Positive MR and Large Temperature—Field Sensitivity in Manganite Based Heterostructures

Studies on the ZnO/La0.5Pr0.2Sr0.3Mn03 （LPSMO）/SrNb0.002Ti0.99803 （SNTO） heterostructure having varying thickness of p-type LPSMO （100 nm - LP1） and （200 nm - LP2） manganite are carried out. ZnO/LPSMO （n-p） and LPSMO/SNTO （p-n） junctions of both the heterostructures exhibit good rectifying behavior in a wide range of temperature and applied field. Forward and reverse bias characteristics of both the junctions of heterostructures show opposite behavior. The observation of negative magnetoresistance （MR） at 5 K and positive MR at 300 K, in both the heterostructures, has been explained in the context of interface region effects and filling of energy bands of LPSMO manganite. Further, at high temperature, the heterostructures exhibit large temperature （46%K-1） and field （40%T-1） sensitivities. Dependence of transport, magnetotransport, I-V and sensing properties of the heterostructures, on the temperature, field and film thicknesses have been discussed in this communication.

Tailoring of structural,optical and electrical properties of anatase TiO_(2)via doping of cobalt and nitrogen ions

Pure(pristine)anatase and mono–doped and co–doped derivatives of TiO_(2)having nitrogen(N)and cobalt(Co)as dopants with respective fixed doping concentrations of 0.7 mol.%and 1.0 mol.%were synthesized using auto–combustion sol–gel technique.The doping effects at corresponding non–metal and transition metal sites of TiO_(2)on the basis of the structural,optical and electrical properties have been investigated.X–ray diffraction(XRD)measurement confirms the formation of pure anatase phase of TiO_(2)for all samples having I41/amd space group of tetragonal structure which has been also verified by the Raman spectroscopy measurement.Various crystallographic parameters have been calculated by performing Rietveld refinement of XRD data including average crystallite size that has been observed in the range of10–15 nm.Pure anatase phase indicates the incorporation of Co^(2+)into TiO_(2)lattice which assists the substitution of N in place of oxygen in co–doped TiO_(2).The band gap tuning towards the visible region from3.2 to 2.1 e V has been achieved with mono–doping and co–doping of the N and Co in TiO_(2)lattice.This can be described in terms of the formation of localized levels of N–2p and Co–3d states in mono–doping and an isolated intermediate band formation in co–doping case.Electrical properties have been investigated in details and explained as the synergetic effects of structural and inherent ionic characters of various dopants.The observed band gaps of all doped samples lie within the visible region which makes them pertinent as the solar energy harnessing materials for photocatalytic and photovoltaic applications.

Size effects on electrical properties of sol–gel grown chromium doped zinc oxide nanoparticles

In this communication, we report the results of the studies on electrical properties of Zn0.95Cr0.05O nanoparticles synthesized using sol-gel method. X-ray diffraction （XRD） and transmission electron microscopy （TEM） measurements were performed for the structural and microstructural behaviors of the nanoparticles. Rietveld analysis was carried out to confirm the single phasic nature. High resolution TEM （HRTEM） confirms the nanoscale nature and polycrystalline orientations in the samples. Dielectric response has been understood in the context of universal dielectric response （UDR） model along with the Koop＇s theory and Maxwell - Wagner （M-W） mechanism. Variation in ac conductivity with frequency has been discussed in detail in terms of power law fits. Results of the impedance measurements have been explained on the basis of crystal cores and crystal boundary density. Cole - cole behavior has been studied for the impedance data. For potential application of nanoparticles, average normalized change （ANC） in impedance has been estimated and discussed in the light of size effects and oxygen vacancies.