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Your search keyword '"Poeppelmeier, K. R."' showing total 254 results
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254 results on '"Poeppelmeier, K. R."'

1. 29Si nuclear magnetic resonance study of URu2Si2 under pressure

Author

Shirer, K. R., Dioguardi, A. P., Bush, B. T., Crocker, J., Lin, C. H., Klavins, P., Cooley, J. C., Maple, M. B., Chang, K. B., Poeppelmeier, K. R., and Curro, N. J.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We report 29Si nuclear magnetic resonance measurements of single crystals and aligned powders of URu2Si2 under pressure in the hidden order and paramagnetic phases. We find that the Knight shift decreases with applied pressure, consistent with previous measurements of the static magnetic susceptibility. Previous measurements of the spin lattice relaxation time revealed a partial suppression of the density of states below 30 K. This suppression persists under pressure, and the onset temperature is mildly enhanced.

Published
2016
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2. Atomic-scale structure of the SrTiO3(001)-c(6x2) reconstruction: Experiments and first-principles calculations

Author

Lanier, C. H., van de Walle, A., Erdman, N., Landree, E., Warschkow, O., Kazimirov, A., Poeppelmeier, K. R., Zegenhagen, J., Asta, M., and Marks, L. D.

Subjects
Condensed Matter - Materials Science
Abstract

The c(6x2) is a reconstruction of the SrTiO3(001) surface that is formed between 1050-1100oC in oxidizing annealing conditions. This work proposes a model for the atomic structure for the c(6x2) obtained through a combination of results from transmission electron diffraction, surface x-ray diffraction, direct methods analysis, computational combinational screening, and density functional theory. As it is formed at high temperatures, the surface is complex and can be described as a short-range ordered phase featuring microscopic domains composed of four main structural motifs. Additionally, non-periodic TiO2 units are present on the surface. Simulated scanning tunneling microscopy images based on the electronic structure calculations are consistent with experimental images.

Published
2007
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3. A Surface Reconstruction with a Fractional Hole: $(\sqrt{5}\times\sqrt{5}) R26.6^\circ$ LaAlO$_3$ (001)

Author

Lanier, C. H., Rondinelli, J. M., Deng, B., Kilaas, R., Poeppelmeier, K. R., and Marks, L. D.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons
Abstract

The structure of the $(\sqrt{5}\times\sqrt{5})R26.6^\circ$ reconstruction of LaAlO$_3$ (001) has been determined using transmission electron diffraction combined with direct methods. The structure is relatively simple, consisting of a lanthanum oxide termination with one lanthanum cation vacancy per surface unit cell. The electronic structure is unusual since a fractional number of holes or atomic occupancies per surface unit cell are required to achieve charge neutrality. Density functional calculations indicate that the charge compensation mechanism occurs by means of highly delocalized holes. The surface contains no oxygen vacancies and with a better than 99% confidence level, the holes are not filled with hydrogen. The reconstruction can be understood in terms of expulsion of the more electropositive cation from the surface followed by an increased covalency between the remaining surface lanthanum atoms and adjacent oxygen atoms., Comment: 4 Pages, 3 Figures

Published
2006
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4. Tunable Conductivity and Conduction Mechanism in a UV light activated electronic conductor

Author

Bertoni, M. I., Mason, T. O., Medvedeva, J. E., Freeman, A. J., Poeppelmeier, K. R., and Delley, B.

Subjects
Condensed Matter - Materials Science
Abstract

A tunable conductivity has been achieved by controllable substitution of a novel UV light activated electronic conductor. The transparent conducting oxide system H-doped Ca12-xMgxAl14O33 (x = 0; 0.1; 0.3; 0.5; 0.8; 1.0) presents a conductivity that is strongly dependent on the substitution level and temperature. Four-point dc-conductivity decreases with x from 0.26 S/cm (x = 0) to 0.106 S/cm (x = 1) at room temperature. At each composition the conductivity increases (reversibly with temperature) until a decomposition temperature is reached; above this value, the conductivity drops dramatically due to hydrogen recombination and loss. The observed conductivity behavior is consistent with the predictions of our first principles density functional calculations for the Mg-substituted system with x=0, 1 and 2. The Seebeck coefficient is essentially composition- and temperature-independent, the later suggesting the existence of an activated mobility associated with small polaron conduction. The optical gap measured remains constant near 2.6 eV while transparency increases with the substitution level, concomitant with a decrease in carrier content., Comment: Submitted for publication

Published
2004
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14. Comparison of thin film and bulk forms of the transparent conducting oxide solution Cd[sub 1+x]In[sub 2-2x]Sn[sub x]O[sub 4].

Author

Kammler, D. R., Mason, T. O., Young, D. L., Coutts, T. J., Ko, D., Poeppelmeier, K. R., and Williamson, D. L.

Subjects
THIN films, SPINEL, OXIDES
Abstract

Physical and structural properties of thin films prepared via rf magnetron sputtering of the transparent conducting oxide spinel Cd[sub 1+x]In[sub 2 - 2x]Sn[sub x]O[sub 4 ] are compared to those reported for bulk specimens (prepared via high-temperature solid state reaction at 1175 °C). Optical band gaps measured on thin films of Cd[sub 1+x]In[sub 2 - 2x]Sn[sub x]O[sub 4 ] were 3.5, 3.70, and 3.65 eV for x=0.15, 0.45, and 0.70, which where 0.57, 0.94, and 0.95 eV higher than their bulk counterparts. Thin film Seebeck coefficients were -18.0, -15.5, and -15.5 µV/K for x = 0.15, 0.45, and 0.70, respectively, which were 27, 24, and 19 µV/K smaller in magnitude than their bulk counterparts. Sn-Mössbauer spectroscopy revealed isomer shifts that averaged 0.2 mm/s for both bulk and thin films specimens. The presence of quadrupole splitting, which averaged near 0.48 mm/s for film specimens and 0.39 mm/s for bulk specimens, suggests that Sn[sup +4] in all specimens is in octahedral coordination. The difference in quadrupole splitting suggests that thin films have a different cation distribution than their bulk counterparts. The effective mass at the base of the conduction band, measured via the method-of-four-coefficients, was found to be 0.25, 0.18, 0.21, and 0.22 m[sub e] for x equal to 0.15, 0.45, 0.70, and 1.0, respectively. A model that explains the changes in optical gap and thermopower as a result of differences in the fundamental band gap (resulting from a changing cation distribution), conduction band curvature, and carrier density is presented. [ABSTRACT FROM AUTHOR]

Published
2001
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16. Microwave absorption of the high-Tc superconductor YBa2Cu3O7.

Author

Poirier, M., Quirion, G., Poeppelmeier, K. R., and Thiel, J. P.

Subjects
SUPERCONDUCTORS, MICROWAVES
Abstract

Focuses on a study that investigated microwave absorption of the high-T[sub c] superconductor ytterbium[sub 2]copper[sub 3]oxygen[sub 7]. Sample and experiment; Results and discussion; Conclusion.

Published
1988
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17. Microwave absorption of aligned crystalline grains of YBa2Cu3O7-x.

Author

Poirier, M., Quirion, G., Quirion, B., D’Orazio, F., Thiel, J. P., Halperin, W. P., and Poeppelmeier, K. R.

Subjects
ANISOTROPY, MAGNETICS, ELECTRICITY, CRYSTALS
Abstract

Presents a study which investigated the anisotropic magnetic and electric properties of aligned crystalline grains of YBa[sub2]Cu[sub3]O[sub7-x]. Sample preparation and experimental details; Results and discussion; Conclusion.

Published
1989
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18. Ag6Mo2O7F3Cl: A New Silver Cathode Material for Enhanced ICD Primary Lithium Batteries

Author

Sauvage, F., Bodenez, V., Tarascon, J.-M., and Poeppelmeier, K. R.

Abstract

As a potential cathode material for the ICD lithium battery, one advantage of Ag6Mo2O7F3Cl (SMOFC) is its enhanced gravimetric capacity of ca.133 mAh/g above 3 V (vs Li+/Li) delivered by two biphasic transitions at 3.46 and 3.39 V (vs Li+/Li). The unique crystal structure of SMOFC enables a high silver ion conduction: σ⊥[001]= 3.10−2S/cm (±2.10−2S/cm) and σ//[001]= 4.10−3S/cm (±2.10−3S/cm) and, hence, an excellent discharge rate capability. Lithium insertion has been monitored by in situXRD measurements with HRTEM investigations. There is a linear isotropic collapse of the structure leading to a fully amorphous structure beyond four inserted lithiums.

Published
2024
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21. A New Layered Copper Oxide: LaSrCuAlO5

Author

Wiley, J. B., primary, Markham, L. M., additional, Vaughey, J. T., additional, McCarthy, T. J., additional, Sabat, M., additional, Hwu, S.-J., additional, Song, S. N., additional, Ketterson, J. B., additional, and Poeppelmeier, K. R., additional

Published
1988
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24. Structural, Optical, and Transport Properties of α- and β-Ag3VO4

Author

Cloet, V., primary, Raw, A., additional, Poeppelmeier, K. R., additional, Trimarchi, G., additional, Peng, H., additional, Im, J., additional, Freeman, A.J., additional, Perry, N. H., additional, Mason, T. O., additional, Zakutayev, A., additional, Ndione, P. F., additional, Ginley, D. S., additional, and Perkins, J. D., additional

Published
2012
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48. Korringa behavior for Cu(2) in YBa2Cu3O6.98

Author

Song, Y. Q., Lee, M., Tea, N., D'Orazio, Franco, Bhattacharja, S., Halperin, W. P., Thiel, J. P., Poeppelmeier, K. R., Welp, U., Crabtree, G. W., and Fang, M. M.

Published
1990

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