Miriam peña alvarez

Miriam peña alvarez
The University of Edinburgh | UoE · Center for Science at Extreme Conditions

PhD

About

64
Publications
9,316
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
865
Citations
Additional affiliations
March 2017 - present
The University of Edinburgh
Position
  • PostDoc Position
December 2011 - April 2016
Complutense University of Madrid
Position
  • PhD Student

Publications

Publications (64)
Article
Through a series of x-ray diffraction, optical spectroscopy diamond anvil cell experiments, combined with density functional theory calculations, we explore the dense CH_{4}-H_{2} system. We find that pressures as low as 4.8 GPa can stabilize CH_{4}(H_{2})_{2} and (CH_{4})_{2}H_{2}, with the latter exhibiting extreme hardening of the intramolecular...
Article
Full-text available
Diamond and graphite are fundamental sources of carbon in the upper mantle, and their reactivity with H 2 -rich fluids present at these depths may represent the key to unravelling deep abiotic hydrocarbon formation. We demonstrate an unexpected high reactivity between carbons’ most common allotropes, diamond and graphite, with hydrogen at condition...
Article
Full-text available
Hydrogen bond networks play a crucial role in biomolecules and molecular materials such as ices. How these networks react to pressure directs their properties at extreme conditions. We have studied one of the simplest hydrogen bond formers, hydrogen chloride, from crystallization to metallization, covering a pressure range of more than 2.5 million...
Article
Through a series of high-pressure x-ray diffraction experiments combined with in situ laser heating, we explore the pressure–temperature phase diagram of germanium (Ge) at pressures up to 110 GPa and temperatures exceeding 3000 K. In the pressure range of 64–90 GPa, we observe orthorhombic Ge-IV transforming above 1500 K to a previously unobserved...
Article
This work describes the synthesis and properties of a dicyanomethylene‐susbtituted indolo[3,2‐b]carbazole diradical ICz‐CN.This quinoidal system dimerises almost completely to (ICz‐CN)2 containing two long C(sp3 )‐C(sp 3) σ‐bonds between the dicyanomethylene units . The minor open‐shell ICz‐CN component in the solid state mixture was identify with...
Article
Full-text available
One of the most striking properties of molecular hydrogen is the coupling between molecular rotational properties and nuclear spin orientations, giving rise to the spin isomers ortho-and para-hydrogen. At high pressure, as intermolecular interactions increase significantly, the free rotation of H 2 molecules is increasingly hindered, and consequent...
Article
We present a method for calculation of Raman modes of the quantum solid phase I hydrogen and deuterium. We use the mean-field assumption that the quantized excitations are localized on one molecule. This is done by explicit solution of the time-dependent Schroedinger equation in an angle-dependent potential, and direct calculation of the polarizati...
Preprint
Full-text available
The laws of quantum mechanics are often tested against the behaviour of the lightest element in the periodic table, hydrogen. One of the most striking properties of molecular hydrogen is the coupling between molecular rotational properties and nuclear spin orientations, giving rise to the spin isomers ortho- and para-hydrogen. At high pressure, as...
Article
Raman spectroscopy demonstrates that the rotational spectrum of solid hydrogen, and its isotope deuterium, undergo profound transformations upon compression while still remaining in phase I. We show that these changes are associated with a loss of quantum character in the rotational modes, ie. with increasing pressure, the angular momentum J gradua...
Article
The Co-H system has been investigated through high-pressure high-temperature x-ray diffraction experiments combined with first principles calculations. On compression of elemental cobalt in a hydrogen medium, we observe fcc cobalt hydride (CoH) and cobalt dihydride (CoH2) at 33 GPa. Laser heating CoH2 in a hydrogen matrix at 75 GPa to temperatures...
Article
A 3D π-conjugated polyradicaloid molecular cage c-Ph14, consisting of three Chichibabin’s hydrocarbon motifs connected by two benzene-1,3,5-triyl bridgeheads, was synthesized. Compared with its linear model compound l-Ph4, the prism-like c-Ph14 has a more rigid structure, which shows significant im-pact on the molecular dynamics, stability, and ele...
Article
The vibrational frequency of hydrogen molecules has been observed to increase strongly with He concentration in helium-hydrogen fluid mixtures. This has been associated with He-H interactions, either directly through chemical bonding [Lim and Yoo, Phys. Rev. Lett. 120, 165301 (2018)] or indirectly through increased local pressure [Loubeyre et al.,...
Article
Full-text available
By combining hydrogen and sulfur within diamond-anvil cells we synthesize (H2S)2H2 at 5 GPa and 373 K. Through a series of Raman spectroscopy, infrared spectroscopy, and synchrotron x-ray diffraction experiments we have constrained the phase diagram of (H2S)2H2 within a wide P−T range. On compression we observe the phase transition sequence of I-II...
Preprint
Full-text available
We present a method for calculation of Raman modes of the quantum solid phase I solid hydrogen and deuterium. We use the mean-field assumption that the quantised excitations are localized on one molecule. This is done by explicit solution of the time-dependent Schroedinger equation in an angle-dependent potential, and direct calculation of the pola...
Article
When compressed in a matrix of solid hydrogen, many metals form compounds with increasingly high hydrogen contents. At high density, hydrogenic sublattices can emerge, which may act as low-dimensional analogues of atomic hydrogen. We show that at high pressures and temperatures, ruthenium forms polyhydride species that exhibit intriguing hydrogen s...
Article
Full-text available
One of the most striking properties of molecular hydrogen is the coupling between molecular rotational properties and nuclear spin orientations, giving rise to the spin isomers ortho- and para-hydrogen. At high pressure, as intermolecular interactions increase significantly, the free rotation of H2 molecules is increasingly hindered, and consequent...
Article
Rare earth element polyhydrides have been predicted to exhibit high-Tc superconductivity at extreme compressions. Through a series of in situ high-pressure high-temperature x-ray powder diffraction experiments combined with density functional theory calculations, we report the emergence of polyhydride species in the praseodymium-hydrogen system. We...
Article
Full-text available
The n-paraphenylene family comprises chains of phenylene units linked together by C-C bonds that are between single- and double-bonded, and where n corresponds to the number of phenylene units. In this work, we compare the response of the optical properties of different phenylene arrangements. We study linear chains (LPP), cyclic systems (CPPs), an...
Preprint
Full-text available
The vibrational frequency of hydrogen molecules has been observed to increase strongly with He concentration in helium hydrogen fluid mixtures. This has been associated with He-H interactions, either directly through chemical bonding, or indirectly through increased local pressure. Here, we demonstrate that the increase in the Raman frequency of th...
Article
Full-text available
Calcium carbonate is a relevant constituent of the Earth’s crust that is transferred into the deep Earth through the subduction process. Its chemical interaction with calcium-rich silicates at high temperatures give rise to the formation of mixed silicate-carbonate minerals, but the structural behavior of these phases under compression is not known...
Article
Full-text available
The original version of this Article omitted references to previous experimental reports on solid hydrogen that are relevant for a full understanding of the context of the previous work. The added references are: 47. Akahama, Y. et al. Evidence from x-ray diffraction of orientational ordering in phase III of solid hydrogen at pressures up to 183 GP...
Article
Full-text available
Hydrogen chemistry at extreme pressures is currently subject to extensive research due to the observed and predicted enhanced physical properties when hydrogen is incorporated in numerous binary systems. Despite the high reactivity of hydrogen, the noble metals (Cu, Ag, and Au) display an outstanding resilience to hydride formation, with no reports...
Article
Full-text available
Diatomic elemental solids are highly compressible due to the weak interactions between molecules. However, as the density increases the intra- and intermolecular distances become comparable, leading to a range of phenomena, such as structural transformation, molecular dissociation, amorphization, and metallisation. Here we report, following the cry...
Article
Transition metal nitrides have applications in a range of technological fields. Recent experiments have shown that new nitrogen-bearing compounds can be accessed through a combination of high temperatures and pressures, revealing a richer chemistry than was previously assumed. Here, we show that at pressures above 50 GPa and temperatures greater th...
Article
The Raman spectra of liquid H 2 (D 2) have been collected in diamond anvil cell as a function of temperature at 3 GPa covering the range from 80 to ∼ 1000 K. Temperatures were measured using two independent methods: by thermocouple and from the relative intensity ratio of the present Raman modes. We find excellent agreement between the two methods...
Article
High pressures in the 0-10 GPa range cause molecules to deform in unusual ways. A series of precisely defined carbon nanohoops consisting of n para-linked phenyl groups, [n]-cycloparaphenylenes ([n]CPPs, n=7, 8, 9, 10, and 12) were studied in this pressure range using Raman spectroscopy and Density Functional Theory (DFT), and compared with more ri...
Article
Through a series of Raman spectroscopy studies, we investigate the behavior of hydrogen-helium and hydrogen-nitrogen mixtures at high pressure across a wide range of concentrations. We find that there is no evidence of chemical association or increased miscibility of hydrogen and helium in the solid state up to pressures of 250 GPa at 300 K. In con...
Article
A recent article by Zhang et al. [Phys. Rev. B 97, 064107 (2018)2469-995010.1103/PhysRevB.97.064107] claimed the high-pressure synthesis and metallization of H3Se, or selenium trihydride, at 23 GPa and 203 K. Here, we demonstrate that the synthesised compound is not H3Se but the previously reported, and already well characterized, (H2Se)2H2. The cl...
Preprint
Full-text available
Through a series of Raman spectroscopy studies, we investigate the behaviour of hydrogen-helium and hydrogen-nitrogen mixtures at high pressure across wide ranging concentrations. We find that there is no evidence of chemical association, miscibility, nor any demixing of hydrogen and helium in the solid state up to pressures of 250 GPa at 300 K. In...
Article
Intermetallic lithium compounds have found a wide range of applications owing to their light mass and desirable electronic and mechanical properties. Here, by compressing pure lithium and zinc mixtures in a diamond-anvil cell, we observe a direct reaction forming the stoichiometric compound LiZn, at pressures below 1 GPa. On further compression abo...
Article
The Raman spectrum of the mechanochromic luminescent tetrathiazolylthiophene has been investigated as a function of pressure and temperature. This study verifies the sensitivity of the Raman spectroscopy as technique to characterize and understand the structural effects causing any mechanochromic changes. Continuous and evident Raman shifts and cha...
Article
Raman spectroscopy under high pressures up to 10 GPa and density functional computations up to 30 GPa are combined to obtain insights into the behavior of a prototypical nanohoop conjugated molecule, [6]cycloparaphenylene, [6]CPP. Upon increasing pressure the nanohoop undergoes deformations, first reversible ovalization and then at even higher pres...
Article
In situ high-pressure high-temperature X-ray powder diffraction studies of the cobalt-hydrogen system reveal the direct synthesis of both the binary cobalt hydride (CoH) and a novel cobalt dihydride (CoH2). We observe the formation of fcc CoH at pressures of 4 GPa, which persists to pressures of 45 GPa. At this pressure, we see the emergence with t...
Article
The observation of high-temperature superconductivity in hydride sulfide (H2S) at high pressures has generated considerable interest in compressed hydrogen-rich compounds. High-pressure hydrogen selenide (H2Se) has also been predicted to be superconducting at high temperatures; however, its behaviour and stability upon compression remains unknown....
Article
Full-text available
New anthanthrone-based polycyclic scaffolds possessing peripheral crowed quinodimethanes have been prepared. While the compounds adopt a closed-shell butterfly shaped structure in the ground state, a curved-to-planar fluxional dynamic inversion is accessible with a low energy barrier through a diradical transition-state. Mainly driven by the releas...
Article
New anthanthrone-based polycyclic scaffolds possessing peripheral crowed quinodimethanes have been prepared. While the compounds adopt a closed-shell butterfly shaped structure in the ground state, a curved-to-planar fluxional dynamic inversion is accessible with a low energy barrier through a diradical transition-state. Mainly driven by the releas...
Article
Full-text available
The properties of graphene depend sensitively on strain and doping affecting its behavior in devices and allowing an advanced tailoring of this material. A knowledge of the strain configuration, i.e. the relative magnitude of the components of the strain tensor, is particularly crucial, because it governs effects like band-gap opening, pseudo-magne...
Article
Full-text available
We find evidence for the surprising formation of polymeric phases under high pressure for conjugated nanohoop molecules. This paper represents one of the unique cases where the molecular-level effects of pressure in crystalline organic solids is addressed and provides a suitable general approach based on vibrational Raman spectroscopy combining exp...
Article
Herein, we report a quinodimethane-type molecule, 2,7-dicyanomethylene-9-(2-ethylhexyl)carbazole (1), one of the shortest π-conjugated biradicaloids reported to be stable in solution at ambient. This carbazole-based quinoidal precursor is able to form a macrocyclic -bonded tetramer (2). The resolved single crystal X-ray structure of tetramer 2 sho...
Article
Raman spectroscopy is a powerful tool for characterizing the local properties of graphene. Here, we introduce a method for evaluating unknown strain configurations and simultaneous doping. It relies on separating the effects of hydrostatic strain (peak shift) and shear strain (peak splitting) on the Raman spectrum of graphene. The peak shifts from...
Article
Full-text available
New stilbenoid and thiophenic compounds terminally functionalized with donor-donor, acceptor-acceptor or donor-acceptor moieties and possessing a central [2.2]paracyclophane unit have been prepared and their properties interpreted in terms of through-bond and through space π-electron delocalization (i.e., π-conjugations). Based on photophysical dat...
Article
Twisted bilayer graphene (tBLG) represents a family of unique materials with optoelectronic properties tuned by the rotation angle between the two layers. The presented work shows an additional way of tweaking the electronic structure of tBLG: by modifying the interlayer distance, for example by a small uniaxial out-of-plane compression. We have fo...
Article
Conducting polymers can be synthesized via irreversible diradical monomer polymerization. A reversible version of this reaction consisting of the formation/dissociation of dimers and polymers from a stable quinonoidal diradical precursor is described. The reaction reversibility is made by a quinonoidal molecule which changes its structure to ar...
Article
Conducting polymers can be synthesized by irreversible diradical monomer polymerization. A reversible version of this reaction consisting of the formation/dissociation of σ-dimers and σ-polymers from a stable quinonoidal diradical precursor is described. The reaction reversibility is made by a quinonoidal molecule which changes its structure to an...
Article
Conducting polymers can be synthesized by irreversible diradical monomer polymerization. A reversible version of this reaction consisting of the formation/dissociation of σ-dimers and σ-polymers from a stable quinonoidal diradical precursor is described. The reaction reversibility is made by a quinonoidal molecule which changes its structure to an...
Article
The reduced and oxidized states of an open-shell diindeno[b,i]anthracene (DIAn) derivative have been investigated by experimental and theoretical techniques. As a result of moderate biradical character and the ability of cyclopenta-fused scaffolds to stabilize both positive and negative charges, DIAn exhibits rich redox chemistry with four observab...
Article
In this work we explore mechanical properties of graphene samples of variable thickness. For this purpose, we coupled a high pressure sapphire anvil cell to a microRaman spectrometer. From the evolution of the G band frequency with stress, we document the importance the substrate has on the mechanical response of graphene. On the other hand, the ap...
Article
Full-text available
Radical cations and dications of [n]CPP from n=5 to n=12 have been studied by Raman spectroscopy and Density Functional Theory. Small [n]CPP dications owe their stability to the closed-shell electronic structure imposed by cyclic conjugation surpassing the destabilizing effect of ring strain and of the electron deficiency of the charged states. Lar...
Article
In this work, we present the first study of highly compressed carbon nanohorns (CNHs). The experiments were performed in a sapphire anvil cell and the morphological changes induced in the CNHs samples were monitored simultaneously by Raman spectroscopy and subsequently by transmission electron microscopy. CNHs samples subjected to a maximum stress...
Article
Cyclic paraphenylenes, [n]CPPs, and linear paraphenylenes, [n]LPPs, formed by n benzenes, are investigated by Raman spectroscopy for n = 5 to 12 and density functional theory (DFT) for n = 4 to 20. The information on the experimental Raman frequencies and intensities, combined with DFT computations and reported X-ray diffraction structures, provide...
Article
Recently, a new family of 2D materials with exceptional optoelectronic properties has stormed into the scene of nanotechnology, the transition metal dichalcogenides (e.g., MoS2). In contrast with graphene, which is a zero band gap semiconductor, many of the single layered materials from this family show a direct band-gap in the visible range. This...
Conference Paper
Full-text available
The research on graphene has attracted much attention since its first successful preparation in 2004. It possesses many unique properties, such as an extreme stiffness and strength, high electron mobility, ballistic transport even at room temperature, superior thermal conductivity and many others. The affection for graphene was followed swiftly by...
Article
Tuning of the electronic structure of 2D materials is a very powerful asset towards tailoring their properties to suit the demands of future applications in optoelectronics. Strain engineering is one of the most promising methods in this regard. We demonstrate that even very small out-of-plane axial compression readily modifies the electronic struc...
Article
Full-text available
A novel strategy was employed to prepare a water-soluble graphene derivative by using dextran-based polymer brushes as solubilizing agents. Graphene oxide was grafted with (3-mercaptopropyl) trimethoxysilane and further decorated with Au nanoparticles. This hybrid nanomaterial was then reduced and anchored with polysaccharide-based polymer brushes...
Article
In this work we report the dispersive behavior of the most characteristic Raman contributions of highly oriented pyrolytic graphite at biaxial stresses up to 10 GPa, using a moissanite anvil cell as a pressure device. The stress coefficients and the relative Gruneisen parameters are obtained for two different excitation wavelengths, 488.0 and 532.0...
Article
Full-text available
A series of four 1:1 host–guest supramolecular complexes of [n]CPPs and C70 have been analyzed by Raman spectroscopy in the solid state and complemented with the analysis of their spectroscopic responses under mechanical and thermal stresses. By following the frequency behaviour of the G and RBM modes we have found that [10]CPP in the [10]CPP@C70 c...
Article
[n]Cycloparaphenylenes behave as molecular templates of "perfectly chemically defined" single-wall carbon nanotubes. These [n]CPP molecules have electronic, mechanical, and chemical properties in size correspondence with their giant congeners. Under mechanical stress, they form charge-transfer salts, or complexes with fullerene, by one-electron con...

Projects

Project (1)
Project
A project funded by Czech Science Foundation focused on various aspects of deformation of 2D materials and the influence of mechanical strain on their (opto)electronic properties.