Cinnabar Structure Research Articles

Theoretical investigations on HgTe chalcogenide materials under high pressure

First principle computations based on Density Functional Theory are made to investigate structural, mechanical, electronic properties and phase transition behaviors of HgTe chalcogenide material. It is obtained that the phase transition sequence of HgTe material is Zincblende → Cinnabar → Rocksalt → Cmcm → CsCl at 2.35 GPa, 5.95 GPa, 14.29 GPa, 52.37 GPa, respectively. The negative and values of the CsCl structure under ambient conditions indicate that this structure is mechanically unstable against the applied deformations. The small values of the elastic constants of HgTe in the cinnabar structure reveal that this structure is less resistant to deformations. The low value of tetragonal shear constant Cs of the parent phase reflects the elastic instability leading to a pressure-induced phase transition. According to our isotropic mechanical results obtained from the Voigt-Reuss-Hill (VRH) approach, the ductility behavior improves in the rocksalt and Cmcm structures which are high-pressure phases. The zincblende and cinnabar structures show semimetal and semiconductor properties in the electronic band calculations, respectively, while rocksalt, Cmcm and CsCl structures are found to be of metallic character.

Pressure-induced phase transitions of ZnSe under different pressure environments

The structural, vibrational and electronic properties of ZnSe under different pressure environments up to ∼40.0 GPa were investigated using a diamond anvil cell in conjunction with ac impedance spectroscopy, Raman spectroscopy and high–resolution transmission electron microscopy. Under the non–hydrostatic condition, ZnSe exhibited a structural phase transition from a zinc–blende to a cinnabar structure at ∼4.9 GPa, indicated by the obvious splitting of the transverse optical mode in the Raman spectra and a noticeable variation in the slope of the electrical conductivity. With increasing pressure, metallization appeared at ∼12.5 GPa, which was characterized by the high–pressure Raman spectroscopy and temperature–dependent electrical conductivity results. When the pressure was increased up to ∼30.0 GPa, another phase transition was identified by the appearance of a new peak in the Raman spectra. Compared to the non–hydrostatic condition, a roughly 2.0 GPa delay of transition pressure for ZnSe was observed at the hydrostatic condition. However, the structural phase transformation was found to be irreversible only under the non–hydrostatic condition. The unique properties displayed by ZnSe under different pressure environments may be attributed to the constrained interlayer interaction owing to the presence of the pressure medium.

Structural Phase Transitions of ZnTe under High Pressure Using Experiments and Calculations**Supported by the National Natural Science Foundation of China under Grant No 11474280, the National Basic Research Program of China under Grant No 2011CB808200, and the Chinese Academy of Sciences under Grant Nos KJCX2-SW-N20 and KJCX2-SW-N03.

The pressure-induced structural transitions of ZnTe are investigated at pressures up to 59.2 GPa in a diamond anvil cell by using synchrotron powder x-ray diffraction method. A phase transition from the initial zinc blende (ZB, ZnTe-I) structure to a cinnabar phase (ZnTe-II) is observed at 9.6 GPa, followed by a high pressure orthorhombic phase (ZnTe-III) with Cmcm symmetry at 12.1 GPa. The ZB, cinnabar (space group P3121), Cmcm, P31 and rock salt structures of ZnTe are investigated by using density functional theory calculations. Based on the experiments and calculations, the ZnTe-II phase is determined to have a cinnabar structure rather than a P31 symmetry.

Structural phase transition, electronic structures and optical properties of ZnTe

The equations of state and phase transition of ZnTe in zinc blende (ZB) and cinnabar (CB) structures under high pressure are investigated by the projected augmented wave method in the scheme of density functional theory. The primitive cell volumes, electronic structures and optical properties are also predicted before and after phase transition. The variations of the calculated total energy with volume, for the structures of ZB and CB, yield the information about the static equation of state and phase stability. The results show that the ZB phase of ZnTe has lower energy, and is more stable than its CB phase. The pressure-induced transition occurs along the common tangent line connecting the tangential points on the two enthalpy-volume curves. The calculations show that the phase transition pressure is 8.6 GPa from the ZB structure to the CB structure. The value is also compatible with those of other available theoretical and experimental results. Just before the ZB phase is transferred to the CB phase at about 8.6 GPa, the volume is reduced by 13.0% relative to the former volume at the ambient pressure condition. The calculated critical volumes and volume compressibilities by using two methods agree well with other results in the literature. The lattice parameters and equations of state of the two structures are also obtained. Metallization case of other similar materials such as ZnS caused by high pressure does not occur here. The CB phase has the behavior of indirect band gap with 0.98 eV along the symmetry of GK. After phase transition, the distributions of density of states of Zn and Te atoms of the CB structure shift towards lower energy, especially in the conduction band bottom, and the band gap decreases. Energy level overlapping is more obvious in the CB structure, and orbital hybridizations still exist, that is the reason why it is the stable phase under high pressure condition. Stronger orbital hybridization helps the transitions between Te 5p and Zn 3d electrons. The main peak of imaginary part of dielectric constant is enhanced apparently with abnormal red shift, while other two peaks disappear at the same time. Macroscopic dielectric constant of ZB structure decreases as pressure increases. For CB structure, the macroscopic dielectric constant with 13.60 eV is not affected by pressure. The results provide a theoretical basis for the polarization research of ZnTe material in static electric field under high pressure.

Theoretical Investigation of GaN

Abstract Using the Full Potential Linear Muffin Tin Orbitals (FPLMTO) method, the structural properties of GaN were studied. Different crystal structures were considered: NaCl, CsCl, wurtzite, zincblende, β-tin, Cinnabar and NiAs structures. The wurtzite is the calculated ground state structure. Results are given for lattice parameters, bulk modulus and its first derivative in the different cases. The phase transitions for GaN were also investigated. The results are compared with the available theoretical and experimental data. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of the volume, the bulk modulus, the variation of the thermal expansion α, as well as the heat capacity Cv were successfully obtained in the whole range from 0 to 30 GPa and temperature range from 0 to 1000 K.

Structural, mechanical and electronic properties of ZnTe polymorphs under pressure

We have performed first principles calculations based on density functional theory (DFT) to study the structural, mechanical and electronic properties, and pressure-induced phase transition behavior of ZnTe. The generalized gradient approximation is employed together with the projector augmented wave potentials to describe the electron-ion interaction. We consider zinc blende (B3) structure as the ambient pressure phase, the cinnabar (B3), Cmcm (B33) and rocksalt (B1) structures as candidates for the high pressure phases. The calculated structural properties are in good agreement with the experiments and earlier ab initio predictions, as is the transition pressure between them. We determine the sequence of the structural phase transition of ZnTe as B3→B9→B33, which agrees well with the experiments. The pressure dependence of the elastic constants and the electronic energy band gap of both the ambient and high pressure structures are reported. Tetragonal shear elastic constant C′ takes very small value in the parent phase, indicating the elastic instability resulting in phase transition to the high pressure structure. The obtained electronic results show that zinc blende structure is the direct energy band gap semiconductor at Γ point, while the cinnabar structure has indirect energy band gap along the symmetry of Γ→K and Cmcm phase displays the metallic behavior.

Electronic and optical properties of high pressure stable phases of ZnS: Comparison of FPLAPW and PW-PP results

A theoretical study of the structural phase transformation of ZnS under high pressure has been performed using first principle plane wave pseudopotential (PW-PP) and full potential linear augmented plane wave method (FPLAPW) calculation in which Zn-3d states are treated as valence states. In both methods, we have used a generalized gradiant approximation for the study of phase transformation and structural parameters. The calculated difference in lattice constants (Δα 0) by PW-PP and FPLAPW methods for zinc-blende, cinnabar and rocksalt structures is equal to 0.003, 0.01 and 0.001 Å respectively. There is a very good agreement between the results of PW-PP and FPLAPW calculations that shows soundness of our choice of pseudopotential. The calculated transition pressure for zinc- blende → rocksalt is in agreement with available measured data. We present calculations of the optical properties for three phases of ZnS. The band gap of different phases of ZnS decreases in order of zinc- blende → cinnabar → rocksalt mainly due to red shift of Zn-s states in the lowest conduction band. Besides, the optical band gap decreases from 2.84 eV (direct) to 0.188 eV (indirect). The shift of calculated complex dielectric function ε 2(ω) for zinc- blende → cinnabar → rocksalt is also discussed in details of optical transition that occurred in different phases.

First principles study of the relative stability and the electronic properties of GaN

Abstract A theoretical study of structural and electronic properties of the GaN compound is presented using the first-principles full-potential augmented plane wave approach within the generalized gradient approximation (GGA). Results are given for lattice parameters, bulk modulus and its first derivatives in the wurtzite, zinc-blende, rock-salt, CsCl, d-β-tin, Immm, Imm2, Cinnabar, Cmcm, and NiAs structures. The relative stability, phase transitions, band gap energies and densities of state for GaN are also presented. The results of these calculations are compared with the available theoretical and experimental data.

The Unusual Solid-State Structure of Mercury Oxide: Relativistic Density Functional Calculations for the Group 12 Oxides ZnO, CdO, and HgO

The solid-state structure of mercury oxide and its low-pressure modifications are known to significantly differ from those found for the corresponding zinc and cadmium compounds, that is, one changes from a simple hexagonal wurtzite or cubic rock salt structure found in zinc oxide and cadmium oxide to unusual chainlike montroydite and cinnabar structures in mercury oxide. Here, we present relativistic and nonrelativistic density functional studies which demonstrate that this marked structural difference is caused by relativistic effects. For HgO, the simple rock salt structure is only accessible at higher pressures. Relativistic effects reduce the cohesive energy by 2.2 eV per HgO unit and decrease the density of the crystal by 14% due to a change in the crystal symmetry. Band structure and density of states calculations also reveal large changes in the electronic structure due to relativistic effects, and we argue that the unusual yellow to red color of HgO is a relativistic effect as well.

HgTe: A potential thermoelectric material in the cinnabar phase

We present the calculations of the electronic structure and transport properties on the zinc-blende (ZB) and cinnabar phases of HgTe using the full-potential linearized augmented plane-wave method and the semiclassical Boltzmann theory. Our results show that n-doped cinnabar HgTe has a significant larger Seebeck coefficient and electrical conductivity along the z axis than those of the n-doped ZB phase. This is mainly attributed to the large structural anisotropy originated from its chainlike bonding characters along the z axis, resulting in the anisotropic energy distribution in the lowest conduction band of cinnabar structure. The resulting ZT values along the z axis of the n-doped cinnabar HgTe are predicted to reach very high values of 0.61 at room temperature and 1.74 at 600 K. Therefore, the current theory suggests that the cinnabar structure of HgTe could be a good thermoelectric material. Future experiments are thus demanded to explore its thermoelectric performance by making use of the high ZT.

A study of the electrical properties of HgS under high pressure

Using a microcircuit fabricated in a diamond anvil cell, we carried out in situ conductivity measurementson α-HgSand β-HgS under high pressure, and investigated the temperature dependenceof the conductivity of the samples under several pressures. Forα-HgS, the results show that the conductivity increases rapidly with increasing pressure from8 to 20 GPa. The energy gap was obtained by fitting linearly the plot of the logarithm ofconductivity versus the reciprocal of temperature. At 29 GPa, the sample becomes metallic,characterized by a negative temperature slope of conductivity and a zero energy gap. Forβ-HgS, a discontinuity of conductivity was observed at 5 GPa, corresponding to a transition from theβ phaseto the α phase. From 5 to 20 GPa, the conductivity rises rapidly with increasing pressure. At 27 GPa,the sample becomes metallic. In comparison with HgSe and HgTe, we obtainedexperimentally the transition pressure of the two samples from the cinnabar structure tothe rock-salt structure, respectively.

Features of the semiconductor-metal transition in GaAs at ultrahigh pressures: New intermediate phases

Using the thermopower method (Seebeck effect), the semiconductor-metal transition that occurs in gallium arsenide single crystals of n and p types at ultrahigh pressures P above ∼11–18 GPa has been studied. It has been found that the transition in n-type samples begins at lower pressures. In the region of the semiconductor-metal phase transition, features have been observed on the thermopower dependences S(P). These features indicate that lattices intermediate between the initial semiconductor structure of zinc blende and the Cmcm high-pressure orthorhombic metallic phase are formed. By analogy with ZnTe, one intermediate phase (semiconductor with hole conductivity) is suggested to have the cinnabar structure and the second intermediate phase (semimetallic with electron conductivity) possibly has the SC16 structure. A model of the semiconductor-metal transition is discussed. The behavior of the thermoelectric properties in GaAs under pressure is compared with the behavior of these properties in other ANB8−N semiconductors, which also undergo the transition to the metallic state.

Electronic structures and metallization ofHgSunder high pressures: First principles calculations and resistivity measurements

The electronic structures of $\mathrm{HgS}$ under high pressures are studied by the first principle calculations and the resistivity measurements under pressures. The widths of the band gaps decrease significantly with increasing pressures, which is consistent with the experimental results of the resistivities. $\mathrm{HgS}$ with cinnabar structure is a direct band gap semiconductor under pressure lower than $8\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. It becomes an indirect band gap semiconductor under the pressures above $8\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. When the pressures are higher than $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, it turns to a semimetal and becomes metallic after the phase transition to rocksalt structure under $26\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$.

Nernst–Ettingshausen and magnetoresistance effects in Hg1–xCdxSe single crystals in vicinity of phase transitions under hydrostatic pressure

AbstractIn the present paper the thermomagnetic longitudinal and transverse Nernst–Ettingshausen (N–E) effects were investigated in Hg1–xCdxSe (x = 0.03, 0.07) single crystals at hydrostatic pressure up to ∼2 GPa. Substitution of Cd atoms into cation sublattice increases strongly the stability of initial zinc blende lattice and shifts the phase transformation into cinnabar structure to higher pressures P ≥ 1.4 GPa. For ternary Hg1–xCdxSe compounds the values of mobility and scattering parameters of charge carriers have been obtained from the N–E and magnetoresistance (MR) effects up to phase transition points 1.4–1.7 GPa. The decreasing of mobility under pressure is consistent with opening of direct semiconductor gap. In vicinity of the structural phase transformations into cinnabar structure an anomaly of transverse N–E effect was observed connected probably with peculiarity of electronic band structure. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical compressibilities of high-pressure ZnTe polymorphs

We report the results of a theoretical study of structural, electronic, and pressure-induced phase transition properties in ZnTe. Total energies of several high-pressure polymorphs are calculated using the density functional theory ~DFT! formalism under the nonlocal approximation. Thermal effects are included by means of a nonempirical Debye-like model. In agreement with optical absorption data, the lowest direct gap of the zinc blende polymorph is found to follow a nonlinear pressure dependence that turns into linear behavior when expressed in terms of the decrease in the lattice parameter. The pressure stability ranges of cubic ~zinc blende and rocksalt!, trigonal ~cinnabar!, and orthorhombic ~Cmcm! polymorphs are computed at static and room temperature conditions. Our calculations agree with the experimental and theoretical reported zinc blende !cinnabar!Cmcmpressure-induced phase sequence. Linear and bulk compressibilities are evaluated for the four polymorphs and reveal an anisotropic behavior of the cinnabar structure, which contrasts with the cubiclike compression of its shortest Zn-Te bonds. The qualitative trend shows a crystal that becomes relatively less compressible in the high-pressure phases. Due to their technical and scientific importance, the structural and electronic behavior of II-VI compounds has been extensively investigated in the past decades. See, for example, Refs. 1 and 2 and references therein. Among the most interesting phenomena, the pressure-induced polymorphism is specially relevant, and demands theoretical and experimental studies to understand the observed changes including the semiconductor-metallic transformation exhibited by many II-VI materials under hydrostatic pressure. These firstorder structural transitions increase the zero-pressure metal coordination in the lattice yielding a narrowing of the band gaps in these solids. The study of compounds belonging to the ZnX (X5O,S,Se,Te) crystal family illustrates quite well how the identification and characterization of the polymorphic sequences have been performed. Besides the common wurtzite ! rocksalt ~ZnO! and zinc blende ! rocksalt ~ZnS! phase transitions, the high-pressure structures of ZnSe and ZnTe have been a matter of debate in the last decade. 2‐7 The x-ray diffraction experiments of Pellicer-Porres et al. 3 allow us now to establish the existence of a ~meta!stable cinnabar phase between the zinc blende and rocksalt structures in ZnSe. Conclusive experimental and theoretical results in ZnTe have recently confirmed the sequence zinc blende ~ZnTe-I! ! cinnabar ~ZnTe-II! !Cmcm ~ZnTe-III!, although the presence of a rocksalt structure ~ZnTe-IV! after ZnTe-III remains unclear. 2,6,7 For ZnTe, static and room temperature phase diagrams, phase transition volumes, and structural parameters of the three phases are available. In addition, the nonlinear response under pressure of the lowest direct absorption gap of ZnTe-I ~Refs. 8 ‐10! have been also reported.

The pseudo-binary mercury chalcogenide alloy HgSe0.7S0.3at high pressure: a mechanism for the zinc blende to cinnabar reconstructivephase transition

The structure of the pseudo-binary mercury chalcogenide alloy HgSe0.7S0.3has been studied by x-ray and neutron powder diffraction at pressures up to8.5 GPa. A phase transition from the cubic zinc blende structure to thehexagonal cinnabar structure was observed at P ∼ 1 GPa.A phenomenological model of this reconstructive phase transition based on adisplacement mechanism is proposed. Analysis of the geometrical relationship betweenthe zinc blende and the cinnabar phases has shown that the possible order parameterfor the zinc blende–cinnabar structural transformation is the spontaneous straine4.This assignment agrees with the previously observed high pressure behaviour ofthe elastic constants of some mercury chalcogenides.

Structural study of ternary mercury chalcogenides at high pressures

The structure of ternary mercury chalcogenides HgSe1-xSx (x=0.3,0.5,0.6) and HgTe1-xSx (x=0.15) was studied by means of powder neutron diffraction at pressures up to 8 GPa. A phase transition from the zinc blende cubic structure to the hexagonal cinnabar structure was observed at P≈1 GPa in HgSe1-xSx systems and at P≈1.6 GPa in HgTe0.85S0.15. A coexistence of these two phases was observed in the vicinity to the transition pressure. Lattice parameters and atomic positional parameters for the high-pressure hexagonal phase were determined.

First principles calculations of the ground-state properties and structural phase transformation in CdO

We have studied the structural properties of CdO in the rock-salt (sodium chloride), cinnabar, orthorhombic cmcm, cesium chloride, nickel arsenide, zinc blende, and wurtzite structures using first-principles total energy calculations. Rock-salt is the calculated ground state structure with $a=4.77\mathrm{\AA{}},$ ${B}_{0}=130\mathrm{GPa}.$ The experimental lattice constant is $a=4.704\mathrm{\AA{}}.$ There is an additional local minimum in the wurtzite structure. Within the precision of the calculations, its total enrgy is the same as the energy of the rock-salt structure. At high pressure $(\ensuremath{\sim}89\mathrm{Gpa}),$ our calculations predict a phase transformation from the NaCl to a CsCl structure.

Stability and Structural Properties of ZnS and ZnSe under High Pressure

The structural phase transformations of ZnS and ZnSe under high pressure are studied by using a first-principles pseudopotential method and the local density approximation for the exchange–correlation potential. ZnS and ZnSe are found to have very similar structural systematics under high pressure. In both compounds, the SC16 phase (simple cubic with 16-atom basis) is predicted to be thermodynamically stable before the rock-salt structure. The cinnabar structure of both systems is found to be unstable. The structural properties of the zinc-blende, rock-salt, cinnabar and SC16 phases are presented.

Theoretical study of the relative stability of structural phases in group-III nitrides at high pressures

We present the results of a first-principles theoretical study of the relative stability of several structural phases of the group‐III nitrides AlN, GaN, and InN that complements the picture of the behavior under pressure of these technologically important materials. Along with structures which have been previously considered in other theoretical studies of these materials ~comprising those of the observed phases: wurtzite, zinc-blende, and rocksalt; and the d-b-Sn, NiAs, and CsCl structures! we have also assessed the stability of several novel structures, viz., the cinnabar structure, the Cmcm structure, and the sc16 structure, which have been recently observed in high-pressure experiments on various related compounds ~e.g., GaAs! and have also been reported to be either stable or close to stable in a certain range of pressures in other III-V and II-VI compounds on the basis of first-principles calculations. Our results indicate, however, that in AlN, GaN, and InN, the high-pressure rocksalt phase remains stable with respect to any other phase considered in this study up to the highest pressures investigated of ;200 GPa, which agrees with the available experimental data. We have further considered the effect of the semicore d orbitals of GaN and InN on the phase diagram of these compounds.