Effect of shock loading on transparency of sapphire crystals

Urtiew, P. A.

doi:10.1063/1.1663807

Cited by 76 publications

(24 citation statements)

References 2 publications

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“…The Hugoniot fit shows no indication of phase transitions observed in a laserheated DAC at 103 and 124 GPa. Under shock compression the onset of opacity 21 and decrease in electrical resistivity of sapphire 22 at 130 GPa correlate with the predicted transition to CaIrO 3 type observed in a DAC. Because of the relatively low bulk temperatures, strong ͑approximately electron volt͒ interatomic bonds, and short experimental lifetimes ͑100 ns͒, shock dissipation in Al 2 O 3 is dominated by entropy generation, shocked sapphire is probably not in thermal equilibrium, and shocked Al 2 O 3 probably never enters the Rh 2 O 3 ͑II͒-type phase.…”

supporting

confidence: 57%

Al2O3as a metallic glass at 300 GPa

Nellis

2010

Phys. Rev. B

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Based on published experiments and theory, we predict that strong covalent single-crystal Al 2 O 3 with a 10 eV band gap becomes a metallic glass at ϳ300 GPa under shock and static compression. The insulator-metal transition is probably entropy driven, i.e., compressive energy is absorbed by breaking bonds. Resulting Al and O atom densities are sufficiently high for hybridization into a metal. Alternatively, if Al and O phase separate, electrical conduction occurs through Al filaments whether or not O conducts. If Al 2 O 3 metallizes, other strong insulators are expected to do so as well.

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supporting

confidence: 57%

Al2O3as a metallic glass at 300 GPa

Nellis

2010

Phys. Rev. B

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“…Urtiew observed that shock-compressed sapphire loses some of its transparency in the infrared at stresses in the range 100 to 130 GPa [13]. More recently, the electrical resistivity of shocked sapphire was found to begin to decrease significantly with increasing shock pressures above 130 GPa [14], which is consistent with Urtiew's results.…”

Section: Introductionsupporting

confidence: 80%

“…Graham and Brooks then measured the Hugoniots of c-cut, a-cut (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), and n-cut (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) sapphire crystals [4]. The normals to the flat surfaces of a-cut and of n-cut crystals are parallel to the a axis and n axis, respectively.…”

Section: Introductionmentioning

confidence: 99%

Response of seven crystallographic orientations of sapphire crystals to shock stresses of 16–86 GPa

Kanel

Nellis

Савиных

et al. 2009

Journal of Applied Physics

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Shock-wave profiles of sapphire (single-crystal Al 2 O 3 ) with seven crystallographic orientations (c, d, r, n, s, g, and m-cut) were measured with time-resolved VISAR interferometry at shock stresses in the range 16 to 86 GPa. Shock propagation was in the direction normal to the surface of each cut. The angle between the c-axis of the hexagonal representation of the sapphire crystal structure and the direction of shock propagation varied from 0 for c-cut up to 90 degrees for m-cut in the basal plane. Based on published shock-induced transparencies for 3 directions of shock propagation, shock-induced optical transparency correlates with the smoothness of the mechanical shock-wave profile. The ultimate goal was to find the direction of shock propagation for which shock-compressed sapphire is most transparent as a window material. In the experiments particle velocity histories were recorded at the interface between a sapphire crystal and a LiF window. In most cases measured wave profiles are noisy as a result of heterogeneity of deformation. Measured values of Hugoniot Elastic Limits (HELs) depend on direction of shock compression and peak shock stress. The largest HEL values (24 GPa) were recorded for shock loading along the c-axis and perpendicular to c along the m-direction. Shock compression along the m-and s-directions is accompanied by the smallest heterogeneity of deformation and the smallest rise time of the plastic shock wave. m-and s-cut sapphire most closely approach ideal elastic-plastic flow, which suggests that m-and s-cut sapphire are probably the sapphire orientations that remains the most transparent to the highest shock pressures. Under purely elastic deformation sapphire demonstrates very high spall strength, which depends on both load duration and peak stress. Plastic deformation of sapphire causes loss of its tensile strength.2

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“…It may also affect the pressure determination in A1203 optical window or pressure medium under ultra-high pressures in shock-compression experiments. In addition, defect production associated with the phase transformation could explain the increased opacity, nonthermal characteristic spectrum and increase in electrical conductivity that has been reported in pure A120• under shock compression [Urtiew, 1974;Yoo et al, 1993;Weir, et al, 1996].…”

Section: Resultsmentioning

confidence: 99%