Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session Y7: Postdeadline CM.2 Phase Transformations |
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Chair: Marion Harmand, LULI, Ecole Polytechnique Room: Grand Crescent |
Friday, July 12, 2013 9:15AM - 9:30AM |
Y7.00001: Melting Kinetic Effects in Metals Caused by a Femtosecond Laser Pulse Polina Krasnova, Dmitry Minakov, Mikhail Povarnitsyn, Pavel Levashov, Konstantin Khishchenko Melting of metals induced by a femtosecond laser pulse represents a non-equilibrium process. At the initial stage of melting and medium evolution the temperature of electrons is significantly higher than that of the ions one. This difference may lead to the increasing of the crystal melting temperature, and also to more complex relations between the temperature of electrons and ions and the transport coefficients (permittivity, thermal conductivity, electron-ion exchange). We have investigated the influence of these effects on the temperature of electrons and ions of an aluminum target using the two-temperature model. A simple kinetic model based on the evaluation of the overheated crystal lifetime was used. We estimated the increasing of the melting temperature by means of quasi-harmonic model and Lindemann criterion, and the equation of state for electrons and spinodal parameters of the crystals by means of numerical modeling using DFT and quantum molecular dynamics. The equation of state for ions is semiempirical. We provided the analysis of kinetic effects of melting of an aluminum target induced by a femtosecond laser pulse for variety of intensities. [Preview Abstract] |
Friday, July 12, 2013 9:30AM - 9:45AM |
Y7.00002: The effect of in-situ high-temperature high-pressure on the structural changes of single-crystal relaxor ferroelectrics PbSc$_{1/2}$Ta$_{1/2}$O$_{3}$ (PST) and PbSc$_{1/2}$Nb$_{1/2}$O$_{3}$ (PSN) Naemi Waeselmann, Boriana Mihailova, Marin Gospodinov, Ullrich Bismayer Relaxor ferroelectrics (relaxor) of the perovskite structure (ABO$_{3})$ have remarkably high dielectric permittivity dependent on temperature and frequency as well as remarkable piezoelectric and electro-optic coefficients. These structurally heterogeneous materials undergo a sequence of structural changes on the mesoscopic scale associated with characteristic temperatures resulting from the development of polar order on temperature decrease. Pressure increase on the other hand favors antiferrodistortive order at room temperature. To explore the importance of the antiferrodistortive coupling on the development of polar order simultaneous high-temperature high-pressure Raman studies were undertaken on single crystals of PST and PSN from 400 - 600 K over pressures extending to 9 GPa. We find that the first pressure-induced transition p$_{\mathrm{c1}}$ decreases with temperature while the second transition p$_{\mathrm{c2}}$ is relatively temperature independent. The behavior of p$_{\mathrm{c1}}$ is interpreted as a weakening of the polar coupling, which in turn facilitates the evolution of the preexisting medium-range antiferodistortive order into a long-range order. The near constant value of p$_{\mathrm{c2}}$ suggests that it is independent of the state of polar coupling and is mainly related to the initial correlation length of antiferrodistortive order. Thus the coexistence of both polar order and antiferrodistortive order is required for the occurrence of the relaxor state. [Preview Abstract] |
Friday, July 12, 2013 9:45AM - 10:00AM |
Y7.00003: Brightness Temperature and Physical-Chemical Transformation of Epoxy Resin under Shock Compression Sergey A. Bordzilovskii, Sergey M. Karakhanov, Konstantin V. Khishchenko The interest in properties of polymers at high pressure and temperature arises from their applications as structural materials in shock-wave experiments. In particular, the optical characteristics of some polymers make it possible to use those as window materials in pyrometric measurements and in VISAR technique. In the present work, we investigate the spectral radiance, which is registered in the direction of shock propagation through the epoxy EC141NF samples loaded to the pressure in the range from 19 to 42~GPa. The brightness temperature of the shocked epoxy EC141NF was measured by the optical pyrometer. Experimental points are in agreement with equation-of-state results within the limits of the error. The conclusion about the absence of the chemical transformation in the epoxy at the pressure 22.5~GPa during the observation time was drawn basing on the registered particle velocity profiles. [Preview Abstract] |
Friday, July 12, 2013 10:00AM - 10:15AM |
Y7.00004: Effect of pressure on band structure properties of Zinc Chalcogenides Dharmbir Singh The first principal calculations have been carried out to study the effect of pressure on band structure of Zinc Chalcogenides. The tight-binding linear muffin-tin orbital method (TB-LMTO) within local density approximation (LDA) has been used to study the band structure properties at abmbient and high pressure. The phase stability is determined from the total energy calculations within the atomic-sphere approximation (ASA). The purely theoretical calculations show that in these materials (i) at ambient pressure, zinc blende type (B3) phase is more stable than rock salt type (B1) phase; and (ii) it exhibits a phase transition from zinc blende (B3) type to NaCl type (B1) type structure at high pressure. At further ultrahigh pressure there is phase transition from NaCl type (B1) phase to CsCl type ($B$2) phase. Although the calculated lattice parameter, transition pressure, volume of collapse is found to be little less than the experimentally observed value, but this has been explained from the fact that the calculation has been carried out at 0 K while the experiments have been performed at room temperature. Ambient {\&} high pressure band structural results are compared with earlier obtained similar results and explained in details. [Preview Abstract] |
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