arXiv subjects

Daniel Errandonea

Publications and source records attributed to Daniel Errandonea.

45 records · Page 3Linked to original sources

arXiv2013

The high-pressure high-temperature phase diagram of calcium fluoride from classical atomistic simulations

We study the phase diagram of calcium fluoride (CaF2) under pressure using classical molecular dynamic simulations performed with a simple pairwise interatomic potential of the Born-Mayer-Huggings form. Our results obtained under conditions 0 < P < 20 GPa and 0 < T < 4000 K reveal a rich variety of multi-phase boundaries involving different crystal, superionic and liquid phases, for all which we provide an accurate parametrization. Interestingly, we predict the existence of three special triple points (i.e. solid-solid-superionic, solid-superionic-superionic and superionic-superionic-liquid coexisting states) within a narrow and experimentally accessible thermodynamic range of 6 < P < 8 GPa and 1500 < T < 2750 K. Also, we examine the role of short-ranged repulsive (SR) and long-ranged attractive (LA) atomic interactions in the prediction of melting lines with the finding that SR Ca-F and LA F-F contributions are most decisive.

cond-mat.mtrl-sci↗

arXiv2011

Ab initio study of compressed Ar(H2)2: structural stability and anomalous melting

We study the structural stability and dynamical properties of Ar(H2)2 under pressure using first-principles and ab initio molecular dynamics techniques. At low temperatures, Ar(H2)2 is found to stabilize in the cubic C15 Laves structure (MgCu2) and not in the hexagonal C14 Laves structure (MgZn2) as it has been assumed previously. Based on enthalpy energy and phonon calculations, we propose a temperature-induced MgCu2 -> MgZn2 phase transition that may rationalize the existing discrepancies between the sets of Raman and infrared vibron measurements. Our AIMD simulations suggest that the melting line of Ar(H2)2 presents negative slope in the interval 60 < P < 110 GPa. We explain the origin of this intriguing physical phenomenon in terms of decoupling of the Ar and H2 degrees of freedom and effective thermal-like excitations arising from coexisting liquid H2 and solid Ar phases.

cond-mat.mtrl-sci↗

arXiv2010

New high-pressure phase of HfTiO4 and ZrTiO4 ceramics

We studied the high-pressure effects on the crystalline structure of monoclinic HfTiO4 and ZrTiO4. We found that the compressibility of these ceramics is highly non-isotropic, being the b-axis the most compressible one. In addition, the a-axis is found to have a small and negative compressibility. At 2.7 GPa (10.7 GPa) we discovered the onset of an structural phase transition in HfTiO4 (ZrTiO4), coexisting the low- and high-pressure phases in a broad pressure range. The new high-pressure phase has a monoclinic structure which involves an increase in the Ti-O coordination and a collapse of the cell volume. The equation of state for the low-pressure phase is also determined.

cond-mat.mtrl-sci↗

arXiv2008

Pressure effects on the structural and electronic properties of ABX4 scintillating crystals

Studies at high pressures and temperatures are helpful for understanding the physical properties of the solid state, including such classes of materials as, metals, semiconductors, superconductors, or minerals. In particular, the phase behaviour of ABX4 scintillating materials is a challenging problem with many implications for other fields including technological applications and Earth and planetary sciences. A great progress has been done in the last years in the study of the pressure-effects on the structural and electronic properties of these compounds. In particular, the high-pressure structural sequence followed by these compounds seems now to be better understood thanks to recent experimental and theoretical studies. Here, we will review studies on the phase behaviour of different ABX4 scintillating materials. In particular, we will focus on discussing the results obtained by different groups for the scheelite-structured orthotungstates, which have been extensively studied up to 50 GPa. We will also describe different experimental techniques for obtaining reliable data at simultaneously high pressure and high temperature. Drawbacks and advantages of the different techniques are discussed along with recent developments involving synchrotron x-ray diffraction, Raman scattering, and ab initio calculations. Differences and similarities of the phase behaviour of these materials will be discussed, on the light of the Fukunaga and Yamaoka and the Bastide diagrams, aiming to improve the actual understanding of their high-pressure behaviour. Possible technological and geophysical implications of the reviewed results will be also commented.

cond-mat.mtrl-sci↗

arXiv2007

High-pressure x-ray diffraction study of SrMoO4 and pressure-induced structural changes

SrMoO4 was studied under compression up to 25 GPa by angle-dispersive x-ray diffraction. A phase transition was observed from the scheelite-structured ambient phase to a monoclinic fergusonite phase at 12.2(9) GPa with cell parameters a = 5.265(9) A, b = 11.191(9) A, c = 5.195 (5) A, and beta = 90.9, Z = 4 at 13.1 GPa. There is no significant volume collapse at the phase transition. No additional phase transitions were observed and on release of pressure the initial phase is recovered, implying that the observed structural modifications are reversible. The reported transition appeared to be a ferroelastic second-order transformation producing a structure that is a monoclinic distortion of the low-pressure phase and was previously observed in compounds isostructural to SrMoO4. A possible mechanism for the transition is proposed and its character is discussed in terms of the present data and the Landau theory. Finally, the EOS is reported and the anisotropic compressibility of the studied crystal is discussed in terms of the compression of the Sr-O and Mo-O bonds.

cond-mat.mtrl-sci↗

arXiv2004

Improving the understanding of the melting behaviour of Mo, Ta, and W at extreme pressures

We discus existent conflicts between experimentally measured and theoretically calculated melting curves of Mo, Ta, and W. By assuming that vacancy formation plays a fundamental role in the melting process, an explanation for the measured melting curves is provided. Furthermore, we show that the Lindemann law fits well all the measured melting curves of bcc transition metals if the Grueneisen parameter is written as a power series of the interatomic distance. For completeness, we examine possible reasons for current disagreements between shock-wave and DAC experiments. To solve them, we propose the existence of an extra high P-T phase for Mo, Ta, and W

cond-mat.mtrl-sci↗

arXiv2004

Pressure-induced alpha-to-omega transition in titanium metal: A systematic study of the effects of uniaxial stress

We investigated the effects of uniaxial stress on the pressure-induced alpha-to-omega transition in pure titanium (Ti) by means of angle dispersive x-ray diffraction in a diamond-anvil cell. Experiments under four different pressure environments reveal that: (1) the onset of the transition depends on the pressure medium used, going from 4.9 GPa (no pressure medium) to 10.5 GPa (argon pressure medium); (2) the a and w phases coexist over a rather large pressure range, which depends on the pressure medium employed; (3) the hysteresis and quenchability of the w phase is affected by differences in the sample pressure environment; and (4) a short term laser-heating of Ti lowers the alpha-to-omega transition pressure. Possible transition mechanisms are discussed in the light of the present results, which clearly demonstrated the influence of uniaxial stress in the alpha-to-omega transition.

cond-mat.mtrl-sci↗

arXiv1997

Investigation of acceptor levels and hole scattering mechanisms in p-gallium selenide by means of transport measurements under pressure

The effect of pressure on acceptor levels and hole scattering mechanisms in p-GaSe is investigated through Hall effect and resistivity measurements under quasi-hydrostatic conditions up to 4 GPa. The pressure dependence of the hole concentration is interpreted through a carrier statistics equation with a single (nitrogen) or double (tin) acceptor whose ionization energies decrease under pressure due to the dielectric constant increase. The pressure effect on the hole mobility is also accounted for by considering the pressure dependencies of both the phonon frequencies and the hole-phonon coupling constants involved in the scattering rates.

cond-mat.mtrl-sci↗

arXiv1997

Tight-Binding study of the electronic and magnetic properties of an L1_0 ordered FeCu alloy

We have calculated the electronic structure of the tetragonal L1$_0$ ordered FeCu by solving self-consistently a tight-binding Hamiltonian for s, p and d electrons. We have found by total energy calculation that this structure is ferromagnetic. In addition, we have determined that the equilibrium ratio between the interlayer and the intralayer lattice parameters is 0.947.

cond-mat↗