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Dhananjai Pandey - One of the best experts on this subject based on the ideXlab platform.
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morphotropic phase Boundary in 1 x bifeo3 xpbtio3 phase coexistence Region and unusually large tetragonality
Applied Physics Letters, 2007Co-Authors: Shuvrajyoti Bhattacharjee, Saurabh Tripathi, Dhananjai PandeyAbstract:It is shown that the tetragonal (T) and rhombohedral (R) structures of (1−x)BiFeO3–xPbTiO3 are stable for xT⩾0.31 and xR⩽0.27, respectively, giving the narrowest width of 0.03, reported so far, for the morphotropic phase Boundary Region in this system. The Rietveld refined structure of the T phase for x=0.31 reveals partial covalent character of the Ti∕Fe–O and Pb∕Bi–O bonds which may be responsible for the unusually large tetragonality.
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evidence for mb and mc phases in the morphotropic phase Boundary Region of 1 x pb mg1 3nb2 3 o3 xpbtio3 a rietveld study
Physical Review B, 2003Co-Authors: Akhilesh Kumar Singh, Dhananjai PandeyAbstract:We present here the results of the room-temperature dielectric measurements and Rietveld analysis of the powder x-ray diffraction data on (1-x)[Pb(Mg 1 / 3 Nb 2 / 3 )O 3 ]-xPbTiO 3 (PMN-xPT) in the composition range 0.20≤x≤0.45 to show that the morphotropic phase Boundary Region contains two monoclinic phases with space groups Cm (or M B type) and Pm (or M C type) stable in the composition ranges 0.27≤x≤0.30 and 0.31≤x≤0.34, respectively. The structure of PMN-xPT in the composition ranges 0≤x≤0.26 and 0.35≤x ≤1 is found to be rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are compared with the predictions of Vanderbilt & Cohen's theory.
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evidence for mb and mc phases in the morphotropic phase Boundary Region of 1 x pb mg1 3nb2 3 o3 xpbtio3 a rietveld study
Physical Review B, 2003Co-Authors: Akhilesh Kumar Singh, Dhananjai PandeyAbstract:We present here the results of the room-temperature dielectric measurements and Rietveld analysis of the powder x-ray diffraction data on $(1\ensuremath{-}x)[\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}]\ensuremath{-}x{\mathrm{PbTiO}}_{3}(\mathrm{PMN}\ensuremath{-}x\mathrm{PT})$ in the composition range $0.20l~xl~0.45$ to show that the morphotropic phase Boundary Region contains two monoclinic phases with space groups Cm (or ${M}_{B}$ type) and Pm (or ${M}_{C}$ type) stable in the composition ranges $0.27l~xl~0.30$ and $0.31l~xl~0.34,$ respectively. The structure of $\mathrm{PMN}\ensuremath{-}x\mathrm{PT}$ in the composition ranges $0l~xl~0.26$ and $0.35l~xl~1$ is found to be rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are compared with the predictions of Vanderbilt Cohen's theory.
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room temperature structure of pb zrxti1 xo3 around the morphotropic phase Boundary Region a rietveld study
Journal of Applied Physics, 2002Co-Authors: Rajeev Ranjan, Shashank Mishra, Dhananjai PandeyAbstract:We have carried out a detailed Rietveld analysis of x-ray powder diffraction data of Pb(ZrxTi1−x)O3 (PZT) compositions across the morphotropic phase Boundary (MPB) Region (x=0.515, 0.520, 0.525, 0.530). It is shown that the structure of PZT is pure tetragonal for x⩽0.515 with space group P4mm. In the MPB Region, 0.515
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structure and the location of the morphotropic phase Boundary Region in 1 x pb mg1 3nb2 3 o3 xpbtio3
Journal of Physics: Condensed Matter, 2001Co-Authors: Akhilesh Kumar Singh, Dhananjai PandeyAbstract:The structure of (1-x)[Pb(Mg1/3Nb2/3)O3]-xPbTiO3 is tetragonal and rhombohedral for x≥0.35 and x≤0.30, respectively. The intrinsic width of the morphotropic phase Boundary Region (0.30
Akhilesh Kumar Singh - One of the best experts on this subject based on the ideXlab platform.
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grain size dependent phase stabilities and presence of a monoclinic pm phase in the morphotropic phase Boundary Region of 1 x bi mg1 2ti1 2 o3 xpbtio3 piezoceramics
Journal of Applied Physics, 2015Co-Authors: Ashutosh Upadhyay, Akhilesh Kumar SinghAbstract:Results of the room temperature structural studies on (1−x)Bi(Mg1/2Ti1/2)O3-xPbTiO3 ceramics using Rietveld analysis of the powder x-ray diffraction data in the composition range 0.28 ≤ x ≤ 0.45 are presented. The morphotropic phase Boundary Region exhibits coexistence of monoclinic (space group Pm) and tetragonal (space group P4 mm) phases in the composition range 0.33 ≤ x ≤ 0.40. The structure is nearly single phase monoclinic (space group Pm) in the composition range 0.28 ≤ x ≤ 0.32. The structure for the compositions with x ≥ 0.45 is found to be predominantly tetragonal with space group P4 mm. Rietveld refinement of the structure rules out the coexistence of rhombohedral and tetragonal phases in the morphotropic phase Boundary Region reported by earlier authors. The Rietveld structure analysis for the sample x = .35 calcined at various temperatures reveals that phase fraction of the coexisting phases in the morphotropic phase Boundary Region varies with grain size. The structural parameters of the two...
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evidence for mb and mc phases in the morphotropic phase Boundary Region of 1 x pb mg1 3nb2 3 o3 xpbtio3 a rietveld study
Physical Review B, 2003Co-Authors: Akhilesh Kumar Singh, Dhananjai PandeyAbstract:We present here the results of the room-temperature dielectric measurements and Rietveld analysis of the powder x-ray diffraction data on (1-x)[Pb(Mg 1 / 3 Nb 2 / 3 )O 3 ]-xPbTiO 3 (PMN-xPT) in the composition range 0.20≤x≤0.45 to show that the morphotropic phase Boundary Region contains two monoclinic phases with space groups Cm (or M B type) and Pm (or M C type) stable in the composition ranges 0.27≤x≤0.30 and 0.31≤x≤0.34, respectively. The structure of PMN-xPT in the composition ranges 0≤x≤0.26 and 0.35≤x ≤1 is found to be rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are compared with the predictions of Vanderbilt & Cohen's theory.
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evidence for mb and mc phases in the morphotropic phase Boundary Region of 1 x pb mg1 3nb2 3 o3 xpbtio3 a rietveld study
Physical Review B, 2003Co-Authors: Akhilesh Kumar Singh, Dhananjai PandeyAbstract:We present here the results of the room-temperature dielectric measurements and Rietveld analysis of the powder x-ray diffraction data on $(1\ensuremath{-}x)[\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}]\ensuremath{-}x{\mathrm{PbTiO}}_{3}(\mathrm{PMN}\ensuremath{-}x\mathrm{PT})$ in the composition range $0.20l~xl~0.45$ to show that the morphotropic phase Boundary Region contains two monoclinic phases with space groups Cm (or ${M}_{B}$ type) and Pm (or ${M}_{C}$ type) stable in the composition ranges $0.27l~xl~0.30$ and $0.31l~xl~0.34,$ respectively. The structure of $\mathrm{PMN}\ensuremath{-}x\mathrm{PT}$ in the composition ranges $0l~xl~0.26$ and $0.35l~xl~1$ is found to be rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are compared with the predictions of Vanderbilt Cohen's theory.
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structure and the location of the morphotropic phase Boundary Region in 1 x pb mg1 3nb2 3 o3 xpbtio3
Journal of Physics: Condensed Matter, 2001Co-Authors: Akhilesh Kumar Singh, Dhananjai PandeyAbstract:The structure of (1-x)[Pb(Mg1/3Nb2/3)O3]-xPbTiO3 is tetragonal and rhombohedral for x≥0.35 and x≤0.30, respectively. The intrinsic width of the morphotropic phase Boundary Region (0.30
Thomas F Nagler - One of the best experts on this subject based on the ideXlab platform.
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osmium and lead isotopes of rare osirru minerals derivation from the core mantle Boundary Region
Earth and Planetary Science Letters, 1999Co-Authors: John M Bird, Anders Meibom, Robert Frei, Thomas F NaglerAbstract:We report exceptionally high Os-186/Os-188 for rare crystals of OsIrRu found in unconsolidated sediment near Port Orford, SW Oregon (USA), that are held to be derived from peridotite: in the nearby Klamath Mountains. These OsIrRu samples differ in composition from OsIr alloys thought to have formed in the upper mantle. They have resided in equilibrium with an evolved and highly supra-chondritic Pt/Os reservoir. We explore these data in the context of the core-mantle mixing model relevant to some deep-seated plume systems, and find the investigated alloys to exhibit an apparent coupled Os-186/Os-188 and Os-187/Os-188 (gamma Os(t = 1.4Ga) = +6 to +10) enrichment relative to the chondritic mantle at similar to 1.4 Ga, Our interpretation is that these samples crystallized at similar to 1.4 Ga in a long-term Pt/Os nod Re/Os enriched Region, similar to that expected for Earth's outer core or the core-mantle transition zone (D " layer). Subsequently, these OsIrRu samples were transported from the core-mantle Boundary Region to the lithosphere as xenoliths in a mantle plume/convection system. Lead isotopes positively exclude a crustal origin of these OsIrRu crystals and support our estimated time of crystallization. (C) 1999 Elsevier Science B.V. All rights reserved.
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osmium and lead isotopes of rare osirru minerals derivation from the core mantle Boundary Region
Earth and Planetary Science Letters, 1999Co-Authors: John M Bird, Anders Meibom, Robert Frei, Thomas F NaglerAbstract:We report exceptionally high Os-186/Os-188 for rare crystals of OsIrRu found in unconsolidated sediment near Port Orford, SW Oregon (USA), that are held to be derived from peridotite: in the nearby Klamath Mountains. These OsIrRu samples differ in composition from OsIr alloys thought to have formed in the upper mantle. They have resided in equilibrium with an evolved and highly supra-chondritic Pt/Os reservoir. We explore these data in the context of the core-mantle mixing model relevant to some deep-seated plume systems, and find the investigated alloys to exhibit an apparent coupled Os-186/Os-188 and Os-187/Os-188 (gamma Os(t = 1.4Ga) = +6 to +10) enrichment relative to the chondritic mantle at similar to 1.4 Ga, Our interpretation is that these samples crystallized at similar to 1.4 Ga in a long-term Pt/Os nod Re/Os enriched Region, similar to that expected for Earth's outer core or the core-mantle transition zone (D " layer). Subsequently, these OsIrRu samples were transported from the core-mantle Boundary Region to the lithosphere as xenoliths in a mantle plume/convection system. Lead isotopes positively exclude a crustal origin of these OsIrRu crystals and support our estimated time of crystallization. (C) 1999 Elsevier Science B.V. All rights reserved.
C. Hidalgo - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of dynamical coupling between turbulent transport and parallel flows in the jet plasma Boundary Region
Physical Review Letters, 2003Co-Authors: C. Hidalgo, M. A. Pedrosa, C. Silva, B. Gonçalves, K. Erents, M. Hron, G F MatthewsAbstract:The dynamical coupling between turbulent transport and parallel flows has been investigated in the plasma Boundary Region of the Joint European Torus tokamak. Experimental results show that there is a dynamical relationship between transport and parallel flows. As the size of transport events increases, parallel flows also increase. These results show that turbulent transport can drive parallel flows in the plasma Boundary of fusion plasmas. This new type of measurement is an important element to unravel the overall picture connecting radial transport and flows in fusion plasmas.
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experimental evidence of fluctuations and flows near marginal stability and dynamical interplay between gradients and transport in the jet plasma Boundary Region
Journal of Nuclear Materials, 2003Co-Authors: C. Hidalgo, M. A. Pedrosa, C. Silva, B. Gonçalves, K. Erents, M. Hron, G F Matthews, R Balbin, A Loarte, R A PittsAbstract:The structure of the naturally occurring velocity shear layer and the dynamical coupling between gradients and transport have been investigated in the JET plasma Boundary Region. The velocity shear layer appears to organize itself to reach a condition in which the radial gradient in the poloidal phase velocity of fluctuations is comparable to the inverse of the correlation time of fluctuations (1/tau). This result suggests that E x B sheared flows organized themselves to be close to marginal stability (i.e. omega(ExB) approximate to 1/tau). The size of turbulent events increases when the plasma deviates from the average gradient. The resulting radial velocity of fluctuations is of the order of 20 m/s for transport events implying a small deviation from the most probable gradient. This value is consistent with a diffusive modeling with B2-Eirene. The radial velocity increases up to 500 m/s for large transport events. (C) 2003 Elsevier Science B.V. All rights reserved.
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statistical characterization of fluctuation wave forms in the Boundary Region of fusion and nonfusion plasmas
Physics of Plasmas, 2000Co-Authors: E Sanchez, C. Hidalgo, M. A. Pedrosa, D Lopezbruna, I Garciacortes, R Balbin, B Van Milligen, C Riccardi, G Chiodini, J BleuelAbstract:The statistical properties of plasma fluctuations have been investigated in the plasma Boundary Region of fusion (tokamaks and stellarators) and nonfusion plasmas. Fluctuations in ion saturation current and floating potential have a near-Gaussian character in the proximity of the velocity shear layer (rsh). However, fluctuations deviate from a Gaussian distribution when moving inside of the plasma edge (r rsh). Furthermore, fluctuations show sporadic pulses that are asymmetric in time. The present analysis shows a coupling of those pulses and the averaged flow in the shear layer Region.
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radial structure of reynolds stress in the plasma Boundary of tokamak plasmas
Physical Review Letters, 1999Co-Authors: C. Hidalgo, M. A. Pedrosa, C. Silva, E Sanchez, H Fernandes, C A F VarandasAbstract:The radial profile of Reynolds stress has been measured in the plasma Boundary Region of the ISTTOK tokamak using a multiarray of Langmuir probes. The electrostatic Reynolds stress component, proportional to the cross correlation of radial and poloidal fluctuating electric fields, shows a radial gradient close to the velocity shear layer location. It is shown that this mechanism may drive significant poloidal flows in the plasma Boundary Region.
John M Bird - One of the best experts on this subject based on the ideXlab platform.
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osmium and lead isotopes of rare osirru minerals derivation from the core mantle Boundary Region
Earth and Planetary Science Letters, 1999Co-Authors: John M Bird, Anders Meibom, Robert Frei, Thomas F NaglerAbstract:We report exceptionally high Os-186/Os-188 for rare crystals of OsIrRu found in unconsolidated sediment near Port Orford, SW Oregon (USA), that are held to be derived from peridotite: in the nearby Klamath Mountains. These OsIrRu samples differ in composition from OsIr alloys thought to have formed in the upper mantle. They have resided in equilibrium with an evolved and highly supra-chondritic Pt/Os reservoir. We explore these data in the context of the core-mantle mixing model relevant to some deep-seated plume systems, and find the investigated alloys to exhibit an apparent coupled Os-186/Os-188 and Os-187/Os-188 (gamma Os(t = 1.4Ga) = +6 to +10) enrichment relative to the chondritic mantle at similar to 1.4 Ga, Our interpretation is that these samples crystallized at similar to 1.4 Ga in a long-term Pt/Os nod Re/Os enriched Region, similar to that expected for Earth's outer core or the core-mantle transition zone (D " layer). Subsequently, these OsIrRu samples were transported from the core-mantle Boundary Region to the lithosphere as xenoliths in a mantle plume/convection system. Lead isotopes positively exclude a crustal origin of these OsIrRu crystals and support our estimated time of crystallization. (C) 1999 Elsevier Science B.V. All rights reserved.
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osmium and lead isotopes of rare osirru minerals derivation from the core mantle Boundary Region
Earth and Planetary Science Letters, 1999Co-Authors: John M Bird, Anders Meibom, Robert Frei, Thomas F NaglerAbstract:We report exceptionally high Os-186/Os-188 for rare crystals of OsIrRu found in unconsolidated sediment near Port Orford, SW Oregon (USA), that are held to be derived from peridotite: in the nearby Klamath Mountains. These OsIrRu samples differ in composition from OsIr alloys thought to have formed in the upper mantle. They have resided in equilibrium with an evolved and highly supra-chondritic Pt/Os reservoir. We explore these data in the context of the core-mantle mixing model relevant to some deep-seated plume systems, and find the investigated alloys to exhibit an apparent coupled Os-186/Os-188 and Os-187/Os-188 (gamma Os(t = 1.4Ga) = +6 to +10) enrichment relative to the chondritic mantle at similar to 1.4 Ga, Our interpretation is that these samples crystallized at similar to 1.4 Ga in a long-term Pt/Os nod Re/Os enriched Region, similar to that expected for Earth's outer core or the core-mantle transition zone (D " layer). Subsequently, these OsIrRu samples were transported from the core-mantle Boundary Region to the lithosphere as xenoliths in a mantle plume/convection system. Lead isotopes positively exclude a crustal origin of these OsIrRu crystals and support our estimated time of crystallization. (C) 1999 Elsevier Science B.V. All rights reserved.