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The high-pressure solid phase stability of molybdenum (Mo) has been the center of a long-standing controversy on its high-pressure melting. In this work, experimental and theoretical researches have been conducted to check its solid phase stability under compression. First, we performed sound velocity measurements from 38 to 160 GPa using the two-stage light gas gun and explosive loading in backward- and forward-impact geometries, along with the high-precision velocity interferometry. From the sound velocities, we found no solid-solid phase transition in Mo before shock melting, which does not support the previous solid-solid phase transition conclusion inferred from the sharp drops of the longitudinal sound velocity [Hixson et al., Phys. Rev. Lett. 62, 637 (1989)]. Then, we searched its structures globally using the multi-algorithm collaborative crystal structure prediction technique combined with the density functional theory. By comparing the enthalpies of body centered cubic structure with those of the metastable structures, we found that bcc is the most stable structure in the range of 0-300 GPa. The present theoretical results together with previous ones greatly support our experimental conclusions. [ABSTRACT FROM AUTHOR]

The Hugoniot of preheated metal is related with its principal Hugoniot by means of the Grüneisen equation of state and the Rankine-Hugoniot equation. Modeling calculations show that the preheating lowers to a certain extent the shock impedance. The evaluated Hugoniot of preheated Mo is comparable with the available experimental data. Hugoniots of 6061-T6 Al flyers of different preheat temperatures in reported Hugoniot experiments on Z pinch [Knudson et al., J. Appl. Phys. 94, 4420 (2003)] are calculated, and the determined shock states of 6061-T6 Al using the impedance-match method are consistent with the reported results. This approach allows a reasonable evaluation for Hugoniot of the preheated metal mainly from its principal Hugoniot. [ABSTRACT FROM AUTHOR]

A series of reverse-impact experiments were performed on vanadium at shock pressure ranging from 32GPa to 88GPa. Particle velocity profiles measured at sample/LiF window interface were used to estimate the sound velocities, shear modulus, and yield stress in shocked vanadium. A phase transition at ~60.5 GPa that may be the body-centered cubic (BCC) to rhombohedral structure was identified by the discontinuity of the sound velocity against shock pressure. This transition pressure is consistent with the results from diamond anvil cell (DAC) experiments and first-principle calculations. However, present results show that the rhombohedral phase has higher strength and shear modulus than the BCC phase, which is contrast to the findings from DAC experiments and theoretical work. [ABSTRACT FROM AUTHOR]

Longitudinal and bulk sound velocities of tin in the shock pressure range from ∼25 to ∼80 GPa were measured using a direct reverse-impact method. The bct to bcc phase transition along the Hugoniot was identified by the discontinuity of the longitudinal sound velocity against shock pressure. The incipient melting on the Hugoniot was also revealed by the transition from longitudinal to bulk sound velocity. The shock pressure for bct-bcc phase transition and incipient melting were constrained to be ∼35 and ∼45 GPa, respectively. It is inferred that the bcc phase possesses higher shear modulus than the bct phase. [ABSTRACT FROM AUTHOR]