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Joseph Gal

Publications and source records attributed to Joseph Gal.

7 recordsLinked to original sources
arXiv2022

Correction of the pressure scales reliant to the thermal pressures shifts in iron (3d) vanadium (4d), iridium and platinum (5d) transition metals

In many published articles isobaric behavior in DAC chambers has been reported On the other hand, a clear isochoric behavior in the chambers were reported. Thus, Isochoric or isobaric condition remain an open question. In isochoric condition, upon increasing the temperature, at each pressure, the examined sample and the PTM both are subject to increases of their volumes which is suppressed by the chamber finite volume, provoking an increase in the thermal pressure over the whole system. For this reason, the pressure scale reported in DAC experiments do not represent the actual pressure experienced by the sample in the cell. The different response of the PTMs to P,T changes is the reason for the variety of melting curves reported in the literature. It is concluded that the pressure scale in DAC experiments need a correction taking in to account the thermal pressure shift. Trusting the first principals DFT- Z methodology it is shown that the melting curve derived by this method should serve as an anchor for the pressure scale correction.

cond-mat.mtrl-sci↗
arXiv2022

The actual pressure and temperature at the melt of elemental vanadium

It is claimed that all of the pressure scales of the reported melting curves derived by diamond anvil cell experiments require a correction which takes into account the pressure thermal shift, where vanadium is an illustrative example. The linear behavior of the thermal pressure (Pth) vs. the temperature, as predicted by first principles theoretical assumptions is then experimentally confirmed. This allows extrapolation to determine of the actual pressure and thermal temperature at the melt. Accounting for the role of the pressure transmitting media in diamond anvil cell experiments, the analysis of elemental vanadium melting curve is presented. It is shown that the appropriate correction of shock waves melting data which takes into account the radiation absorbed by the LiF window, applies only to vanadium metal. The correct pressure scale of vanadium metal as derived by diamond anvil cell is presented.

cond-mat.mtrl-sci↗
arXiv2022

Comment on the Evidence of isostructural phase transitions in elemental zirconium

It is argued that the article by O.Bannon et al. ; High pressure stability of beta-Zr: no evidence for isostructural phase transitions, published recently -July 2021 - in High Pressure Research has no experimental foundation and the statement no evidence is absolutly misleading. Isostructural phase transition has been reported only in Ce metal, thus, the Beta-Zr to beta prime -Zr isostructural phase transitions has fundamental interest in condensed matter physics.

cond-mat.mtrl-sci↗
arXiv2020

Cascading crystallographic transitions and melting curve of elemental zirconium

Precise fitting of the experimental data analyzed separately for each identified crystallographic phase alpha, omega, beta, beta prime and beta double prime yield different bulk moduli Bo and Bo prime and different zero pressure volumes (Vo) than those claimed in the literature. Special attention is given to the bcc phases indicating cascading transitions beta to beta prime to beta double prime associated with volume collapse. The present analysis reveals the existence of a bcc-beta prime phase which is reported here for the first time. It is shown that the first order volume collapse at about 58GPa beta to beta prime is followed by a moderate transition to the bcc-beta double prime phase. The beta prime phase is stable up to 110GPa. Above 110GPa the bcc-beta double prime is dominant and stable up to about 220GPa. The derived bcc-double prime bulk moduli are confirmed by the Lindemann-Gilvarry criterion as Bo and Bo prime simultaneously fit both the P-V EOS and the P-T melting data points (combined approach). The calculated melting curve of elemental Zr, taking into account the thermal pressure Poth shift and the elevated melting Tmo prime at Poth , yield very good fit of the experimental melting data permitting a safe extrapolation to high pressures and temperatures. In addition, the combined approach lead to direct determination of the Greuneisen parameter gammao, needed for applying the approximated Lindemann-Gilvarry melting formula.

cond-mat.mtrl-sci↗
arXiv2020

Evidence of liquid-liquid phase transition in compressed Ar probed by the thermal expansion of Mo, Ta and W at high pressures

The long standing controversy between the melting curves of the bcc Mo,Ta,W and vanadium (V) metals measured by diamond anvil Cells (DAC) and the shock dynamic experiments is explained by the behavior the liquid or solid pressure transmitting mediums compressed by the thermal expansion of the these transition metals. This explains the observed isobaric behavior of the laser heated DAC experiments containing different transmitting mediums reported in the literature, thus solving the standing enigma described in very many publications.

cond-mat.mtrl-sci↗
arXiv2019

Melting curves of Al,Cu,U and Fe metals utilizing the Lindemann-Gilvarry criterion and parameterization of the equations of state

The prediction of the melting curve of metals by extrapolation to high pressures and temperatures based on the Lindemann-Gilvarry criterion (LG) assuming harmonic Debye solid is presented. The LG formulation uses the bulk modulus B and its pressure derivative B' as fit parameters deduced directly from the equation of state, however, the results are not unique and strongly depends on the chosen equation of state (EOS). By introducing a constraint that the bulk moduli parameters B and B' must simultaneously obey the Lindemann-Gilvarry criterion (LG) and the EOS, consistent bulk moduli are derived. The cold pressure Pc and the cold melting curve are obtained by introducing an effective Grüneisen parameter ($γ$eff) to the LG approximated equation together with the above constraint. It is claimed that isochoric condition exists in diamond anvil cells (DAC), thus upon raising the temperature and approaching the melt constant volume is maintained. Isochoric condition in the DAC means that the developed thermal pressure (Pth) should be accounted in the LG formulation. Therefor, the actual pressure (Pc+Pth) sensed by the sample confined in the DAC should be inserted to the LG melting formula. This brings along the demand that the shock waves Hugoniot melting data should serve as anchor for deriving the correct melting curves of metals where the Grüneisen parameter $γ$ at ambient conditions ($γ$ o) is directly determined. The melting curves up to ultra high pressures of Al, Cu, U and Fe metals are presented and discussed. In this manner, special attention is given to $ε$-Fe as isobaric condition in the DAC has been claimed. Utilizing the present approach we obtain the melting temperature of iron in the earth inner core boundary (ICB, 330GPa) is 5900$\pm$100K.

cond-mat.mtrl-sci↗