ZnS-type Structure Research Articles

Self-diffusion processes in stoichiometric iron mononitride

In this work, we studied atomic self-diffusion and structural phase transformation in a single phase iron mononitride (FeN) thin film deposited at an optimized substrate temperature (Ts) of 423 K. At this Ts, the FeN film exhibits a tetrahedral coordination between Fe and N atoms (ZnS-type structure with a lattice parameter of 4.28 Å). The structure of the FeN film was studied by combining x-ray diffraction with Fe and N K-edge x-ray absorption spectroscopy and conversion electron Mössbauer spectroscopy measurements. Self-diffusion of Fe and N was measured using secondary ion mass spectroscopy depth profiling in trilayer structures: [FeN(50 nm)/57FeN(2 nm)/FeN(50 nm)] and [FeN(50 nm)/Fe15N(2 nm)/FeN(50 nm)] deposited on an amorphous quartz substrate using reactive magnetron sputtering. It was found that atomic self-diffusion is strongly associated with thermal stability. Before reaching the phase decomposition temperature, the self-diffusion of N was found to be slower than Fe. Upon phase decomposition, both Fe and N diffuse rapidly, and at this stage, the self-diffusion of N takes over Fe. Within the thermally stable state, slower N diffusion indicates that Fe–N bonds are stronger than Fe–Fe bonds in FeN. This behavior was predicted theoretically and has been evidenced in this work.

Stable Supersupertetrahedron with Infinite Order via the Assembly of Supertetrahedral T4 Zinc-Indium Sulfide Clusters.

A new family member of T p, q-based hierarchical chalcogenide architecture was created by assembling regular T4-ZnInS clusters into a periodically "hollowed-out" cubic ZnS-type structure framework (T4,∞) via the cross-linker of the tetracoordinated corner μ4-S2-. Ion-exchange and CO2 adsorption experiments suggest that such a structure with a corner μ4-S2- linker has structural stability superior to those of previously reported chalcogenide open frameworks composed of the same T4-ZnInS clusters with a bicoordinated (μ2-S2-) or a tricoordinated (μ3-S2-) cross-linker. Importantly, this case further demonstrates the feasibility of systematically engineering stable porous crystalline chalcogenide frameworks by a "hollow-out" strategy.

Highly Coordinated Iron and Cobalt Nitrides Synthesized at High Pressures and High Temperatures.

Highly coordinated iron and cobalt nitrides were successfully synthesized via direct chemical reaction between a transition metal and molecular nitrogen at pressures above approximately 30 GPa using a laser-heated diamond anvil cell. The synthesized novel transition metal nitrides were found to crystallize into the NiAs-type or marcasite-type structure. NiAs-type FeN could be quenched at ambient pressure, although it was gradually converted to the ZnS-type structure after the pressure was released. On the other hand, CoN was recovered with ZnS-type structure through a phase transition from NiAs-type structure at approximately a few gigapascals during decompression. Marcasite-type CoN2 was also synthesized at pressures above approximately 30 GPa. High-pressure in situ X-ray diffraction measurement showed that the zero-pressure bulk modulus of marcasite-type CoN2 is 216(18) GPa, which is comparable to that of RhN2. This indicates that the interatomic distance of the N-N dimer in marcasite-type CoN2 is short because of weak orbital interaction between cobalt and nitrogen atoms, as in RhN2. Surprisingly, a first-principles electronic band calculation suggests that the NiAs-type FeN and CoN and marcasite-type CoN2 exhibit metallic characteristics with magnetic moments of 3.4, 0.6, and 1.2 μB, respectively. The ferromagnetic NiAs-type structure originates from the anisotropic arrangement of transition atoms stacked along the c axis.

High temperature neutron powder diffraction study of the Cu12Sb4S13 and Cu4Sn7S16 phases

Ternary copper-containing sulfides Cu12Sb4S13 and Cu4Sn7S16 have attracted considerable interest since few years due to their high-efficiency conversion as absorbers for solar energy and promising thermoelectric materials. We report therein on the decomposition study of Cu12Sb4S13 and Cu4Sn7S16 phases using high temperature in situ neutron powder diffraction. Our results obtained at a heating rate of 2.5K/min indicate that: (i) Cu12Sb4S13 decomposes above ≈792K into Cu3SbS3, and (ii) Cu4Sn7S16 decomposes above ≈891K into Sn2S3 and a copper-rich sulfide phase of sphalerite ZnS-type structure with an assumed Cu3SnS4 stoichiometry. Both phase decompositions are associated to a sulfur volatilization. While the results on Cu12Sb4S13 are in fair agreement with recent published data, the decomposition behavior of Cu4Sn7S16 differs from other studies in terms of decomposition temperature, thermal stability and products of reaction. Finally, the crystal structure refinements from neutron powder diffraction data are reported and discussed for the Cu4Sn7S16 and tetrahedrite Cu12Sb4S13 phases at 300K, and for the high temperature form of skinnerite Cu3SbS3 at 843K.

Structural, elastic and mechanical properties of group III-nitrides in zinc-blend structure

The pressure induced crystal properties of group III-nitrides have been investigated by means of modified interaction potential model (MIPM) which consists of Coulomb, three-body and short-range overlap repulsive up to second neighbour ions, covalency effect and van der Waal’s interactions. These compounds exhibit first-order phase transition from their initial ZnS-type structure to NaCl-type structure at pressures 555, 21, 37 and 8.2GPa for XN (X=B, Al, Ga and In) respectively. Their equation of state shows volume collapse of 3.6%, 17%, 16.53% and 17.73%. The elastic constants and thermophysical properties have also been obtained at zero and high pressures. The results are in good agreement with the experimental and theoretical data where available. This model is capable of explaining the phase transition, Cauchy’s discrepancy and elastic and mechanical properties successfully.

Assembly of Supertetrahedral T5 Copper−Indium Sulfide Clusters into a Super-Supertetrahedron of Infinite Order

A Cu-In-S semiconductor consisting of a single piece of a super-supertetrahedron of infinite order has been synthesized through the self-assembly of the largest known Cu-In-S T(5) supertetrahedral cluster. One of the most fascinating structural features of this material is its dual hierarchical architecture. Its open-framework architecture can be considered as a "hollowed-out" cubic ZnS-type structure with exactly 64.8% of the total of 1000 atoms in the 5 x 5 x 5 zinc blende supercell removed. The synthetic realization of this material serves to demonstrate a new method for property engineering of semiconducting materials.

Pressure induced mechanical properties of boron based pnictides

The elastic and thermodynamical properties of the III–V semiconductors as BY (Y = N, P, As) are calculated in zincblende and NaCl phases by formulating an effective interionic interaction potential. This potential consists of the long-range Coulomb, the Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbour ions and the van der Waals (vdW) interaction. The variations of elastic constants with pressure follow a systematic trend identical to that observed in other compounds of ZnS type structure family and the Born relative stability criteria is valid in boron monopnictides. From the elastic constants the Poisson's ratio ν, the ratio R S / B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic wave velocity, average wave velocity and thermodynamical property Debye temperature are calculated. By analyzing the Poisson's ratio ν and the ratio R S / B we conclude that at low pressures the boron monopnictides are brittle in nature in ZnS phase and ductile nature at high pressures in both ZnS and NaCl phases. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of ductile (brittle) nature of BY compounds.

Structural characterization of sputtered single-phase γ‴ iron nitride coatings

Single-phase γ‴-FeN films were deposited by d.c. magnetron sputtering in a reactive Ar/N 2 atmosphere. The films were characterized by X-ray diffraction, scanning and transmission electron microscopies, electron energy-loss and Mössbauer spectroscopy. The average lattice parameter of the γ‴ cubic cell is 0.455 nm. Microstructure studies by electron microscopies revealed nanostructured columnar films with no preferential orientation. Diffraction peak intensities (X-ray and electron diffraction) are close to the theoretical values for a ZnS-type structure while profile analysis of the X-ray diffraction pattern using Rietveld refinement method demonstrated that the γ‴-phase is of ZnS-type. The energy-loss near-edge structures of N K-edge of the γ‴-phase is similar to those of the ZnS-type γ″-phase suggesting an identical local atomic environment for N atoms. On the contrary, Mössbauer spectra of both structures are different, which is understood as a consequence of numerous vacancies in the γ‴ structure. Investigations of magnetic properties showed that the γ‴-FeN compound is paramagnetic from room temperature to 2 K. The main conclusion of this work is that the γ‴-FeN phase is of ZnS-type, and not of NaCl-type as it is usually reported.

Local coordination influence on the magnetic properties ofiron nitride

The electronic structure and magnetic properties of cubic iron nitrides FeNwith NaCl- and ZnS-type structures have been calculated by employing afirst-principle full-potential linearized muffin-tin orbital method. Theresults show that the local Fe-N octahedral coordination with a centrednitrogen atom is an advantageous one with which to exhibit a large exchangesplitting. Meanwhile, the local Fe-N tetrahedral coordination produces anon-magnetic phase, the ZnS-type structure. A super-exchange interaction canreasonably explain the magnetism of the FeN nitrides. In comparison with otherFe-N compounds, we find a linear dependence of the magnetic moment of ironatoms with the volume, which corresponds to the octahedral coordination.Furthermore, a magnetic moment instability is presented in the NaCl-typestructure.

Electronic, Structural and Magnetic Properties of Transition-Metal Mononitrides

The electronic, structural and magnetic properties of all transition-metal mononitrides are investigated by FLAPW band calculations. The equilibrium lattice constants estimated for NaCl-type ScN, TiN and VN and for ZnS-type FeN and CoN are in good agreement with the experimental data. The bulk modulus of MN tends to be larger than that of the single fcc crystal phase of the corresponding transition metal. For all MNs the total energy of the NaCl-type structure is lower than that of the ZnS-type structure: for ScN∼CrN the energy difference is about 100 mRyd, and for MnN∼CuN it is small (<30 mRyd). For MnN, FeN and CoN it is suggested that if their purely bulk samples of NaCl-type are synthesized, the ferromagnetic states may be realized.

Effect of the degree of ordering of structural vacancies on the fine structure of the valence-band top in cubic boron nitride

The electronic energy structure of the defect system of c-BNx with ZnS-type structure is calculated in the multiple-scattering theory by the local coherent potential method. The cluster version of the MT approximation is used to calculate the crystal potential. The effect of the relaxation of the crystal lattice on the electronic structure of nonstoichiometric boron nitride c-BN0.75 is studied and a comparison is made with the electronic energy structure of c-BN in the same approximation.

Strong element dependence of C 1s and Si 2p X-ray photoelectron diffraction profiles for identical C and Si local geometries in β-SiC

We have measured photoelectron diffraction polar profiles for a β-SiC film grown epitaxially on Si(001). Tha data reveal dominant single domain growth with a good crystallinity but the C 1s and Si 2p profiles exhibit remarkably strong differences in spite of the identical geometries of the sites occupied by these elements in the ZnS-type lattice. Most obvious are the large angular shifts and changes in intensity between expected and measured forward scattering peaks. Our results obtained at low angular resolution (∼ 5°) in the high kinetic energy range (∼ 1000 eV) provide a striking example of the limitations of the often invoked forward scattering picture. The measured profiles are rather well reproduced by single scattering cluster simulations. The observed elemental dependence can be traced back to the marked change in complex scattering amplitude between C and Si along with the very general fact, by no means restricted to the SiC(001) case, that a large number of scatterers, in particular out-of-chain atoms with a low scattering angle, make a substantial contribution to the photoelectron wave around forward scattering directions. The related energy and element dependent interference effects are particularly strong along the low density [001] C chains of the open ZnS-type structure and reflect in a drastic peak splitting due to the strong scattering at lateral Si atoms. In contrast, the [001] Si chains in β-SiC lead to an essentially structureless forward scattering peak due to the lower scattering amplitude of lateral C atoms.

Structure and optical properties of CdSe quantum dots embedded in CaF2 vacuum-deposited films

CdSe nano-crystallites as quantum dots are prepared in CaF2 films by a simultaneous vacuumdeposition technique. The crystallites have a ZnS-type structure and a parallel epitaxial orientation in the CaF2 films, the size being 2–5 nm. Annealed samples realize CdSe quantum dots of 5 nm in size, the lattice being shrunk by 3 % due to the embedding effect. The CdSe-CaF2 composite film is a new type of sample of semiconductor quantum dots embedded in insulators, different from previous ones embedded in glass. The non-linear optical properties are measured in relation to the atomic structures.

57Fe Mössbauer study of FeNx (x=0.25≈0.91) alloys

57Fe Mossbauer measurements have been perforned at the first time on iron nitrides, FeNx(x>0.5), films prepared by rf sputtering and the measurements for γ-FeN0.09, γ'-Fe4N, e-Fe2–3N and ζ-Fe2N have been also performed. Two new phases for x>0.5 have been identified: One has a ZnS-type structure denoted by γ" Another phase is denoted by γ''' in which iron atoms constitute a fcc lattice but the details of occupation sites of nitrogen atoms are not yet clear. The isomer shift of γ" relative to α-Fe at 300 K is rather small in comparison with that of other well known nitrides. The roam temperature Mossbauer spectra of γ''' consist of a sum of two doublets. Mossbauer spectra of γ" at 10 K do not indicate magnetically split pattern, but those of γ''' show magnetically split patterns at 10 K with the hyperfine fields of 30 T and 48 T, respectively. The component of 48 T is due to oxides, not due to nitrides.

X-ray crystal truncation rod scattering: II. An effect of two-dimensional symmetry of the GaAs(001) surface

The X-ray scattering, CTR scattering, from the (001) surface of the ZnS type structure was formulated by introducing the structure factor for the spiral chain connecting one atom with another extended along the [001] direction from the (001) surface. On the basis of this formula it is shown that the the intensity of the CTR scattering elongated from the 111 Bragg point from the (001) surface of GaAs is different from that elongated from the 1 1 1 Bragg point, because of the two-fold rotational symmetry of the (001) surface of this crystal around the [001] axis, while the intensities are the same for both Bragg points, being subject to the bulk symmetry. This intensity difference was confirmed by the experimental observation, although the observed difference is not as large as expected from the theoretical prediction for the ideal (001) surface of GaAs. From the analysis of the CTR scattering the surface roughness of a mechano-chemically polished (001) surface of GaAs was estimated to extend in eight atomic sheets near the surface. The lattice spacing for the first layer of the surface was found to be shrunk from an ideal spacing by about 3% and that for the second layer by about 1%.

Strain derivatives of high and low frequency dielectric constants of cuprous halides

A phenomenological lattice theory is derived to study the strain derivatives of the high and low frequency dielectric constants of solids with the ZnS type structure. The theory is used to analyse the peculiar photo-elastic behaviour and the mechanism of polarisation in cuprous halides.

Asymmetry of depth oscillations for 〈110〉 channeling in GaP

For 〈110〉 channeling, the yield of helium backscattering from gallium and from phosphorus atoms near the surface of a GaP crystal has been studied. For symmetric tilts in the {110} plane, the yield exhibits strong asymmetry, with opposite direction of the asymmetry for the two sublattices. Based on computer simulation of particle trajectories, the asymmetry is explained as a consequence of the asymmetric arrangement of 〈110〉 rows of gallium and phosphorous atoms, respectively. The effect has previously been shown to be very useful for distinguishing between impurity substitutions of the two types of atoms in a compound with ZnS-type structure.

Crystallization of amorphous Te-20 at% Sn alloy

Amorphous Te-20 at% Sn alloy was obtained by rapid cooling from the liquid state. Phase transitions occurring during continuous heating of amorphous films were studied by differential thermal analysis, X-ray diffraction and transmission electron microscopy. It was found that the crystallization of the amorphous phase begins at 382 K and proceeds via nucleation and growth of metastable phases MS1 and MS2. The first of these phases was assigned the primitive cubic structure with lattice parameter a=3.2A. The second phase, being a Te (Sn) solution, was assigned the hexagonal structure with lattice parameters a=4.45A and c=5.85A. During heating at 410 K the remaining amorphous phase decomposed into a mixture of Te crystals together with metastable phase MS3, which probably has the ZnS type structure with lattice parameter a=6.05A. Within the temperature range 450 to 550 K the MS1 phase was transformed into SnTe, and the MS2 phase into Te. The metastable intermediate phase MS3 decomposed only near the solidus temperature, and the alloy attained its equilibrium structure.

Semiempirical LCAO band structure calculation for InSb with zincblende and rocksalt type structure

Electronic band structure is calculated for InSb with ZnS and NaCl type structure by the extended Hückel theory. The result shows that InSb becomes metallic by transforming the structure from ZnS to NaCl type in agreement with the experimental result.