EPR evidence for activation of trap centers in PTCR BaTiO3BaTiO_3 ceramics

Donor-doped $BaTiO_3$ ceramics, exhibiting PTCR, showed an EPR signal with g=1.997 which acquires high intensity above $T_C$. This is indicative of activation of the corresponding defect centers, possibly $V′_{Ba}$.. The intensity of g=1.997 varies with Ba/Ti ratio, rate of cooling from the sintering temperature and the addition of $TiO_2$ as sintering agent. The signal intensity decreases with increase in grain size and is weak in La-doped $BaTiO_3$ single crystals. Therefore the concentration of $V_{Ba}$ is more around the grain boundaries than that in the bulk of grains. Activated trap centers around $T_C$ also arises from background impurities; those with change of electronic state: $M^{n+1}$+ e′ = $M^{n+}$ (eg:-Mn) and those associated with oxygen vacancies: $M^{P+}-V_O(e′)$ $(eg:-Fe^{3+})$. Activation of these trap centers are not dependent on the disappearance of spontaneous polarization but to the structural changes during phase transformation. The trapped charge carriers are not available for conduction and hence the increase in electrical resistivity

Synthesis and characterization of single-crystalline alpha-MoO3 nanofibers for enhanced Li-ion intercalation applications

High quality, single-crystalline alpha-MoO3 nanofibers are synthesized by rapid hydrothermal method using a polymeric nitrosyl-complex of molybdenum(II) as molybdenum source without employing catalysts, surfactants, or templates. The possible reaction pathway is decomposition and oxidation of the complex to the polymolybdate and then surface condensation on the energetically favorable 001] direction in the initially formed nuclei of solid alpha-MoO3 under hydrothermal conditions. Highly crystalline alpha-MoO3 nanofibers have grown along 001] with lengths up to several micrometres and widths ranging between 280 and 320 nm. The alpha-MoO3 nanofibers exhibit desirable electrochemical properties such as high capacity reversibility as a cathode material of a Li-ion battery

Synthesis and characterization of self-assembled nanofiber-bundles of V(2)O(5): their electrochemical and field emission properties

High-quality self-assembled V(2)O(5) nanofiber-bundles (NBs) are synthesized by a simple and direct hydrothermal method using a vanadium(V) hydroxylamido complex as a vanadium source in the presence of HNO(3). The possible reaction pathway for the formation of V(2)O(5) NBs is discussed and demonstrated that HNO(3) functions both as an oxidizing and as an acidification agent. V(2)O(5) NBs are single-crystals of an orthorhombic phase that have grown along the [010] direction. A bundle is made of indefinite numbers of homogeneous V(2)O(5) nanofibers where nanofibers have lengths up to several micrometres and widths ranging between 20 and 50 nm. As-prepared V(2)O(5) NBs display a high electrochemical performance in a non-aqueous electrolyte as a cathode material for lithium ion batteries. Field emission properties are also investigated which shows that a low turn-on field of similar to 1.84 V mu m(-1) is required to draw the emission current density of 10 mu Lambda cm(-2)