Vanesa P. Cuenca-Gotor

Pressure-induced phase transition and band-gap collapse in the wide-band-gap semiconductor InTaO4

This paper was partially supported by the Spanish Ministerio de Economia y Competitividad (MINECO) under Grants No. MAT2013-46649-C04-01/02/03 and No. MAT2015-71070-REDC (MALTA Consolider). The XRD experiments were performed at the MSPD-BL04 beamline at ALBA Synchrotron with the collaboration of ALBA staff. We thank S. Agouram from SC-SIE at Universitat de Valencia for technical support with the transmission electron microscope measurements.

Ordered helium trapping and bonding in compressed arsenolite: Synthesis of As4O6 2He

The compression of arsenolite (cubic As2O3) has been studied from a joint experimental and theoretical point of view. Experimental X-ray diffraction and Raman scattering measurements of this molecular solid at high pressures with different pressure-transmitting media have been interpreted with the help of ab initio calculations. Our results confirm arsenolite as one of the softest minerals in absence of hydrogen bonding and provide evidence for helium trapping above 3 GPa between adamantane-type As4O6 cages, thus leading to a new compound with stoichiometry He2As4O6. Helium trapping alters all properties of arsenolite. In particular, pressure-induced amorphization, which occurs in pure arsenolite above 15 GPa, is impeded when He is trapped between the As4O6 cages; thus resulting in a mechanical stability of He2As4O6 beyond 30 GPa. Our work paves the way for the modification of the properties of other molecular solids by compression depending on their ability to trap relatively small atomic or molecular species and form new compounds. Furthermore, our work suggests that compression of molecular solids with noble gases as helium could result in unexpected results compared to other pressure-transmitting media.

Structural and Vibrational Properties of Corundum-type In2O3 Nanocrystals under Compression.

This work reports the structural and vibrational properties of nanocrystals of corundum-type In2O3 (rh-In2O3) at high pressures by using angle-dispersive x-ray diffraction and Raman scattering measurements up to 30 GPa. The equation of state and the pressure dependence of the Raman-active modes of the corundum phase in nanocrystals are in good agreement with previous studies on bulk material and theoretical simulations on bulk rh-In2O3. Nanocrystalline rh-In2O3 showed stability under compression at least up to 20 GPa, unlike bulk rh-In2O3 which gradually transforms to the orthorhombic Pbca (Rh2O3-III-type) structure above 12-14 GPa. The different stability range found in nanocrystalline and bulk corundum-type In2O3 is discussed.

Pressure-Driven Isostructural Phase Transition in InNbO4: In Situ Experimental and Theoretical Investigations

The high-pressure behavior of technologically important visible-light photocatalytic semiconductor InNbO4, adopting a monoclinic wolframite-type structure at ambient conditions, was investigated using synchrotron-based X-ray diffraction, Raman spectroscopic measurements, and first-principles calculations. The experimental results indicate the occurrence of a pressure-induced isostructural phase transition in the studied compound beyond 10.8 GPa. The large volume collapse associated with the phase transition and the coexistence of two phases observed over a wide range of pressure shows the nature of transition to be first-order. There is an increase in the oxygen anion coordination number around In and Nb cations from six to eight at the phase transition. The ambient-pressure phase has been recovered on pressure release. The experimental pressure-volume data when fitted to a Birch-Murnaghan equation of states yields the value of ambient pressure bulk modulus as 179(2) and 231(4) GPa for the low- and high-pressure phases, respectively. The pressure dependence of the Raman mode frequencies and Grüneisen parameters was determined for both phases by experimental and theoretical methods. The same information is obtained for the infrared modes from first-principles calculations. Results from theoretical calculations corroborate the experimental findings. They also provide information on the compressibility of interatomic bonds, which is correlated with the macroscopic properties of InNbO4.

Vibrational and elastic properties of As4O6 and As4O6·2He at high pressures: Study of dynamical and mechanical stability

The formation of a new compound with stoichiometry As4O6·2He at relatively low pressure (3 GPa) has been recently reported when arsenolite (As4O6) powder is compressed with helium as a pressure-transmitting medium. In this work, we study the lattice dynamics of As4O6 and As4O6·2He at high pressures from an experimental and theoretical perspective by means of Raman scattering measurements and ab initio calculations and report the theoretical elastic properties of both compounds at high pressure. Raman scattering measurements show a completely different behaviour of As4O6 and As4O6·2He at high pressures. Furthermore, the theoretical calculation of phonon dispersion curves and elastic stiffness coefficients at high pressure in both compounds allow us to discuss their dynamical and mechanical stability under hydrostatic compression. Both compounds are dynamically stable even above 35 GPa, but As4O6 becomes mechanically unstable at pressures beyond 19.7 GPa. These results allow explaining the pressure-induced ...