Armando Beltrán | Universitat Jaume I de Castelló (original) (raw)
Papers by Armando Beltrán
Physical Review B, May 18, 2012
We report an experimental and theoretical study of antimony oxide (Sb 2 O 3) in its cubic phase (... more We report an experimental and theoretical study of antimony oxide (Sb 2 O 3) in its cubic phase (senarmontite) under high pressure. X-ray diffraction and Raman scattering measurements up to 18 and 25 GPa, respectively, have been complemented with ab initio total-energy and lattice-dynamics calculations. X-ray diffraction measurements do not provide evidence of a space-group symmetry change in senarmontite up to 18 GPa. However, Raman scattering measurements evidence changes in the pressure coefficients of the Raman mode frequencies at 3.5 and 10 GPa, respectively. The behavior of the Raman modes with increasing pressure up to 25 GPa is fully reproduced by the lattice-dynamics calculations in cubic Sb 2 O 3. Therefore, the combined analysis of both experiments and lattice-dynamics calculations suggest the occurrence of two isostructural phase transformations at 3.5 and 10 GPa, respectively. Total-energy calculations show that the isostructural phase transformations occur through local atomic displacements in which senarmontite loses its molecular character to become a three-dimensional solid. In addition, our calculations provide evidence that cubic senarmontite cannot undergo a phase transition to orthorhombic valentinite at high pressure, and that a phase transition to a β-Bi 2 O 3-type structure is possible above 25 GPa.
Journal of Physics: Condensed Matter, Oct 31, 2013
An experimental and theoretical study of the structural properties of monoclinic bismuth oxide (... more An experimental and theoretical study of the structural properties of monoclinic bismuth oxide (-Bi 2 O 3) under high pressures is here reported. Both synthetic and mineral bismite powder samples have been compressed up to 45 GPa and their equations of state have been determined with angle-dispersive x-ray diffraction measurements. Experimental results have been also compared to theoretical calculations which suggest the possibility of several phase transitions below 10 GPa. However, experiments reveal only a pressure-induced amorphisation between 15 and 25 GPa, depending on sample quality and deviatoric stresses. The amorphous phase has been followed up to 45 GPa and its nature discussed.
Physical Review B, Sep 15, 2009
Theoretical investigations concerning the possible titanium silicate polymorphs have been perform... more Theoretical investigations concerning the possible titanium silicate polymorphs have been performed using density functional theory at B3LYP level. Total-energy calculations and geometry optimizations have been carried out for all phases involved. The following sequence of pressure-driven structural transitions has been found: CrVO 4-type, Cmcm ͑in parenthesis the transition pressure͒, → zircon-type, I4 1 / amd ͑0.8 GPa͒, → scheelite-type, I4 1 / a ͑3.8 GPa͒. At higher pressure the last phase is found to be stable at least up to 25 GPa. The equation of state of the different polymorphs is also reported. We found that the highest bulk modulus corresponds to the zircon and scheelite phases with values of 248 and 238 GPa, respectively. The orthorhombic Cmcm phase is the most compressible of all the studied structures with a bulk modulus of 124 GPa, being also the most stable phase at ambient pressure. Finally, calculations of the electronic structure, vibrational and dielectric properties of TiSiO 4 are also reported.
HAL (Le Centre pour la Communication Scientifique Directe), Oct 22, 2015
Journal of Physical Chemistry C, Mar 29, 2011
Inorganic Chemistry, Dec 19, 2011
Theoretical investigations concerning possible calcium sulfate, CaSO(4), high-pressure polymorphs... more Theoretical investigations concerning possible calcium sulfate, CaSO(4), high-pressure polymorphs have been carried out. Total-energy calculations and geometry optimizations have been performed by using density functional theory at the B3LYP level for all crystal structures considered. The following sequence of pressure-driven structural transitions has been found: anhydrite, Cmcm (in parentheses the transition pressure) → monazite-type, P2(1)/n (5 GPa) → barite-type, Pnma (8 GPa), and scheelite-type, I4(1)/a (8 GPa). The equation of state of the different polymorphs is determined, while their corresponding vibrational properties have been calculated and compared with previous theoretical results and experimental data.
Physical Review B, Sep 2, 2009
We report here the combined results of angle-dispersive x-ray diffraction experiments performed o... more We report here the combined results of angle-dispersive x-ray diffraction experiments performed on ThGeO 4 up to 40 GPa and total-energy density-functional theory calculations. Zircon-type ThGeO 4 is found to undergo a pressure-driven phase transition at 11 GPa to the tetragonal scheelite structure. A second phase transition to a monoclinic Mfergusonite type is found beyond 26 GPa. The same transition has been observed in samples that crystallize in the scheelite phase at ambient pressure. No additional phase transition or evidence of decomposition of ThGeO 4 has been detected up to 40 GPa. The unit-cell parameters of the monoclinic high-pressure phase are a = 4.98(2) Å, b = 11.08(4) Å, c = 4.87 (2) Å, and β = 90.1(1), Z = 4 at 28.8 GPa. The scheelite-fergusonite transition is reversible and the zircon-scheelite transition non-reversible. From the experiments and the calculations, the room temperature equation of state for the different phases is also obtained. The anisotropic compressibility of the studied crystal is discussed in terms of the differential compressibility of the Th-O and Ge-O bonds.
Physical review, Dec 31, 2002
The equations of state and phase diagrams of the cubic spinel and two high-pressure polymorphs of... more The equations of state and phase diagrams of the cubic spinel and two high-pressure polymorphs of MgAl 2 O 4 have been investigated up to 65 GPa using density functional theory, the space-filling polyhedral partition of the unit cell, and the static approximation. Energy-volume curves have been obtained for the spinel phase, the recently observed calcium ferrite-type and calcium titanite-type phases, and the MgOϩ␣-Al 2 O 3 mixture. Zero-pressure unit lengths and compressibilities are well described by the theoretical model, that predicts static bulk moduli about 215 GPa for all the high-pressure forms. Computed equations of state are also in good agreement with the most recent experimental data for all compounds and polymorphs considered. We do not find a continuous pressure-induced phase sequence but the static simulations predict that the oxide mixture, the ferrite phase, and the titanite phase become more stable than the spinel form at 15, 35, and 62 GPa, respectively. A microscopic analysis in terms of polyhedral and bond compressibilities leads to identify the ionic displacements accompanying the phase transformations and to an appealing interpretation of the spinel response to compression.
Organometallics, Jan 20, 2004
Surface Science, Jun 1, 1999
A theoretical analysis based on the Hartree-Fock pseudopotential method and a density-functional ... more A theoretical analysis based on the Hartree-Fock pseudopotential method and a density-functional theory calculation using a hybrid combination of general gradient approximation with pseudopotential procedure has been carried out to study the adsorption and dissociation of methanol on the stoichiometric SnO 2 (110) surface. The dependence of the results upon model system and computing method is discussed. An optimization procedure of adsorbate and substrate atom positions on a six-layer slab model has been selected to characterize the corresponding geometric parameters, adsorption energy and charge-transfer processes related with the molecularly adsorbed CH 3 OH and dissociative channels to yield methoxy or methyl fragments. In the high-coverage limit (h=1), we find that dissociation of the methanol molecule via the heterolytic cleavage of the CMO bond is favoured. At lower coverage (h=1/2), this channel and the molecularly adsorbed methanol present similar adsorption energies.
Electrochemical and Solid State Letters, 2005
ABSTRACT Lithium insertion into amorphous WO3 films prepared by the electron beam evaporation tec... more ABSTRACT Lithium insertion into amorphous WO3 films prepared by the electron beam evaporation technique was investigated by measurements of voltage-composition curve and chemical diffusion coefficient. The extraction of equilibrium and kinetic parameters allows the determination of the jump diffusion coefficient dependence on composition. In addition, first-principles calculations combining a pseudopotential plane wave scheme have been performed with the aim of providing a better understanding of the dependence of the potential barrier height for the hopping pathway with the insertion level for crystalline compounds. Our results predict a lowering of the barrier height for less doped systems and both experiments and simulations exhibit a relation of the type Delta E proportional to ck(B)T ln x for the composition range x < 0.3. (c) 2005 The Electrochemical Society.
Journal of Physical Chemistry C, Jan 11, 2019
This work presents first-principle calculations on the pressure-dependence of the stabilities, st... more This work presents first-principle calculations on the pressure-dependence of the stabilities, structures, and electronic properties of several polymorphs of ZnV2O6 under the pressure range 0-30 GPa. These properties are analyzed and discussed in detail using the different parameterizations of the exchange-correlation functional (B3LYP, HSE06, and PBE), and the results are compared with available experimental data. An extensive search process was carried out on the potential energy surface for a set of twelve possible polymorphs. Ten of them are stationary points, but only five have positive frequency values in the range of 0-30 GPa, i.e., monoclinic brannerite (C2/m and C2), orthorhombic columbite (Pbcn), trigonal CaAs2O6-type (P321), and triclinic NiV2O6-type (P1 ̅). The monoclinic ThTi2O6-type (C2/c) phase presents a very low imaginary frequency around 50 cm-1. Orthorhombic SrV2O6-type and BaV2O6-type, tetragonal trirutile and trigonal PbSb2O6-type structures show several imaginary negative frequencies between-400 and-100 cm-1. These imaginary frequencies are indicative of structural instabilities. All attempts to try to converge the calculations to obtain the MoLa2O6-type and HgV2O6-type polymorphs, by using the three functionals, have been unsuccessful. For both brannerite,ThTi2O6-type, columbite, CaAs2O6-type, NiV2O6-type structures numerical and analytical fittings were performed to obtain the lattice parameters, the bulk modulus, B, and their pressure derivative, B′, and the energy-volume relationship of phases are analyzed. Vibrational calculations were performed at each pressure for each polymorph and compared with available experimental data. This study reports, for the first time, a complex and unexpected structural and chemical behavior as a function of pressure. An analysis of the results shows that brannerite monoclinic polymorphs present similar energies, suggesting that both structures may coexist in the range of pressures that were studied. Theoretical prediction reveals that, as the pressure increases, the most stable polymorph of ZnV2O6 moves from the monoclinic phase, C2/m (and C2), to the orthorhombic columbite structure (Pbcn) and the corresponding transition pressure is computed to be 5 GPa at the B3LYP level; however, using the HSE06 and PBE functionals, the FeNb2O6-type structure is the most stable polymorph from ambient pressure up to 30 GPa. In addition the calculations show that the ThTi2O6-type phase (C2/c) becomes more stable than the other two monoclinic structures above 15, 13, and 8 GPa using the B3LYP, HSE06, and PBE functionals, respectively. The findings reported here indicate that the method used to predict relative phase stabilities and phase transitions should be chosen carefully, and that the results should be scrutinized with a critical eye. We analyze the variations of different vibrational frequencies and V−O and Zn−O bond lengths as pressure is applied, and the results confirm that Badger's lineal relationships were not found for the monoclinic polymorphs (C2/m, C2, and C2/c) due to the presence of a charge transfer process from the ZnO6 to the VO6 polyhedra. In addition, we determined the stability of ZnV2O6 against binary oxides (VO2, V2O5, and ZnO), or metals (Zn and V) and oxygen, and the results reveal that the decomposition channels are not energetically feasible. The present work provides a new perspective on the variations of crystal structures and physical properties at high pressure in ZnV2O6 polymorphs. With the wealth of data presented, this study aims to encourage further basic and experimental research on an interesting case of ZnV2O6based materials with novel properties that may be the basis of important innovations for industrial applications.
Journal of Physical Chemistry A, Nov 11, 2004
ABSTRACT
Journal of Physical Chemistry B, Aug 12, 2008
Physical review, Jun 30, 2016
Physical review, Oct 23, 2001
Quantum-mechanical simulations have been performed to investigate pressure effects on the crystal... more Quantum-mechanical simulations have been performed to investigate pressure effects on the crystal geometry, chemical bonding, and the electronic structure of anatase TiO 2. Total energy calculations are carried out using the density functional formalism under the nonlocal B3LYP approximation. The optimized unit cell equilibrium parameters and the bulk and linear compressibilities are determined to be in good agreement with recent experimental data. The topology of the electron density is examined by means of the atoms in molecules ͑AIM͒ theory. Computed AIM charges and topological properties of the bond critical points reveal a partially ionic behavior of the crystal that complements the description obtained from the band structure and the projected density of states analysis. A microscopic interpretation of the crystal response to hydrostatic pressure is given in terms of the elementary polyhedra and the AIM atomic volumes that fill the unit cell space.
High Pressure Research, 2002
ABSTRACT A theoretical investigation of the MgAl 2 O 4 crystal response to high-pressure conditio... more ABSTRACT A theoretical investigation of the MgAl 2 O 4 crystal response to high-pressure conditions has been carried out to determine its stability against decomposition towards MgO and f -Al 2 O 3 , and towards recently observed orthorhombic phases. We have evaluated total energy versus volume curves using the density functional formalism under the non-local B3LYP approximation, as implemented in the CRYSTAL package. Numerical and analytical fittings have been carried out to determine the equilibrium unit cell geometry and equation of state parameters for all the structures and compounds involved in the phase diagram. The macroscopic compressibility of the spinel phase is interpreted considering the compressibility of its elementary MgO 4 and AlO 6 coordination polyhedra, and implications to understand the phase stability are suggested.
Se crean los programas madelpi y radios, asi como su implentacion en ordenadores personales y a d... more Se crean los programas madelpi y radios, asi como su implentacion en ordenadores personales y a destacar que el metodo ion perturbado ab initio abre importantes perspectivas a la investigacion de las propiedades de nuevos materiales inorganicos de interes tecnologico.Se aplican metodologias teoricas al calculo de energias de red de estructuras ionicas y como se ve afectada la misma por la sustitucion de diferentes iones, contrastandose los resultados con datos experimentales.
The Journal of Physical Chemistry, Aug 1, 1994
A theoretical description of local relaxation effects induced by the presence of impurity centers... more A theoretical description of local relaxation effects induced by the presence of impurity centers V4+ at the tetrahedral and dodecahedral sites of ZrSi04 is presented. The crystal structure is analyzed via optimization of local equilibrium geometries and computation of the force constant associated with the symmetric vibrational mode at each impurity center. The theoretical study is carried out using an extension of the ab initio perturbed ion method. The relative stability of vanadium-substituted vacancies in ZrSi04 is examined in light of previous results reported by the present authors and the vibrational analysis here addressed. Local geometries were optimized by relaxing various sets of ions around each substituted center. An increased substitution energy together with a pronounced decrease of the breathing vibrational mode on the 4-fold-coordinated site shows that this substitution is unstable while that on the 8-fold-coordinated ion site is energetically favorable and the local geometry is minimally relaxed. Selective doping on each center leads to a decreased force constant as compared to that obtained for the pure crystal structure.
Physical Review B, May 18, 2012
We report an experimental and theoretical study of antimony oxide (Sb 2 O 3) in its cubic phase (... more We report an experimental and theoretical study of antimony oxide (Sb 2 O 3) in its cubic phase (senarmontite) under high pressure. X-ray diffraction and Raman scattering measurements up to 18 and 25 GPa, respectively, have been complemented with ab initio total-energy and lattice-dynamics calculations. X-ray diffraction measurements do not provide evidence of a space-group symmetry change in senarmontite up to 18 GPa. However, Raman scattering measurements evidence changes in the pressure coefficients of the Raman mode frequencies at 3.5 and 10 GPa, respectively. The behavior of the Raman modes with increasing pressure up to 25 GPa is fully reproduced by the lattice-dynamics calculations in cubic Sb 2 O 3. Therefore, the combined analysis of both experiments and lattice-dynamics calculations suggest the occurrence of two isostructural phase transformations at 3.5 and 10 GPa, respectively. Total-energy calculations show that the isostructural phase transformations occur through local atomic displacements in which senarmontite loses its molecular character to become a three-dimensional solid. In addition, our calculations provide evidence that cubic senarmontite cannot undergo a phase transition to orthorhombic valentinite at high pressure, and that a phase transition to a β-Bi 2 O 3-type structure is possible above 25 GPa.
Journal of Physics: Condensed Matter, Oct 31, 2013
An experimental and theoretical study of the structural properties of monoclinic bismuth oxide (... more An experimental and theoretical study of the structural properties of monoclinic bismuth oxide (-Bi 2 O 3) under high pressures is here reported. Both synthetic and mineral bismite powder samples have been compressed up to 45 GPa and their equations of state have been determined with angle-dispersive x-ray diffraction measurements. Experimental results have been also compared to theoretical calculations which suggest the possibility of several phase transitions below 10 GPa. However, experiments reveal only a pressure-induced amorphisation between 15 and 25 GPa, depending on sample quality and deviatoric stresses. The amorphous phase has been followed up to 45 GPa and its nature discussed.
Physical Review B, Sep 15, 2009
Theoretical investigations concerning the possible titanium silicate polymorphs have been perform... more Theoretical investigations concerning the possible titanium silicate polymorphs have been performed using density functional theory at B3LYP level. Total-energy calculations and geometry optimizations have been carried out for all phases involved. The following sequence of pressure-driven structural transitions has been found: CrVO 4-type, Cmcm ͑in parenthesis the transition pressure͒, → zircon-type, I4 1 / amd ͑0.8 GPa͒, → scheelite-type, I4 1 / a ͑3.8 GPa͒. At higher pressure the last phase is found to be stable at least up to 25 GPa. The equation of state of the different polymorphs is also reported. We found that the highest bulk modulus corresponds to the zircon and scheelite phases with values of 248 and 238 GPa, respectively. The orthorhombic Cmcm phase is the most compressible of all the studied structures with a bulk modulus of 124 GPa, being also the most stable phase at ambient pressure. Finally, calculations of the electronic structure, vibrational and dielectric properties of TiSiO 4 are also reported.
HAL (Le Centre pour la Communication Scientifique Directe), Oct 22, 2015
Journal of Physical Chemistry C, Mar 29, 2011
Inorganic Chemistry, Dec 19, 2011
Theoretical investigations concerning possible calcium sulfate, CaSO(4), high-pressure polymorphs... more Theoretical investigations concerning possible calcium sulfate, CaSO(4), high-pressure polymorphs have been carried out. Total-energy calculations and geometry optimizations have been performed by using density functional theory at the B3LYP level for all crystal structures considered. The following sequence of pressure-driven structural transitions has been found: anhydrite, Cmcm (in parentheses the transition pressure) → monazite-type, P2(1)/n (5 GPa) → barite-type, Pnma (8 GPa), and scheelite-type, I4(1)/a (8 GPa). The equation of state of the different polymorphs is determined, while their corresponding vibrational properties have been calculated and compared with previous theoretical results and experimental data.
Physical Review B, Sep 2, 2009
We report here the combined results of angle-dispersive x-ray diffraction experiments performed o... more We report here the combined results of angle-dispersive x-ray diffraction experiments performed on ThGeO 4 up to 40 GPa and total-energy density-functional theory calculations. Zircon-type ThGeO 4 is found to undergo a pressure-driven phase transition at 11 GPa to the tetragonal scheelite structure. A second phase transition to a monoclinic Mfergusonite type is found beyond 26 GPa. The same transition has been observed in samples that crystallize in the scheelite phase at ambient pressure. No additional phase transition or evidence of decomposition of ThGeO 4 has been detected up to 40 GPa. The unit-cell parameters of the monoclinic high-pressure phase are a = 4.98(2) Å, b = 11.08(4) Å, c = 4.87 (2) Å, and β = 90.1(1), Z = 4 at 28.8 GPa. The scheelite-fergusonite transition is reversible and the zircon-scheelite transition non-reversible. From the experiments and the calculations, the room temperature equation of state for the different phases is also obtained. The anisotropic compressibility of the studied crystal is discussed in terms of the differential compressibility of the Th-O and Ge-O bonds.
Physical review, Dec 31, 2002
The equations of state and phase diagrams of the cubic spinel and two high-pressure polymorphs of... more The equations of state and phase diagrams of the cubic spinel and two high-pressure polymorphs of MgAl 2 O 4 have been investigated up to 65 GPa using density functional theory, the space-filling polyhedral partition of the unit cell, and the static approximation. Energy-volume curves have been obtained for the spinel phase, the recently observed calcium ferrite-type and calcium titanite-type phases, and the MgOϩ␣-Al 2 O 3 mixture. Zero-pressure unit lengths and compressibilities are well described by the theoretical model, that predicts static bulk moduli about 215 GPa for all the high-pressure forms. Computed equations of state are also in good agreement with the most recent experimental data for all compounds and polymorphs considered. We do not find a continuous pressure-induced phase sequence but the static simulations predict that the oxide mixture, the ferrite phase, and the titanite phase become more stable than the spinel form at 15, 35, and 62 GPa, respectively. A microscopic analysis in terms of polyhedral and bond compressibilities leads to identify the ionic displacements accompanying the phase transformations and to an appealing interpretation of the spinel response to compression.
Organometallics, Jan 20, 2004
Surface Science, Jun 1, 1999
A theoretical analysis based on the Hartree-Fock pseudopotential method and a density-functional ... more A theoretical analysis based on the Hartree-Fock pseudopotential method and a density-functional theory calculation using a hybrid combination of general gradient approximation with pseudopotential procedure has been carried out to study the adsorption and dissociation of methanol on the stoichiometric SnO 2 (110) surface. The dependence of the results upon model system and computing method is discussed. An optimization procedure of adsorbate and substrate atom positions on a six-layer slab model has been selected to characterize the corresponding geometric parameters, adsorption energy and charge-transfer processes related with the molecularly adsorbed CH 3 OH and dissociative channels to yield methoxy or methyl fragments. In the high-coverage limit (h=1), we find that dissociation of the methanol molecule via the heterolytic cleavage of the CMO bond is favoured. At lower coverage (h=1/2), this channel and the molecularly adsorbed methanol present similar adsorption energies.
Electrochemical and Solid State Letters, 2005
ABSTRACT Lithium insertion into amorphous WO3 films prepared by the electron beam evaporation tec... more ABSTRACT Lithium insertion into amorphous WO3 films prepared by the electron beam evaporation technique was investigated by measurements of voltage-composition curve and chemical diffusion coefficient. The extraction of equilibrium and kinetic parameters allows the determination of the jump diffusion coefficient dependence on composition. In addition, first-principles calculations combining a pseudopotential plane wave scheme have been performed with the aim of providing a better understanding of the dependence of the potential barrier height for the hopping pathway with the insertion level for crystalline compounds. Our results predict a lowering of the barrier height for less doped systems and both experiments and simulations exhibit a relation of the type Delta E proportional to ck(B)T ln x for the composition range x < 0.3. (c) 2005 The Electrochemical Society.
Journal of Physical Chemistry C, Jan 11, 2019
This work presents first-principle calculations on the pressure-dependence of the stabilities, st... more This work presents first-principle calculations on the pressure-dependence of the stabilities, structures, and electronic properties of several polymorphs of ZnV2O6 under the pressure range 0-30 GPa. These properties are analyzed and discussed in detail using the different parameterizations of the exchange-correlation functional (B3LYP, HSE06, and PBE), and the results are compared with available experimental data. An extensive search process was carried out on the potential energy surface for a set of twelve possible polymorphs. Ten of them are stationary points, but only five have positive frequency values in the range of 0-30 GPa, i.e., monoclinic brannerite (C2/m and C2), orthorhombic columbite (Pbcn), trigonal CaAs2O6-type (P321), and triclinic NiV2O6-type (P1 ̅). The monoclinic ThTi2O6-type (C2/c) phase presents a very low imaginary frequency around 50 cm-1. Orthorhombic SrV2O6-type and BaV2O6-type, tetragonal trirutile and trigonal PbSb2O6-type structures show several imaginary negative frequencies between-400 and-100 cm-1. These imaginary frequencies are indicative of structural instabilities. All attempts to try to converge the calculations to obtain the MoLa2O6-type and HgV2O6-type polymorphs, by using the three functionals, have been unsuccessful. For both brannerite,ThTi2O6-type, columbite, CaAs2O6-type, NiV2O6-type structures numerical and analytical fittings were performed to obtain the lattice parameters, the bulk modulus, B, and their pressure derivative, B′, and the energy-volume relationship of phases are analyzed. Vibrational calculations were performed at each pressure for each polymorph and compared with available experimental data. This study reports, for the first time, a complex and unexpected structural and chemical behavior as a function of pressure. An analysis of the results shows that brannerite monoclinic polymorphs present similar energies, suggesting that both structures may coexist in the range of pressures that were studied. Theoretical prediction reveals that, as the pressure increases, the most stable polymorph of ZnV2O6 moves from the monoclinic phase, C2/m (and C2), to the orthorhombic columbite structure (Pbcn) and the corresponding transition pressure is computed to be 5 GPa at the B3LYP level; however, using the HSE06 and PBE functionals, the FeNb2O6-type structure is the most stable polymorph from ambient pressure up to 30 GPa. In addition the calculations show that the ThTi2O6-type phase (C2/c) becomes more stable than the other two monoclinic structures above 15, 13, and 8 GPa using the B3LYP, HSE06, and PBE functionals, respectively. The findings reported here indicate that the method used to predict relative phase stabilities and phase transitions should be chosen carefully, and that the results should be scrutinized with a critical eye. We analyze the variations of different vibrational frequencies and V−O and Zn−O bond lengths as pressure is applied, and the results confirm that Badger's lineal relationships were not found for the monoclinic polymorphs (C2/m, C2, and C2/c) due to the presence of a charge transfer process from the ZnO6 to the VO6 polyhedra. In addition, we determined the stability of ZnV2O6 against binary oxides (VO2, V2O5, and ZnO), or metals (Zn and V) and oxygen, and the results reveal that the decomposition channels are not energetically feasible. The present work provides a new perspective on the variations of crystal structures and physical properties at high pressure in ZnV2O6 polymorphs. With the wealth of data presented, this study aims to encourage further basic and experimental research on an interesting case of ZnV2O6based materials with novel properties that may be the basis of important innovations for industrial applications.
Journal of Physical Chemistry A, Nov 11, 2004
ABSTRACT
Journal of Physical Chemistry B, Aug 12, 2008
Physical review, Jun 30, 2016
Physical review, Oct 23, 2001
Quantum-mechanical simulations have been performed to investigate pressure effects on the crystal... more Quantum-mechanical simulations have been performed to investigate pressure effects on the crystal geometry, chemical bonding, and the electronic structure of anatase TiO 2. Total energy calculations are carried out using the density functional formalism under the nonlocal B3LYP approximation. The optimized unit cell equilibrium parameters and the bulk and linear compressibilities are determined to be in good agreement with recent experimental data. The topology of the electron density is examined by means of the atoms in molecules ͑AIM͒ theory. Computed AIM charges and topological properties of the bond critical points reveal a partially ionic behavior of the crystal that complements the description obtained from the band structure and the projected density of states analysis. A microscopic interpretation of the crystal response to hydrostatic pressure is given in terms of the elementary polyhedra and the AIM atomic volumes that fill the unit cell space.
High Pressure Research, 2002
ABSTRACT A theoretical investigation of the MgAl 2 O 4 crystal response to high-pressure conditio... more ABSTRACT A theoretical investigation of the MgAl 2 O 4 crystal response to high-pressure conditions has been carried out to determine its stability against decomposition towards MgO and f -Al 2 O 3 , and towards recently observed orthorhombic phases. We have evaluated total energy versus volume curves using the density functional formalism under the non-local B3LYP approximation, as implemented in the CRYSTAL package. Numerical and analytical fittings have been carried out to determine the equilibrium unit cell geometry and equation of state parameters for all the structures and compounds involved in the phase diagram. The macroscopic compressibility of the spinel phase is interpreted considering the compressibility of its elementary MgO 4 and AlO 6 coordination polyhedra, and implications to understand the phase stability are suggested.
Se crean los programas madelpi y radios, asi como su implentacion en ordenadores personales y a d... more Se crean los programas madelpi y radios, asi como su implentacion en ordenadores personales y a destacar que el metodo ion perturbado ab initio abre importantes perspectivas a la investigacion de las propiedades de nuevos materiales inorganicos de interes tecnologico.Se aplican metodologias teoricas al calculo de energias de red de estructuras ionicas y como se ve afectada la misma por la sustitucion de diferentes iones, contrastandose los resultados con datos experimentales.
The Journal of Physical Chemistry, Aug 1, 1994
A theoretical description of local relaxation effects induced by the presence of impurity centers... more A theoretical description of local relaxation effects induced by the presence of impurity centers V4+ at the tetrahedral and dodecahedral sites of ZrSi04 is presented. The crystal structure is analyzed via optimization of local equilibrium geometries and computation of the force constant associated with the symmetric vibrational mode at each impurity center. The theoretical study is carried out using an extension of the ab initio perturbed ion method. The relative stability of vanadium-substituted vacancies in ZrSi04 is examined in light of previous results reported by the present authors and the vibrational analysis here addressed. Local geometries were optimized by relaxing various sets of ions around each substituted center. An increased substitution energy together with a pronounced decrease of the breathing vibrational mode on the 4-fold-coordinated site shows that this substitution is unstable while that on the 8-fold-coordinated ion site is energetically favorable and the local geometry is minimally relaxed. Selective doping on each center leads to a decreased force constant as compared to that obtained for the pure crystal structure.