Shrikant Saini
Hiroshima University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Shrikant Saini.
Applied Physics Letters | 2013
Paolo Mele; Shrikant Saini; Hiroaki Honda; Kaname Matsumoto; Koji Miyazaki; H. Hagino; A. Ichinose
We have prepared 2% Al doped ZnO (AZO) thin films on SrTiO3 (STO) and Al2O3 substrates by Pulsed Laser Deposition technique at various deposition temperatures (Tdep = 300 °C–600 °C). Transport and thermoelectric properties of AZO thin films were studied in low temperature range (300 K–600 K). AZO/STO films present superior performance respect to AZO/Al2O3 films deposited at the same temperature, except for films deposited at 400 °C. Best film is the fully c-axis oriented AZO/STO deposited at 300 °C, which epitaxial strain and dislocation density are the lowest: electrical conductivity 310 S/cm, Seebeck coefficient −65 μV/K, and power factor 0.13 × 10−3 W m−1 K−2 at 300 K. Its performance increases with temperature. For instance, power factor is enhanced up to 0.55 × 10−3 W m−1 K−2 at 600 K, surpassing the best AZO film previously reported in literature.
Japanese Journal of Applied Physics | 2014
Shrikant Saini; Paolo Mele; Hiroaki Honda; Dave J. Henry; Patrick E. Hopkins; Leopoldo Molina-Luna; Kaname Matsumoto; Koji Miyazaki; Ataru Ichinose
2% Al-doped ZnO (AZO) thin films fabricated at 300 °C by pulsed laser deposition (PLD) on amorphous fused silica demonstrated the high quality crystallinity and grain connection, which correlates to the high thermoelectric performance: electrical conductivity σ = 923 S/cm and Seebeck coefficient S = −111 µV/K at 600 K. Its power factor (S2 · σ) is 1.2 × 10−3 W m−1 K−2, twofold better than films deposited on crystalline SrTiO3 under the same experimental conditions. Using our measured thermal conductivity (κ) at 300 K (4.89 W m−1 K−1), the figure of merit, ZT = (S2 · σ · T/κ), is calculated as 0.045 at 600 K, 5 times larger than ZT of our previously reported bulk ZnO.
Scientific Reports | 2017
Shrikant Saini; Haritha Sree Yaddanapudi; Kun Tian; Yinong Yin; David Magginetti; Ashutosh Tiwari
The potential of thermoelectric materials to generate electricity from the waste heat can play a key role in achieving a global sustainable energy future. In order to proceed in this direction, it is essential to have thermoelectric materials that are environmentally friendly and exhibit high figure of merit, ZT. Oxide thermoelectric materials are considered ideal for such applications. High thermoelectric performance has been reported in single crystals of Ca3Co4O9. However, for large scale applications single crystals are not suitable and it is essential to develop high-performance polycrystalline thermoelectric materials. In polycrystalline form, Ca3Co4O9 is known to exhibit much weaker thermoelectric response than in single crystal form. Here, we report the observation of enhanced thermoelectric response in polycrystalline Ca3Co4O9 on doping Tb ions in the material. Polycrystalline Ca3−xTbxCo4O9 (x = 0.0–0.7) samples were prepared by a solid-state reaction technique. Samples were thoroughly characterized using several state of the art techniques including XRD, TEM, SEM and XPS. Temperature dependent Seebeck coefficient, electrical resistivity and thermal conductivity measurements were performed. A record ZT of 0.74 at 800 K was observed for Tb doped Ca3Co4O9 which is the highest value observed till date in any polycrystalline sample of this system.
Superconductor Science and Technology | 2015
Alok K. Jha; Kaname Matsumoto; Tomoya Horide; Shrikant Saini; Paolo Mele; Ataru Ichinose; Yutaka Yoshida; Satoshi Awaji
The effect of hybrid (columnar and spherical together) artificial pinning centers (APCs) on the vortex pinning properties of YBa2Cu3O7−δ (YBCO) thin films is investigated in detail on the basis of variation of critical current density (J C ) with applied magnetic field and also with the orientation of the applied magnetic field at 65 K and 77 K. Premixed YBCO + BaSnO3 composite targets are used for the deposition of the YBCO films which consist of self-assembled BaSnO3 nanocolumns (1D APCs); on the other hand, for the deposition of the YBCO films with hybrid APCs (BaSnO3 nanocolumns together with Y2O3 nanoparticles), the surface of the premixed YBCO + BaSnO3 composite targets are modified by putting a thin Y2O3 sectored piece on the premixed YBCO + BaSnO3 composite targets by means of silver paste. F pmax value increases systematically with incorporation of 1D and 1D and 3D APCs and it also shifts towards higher applied magnetic fields. Films with 1D APCs exhibit a strong J C peak at Θ = 0° (H//c-axis) whereas films consisting of hybrid APCs exhibit enhanced J C at all the investigated angular regimes. A possible mechanism of vortex pinning in samples with hybrid APCs is also discussed suggesting the role of 1D and 3D APCs.
Superconductor Science and Technology | 2014
Alok K. Jha; Kaname Matsumoto; Tomoya Horide; Shrikant Saini; Paolo Mele; Yutaka Yoshida; Satoshi Awaji
We report the controlled incorporation of perovskite, BaSnO3 (BSO), and double-perovskite, YBa2NbO6 (YBNO), nanocolumnar structures into a YBa2Cu3O7?? (YBCO) film matrix by controlling the target rotation speed. A surface modified target approach has been employed to deposit YBCO+BSO and YBCO+YBNO nanocomposite films using a laser ablation technique. The effect of target rotation speed on the microstructure and subsequently on the superconducting properties has been studied in detail. The density of BSO and YBNO nanocolumnar structures is found to depend on the target rotation speed, which subsequently affects the vortex pinning properties of the superconducting films in the absence and presence of applied magnetic fields. Three rotation speeds, 3, 2 and 1?s/rot., have been attempted in this study. Compared to pure YBCO, the YBCO+BSO and YBCO+YBNO nanocomposite films exhibit superior in-field critical current density (JC) and also exhibit a strong JC peak for H???c-axis, indicating strong c-axis pinning. The irreversibility line has also been found to improve significantly in the nanocomposite films. For both the target combinations (YBCO+BSO and YBCO+YBNO), the target rotation speed of 2?s/rot. has been found to give the optimum superconducting properties.
IEEE Transactions on Applied Superconductivity | 2015
Alok K. Jha; Kaname Matsumoto; Tomoya Horide; Shrikant Saini; Paolo Mele; Yutaka Yoshida; Satoshi Awaji
The effect of hybrid (columnar and spherical) artificial pinning centers (APCs) on the vortex pinning properties of YBCO thin films is studied in this paper on the basis of variation of critical current density JC with applied magnetic held and also with the orientation of the applied magnetic held. YBCO+BSO3% composite target is used for preparing film with 1-D (columnar) APCs, whereas the same composite target is modified by putting two differently sized (2.2 area% and 3 area%) Y2O3 sectored pieces for preparing films having different concentrations of 3-D (spherical) APCs along with 1-D APCs. Film consisting of only 1-D APCs exhibits enhanced in-held JC values as compared to the one without any APC, and the ones consisting of hybrid APCs exhibit even better JC-B characteristics with increase in the fraction of 3-D APCs. Fp max. values increase systematically with incorporation of 1-D and 1-D + 3-D APCs, and it also shifts toward higher applied magnetic fields. Film with 1-D APCs exhibits strong JC peak at Θ = 0° (H//c-axis), whereas films consisting of hybrid APCs exhibit enhanced JC at all the investigated angular regime. A possible mechanism of vortex pinning in samples with hybrid APCs is also discussed, suggesting the role of 1-D and 3-D APCs.
Japanese Journal of Applied Physics | 2010
Shrikant Saini; Gui Shik Kim; Sang-Jae Kim
We have fabricated intrinsic Josephson junction array stack in a Bi2Sr2Ca2Cu3O10+δ (Bi-2223) single crystal whisker using three dimensional focused ion beam milling technique. We report measurements of current density depend on junctions array at 30 K upon the junction cross-sectional area S showing a strong suppression in critical current density for junctions with S≤1 µm2. We discussed quantum fluctuations of phase in submicron junctions which is a cause for suppression of critical current density.
Journal of Applied Physics | 2017
Alok K. Jha; Kaname Matsumoto; Tomoya Horide; Shrikant Saini; Paolo Mele; Ataru Ichinose; Yutaka Yoshida; Satoshi Awaji
The effect of incorporation of nanoscale Y2BaCuO5 (Y211) inclusions on the vortex pinning properties of YBa2Cu3O7-δ (YBCO or Y123) superconducting thin films is investigated in detail on the basis of variation of critical current density (JC) with applied magnetic field and also with the orientation of the applied magnetic field at two different temperatures: 77 K and 65 K. Surface modified target approach is employed to incorporate nanoscale Y211 inclusions into the superconducting YBCO matrix. The efficiency of Y211 nanoinclusions in reducing the angular anisotropy of critical current density is found to be significant. The observed angular dependence of the critical current density is discussed on the basis of mutually occupied volume by a vortex and spherical and/or planar defect. A dip in JC near the ab-plane is also observed which has been analyzed on the basis of variation of pinning potential corresponding to a spherical (3-D) or planar (2-D) pinning center and has been attributed to a reduced int...
IEEE Transactions on Applied Superconductivity | 2016
Alok K. Jha; Kaname Matsumoto; Tomoya Horide; Shrikant Saini; Paolo Mele; Ataru Ichinose; Yutaka Yoshida; Satoshi Awaji
BaSnO 3 (BSO) nanocolumns and Y 2BaCuO5 (Y211) nanoparticles have been successfully incorporated into YBCO thin films by premixed and surface-modified target approach. The effect of these artificially incorporated nanostructures on the vortex pinning properties of YBCO films is investigated based on the variation of critical current density (JC) with applied magnetic field and its variation with respect to the orientation of the applied magnetic field at two different temperatures: 77 and 65 K. The incorporation of Y211 nanoparticles into both YBCO and YBCO + BSO2% films results in improved JC-H characteristics, which is reflected in the enhanced pinning force density (Fp) values. The angular dependent JC measurement reveals that the YBCO film containing BSO nanocolumns exhibits JC peak along the c-axis, whereas the film containing Y211 nanoparticles exhibits isotropic enhancement in the JC values along the entire investigated angular regime. The YBCO film consisting of both kinds of nanostructures (BSO nanocolumns together with Y211 nanoparticles), on the other hand, exhibits mixed characteristics of different kinds of pinning: strong c-axis JC peak together with isotropically enhanced JC in the intermediate angular regime. A possible vortex pinning mechanism due to different kinds of artificially incorporated nanostructures is also discussed.
IEEE Transactions on Applied Superconductivity | 2011
Shrikant Saini; M. Takamura; Masashi Mukaida; Sang-Jae Kim
The <i>a</i>-axis oriented YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> thin films were grown on SrLaGaO<sub>4</sub> (100) substrate with a buffer layer of 50 nm thick Gd<sub>2</sub>CuO<sub>4</sub> using pulsed laser deposition technique. The thickness of Y-123 thin film was about 500 nm. Intrinsic Josephson junctions (CuO<sub>2</sub> planes) were aligned perpendicular to the substrate in the thin films. The bridge type pattern was fabricated using focused ion beam milling technique in such a way so that the current flow along the <i>c</i> -axis in thin film. The dimensions of bridge were 1 μm in length along the <i>c</i>-axis and 5 μm in width along the b-axis. The resistance vs. temperature characteristics showed transition temperature of about 89 K. The critical current density (J<sub>c</sub>) of 2×10<sup>6</sup> A/cm<sup>2</sup> was measured from current-voltage (I-V) characteristics at 10 K. The samples were irradiated with external microwave at 20 GHz and the J<sub>c</sub> was suppressed with increase in power. This suppression in J<sub>c</sub> indicates the formation of layered structure with strong coupling. The voltage steps were appeared with microwave irradiation in I-V characteristics. The values of voltage steps were irregular and change with increase in power. We have also studied all <i>a</i>-axis oriented multilayered thin films of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> (Y123) and PrBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> (Pr123). We fabricated a submicron stack in which Josephson junctions were forming by Y123 and Pr123. The submicron stack showed response with microwave irradiation of different frequency and power. The transport characteristics of these thin films are discussed in detail.