Synthesis and electrical properties of cubic NaxWO3Na_{x}WO_{3} thin films across the metal-insulator transition

Highly oriented (1 0 0) $Na_{x}WO_{3}$ thin films were fabricated in the composition range 0.1 \leq x \leq 0.46 by pulsed laser deposition technique. The films showed transition from metallic to insulating behaviour at a critical composition between x = 0.15 and 0.2. The pseudo-cubic symmetry of $Na_{x}WO_{3}$ thin films across the transition regionis desirable for understanding the composition controlled metal-insulator transition in the absence of any structural phase transformation. The electrical transport properties exhibited by these films across the transition regime were investigated. While the resistivity varied as T-2 at low temperatures in the metallic regime, avariable range hopping conduction was observed for the insulating samples. For metallic compositions, a non-linear dependence of resistivity in temperature was also observed from 300 to 7 K, whose exponent varied with the composition of the film

Investigations on magnetic characteristics of the soil and their influence on its dielectric response

Conventionally, soils have been characterized based on their physical, chemical and mineralogical characteristics. However, in order to address various geo-environmental issues that have become a threat for the modem day civilization, soils have also been characterized based on their electrical properties. Furthermore, it has been demonstrated that the electrical properties of the soil mass (i.e., the soil compacted at a certain dry density and water content) are instrumental, primarily, in measuring its volumetric moisture content. In this context, though several efforts have been made by earlier researchers to determine dielectric response of the soil mass, the effect of soil magnetic characteristics on dielectric response and volumetric moisture content has not been established yet. Hence, development of a methodology to determine magnetic characteristics and their relationship with the dielectric response of the soil mass, if any, becomes quite intriguing. With this in view, soils of entirely different characteristics were tested for their magnetic characteristics (viz., remnant magnetization, coercivity and magnetic hysteresis area) by employing a magnetometer. Furthermore, these characteristics have been correlated with the physical, chemical, mineralogical and electrical properties (dielectric dispersion obtained from an impedance analyzer) of the soil. The study demonstrates that the parameter "area of magnetic hysteresis" of the air dried soils has significant influence on soil specific parameters such as specific gravity, iron content and dielectric constant. This preliminary study also proposes a hypothesis to obtain volumetric moisture content of the soil mass based on its magnetic characteristics and dielectric constant, which can be obtained from an impedance analyzer. However, efficiency and utility of the proposed hypothesis should be demonstrated by testing a large number of soils from different parts of the world

Strain-induced Metallic Behavior in PrNiO3PrNiO_3 Epitaxial Thin Films

Electrical transport properties of $RniO_3$ (R=Pr, Nd, Sm) thin films grown by pulsed laser deposition have been studied. RNiO3 films grow in the (1 0 0) direction on a $LaAlO_3$ (1 0 0) substrate. Unlike the polycrystalline solid, $PrNiO_3$ films showed metallic behavior. The first-order metal-to-insulator transition observed in polycrystalline solids is suppressed in $RniO_3$ films. The effect of lattice strain in the films influencing the transport properties has been studied by varying the thickness of $PrNiO_3$ film on $LaAlO_3$ (1 0 0) and also by growing them on $SrTiO_3$ (1 0 0) and $\alpha-Al_2O_3 (1 \={1}02)$ substrates. Deviation in the transport properties is explained due to the strain-induced growth of the films. Further, we show that the transport property of a $LaNiO_3$ film is also influenced by a similar strain effect

Evaluation of the Performance of TDR and Capacitance Techniques for Soil Moisture Measurement

Though researchers have employed various techniques (gravimetric, electromagnetic, neutron scattering, heat pulse, microwave, and optical remote sensing techniques) for soil moisture measurement, dielectric-based techniques (Time Domain Reflectometry [TDR] and capacitance technique [CT]) have gained much more popularity, mainly due to revolutionary developments in the fields of electronics and data communication systems. However, the suitability and relative performance of these techniques for moisture measurement of soils is a point of debate. Hence, in order to address this issue, extensive studies were conducted on soils of entirely different characteristics, compacted at various compaction states (dry densities and water contents) by employing TDR and capacitance probes. Subsequently, the dielectric constant of the soil and its bulk electrical conductivity were obtained using these probes and compared against each other and those computed from Topp's equation, which is a well-established relationship between the dielectric constant of the soil and its volumetric moisture content. An attempt was also made to correlate Ka values obtained from the dielectric techniques and Topp's equation with those of the Time Propagation (TP) Mixing model, which incorporates the properties of the soil matrix as well. It has been observed that the Ka-TDR matches well with the Ka-Topp and Ka-TP, while the best match has been observed between Ka-TDR and Ka-Topp as compared to the Ka-CT. As such, the study demonstrates clearly that Topp's equation, which ignores the soil-specific parameters, is capable of determining the soil moisture content appropriately. This study proposes an empirical equation that relates dielectric constants obtained from Topp's equation to those obtained from TDR, CT, and the TP Mixing model. Such a relationship can be further utilized for estimating the volumetric soil moisture content

The suppression of structural phase transformation in LaVO3LaVO_{3} and La1−xSrxVO3La_{1-x}Sr_{x}VO_{3} thin films fabricated by pulsed laser deposition

Highly oriented (100) thin films of $LaVO_{3}$ and $La_{1-x}Sr_{x}VO_{3}$ have been fabricated by pulsed laser deposition in a reducing atmosphere. The films show a transition from insulating to metallic behaviour in the composition region of x, 0.175 < x < 0.200. In the single crystals of the antiferromagnetic insulating phase, a first-order structural phase transition is observed few degrees below the magnetic transition, which manifests itself as a kink in the temperature dependence of resistivity. In the highly oriented thin films of $LaVO_{3}$ and $La_{1-x}Sr_{x}VO_{3}$ fabricated on lattice matched substrates in this study, the structural phase transformation in the insulating phase has been suppressed. The electrical conduction is found to take place via hopping through localized states at low temperatures. The metallic compositions show a non-linear $(T^{1.5})$ behaviour in the temperature dependence of resistivity. V (2p) core level spectra of these films show a gradual change in the relative intensities of $V^{3+}$ and $V^{4+}$ ions as the value of x increases

The effect of strain on nonlinear temperature dependence of resistivity in SrMoO3SrMoO_3 and SrMoO3−xNxSrMoO_{3-x}N_x films

Highly oriented $SrMoO_3$ thin films have been fabricated by pulsed laser deposition of $SrMoO_4$ in hydrogen. The films are found to grow along the (1 0 0) direction on $LaAlO_3$ (1 0 0) and $SrTiO_3$ (1 0 0) substrates. The method has been extended for the fabrication of oxynitride thin films, using ammonia as the reducing medium. The resistivity measurements show nonlinear temperature dependent $(T^n)$ behaviour in the temperature interval of 10–300 K. The conduction mechanism is largely affected by the strain due to the substrate lattice. A combination of $T$ and $T^2$ dependence of resistivity on temperature is observed for films having lesser lattice mismatch with the substrate. The X-ray photoelectron spectroscopic studies confirm the formation of $SrMoO_3$ and $SrMoO_{3-x}N_x$ films

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Bioconversion of D-xylose to D-xylonic acid by Pseudoduganella danionis

821-824Sugar acids are organic acids formed by the oxidation of carbonyl or hydroxyl group of monosaccharides to carboxylic acid group. D-xylonic acid derived via bioconversion of D-xylose is a promising platform chemical with various applications in food, chemical, agriculture, and pharmaceutical industries. The efficacy of a newly isolated culture identified as Pseudoduganella danionis to produce D-xylonic acid from D-xylose was investigated. The culture appeared to be potent for a feasible bioprocess development for xylonic acid production. Production medium containing 10 g/L D-xylose resulted in 6.5 g/L D-xylonic acid production after 120 h of incubation with 1% (v/v) inoculum of P. danionis

Structure and electrical properties of sodium tungsten bronzes thin films

Highly oriented thin films of $Na_xWO_3 (x=0.25–0.7)$ are grown on sapphire (1 1 0 2) and $SrTiO_3$ (1 0 0) substrates by pulsed laser deposition. The colour of the films changes from blue through red to bronze yellow on varying the sodium content. The films are composed of particles less than 100 nm size. As in bulk $Na_xWO_3$, the resistivity is found to decrease on increasing the sodium content, and at around x=0.25, a non-metal to metal transition is clearly observed. The conductivity measurement of Na_0_._2_5WO_3 shows a crossover from temperature-activated Arrhenius behaviour at high temperatures to a variable range hopping mechanism near 70 K. The metallic samples show linear dependence of resistivity above 50 K. XPS studies confirm the presence of sodium in +1 and tungsten in +5 and +6 oxidation states