and E_〈111〉 in nickel‐base superalloys to within about ±3%. It was also observed that the alloys ERBO/1 and LEK94 show weak but significant anomalies in both thermal expansion and temperature coefficients of elastic constants above about 900 K. These anomalies are probably related to the gradual dissolution of the γ′‐precipitates at higher temperatures.     

Ultrasonic measurements of microelectronic molding compounds

We report ultrasonic measurements on commercial molding compounds used in the microelectronic industries. The elastic moduli of epoxy resins loaded with silica particles have been measured using ultrasonic wave propagation. Precise measurements of velocity propagation and attenuation were carried out in a large temperature (4–420 K) and frequency (1–100 MHz) ranges. The influence of frequency on the attenuation is discussed.     

Investigations on Structural Characteristics,Thermal Stability,and Hygroscopicity of Sisal Fibers at Elevated Temperatures

An effort has been made to study the thermophysical properties of sisal plant fiber available in North-East India in the temperature range from 310 K to 760 K. The effect of heat on the structural characteristics of the fiber using X-ray diffraction and the chemical behavior by the infrared (IR) technique has been examined. Thermodynamic studies of the fiber have been carried out using thermogravimetric (TG), derivative TG (DTG), and differential scanning calorimetric methods. The hygroscopic properties of the fiber have been investigated in the temperature range from 310 K to 430 K at different relative air humidities using an ordinary gravimetric analysis. The interplanar spacings of the sample heated to 370 K remained same with respect to their normal values, but the degree of crystallinity and crystallite sizes increased slightly. The degree of crystallinity of the sample heated to 450 K is decreased by 10.32 % from its normal value, and the corresponding interplanar spacings and crystallite sizes are decreased by a small amount. A sample heated to 530 K shows transformation of the fiber’s crystalline structure to an amorphous state. The fiber shows thermal stability up to 500 K and follows two different closely related thermal decomposition processes in the temperature range of approximately 500 K to 630 K. Tests performed in oxygen can lead to combustion of the fibers in the temperature range of approximately 710 K to 720 K. The IR study of the sample heated at temperatures from 370 K to 600 K provides meaningful data to ascertain decomposition of the native structure of the fibers. The hygroscopicity of the fiber under heated conditions is less with respect to the value under ambient conditions. The saturation limit of moisture absorption of the fiber per gram varies and depends on the source as well as pretreatment of the sample.     

Effect of thermal treatment on elastic properties of SiO2–Na2O–CaO–P2O5 glasses for biomedical applications

Glasses of the system SiO₂–Na₂O–CaO–P₂O₅ have been prepared for different compositions of SiO₂ employing the normal melting and annealing technique. The glasses of different compositions have been subjected to different thermal treatments to explore the change in structure, mechanical and other related properties. The ultrasonic velocities and attenuation measurements have been made on different compositions of the pure and thermal-treated glasses at a fundamental frequency of 5 MHz at 303 K. The observed linear increase in density, velocities and elastic moduli with increase in thermal treatment temperature is same in all composition studied. The above results reveal an increase in hardness and the predominant nature of network bonds per unit volume rather than the coordination/cross-link changes, with the influence of thermal treatment.