Phase Transition of La0.62Sr0.38MnO3 Perovskite Manganites

Bulk and nano La0.62Sr0.38MnO3 perovskite manganite samples were prepared using solid state and sonochemical reaction respectively. The ultrasonic velocities measurement was made on prepared samples using ultrasonic through transmission method, at a fundamental frequency of 5 MHz over wide range of temperatures. The temperature dependence of the ultrasonic parameters shows an interesting anomaly in bulk and nano perovskite samples. The observed dramatic softening and hardening in sound velocities are related to phase transitions. Further, a decrease in grain size in the nanostructured sample leads to a shift in the ferromagnetic transition temperature (TC) from 375 to 370 K.

Структура и диэлектрические свойства наноструктурированной керамики Bi-=SUB=-1-x-=/SUB=-Sm-=SUB=-x-=/SUB=-FeO-=SUB=-3-=/SUB=-

The structure and dielectric properties of polycrystalline multiferroics of the Bi1-xSmxFeO3 system (x = 0-0.2) are investigated. X-ray diffraction revealed that two phases coexist in the x = 0.1 nanostructured sample: rhombohedral R3c and orthorhombic Pbam. On the temperature dependences of the dielectric constant ε'(T), four anomalies characteristic of phase transformations were found in the temperature range of ~ 180°С, ~ 250°С, ~ 300°С and TN ~ 350°С. It is shown that with increasing samarium concentration, the dielectric constant ε' increases, and tgδ decreases

Design and Analysis of Electrostatically Actuated Mechanical Sensor for Graphene

Very little is known about the fracture behaviors of novel nanomaterials such as carbon nanotubes and graphene due to the difficulty of sample manipulation and in situ detection of their failure mechanism. In the present study, the design and analysis of a Microelectromechanical System (MEMs) device is presented for the tensile testing of single layer graphene. The electrostatically actuated dual parallel plate actuators in the proposed MEMS device enable in situ measurement in a scanning electron microscope by stretching the two ends of a nanostructured sample simultaneously. The elongation in the specimen is obtained by nonlinear finite element analysis using COMSOL, and MATLAB. For the validation of the proposed MEMS device, a lumped model of the system is utilized to analyze the stress-strain behavior of the nanostructured sample under the force generated by the electrodes.

Effect of Surfactant Addition on Bi2Te3 Nanostructures Synthesized by Hydrothermal Method

In the present work, we have prepared Bi2Te3nanostructures with different morphologies such as nano-spherical, nanoplates and nanoflakes obtained using various surfactant additions (EG, PVP, and EDTA) by a hydrothermal method. The shape of the nanoparticles can be controlled by addition of surfactants. The samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the minority BiOCl phase disappears after maintained pH at 10 with EG as surfactant. SEM bulk microstructure reveals that the sample consists of fine and coarse grains. Temperature dependence of thermoelectric properties of the nanostructured bulk sample was investigated in the range of 300-450K. The presence of nanograins in the bulk sample exhibits a reduction of thermal conductivity and less effect on electrical conductivity. As a result, a figure of merit of the sintered bulk sample reached 0.2 at 400 K. A maximum micro Vickers hardness of 102 Hv was obtained for the nanostructured sample, which was higher than the other reported results.

Synthesis and Mechanical/Electrochemical Characterization of TiO2Nanotubular Structures Obtained at High Voltage

The synthesis of TiO2nanotubular arrays obtained through anodization of Ti foils in ethylene glycol (3% volume DI H2O + 0.25 wt.% NH4F) at high voltage is reported. The physical, chemical, electrochemical, and mechanical characterization was made to the TiO2nanotubular arrays. The morphological characterization showed a cylindrical geometry (112 nm inner diameter and 65 μm length), determining a rugosity factor of 1840 points. The electrochemical characterization was carried out exposing four samples: Ti, TiO2amorphous, and two crystalline TiO2nanotubular arrays (450 and 600°C) in two aqueous solutions of different pH: 1 M Na2SO4and 1 M Na2SO4+ H2SO4, using the potentiodynamic polarization curves. The mechanical characterization was performed through the nanoindentation technique applying three different loads (2.5, 5.0, and 10 mN) on the amorphous and the two crystalline TiO2nanotubular samples, obtaining the mechanical parameters such as the hardness, the elastic module, and the maximum penetration depth. The TiO2nanostructured sample crystallized at 600°C had the best electrochemical stability in both media and presented an elastic modulus of 22.42 GPa when it was tested applying a load of 2.5 mN, whereas the amorphous sample presented the major hardness at the loads of 5 and 10 mN.