Structural, optical and high pressure electrical resistivity studies of pure NiO and Cu-doped NiO nanoparticles

In this paper, pure NiO and Cu-doped NiO nanoparticles are prepared by co-precipitation method. The electrical resistivity measurements by applying high pressure on pure NiO and Cu-doped NiO nanoparticles were reported. The Bridgman anvil set up is used to measure high pressures up to 8 GPa. These measurements show that there is no phase transformation in the samples till the high pressure is reached. The samples show a rapid decrease in electrical resistivity up to 5 GPa and it remains constant beyond 5 GPa. The electrical resistivity and the transport activation energy of the samples under high pressure up to 8 GPa have been studied in the temperature range of 273–433 K using diamond anvil cell. The temperature versus electrical resistivity studies reveal that the samples behave like a semiconductor. The activation energies of the charge carriers depend on the size of the samples.

Pressure Dependence of the Electrical Resistivity in Polymer Polyaniline

Polyaniline (PAN) was prepared by using a technique of chemical synthesis to obtain the insulating emeraldine base form. And then PAN was doped with toluenesulfonic acid (TSA), HCl, or camphor sulfonic acid (CSA) to protonate it into conducting salt form. The morphologies and electrical property of PAN under atmospheric pressure were investigated. Subsequently, the high pressure using a Bridgman anvil cell was applied on the doped PAN, and the effect of high pressure on the properties of doped PAN was analyzed. At normal pressure, the conductivity of PAN increases as the PH value increases. While at high pressures, the conductivity of PAN increases, and then it becomes independent of pressure. The results indicate that the conductivity of PAN is related to the presence of the polaron band, and the doped PAN under high pressure will be enhanced strongly in conductivity because of overlap of polaron band andπband. However, with the further increase of the applied pressure, scattering mechanisms of carriers limit the conductivity of PAN.

Effect of Severe Plastic Deformation by Torsion on Structure and Properties of Ni54Mn21Ga25 and Ni54Mn20Fe1Ga25

We report on the effect of severe plastic deformation by torsion under the Bridgman anvil pressure (SPDT) on structure and physical properties of the Ni54Mn21Ga25 and Ni54Mn20Fe1Ga25 alloys. Two types of samples were studied: ordered (cast) samples and nanocrystalline samples disordered by SPDT. The thermal expansion, thermo EMF, electro- and magnetoresistivity, Hall effect, and magnetization were measured from 4.2 to 800 K and in magnetic fields of up to 15T. We show that the deviation from the stoichiometric Ni50Mn25Ga25 composition shifts the temperatures of the martensitic transition TM and the magnetic (Curie) transition TC to room temperature. Large changes in the physical properties near TM and TC were discovered. The alloys become amorphous and nanocrystalline after the SPDT treatment. This process is accompanied by the disappearance of the martensitic transformations and of the nanocrystalline modulated substructures and, consequently, by the suppression of the magnetic shape-memory effect. The physical properties of the disordered alloys are also strongly changed. Subsequent annealing at Т ≥ 700 K leads to a practically full restoration of the structure and all properties characteristic of the initial cast alloys.