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in creator/contributor: "Weir, S.T."

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Rayleigh-taylor instability growth experiments in a cylindrically convergent geometry

Convergent geometry Rayleigh-Taylor experiments have been performed with a 122-point detonation initiation system on cylinders having sinusoidal perturbations on the outer surface ranging from mode-6 to mode-36. Experiments were performed with various perturbation mode numbers, perturbation amplitudes, and ring accelerations. Feedthrough perturbation growth on the inner surface was observed in several experiments, and in one experiment the feed through perturbation underwent a phase inversion. … more

Date: June 11, 1997

Creator: Weir, S. T., LLNL

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Static ultra-high pressure study of lanthanide and actinide metals using a diamond-anvil cell

Structural phase transformation in lanthanides and actinides were investigated as a function of pressure up to 300 GPa at room temperature. Except in Ce and Pr, no large volume changes were noticed for these metals as thy went through several phase changes. The appearance of a bct ultra-high pressure phase in Ce, Sm, Th, and possibly in Np, raises the possibility that the ultimate high pressure structure for the 4f and 5f metals may be the bct structure. On the other hand, it is also possible t… more

Date: June 30, 1993

Creator: Akella, J.; Smith, G. S. & Weir, S. T.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Electrical conductivity of hydrogen shocked to megabar pressures

The properties of ultra-high pressure hydrogen have been the subject of much experimental and theoretical study. Of particular interest is the pressure-induced insulator-to-metal transition of hydrogen which, according to recent theoretical calculations, is predicted to occur by band-overlap in the pressure range of 1.5-3.0 Mbars on the zero temperature isotherm. Extremely high pressures are required for metallization since the low-pressure band gap is about 15 eV. Recent static-pressure diamon… more

Date: August 1, 1993

Creator: Weir, S. T.; Nellis, W. J. & Mitchell, A. C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Phase changes in f-electron metals: discrepancies between experiment and theory

Using a diamond anvil cell, phase transformation and RT equation of state for lanthanide and actinides were studied to multimegabars. Experimental data are compared with theoretical crystal structural changes and P-V relations. A generalized trend for phase transformations in lanthanides can be seen, which has broad agreement with theory. Broad agreement is also seen for structural changes in lighter actinides, with some discrepancies. It is concluded that an accurate, robust theoretical base f… more

Date: October 1, 1996

Creator: Akella, J.; Weir, S. T.; Smith, G. S. & Ruddle, C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

High-Pressure Magnetic Susceptibility Experiments on the Heavy Lanthanides Gd, Tb, Dy, Ho, Er, and Tm

The high pressure magnetic properties of the heavy lanthanide elements Gd, Tb, Dy, Ho, Er, and Tm have been investigated using ac magnetic susceptibility with a diamond anvil cell. It is found that the magnetic transition temperatures monotonically decrease with increasing pressure. In addition, the amplitudes of the magnetic transition signals decrease with increasing pressure, with the signals all eventually disappearing at pressures by 20 GPa. In contrast to previous studies, we see no evide… more

Date: November 19, 2004

Creator: Jackson, D. D.; Malba, V.; Weir, S. T.; Baker, P. A. & Vohra, Y. K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Diamond Anvils With Integrated Diamond-Encapsulated Microprobes for High-Pressure Electrical Transport Experiments

We have fabricated diamond anvils specially designed for use in ultra-high pressure electrical transport experiments. These anvils, which we refer to as ''designer anvils'', feature thin-film metal microprobes which are encased in a layer of high-quality, epitaxial, chemically vapor deposited (CVD) diamond. The synthetic diamond film ensures that the microprobes are survivable to Mbar pressures, and also serves to electrically insulate the microprobes from the high-pressure gasket. High-pressur… more

Date: July 21, 1999

Creator: Akella, J.; Catledge, S. A.; Vohra, Y. K. & Weir, S. T.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Disks of YBa{sub 2}Cu{sub 3}O{sub 7} shocked to 10 GPa pressures

The brittle superconducting oxide YBa{sub 2}Cu{sub 3}O{sub 7} was shocked to 6.6 and 10.3 GPa without macroscopic fracture. The melt-textured disk-shaped specimen was preferentially oriented and was shock-compressed at an angle of about 30{degrees} from the effective c axis of this orthorhombic-phase specimen. Subsequent anneals of the 6.6 GPa specimen in oxygen at 890{degrees}C produced a magnetic hysteresis which is enhanced relative to the initial unshocked state, as expected for shock-induc… more

Date: August 1, 1993

Creator: Nellis, W. J.; Weir, S. T.; Hinsey, N. A.; Balachandran, U.; Kramer, M. J. & Raman, R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The suppression of magnetism and the development of superconductivity within the collapsed tetragonal phase of Ca0.67Sr0.33Fe2As2 at high pressure

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Date: March 5, 2012

Creator: Jeffries, J R; Butch, N P; Kirshenbaum, K; Saha, S R; Weir, S T; Vohra, Y K et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Electrical Conductivity of the Lower-Mantle Ferropericlase

Electrical conductivity of the lower-mantle ferropericlase-(Mg{sub 0.75},Fe{sub 0.25})O has been studied using designer diamond anvils to pressures over one megabar and temperatures up to 500 K. The electrical conductivity of (Mg{sub 0.75},Fe{sub 0.25})O gradually rises by an order of magnitude up to 50 GPa but decreases by a factor of approximately three between 50 to 70 GPa. This decrease in the electrical conductivity is attributed to the electronic high-spin to low-spin transition of iron i… more

Date: April 19, 2007

Creator: Lin, J. F.; Weir, S. T.; Jackson, D. D.; Evans, W. J.; Vohra, Y. K.; Qiu, W. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

X-ray diffraction studies using diamond coated rhenium gasket to megabar pressures

X-ray diffraction studies at megabar pressures are limited by the sample thickness between the diamond anvils. High strength gaskets are desirable to improve the quality of x-ray diffraction data. We present a technique which employs a microwave plasma chemical vapor deposited diamond layer on one side of a rhenium gasket. As a test case, we show energy dispersive x-ray diffraction data on rare earth metal neodymium to 153 GPa using a synchrotron source. The increased sample thickness results i… more

Date: September 30, 1999

Creator: Akella, J; Catledge, S A; Chesnut, G N; Prokop, H; Vohra, Y K & Weir, S T

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Pressure-Induced Metallization of the Mott Insulator MnO

High-pressure electrical conductivity experiments have been performed on the Mott insulator MnO to a maximum pressure of 106 GPa. We observe a steady decrease in resistivity to 90 GPa, followed by a large, rapid decrease by a factor of 10{sup 5} between 90 and 106 GPa. Temperature cycling the sample at 87 and 106 GPa shows insulating and metallic behavior at these pressures, respectively. Our observations provide strong evidence for a pressure-induced Mott insulator-to-metal transition with an … more

Date: January 12, 2004

Creator: Patterson, J. R.; Aracne, C. M.; Jackson, D. D.; Weir, S. T.; Malba, V.; Baker, P. A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The interplay between magnetism, structure, and strong electron-phonon coupling in binary FeAs under pressure

Unlike the ferropnictide superconductors, which crystallize in a tetragonal crystal structure, binary FeAs forms in an orthorhombic crystal structure, where the local atomic environment resembles a highly distorted variant of the FeAs{sub 4} tetrahedral building block of the ferropnictide superconductors. However, like the parent compounds of the ferropnictide superconductors, FeAs undergoes magnetic ordering at low temperatures, with no evidence favoring a superconducting ground state at ambie… more

Date: November 10, 2010

Creator: Jeffries, J R; Butch, N P; Cynn, H; Saha, S R; Kirshenbaum, K; Weir, S T et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Shock compaction of high- Tc superconductors

We present the results of shock compaction experiments on high-{Tc} superconductors and describe the way in which shock consolidation addresses critical problems concerning the fabrication of high J{sub c} bulk superconductors. In particular, shock compaction experiments on YBa{sub 2}Cu{sub 3}O{sub 7} show that shock-induced defects can greatly increase intragranular critical current densities. The fabrication of crystallographically aligned Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} samples by shoc… more

Date: September 1, 1990

Creator: Weir, S.T.; Nellis, W.J.; McCandless, P.C.; Brocious, W.F. (Lawrence Livermore National Lab., CA (USA)); Seaman, C.L.; Early, E.A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department