We present a first-principles study of multiferroic BiFeO3 at high pressures. Our work reveals the main structural (change in Bi's coordination and loss of ferroelectricity), electronic (spin crossover and metallization), and magnetic (loss of order) effects favored by compression and how they are connected. Our results are consistent with the striking manifold transition observed experimentally by Gavriliuk et al. [Phys. Rev. B 77, 155112 (2008)] and provide an explanation for it.
The electronic structures of element cerium under high pressure remain unclear all the time. We tried to calculate the electronic structures of $α'$, $α"$, and $ε$-Ce which only exist in the presence of pressure, by using the combination of traditional density functional theory and single-site dynamical mean-field theory. The momentum-resolved band structures, total and partial density of states, 4$f$ electronic configurations of these phases were exhaustively studied. We found that the 4$f$ electrons tend to be itinerant, and the hybridizations between the 4$f$ and $spd$ conduction electrons …
Alkali metals display unexpected properties at high pressure, including emergence of low symmetry crystal structures, that appear to occur due to enhanced electronic correlations among the otherwise nearly-free conduction electrons. We investigate the high pressure electronic and structural ground state of K, Rb, and Cs using x-ray absorption spectroscopy and x-ray diffraction measurements together with ab initio theoretical calculations. The sequence of phase transitions under pressure observed at low temperature is similar in all three heavy alkalis except for the absence of the oC84 phase i…
We present bulk property measurements of NpIr, a newly synthesized member of the Np-Ir binary phase diagram, which is isostructural to the non-centrosymmetric pressure-induced ferromagnetic superconductor UIr. Magnetic susceptibility, electronic transport properties at ambient and high pressure, and heat capacity measurements have been performed for temperature T = 0.55 - 300 K, in a range of magnetic fields up to 14 T and under pressures up to 17.3 GPa. These reveal that NpIr is a moderately heavy fermion Kondo system with strong antiferromagnetic interactions, but there is no evidence of any…
We report temperature dependent measurements of ambient pressure specific heat, magnetic susceptibility, anisotropic resistivity and thermal expansion as well as in-plane resistivity under pressure up to 20.8 kbar on single crystals of EuAg$_4$As$_2$. Based on thermal expansion and in-plane electrical transport measurements at ambient pressure this compound has two, first order, structural transitions in 80 - 120 K temperature range. Ambient pressure specific heat, magnetization and thermal expansion measurements show a cascade of up to seven transitions between 8 and 16 K associated with the …
We have performed the first high-pressure magnetotransport and x-ray diffraction measurements on ferromagnetic LaCo5, confirming the theoretically predicted electronic topological transition driving the magneto-elastic collapse seen in the related compound YCo5. Our x-ray diffraction results show an anisotropic lattice collapse of the c-axis near 10 GPa that is also commensurate with a change in the majority charge carriers evident from high-pressure Hall effect measurements. The coupling of the electronic, magnetic and lattice degrees of freedom is further substantiated by the evolution of th…
We report the electronic properties of the NdNiO3, prepared at the ambient oxygen pressure condition. The metal-insulator transition temperature is observed at 192 K, but the low temperature state is found to be less insulating compared to the NdNiO3 prepared at high oxygen pressure. The electric resistivity, Seebeck coefficient and thermal conductivity of the compound show large hysteresis below the metal-insulator transition. The large value of the effective mass (m* ~ 8me) in the metallic state indicate the narrow character of the 3d band. The electric conduction at low temperatures (T = 2 …
Some of the most exotic material properties derive from electronic states with short correlation length (~10-500 Å), suggesting that the local structural symmetry may play a relevant role in their behavior. Here we discuss the combined use of polarized x-ray absorption fine structure and x-ray diffraction at high pressure as a powerful method to tune and probe structural and electronic orders at multiple length scales. Besides addressing some of the technical challenges associated with such experiments, we illustrate this approach with results obtained in the cuprate La$_{1.875}$Ba$_{0.125}$Cu…
High pressure x-ray diffraction (XRD) measurements on RMnO3 (R=Dy, Ho and Lu) reveals that varying structural changes occurs for different R ions. Large lattice changes (orthorhombic strain) occur in DyMnO3 and HoMnO3 while the Jahn-Teller (JT) distortion remains stable. On the other hand, in LuMnO3, Mn-O bond distortions are observed in the region 4-8 GPa with the broad minimum in the JT distortion. High pressure IR measurements indicate that a phonon near 390 cm-1 corresponding to the complex motion of the Mn and O ions changes anomalously for LuMnO3. It softens in the 4-8 GPa region, which …
The popular dual electronic (Mott) and structural (Peierls) transitions in VO2 are explored using x-ray absorption spectromicroscopy with high spatial and spectral resolutions. It is found that during both heating and cooling, the electronic transition always precedes the structural Peierls transition. Between the two transitions, there are intermediate states that are spectrally isolated here.
We study the structural evolution of Sr$_3$Ir$_2$O$_7$ as a function of pressure using x-ray diffraction. At a pressure of 54 GPa at room temperature, we observe a first-order structural phase transition, associated with a change from tetragonal to monoclinic symmetry, and accompanied by a 4% volume collapse. Rietveld refinement of the high-pressure phase reveals a novel modification of the Ruddlesden-Popper structure, which adopts an altered stacking sequence of the perovskite bilayers. As the positions of the oxygen atoms could not be reliably refined from the data, we use density functional…
A pressure-induced simultaneous metal-insulator transition (MIT) and structural-phase transformation in lithium hydride with about 1% volume collapse has been predicted by means of the local density approximation (LDA) in conjunction with an all-electron GW approximation method. The LDA wrongly predicts that the MIT occurs before the structural phase transition. As a byproduct, it is shown that only the use of the generalized-gradient approximation together with the zero-point vibration produces an equilibrium lattice parameter, bulk modulus, and an equation of state that are in excellent agre…
We employ the density functional theory to study a structural transition of MnO from B1 (rocksalt) to B8 (NiAs) structures that was observed experimentally at pressures around 100 GPa. We utilize all-electron description as well as norm-conserving pseudopotentials and demonstrate that these two approaches can significantly differ in quantitative predictions. We explicitly show that even small-core pseudopotentials exhibit transferability inaccuracies for quantities sensitive to the energy differences between high- and low-spin polarizations of valence electrons.
The pressure-induced structural phase transition in the intermediate-valence compound CeNi has been investigated by X-ray and neutron powder diffraction techniques. For the first time it is shown that the structure of the pressure-induced CeNi phase (phases) can be described in terms of the Pnma space group. Equations of state for CeNi on both sides of the phase transition are derived and an approximate P-T phase diagram is suggested for P < 8 GPa and T < 300 K. The observed Cmcm -> Pnma structural transition is analyzed using density functional theory (DFT) calculations, which successfully re…
A detailed high pressure investigation is carried out using x-ray diffraction, Raman spectroscopy and low temperature resistivity measurements on hexagonal ZrSe$_{2}$ having an excess of 3 at.\% Zr. Structural studies show that the sample goes through a gradual structural transition from hexagonal to monoclinic phase, with a mixed phase in the pressure range 5.9 GPa to 14.8 GPa. Presence of a minimum in the $c/a$ ratio in the hexagonal phase and a minimum in the full width half maximum of the $A_{1g}$ mode at about the same pressure indicates an electronic phase transition. The sample shows a …
We determine the equation of state of stoichiometric FeO employing the diffusion Monte Carlo method. The fermionic nodes are fixed to those of a wave function having the form of a single Slater determinant. The calculated ambient pressure properties (lattice constant, bulk modulus and cohesive energy) agree very well with available experimental data. At approximately 65 GPa, the lattice structure is found to change from rocksalt type (B1) to NiAs based (inverse B8).
Density functional methods have been used to calculate the electronic properties of aligned smalldiameter single-walled carbon nanotubes under hydrostatic pressures. Abrupt pressure induced semiconductor-metal and metal-semiconductor transitions concomitant with changes in structure are observed. Novel and unexpected unit cell nanotube cross-sections are found. These tubes are observed to form interlinking structures at very high pressures. The large changes in electronic structure and the ability of different small diameter nanotubes to respond in different pressure regimes suggest their use …
Rare-earth nickelates exhibit a metal-insulator transition accompanied by a structural distortion that breaks the symmetry between formerly equivalent Ni sites. The quantitative theoretical description of this coupled electronic-structural instability is extremely challenging. Here, we address this issue by simultaneously taking into account both structural and electronic degrees of freedom using a charge self-consistent combination of density functional theory and dynamical mean-field theory, together with screened interaction parameters obtained from the constrained random phase approximatio…
We study the electronic structure change of yttrium trihydride $\mathrm{YH_3}$ by applying a hydrostatic pressure. At zero pressure, $\mathrm{YH_3}$ has the structure with energy favored symmetry group $P\bar{3}c1$ (165). From first principle calculation, we argue that the band crossings are caused by overlapping of an electron- and hole-like bands. Besides the space inversion symmetry ($\mathcal{I}$) and the time reversal symmetry, the band structure also exhibits an approximate particle-hole symmetry. Thus, $\mathrm{YH_3}$ can be viewed as a pseudo nodal surface semimetal belongs to class BD…
Formation of a defect face-centered cubic structure containing metal vacancies in Ni-H and Pd-H alloys was observed experimentally at high temperature annealing under high hydrogen pressure. Appearance of vacancies in the fcc structure of the Pd hydride and several other metal hydrides can be accounted for by electronic origin assuming that valence electron energy is minimized due to Hume-Rothery effects.
Photoluminescence (PL) properties of materials containing transition-metal ions depend on a variety of structural factors such as electronic structure, site symmetry and neighbouring atoms. These factors play a crucial role for the occurrence PL i.e. the PL quantum yield. This work investigates different mechanisms leading to non-radiative deexcitation processes and whether they can be modified by applying high pressure.
We report the simultaneous measurement of the structural and electronic components of the metal-insulator transition of VO$_2$ using electron and photoelectron spectroscopies and microscopies. We show that these evolve over different temperature scales, and are separated by an unusual monoclinic-like metallic phase. Our results provide conclusive evidence that the new monoclinic-like metallic phase, recently identified in high-pressure and nonequilibrium measurements, is accessible in the thermodynamic transition at ambient pressure, and we discuss the implications of these observations on the…
Pressure-induced changes in the Fermi surface of Cd up to 40 GPa are studied using highly accurate density-functional theory calculations. The topology of Fermi surface changes at pressures of 2, 8, 12 , 18 and 28 GPa indicating electronic topological transitions (ETTs). Structural parameters, compressibility data and elastic constant reveal anomalies across these ETTs. The computed equation of state at 300 K is in excellent agreement with the experimental data. In view of the highly controversial nature of these ETTs the present studies are aimed at motivating the experimentalists for their d…
Raman spectroscopic studies have been carried out on CaCrO4 under pressure up to 26GPa at ambient temperature. The Raman spectra showed CaCrO4 experienced a continuous structural phase transition started at near 6GPa, and finished at about 10GPa. It is found that the high-pressure phase could be quenched to ambient conditions. Pressure dependence of the Raman peaks suggested there existed four pressure regions related to different structural characters. We discussed these characters and inferred that the nonreversible structural transition in CaCrO4, most likely was from a zircon-type (I41/amd…
High-sensitivity $^{27}$Al nuclear magnetic resonance (NMR) measurements of aluminum metal under hydrostatic pressure of up to 10.1 GPa reveal an unexpected negative curvature in the pressure-dependence of the electronic density of states measured through shift and relaxation, which violates free electron behavior. A careful analysis of the Fermiology of aluminum shows that pressure induces an electronic topological transition (Lifshitz transition) that is responsible for the measured change in the density of states. The experiments also reveal a sudden increase in the NMR linewidth above 4.2 …
The effect of pressure on the hexagonal close-packed structure of titanium is investigated. The lattice parameters of the equilibrium structure were determined in terms of the Gibbs free energy using the Epitaxial Bain Path method. When this process was repeated for several pressures, the effect of pressure on the lattice parameters was revealed. The calculated lattice parameters were in good agreement with the experimental and theoretical results. The effects of pressure on parameters depending on the electronic structure such as conductivity and resistivity in the ground state were also inve…
The negatively charged nitrogen-vacancy (NV-) center in diamond has realized new frontiers in quantum technology. Here, the center's optical and spin resonances are observed under hydrostatic pressures up to 60 GPa. Our observations motivate powerful new techniques to measure pressure and image high pressure magnetic and electric phenomena. Our observations further reveal a fundamental inadequacy of the current model of the center and provide new insight into its electronic structure.
The effect of pressure on the structural, elastic and electronic properties of the intermetallic compound MgCu with a CsCl-type structure have been investigated using ab-initio technique. The optical properties have been studied under normal pressure. We have carried out the plane-wave pseudopotential approach within the framework of the first-principle density functional theory (DFT) implemented within the CASTEP code. The calculated structural parameters show a good agreement with the experimental and other theoretical results.
Density functional theory based study of the pressure dependent physical properties of binary SnS compound has been carried out. The computed elastic constants reveal that SnS is mechanically stable and brittle under ambient conditions. With increasing pressure, the compound becomes ductile. The Poisson's ratio also indicates brittle-ductile transition with increasing pressure. The hardness of SnS increases significantly with pressure. The compound possesses elastic anisotropy. The ground state electronic band structure is semiconducting with a small band gap which becomes metallic under press…
We report high pressure structural phase transformation sequence in a layered Iron-based superconducting compound FeSe0.3Te0.7 to 31 GPa at room temperature. The ambient pressure PbO type tetragonal phase (Space Group - P4/nmm) transforms to a monoclinic phase (Space group - P21/m) at a pressure of 7.3 \pm 0.9 GPa. This monoclinic phase is similar to the one observed below 100 K at ambient pressure. On further increase of pressure above 12 GPa, a transformation to an amorphous phase is observed that is completed by 20 GPa. The amorphous phase is found to be stable to the highest pressure of 31…
We investigate the electronic and structural changes at the nanoscale in vanadium dioxide (VO2) in the vicinity of its thermally driven phase transition. Both electronic and structural changes exhibit phase coexistence leading to percolation. In addition, we observe a dichotomy between the local electronic and structural transitions. Nanoscale x-ray diffraction reveals local, non-monotonic switching of the lattice structure, a phenomenon that is not seen in the electronic insulator-to-metal transition mapped by near-field infrared microscopy.
An organic-inorganic halide perovskite of CH3NH3SnI3 with significantly improved structural stability is obtained via pressure-induced amorphization and recrystallization. In situ high-pressure resistance measurements reveal an increased electrical conductivity by 300% in the pressure-treated perovskite. Photocurrent measurements also reveal a substantial enhancement in visible-light responsiveness. The mechanism underlying the enhanced properties is demonstrated to be associated with the improved structural stability.
The behaviour of alkaline carbonates at high pressure is poorly understood. Indeed, theoretical and experimental investigations of general trends of pressure induced structural changes appear in the literature only sporadically. In this article we use a combination of ab-initio calculations and high-pressure experiments in diamond anvil cell to determine crystal structures of high-pressure phases of K2CO3. The comparison with experimental data on Li2CO3 allows to reconstruct the common structural trend, which is consistent with the simple rule that the structure of high-pressure polymorph is t…
The structural behavior of UO2 under high pressure up to 300GPa has been studied by first-principles calculations with LSDA+U approximation. The results show that a pressure-induced structural transition to the cotunnite-type (orthorhombic Pnma) phase occurs at 38GPa. It agrees well with the experimentally observed ~42 GPa. An isostructural transition following that is also predicted to take place from 80 to 130GPa, which has not yet been observed in experiments. Further high compression beyond 226GPa will result in a metallic and paramagnetic transition. It corresponds to a volume of 90A^3 pe…
I discuss the behaviour of Group 1 and 2 elements under pressure, describing crystallography based on diamond anvil pressure cell experiments and electronic structure calculations. In addition to these precise methods, we discuss more intuitive pictures of both the electronic driving force for the transitions, and the structural motifs which optimise the electronic energy by opening pseudogaps at the Fermi energy.
In recent years, a low pressure transition around P $\sim$ 3 GPa exhibited by the A$_2$B$_3$-type 3D topological insulators is attributed to an electronic topological transition (ETT) for which there is no direct evidence either from theory or experiments. We address this phase transition and other transitions at higher pressure in bismuth selenide (Bi$_2$Se$_3$) using Raman spectroscopy at pressure upto 26.2 GPa. We see clear Raman signatures of an isostructural phase transition at P $\sim$ 2.4 GPa followed by structural transitions at $\sim$ 10 GPa and 16 GPa. First-principles calculations r…
The energy spectrum of vacancies in n-type bulk crystals of undoped arsenides: InAs, GaAs, CdSnAs2 and CdGeAs2 has been investigated upon the data on pressure and temperature dependences of kinetic coefficients. It is concluded, that deep donor levels correspond to native vacancies of arsenic in these semiconductor materials. The vacancy level positions in the energy scale relatively to the conductivity band edge and their pressure coefficients are defined.
We studied the pressure effects on the electronic and structural properties of LaOFeAs by first-principles calculations. For the anti-ferromagnetic (AFM) phase with stripe- like aligned Fe spins, the electronic density of states at the Fermi level (N (EF)) slightly descends first with increasing applied pressure, then bounces up with further increasing pressure (or decreasing volume), and reaches its maximum at ~ 29.2 GPa with the volume ~ 80% of the ambient pressure value (V0). At this volume (V = 0.8V0), the LaOFeAs crystal undergoes a structural phase transition from the orthorhombic struct…
Rare-earth monopnictides are predicted to be nontrivial semimetal candidates and show pressure-induced superconductivity. Here, we grow LuBi single crystal and study the magnetization, transport behaviors and electronic band structures to reveal its topological semimetal feature and superconductivity under pressure. At 0 GPa, the quantum oscillations indicate that there are several topologically nontrivial carrier pockets around the Fermi level, among which the hole ones are isotropic in shape, while the electron ones are anisotropic and responsible for the angular magnetoresistance. Upon comp…
An unambiguous crystallographic structure solution for the observed phases II-VI of high pressure hydrogen does not exist due to the failure of standard structural probes at extreme pressure. In this work we propose that nuclear magnetic resonance spectroscopy provides a complementary structural probe for high pressure hydrogen. We show that the best structural models available for phases II, III, and IV of high pressure hydrogen exhibit markedly distinct nuclear magnetic resonance spectra which could therefore be used to discriminate amongst them. As an example, we demonstrate how nuclear mag…
Results of the first-principles calculations are presented for the group-VB metals V, Nb and Ta up to couple of megabar pressure. An unique structural phase transition sequence BCC-->(at 60 GPa) rhombohedral (angle=110.5 degree)-->(at ~ 160 GPa)rhombohedral(angle=108.5 degree)--> (at ~ 430 GPa) BCC is predicted in V. We also find that BCC-V becomes mechanically and vibrationally unstable at around 112 GPa pressure. Similar transitions are absent in Nb and Ta.
We report Raman scattering and visible to near-infrared absorption spectra of solid hydrogen under static pressure up to 285 GPa at 85-140 K. We obtain pressure dependences of vibron and phonon modes in agreement with previously determined to lower pressures. The results indicate the stability of the ordered molecular phase III to the highest pressure reached and provide constraints on the insulator-to-metal transition pressure.
The structural properties under hydrostatic pressure up to 3 GPa of the layered rare earth carbide halide superconductor Y2C2I2 are studied by neutron powder diffraction at room temperature. The compressibilities are anisotropic, such that the compressibility perpendicular to the layers being approximately twice as large as within the layers. The atomic positional parameters determined from the powder diffraction patterns as a function of pressure were used as the basis for highly resolved electronic structure calculations. These reveal the electronic density of states at E_F to increase with …
We grew highly textured phase pure VO2 thin films on c-plane Al2O3 substrates with different oxygen partial pressure. X-ray absorption and photoemission spectroscopy confirm the identical valence state of vanadium ions despite the different oxygen pressure during the deposition. As the O2 flow rate increases, the [010] lattice parameter for monoclinic VO2 was reduced and coincidently distinctive changes in the metal- semiconductor transition (MST) and transport behaviors were observed despite the identical valence state of vanadium in these samples. We discuss the effect of the oxygen partial …
The pressure- and anion-dependent electronic structure of EuX (X=Te, Se, S, O) monochalcogenides is probed with element- and orbital-specific X-ray absorption spectroscopy in a diamond anvil cell. An isotropic lattice contraction enhances the ferromagnetic ordering temperature by inducing mixing of Eu 4{\it f} and 5{\it d} electronic orbitals. Anion substitution (Te $\to$ O) enhances competing exchange pathways through spin-polarized anion {\it p} states, counteracting the effect of the concomitant lattice contraction. The results have strong implications for efforts aimed at enhancing FM exch…
Ab initio calculations show an antiferromagnetic-ferromagnetic phase transition around 9-10 GPa and a magnetic anomaly at 12 GPa in BiFeO3. The magnetic phase transition also involves a structural and insulator-metal transition. The G-type AFM configuration under pressure leads to an increase of the y component and decrease of the z component of the magnetization, which is caused by the splitting of the dz2 orbital from doubly degenerate eg states. Our results agree with recent experimental results.
The influence of pressure on the structural and elastic properties of ScM (M = Rh, Cu, Ag, Hg) compounds has been performed by using ab initio approach pseudopotential plane- wave method based on the density functional theory within the generalized gradient approximation (GGA). The optical properties have been investigated under zero pressure. It is found that the optimized lattice parameters for all metals are in good agreement with the experimental data and other available theoretical values.
We use in-situ high pressure angle dispersive x-ray diffraction measurements to determine the equation of state of cubic tin nitride Sn3N4 under pressure up to about 26 GPa. While we find no evidence for any structural phase transition, our estimate of the bulk modulus (B) is 145 GPa, much lower than the earlier theoretical estimates and that of other group IV-nitrides. We corroborate and understand these results with complementary first-principles analysis of structural, elastic and vibrational properties of group IV-nitrides, and predict a structural transition of Sn3N4 at a higher pressure …
Determining the electronic and dielectric properties of water at high pressure and temperature is an essential prerequisite to understand the physical and chemical properties of aqueous environments under supercritical conditions, e.g. in the Earth interior. However optical measurements of compressed ice and water remain challenging and it has been common practice to assume that their band gap is inversely correlated to the measured refractive index, consistent with observations reported for hundreds of materials. Here we report ab initio molecular dynamics and electronic structure calculation…
Raman spectra of the MgB2 ceramic samples were measured as a function of pressure up to 32 GPa at room temperature. The spectrum at normal conditions contains a very broad peak at ~590 cm-1 related to the E2g phonon mode. The frequency of this mode exhibits a strong linear dependence in the pressure region from 5 to 18 GPa, whereas beyond this region the slope of the pressure-induced frequency shift is reduced by about a factor of two. The pressure dependence of the phonon mode up to ~ 5GPa exhibits a change in the slope as well as a "hysteresis" effect in the frequency vs. pressure behavior. …
We introduce the notion of electronic enthalpy for first-principles structural and dynamical calculations of finite systems under pressure. An external pressure field is allowed to act directly on the electronic structure of the system studied via the ground-state minimization of the functional $E+PV_{q}$, where $V_{q}$ is the quantum volume enclosed by a charge isosurface. The Hellmann-Feynman theorem applies, and assures that the ionic equations of motion follow an isoenthalpic dynamics. No pressurizing medium is explicitly required, while coatings of environmental ions or ligands can be int…
Using the density-functional-based tight-binding method we performed a systematic comparative study of stability, structural and electronic properties for 12 various types of graphene allotropes, which are likely candidates for engineering of novel graphene-like materials.
We consider different structures, which can be obtained by polymerization of aromatic organic molecules under high pressures. These 2D and 3D covalently bonded organic polymers and their functionalization can pave the way to production of energy storage and conversion devices. High-pressure synthesis might serve as a useful hint for production of these structures and their functionalized analogs by means of wet chemical synthesis.
We investigate the effect of controlled annealing on the structural and electronic phase evolution of Tin dioxide from Tin (II) oxyhydroxide prepared by simple precipitation method. Thermogravimetric analysis suggests a complex weight loss-gain process involved, passing through an intermediate phase of tin oxide nanoparticles. The probable structural and electronic phase evolution is discussed using detailed X-ray diffraction and X-ray photoelectron spectroscopy investigations.
The structural behaviour of CsCdF3 under pressure is investigated by means of theory and experiment. High-pressure powder x-ray diffraction experiments were performed up to a maximum pressure of 60 GPa using synchrotron radiation. The cubic $Pm\bar{3}m$ crystal symmetry persists throughout this pressure range. Theoretical calculations were carried out using the full-potential linear muffin-tin orbital method within the local density approximation and the generalized gradient approximation for exchange and correlation effects. The calculated ground state properties -- the equilibrium lattice co…
The electronic structure of four ternary-metal oxides containing isolated vanadate ions is studied. Zircon-type YVO4, YbVO4, LuVO4, and NdVO4 are investigated by high-pressure optical-absorption measurements up to 20 GPa. First-principles calculations based on density-functional theory were also performed to analyze the electronic band structure as a function of pressure. The electronic structure near the Fermi level originates largely from molecular orbitals of the vanadate ion, but cation substitution influence these electronic states. The studied ortovanadates, with the exception of NdVO4, …
We report a detailed ab initio investigation on hydrogen bonding, geometry, electronic structure, and lattice dynamics of ice under a large high pressure range, including the ice X phase (55-380GPa), the previous theoretically proposed higher-pressure phase ice XIIIM (Refs. 1-2) (380GPa), ice XV (a new structure we derived from ice XIIIM) (300-380GPa), as well as the ambient pressure low-temperature phase ice XI. Different from many other materials, the band gap of ice X is found to be increasing linearly with pressure from 55GPa up to 290GPa, the electronic density of states (DOS) shows that …
Density functional theory (DFT) based calculations have been conducted to draw a broad picture of pressure induced band structure evolution in various phases of organic and inorganic halide perovskite materials. Under a wide range of pressure applied, distinct band structure behaviors including magnitude change of band gap, direct-indirect/indirect-direct band gap transitions and CBM/VBM shifts, have been observed between organic and inorganic perovskites among different phases. Through atomic and electronic structure calculations, band gap narrowing/widening has been rationalized through crys…
Charge dynamics in the Weyl semimetals NbIrTe$_4$ and TaIrTe$_4$ under pressure: Signatures of an electronic phase transition
University of Augsburg（奥格斯堡大学）；Tanta University（坦塔大学）；National High Magnetic Field Laboratory, Florida State University（佛罗里达州立大学国家高磁场实验室）；Baylor University（贝勒大学）；Pennsylvania State University（宾夕法尼亚州立大学）
