Stannite-type Structure Research Articles

The impact of a magnetic ion on the thermoelectric properties of copper-rich quaternary selenides

A series of copper-based p-type chalcogenide semiconductors, Cu2+x BGe1−x Se4 (B = Zn, Fe; 0 ⩽ x ⩽ 0.15), was prepared by high-temperature methods, to explore the impact of replacement of the closed-shell ion, Zn2+, with the magnetically active, Fe2+ cation. Powder x-ray diffraction in conjunction with Rietveld refinement reveals that zinc-containing materials are described in the kesterite-type structure (space group: ) and contain trace amounts of secondary phases, whereas in the iron analogues, described in the stannite-type structure (space group: I ), single-phase behaviour persists to x = 0.1. Excess copper ions lead to the formation of holes and the electrical resistivity of both series is reduced from that of the stoichiometric end members. In the case of the iron-containing materials, this is shown to be due to an increase in the hole mobility, µ. This decrease in resistivity offsets the observed reduction in Seebeck coefficient and both series exhibit an improvement in thermoelectric performance. The lower electrical resistivity of the iron-containing materials, leads to higher figures-of-merit, compared to those of the zinc-containing materials at the same level of copper excess. The maximum figure-of-merit, ZT = 0.3 is attained for Cu2.075FeGe0.925Se4 at the comparatively low temperature of 575 K. This is an increase of ca. 62% from that of the end member phase and ca. 67% higher than that of the zinc analogue at the same level of substitution.

The mechanical and optoelectronic properties of (Cu1-xAgx)2ZnSnSe4 solid solutions: A theoretical study

A theoretical investigation of the structural, mechanical, electronic, and optical properties of (Cu1-xAgx)2SnZnSe4 (CAZTSe) solid solutions has been performed. The kesterite-type structure is more stable than the stannite-type structure for A2ZnSnX4 (A = Cu, Ag; X = S, Se) at room temperature. The tendency for phase segregation is greatly reduced for CAZTSe solid solutions with increasing the concentration of Ag doping. The mechanical stability and the nature of ductility are found for each compound. The results show that the electronic properties are calculated well by the PBE0 functional. The bowing band gap observed from experiments could be explained from the existence of the metastable structure. The band gap is increased by increasing the concentration of Ag doping. The optical properties are greatly affected by Ag doping. The light absorption capacity is reduced from 400 to 800 nm, while the absorption coefficient is slightly improved between 300 and 400 nm.

Application of artificial neural network and global optimization techniques for high throughput modeling of the crystal structure of stannites and kesterites.

This study aims to apply artificial neural networks for the prediction of the lattice parameters of materials with stannite- and kesterite-type structure, and to compare the results of predictions with that obtained in the calculations exploiting the density functional theory. Crystallographic data for 49 compounds with stannite-type structure and for four compounds with the kesterite-type structure are found and, based on it, crystal structures are calculated using the density functional theory (DFT) method in a two-step relaxation procedure for all compounds. An multilayer Perceptron is constructed, which then is trained on gathered crystallographic data. Values predicted by a neural network (lattice parameters) are compared with experimental data and with results of DFT calculations. Moreover, a global optimization method (the Uspex code) is used to find potentially novel crystal structures for investigated chemical compositions. The results are discussed in the term of advantages and disadvantages of each method.

Crystallographic and optical properties and band diagrams of CuGaS2 and CuGa5S8 phases in Cu-poor Cu2S–Ga2S3 pseudo-binary system

We synthesized Cu-poor Cu–Ga–S samples such, as CuGaS2 and CuGa5S8 with the composition of (1 − x)Cu2S–(x)Ga2S3 with 0.5 ≤ x ≤ 1.0, by a mechanochemical process and sequential heating. The crystal structure changes from tetragonal chalcopyrite-type CuGaS2 (0.5 ≤ x ≤ 0.55) to tetragonal stannite-type CuGa5S8 (x = 0.8). For samples with 0.60 ≤ x ≤ 0.75, the diffraction peaks were identified to be those of a mixed phase of the chalcopyrite- and stannite-type structures. The band-gap energies of Cu-poor Cu–Ga–S samples increase in a stepwise manner with increasing x. The band-gap energy of CuGa5S8 (x = 0.8) with the tetragonal stannite-type structure is approximately 2.66 eV, which is wider than that of chalcopyrite-type CuGaS2 (2.45 eV). The energy levels of valence band maxima (VBMs) were estimated from the ionization energies measured by photoemission yield spectroscopy (PYS). The energy levels of the VBM and conduction band minimum (CBM) of the Cu-poor Cu–Ga–S samples decrease significantly with increasing x (decreasing Cu/Ga ratio). The energy level of the VBM of CuGaS2 (−5.8 eV) is considerably deeper than those of CuInSe2 (−5.2 eV) and CuInS2 (−5.5 eV). The VBM of stannite-type CuGa5S8 with x = 0.8 (−6.4 eV) is much deeper than that of chalcopyrite-type CuGaS2 (−5.8 eV) and stannite-type CuIn3Se5 (−5.6 eV). In order to understand the band structures of chalcopyrite-type CuGaS2 and stannite-type CuGa5S8, we performed first-principles calculations using the Heyd–Scuseria–Ernzerhof (HSE06), nonlocal screened hybrid density functional method. The theoretical band-gap energy of stannite-type CuGa5S8 (2.2 eV) is wider than that of chalcopyrite-type CuGaS2 (2.0 eV). Both the theoretical and experimental band gaps of stannite-type CuGa5S8 are about 0.2 eV wider than those of chalcopyrite-type CuGaS2.

Crystallographic and optical properties of CuGa3S5, CuGa3Se5 and CuIn3(S,Se)5 and CuGa3(S,Se)5 systems

To clarify the solid solution regions of CuIn3(SxSe1−x)5 and CuGa3(SxSe1−x)5 systems and their optical properties, we prepared CuIn3(S,Se)5 and CuGa3(S,Se)5 samples by a mechanochemical process and post-heating. Single-phase solid solutions with a tetragonal stannite-type structure could not be obtained for CuIn3(SxSe1−x)5 with 0≤x<0.1. On the other hand, we successfully obtained single-phase solid solutions with a tetragonal stannite-type structure for CuGa3(SxSe1−x)5 with 0.0≤x≤1.0. The solid solution region of the CuGa3(SxSe1−x)5 system is much wider than that of the CuIn3(SxSe1−x)5 system. The band gap energy of the CuGa3(SxSe1−x)5 solid solution linearly increased from 1.85eV of CuGa3Se5 (x=0.0) to 2.58eV of CuGa3S5 (x=1.0). The energy levels of the valence band maxima (VBMs) were estimated from the ionization energies measured by photoemission yield spectroscopy (PYS). The ionization energy of stannite-type CuGa3Se5 (5.69eV) is approximately equal to that of CuIn3Se5 (5.65eV). The energy levels of the VBMs of the CuGa3(SxSe1−x)5 solid solution decrease with increasing S content, x=S/(S+Se) ratio. The conduction band minimum (CBM) levels of CuGa3(SxSe1−x)5 are almost constant with x=S/(S+Se) ratio. CuIn3Se5, CuGa3Se5, CuGa3S5 and CuGa3(S,Se)5 solid solution are expected to be useful for controlling the valence band offset (ΔEv) and the conduction band offset (ΔEc) at the interface between buffer layer and absorber layer in CIGS solar cells.

Structural Characterization of Two New Quaternary Chalcogenides: CuCo2InTe4 and CuNi2InTe4

The crystal structure of the chalcogenide compounds CuCo2InTe4 and CuNi2InTe4, two new members of the I-II2-III-VI4 family, were characterized by Rietveld refinement using X-ray powder diffraction data. Both materials crystallize in the tetragonal space group I4 2m (No. 121), Z = 2, with a stannite-type structure, with the binaries CoTe and NiTe as secondary phases.

Nanocrystalline Cu2ZnSnSe4 thin films for solar cells application: Microdiffraction and structural characterization

This work presents a study of the structural characterization of Cu2ZnSnSe4 (CZTSe) thin films by X-ray diffraction (XRD) and microdiffraction measurements. Samples were deposited varying both mass (MX) and substrate temperature (TS) at which the Cu and ZnSe composites were evaporated. CZTSe samples were deposited by co-evaporation method in three stages. From XRD measurements, it was possible to establish, with increased Ts, the presence of binary phases associated with the quaternary composite during the material's growth process. A stannite-type structure in Cu2ZnSnSe4 thin films and sizes of the crystallites varying between 30 and 40 nm were obtained. X-ray microdiffraction was used to investigate interface orientations and strain distributions when deposition parameters were varied. It was found that around the main peak, 2ϴ = 27.1°, the Cu1.8Se and ZnSe binary phases predominate, which are formed during the subsequent material selenization stage. A Raman spectroscopy study revealed Raman shifts associated with the binary composites observed via XRD.

Crystal structure and Raman scattering characterization of Cu2Fe1-xCoxSnS4 chalcogenide compounds

This work reports the synthesis by solid–state reaction of Cu2Fe1-xCoxSnS4 solid solutions. Crystal structures of Cu2Fe0.8Co0.2SnS4 and Cu2Fe0.6Co0.4SnS4 were investigated by single crystal X-ray diffraction. Both phases crystallize in the tetragonal stannite-type structure. The volume of the tetrahedral [MS4] (M = Fe, Co) presented the highest distortion, with Edge-Length Distortion (ELD) indices ∼2% from the ideal tetrahedron. The powder X-ray diffraction (XRD) patterns of Cu2Fe1-xCoxSnS4 (x = 0.2, 0.4, 0.6 and 0.8) has been refined by Rietveld method. No secondary phases were detected in XRD patterns. An analysis of the vibrational properties of Cu2Fe1-xCoxSnS4 was performed using Raman scattering measurements. The Raman peaks were analyzed by fitting of the spectra and subsequently identifying the vibrational modes by comparison with experimental and theoretical data from Cu2FeSnS4 (CFTS) and Cu2CoSnS4 (CCTS) end-members. The spectra from Cu2Fe1-xCoxSnS4 show that there is a variation in the frequency of the main A1 peak at ∼320 cm−1 together with a decrease in the secondary mode intensity at ∼285 cm−1. Full Width at Half Maximum (FWHM) and the intensity of the Raman peaks reflect the high crystallinity of Cu2Fe1-xCoxSnS4 solid solutions. The oxidation states of the metals were confirmed by temperature-dependent magnetization measurements performed in the antiferromagnetic Cu2Fe1-xCoxSnS4 solid solutions.

Raman spectrum of Cu2CdSnSe4 stannite structure semiconductor compound

Raman spectrum of Cu2CdSnSe4 quaternary semiconductor compounds with tetragonal stannite-type structure (space group I4¯2m), a material which has been recognized recently as a potential candidate for thermoelectric applications, has been studied. Most of the fourteen Raman lines expected for this compound according to group theory analysis were observed in the spectrum. Besides to the two strongest A1-symmetry stannite modes at 172 and 192 cm−1 originated from the motion of Se anion around the Cu and Sn cations which remain at rest, the leftover observed Raman lines were tentatively assigned to specific eigenmodes of the stannite crystal structure by comparing these line frequencies with those obtained for this compound from IR measurements as well as with those calculated Raman modes for the Cu2ZnSnSe4 stannite-compound reported in the literature. Two spurious Raman lines related to the presence in this compound of SnSe and SnSe2 minority secondary phases have also been found in the Raman spectrum.

Raman spectra of Cu2BIICIVX4VI magnetic quaternary semiconductor compounds with tetragonal stannite type structure

A comparative study of the Raman spectra of Cu2BIICIVS4VI and Cu2BIICIVSe4VI(where B = Mn or Fe) magnetic quaternary semiconductor compounds with stannite-type structure (I4¯2m) has been done. Most of the fourteen Raman lines expected for these materials were observed in the spectra. The two strongest lines observed have been assigned to the IR inactive A11 and A12 stannite modes that originated from the motion of the S or Se anion around the Cu and CIV cations remaining at rest. The shift in the frequency of these two lines of about 150 cm−1 to lower energies observed in Cu2BIICIVSe4VI compounds as compared to those in Cu2BIICIVS4VI ones, can then be explained as due to the anion mass effect. Based on the fact that values of these frequencies depend mainly on anion mass and bond-stretching forces between nearest-neighbor atoms, the vibrational frequencies v¯(A12) and v¯(A12) of both modes for several Cu2BIICIVX4VI stannite compounds (where X = S, Se, or Te) very close to the experimental data reported for these materials were calculated from a simple model that relates these stretching forces to the anion-cation bond-distances.

Crystal structure and thermoelectric properties of Cu2Cd1−xZnxSnSe4 solid solutions

Cu2Cd1–xZnxSnSe4 solid solutions were synthesized, and their phase constitutions and thermoelectric properties were investigated. The solid solutions crystallized in the stannite-type structure for Zn contents x up to 0.65 and in the kesterite-type structure for 0.7 ≤ x ≤ 1.0. The lattice parameter a and cell volume V of the compounds decreased linearly with increasing x for both the stannite-type (0 ≤ x ≤ 0.65) and the kesterite-type (0.7 ≤ x ≤ 1) structures. The lattice parameter c decreased with increasing x for the compounds with the kesterite-type structure but increased for the compounds with the stannite-type structure. The c/a ratio increased with increasing Zn content, which indicated an weakening of the lattice distortion. The Seebeck coefficient tended to decrease with increasing Zn content, whereas the electrical conductivity and thermal conductivity increased. The figure of merit ZT increased with increasing x over the composition range of 0 ≤ x ≤ 0.60 and then fluctuated with a further increase in x. A maximum ZT of 0.23 was achieved for Cu2Cd0.4Zn0.6SnSe4 at 720 K.

Magnetic properties and cation ordering of nanopowders of the synthetic analogue of kuramite, Cu3SnS4

An extensive characterisation of the magnetic properties of synthetic powders of kuramite, with formal composition Cu3SnS4, was performed. Powders were investigated through superconducting quantum interference device (SQUID) magnetometry, electron paramagnetic resonance (EPR) spectroscopy, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM) and microanalysis. SEM and TEM reveal the presence of nanodimensioned particles. XRPD clearly shows that Cu3SnS4 crystallised in a cubic sphalerite-type structural model, in spite of the stannite-type tetragonal structure described for the natural phase. This difference arises from a full random distribution of cations. Synthetic kuramite nanopowders exhibit a marked paramagnetism, originated by the presence of Cu(II), definitely assessed by EPR measurements. Moreover, the overall magnetic behaviour of the sample cannot be simply ascribed to diluted paramagnetism, and this suggests the presence of strong superexchange interactions among Cu(II) ions even at room temperature. The main consequences of these results are the definitive assessment of the chemical formula Cu(I)2Cu(II)SnS4 and of a random distribution of Cu(II), Cu(I) and Sn(IV) ions within the available tetrahedral sites.

On the crystal structure of the defective ternary compound [formula omitted

In order to resolve the crystal structure and the corresponding space group of the tetrahedrally coordinated II–III 2–V I 4 defective semiconductor ZnGa 2Se 4, a study of the magnetic susceptibility of the alloy system Zn 1− z Mn z Ga 2Se 4 is performed. The analysis of the Curie–Weiss temperature confirms, consistently with the phase diagram previously reported, that the room temperature crystal structure of the alloy system Zn 1− z Mn z Ga 2Se 4 in all the composition ranges ( 0 ≤ z ≤ 1 ) is of defect chalcopyrite type with space group I 4 ̄ while samples obtained at temperatures higher than about 500 °C, which are rapidly cooled to room temperature, crystallizes in the partially disordered stannite-type structure I 4 ̄ 2 m . Hence, a careful process of crystal growth of this system, including a study of the phase diagram, annealing at adequate temperature, and slow cooling of the samples is necessary in order to obtain specimens in the ordered phase.

Structural study of the semimagnetic semiconductor Zn0.5Mn0.5In2Te4

AbstractThe semimagnetic semiconductor alloy Zn0.5Mn0.5In2Te4 was refined from an X‐ray powder diffraction pattern using the Rietveld method. This compound crystallizes in the space group I42m (Nº 121), Z = 2, with unit cell parameters a = 6.1738(1) Å, c = 12.3572(4) Å, V = 471.00(2) Å3, c/a = 2.00. This material crystallizes in a stannite‐type structure. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Cu2ZnSnS4 thin films prepared by sulfurizing different multilayer metal precursors

Cu2ZnSnS4 (CZTS) thin films were successfully fabricated on glass substrates by sulfurizing Cu-Sn-Zn multilayer precursors, which were deposited by ion beam sputtering and RF magnetron sputtering, respectively. The structural, electrical and optical properties of the prepared films under various processing conditions were investigated in detail. Results showed that the as-deposited CZTS thin films with the precursors by both ion beam sputtering and RF magnetron sputtering have a composition near stoichiometric. The crystallization of the samples, however, has a strong dependence on the atomic percent of constituents of the prepared CZTS films. A single phase stannite-type structure CZTS with a large absorption coefficient of 104/cm in the visible range could be obtained after sulfurization at 520°C for 2 h. The samples relative to the RF magnetron sputtering showed a low resistivity of 0.073 Ωcm and band gap energy of about 1.53 eV. The samples relative to the ion beam sputtering exhibited a resistivity of 0.36 Ωcm and the band gap energy is about 1.51 eV.

High-pressure x-ray diffraction study on the structure and phase transitions of the defect-stannite ZnGa2Se4 and defect-chalcopyrite CdGa2S4

X-ray diffraction measurements on the sphalerite-derivatives ZnGa2Se4 and CdGa2S4 have been performed upon compression up to 23 GPa in a diamond-anvil cell. ZnGa2Se4 exhibits a defect tetragonal stannite-type structure (I4¯2m) up to 15.5 GPa and in the range from 15.5 to 18.5 GPa the low-pressure phase coexists with a high-pressure phase, which remains stable up to 23 GPa. In CdGa2S4, we find that the defect tetragonal chalcopyrite-type structure (I4¯) is stable up to 17 GPa. Beyond this pressure a pressure-induced phase transition takes place. In both materials, the high-pressure phase has been characterized as a defect-cubic NaCl-type structure (Fm3¯m). The occurrence of the pressure-induced phase transitions is apparently related with an increase in the cation disorder on the semiconductors investigated. In addition, the results allow the evaluation of the axial compressibility and the determination of the equation of state for each compound. The obtained results are compared to those previously reported for isomorphic digallium sellenides. Finally, a systematic study of the pressure-induced phase transition in 23 different sphalerite-related ABX2 and AB2X4 compounds indicates that the transition pressure increases as the ratio of the cationic radii and anionic radii of the compounds increases.

Pulsed laser deposition of quaternary Cu2ZnSnSe4 thin films

AbstractWe report the successful growth of quaternary Cu2ZnSnSe4 (CZTSe) thin films by pulsed laser deposition (PLD) using Nd:YAG laser. It was found that CZTSe films atomic ratios were close to target atomic ratios with a slight metal excess and selenium deficiency. Quaternary CZTSe films grew and crystallized as a stannite‐type structure even at room temperature. All CZTSe films showed a p‐type electrical conductivity with a high absorption coefficient of 104–105 cm–1, a bandgap of 1.5 eV and a carrier concentration of the order of 1017–1018 cm–3. These results show that pulsed laser deposition could be employed as a particularly effective deposition method for the preparation of quaternary compounds thin films. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Cu 2ZnSnS 4 thin films prepared by sulfurization of ion beam sputtered precursor and their electrical and optical properties

Cu 2ZnSnS 4(CZTS) thin films were successfully prepared by sulfurization of ion bean sputtered precursors on soda-lime glass substrate. The single phase of stannite-type structure CZTS films were obtained as revealed in EDS and XRD analysis when the ratios of the constituents of CZTS thin films are close to stoichiometric by optimizing the conditions of precursor preparation and sulfurization. A low sheet resistivity as about 0.156 ω·cm and a high absorption coefficient as 1 × 10 4 cm −1 were achieved in this method by Hall effect measurements and UV-VIS spectrophotometer. The optical band-gap energy of the CZTS sample is about 1.51 eV, which is very close to the optimum value for a solar-cell absorber.

Characterization of Mixed Crystals in the System Cu2MnxCo1−xGeS4 and Investigations of the Tetrahedra Volumes

AbstractIn a series of investigations on normal tetrahedral compounds we present mixed crystals in the system Cu2MnxCo1−xGeS4 (0 &lt; x &lt; 1) and an inspection of their tetrahedra volumes. Cu2CoGeS4 crystallizes tetragonal in a stannite type structure, Cu2MnGeS4 crystallizes orthorhombic in the wurtzstannite structure type. The crystal structures of Cu2CoGeS4 and Cu2Mn0.68Co0.32GeS4 were refined from single crystal diffraction data. The refinement of Cu2CoGeS4 converged to R = 0.0547 and wR2 = 0.0847 for 299 unique reflections. The refinement of Cu2Mn0.68Co0.32GeS4 converged to R = 0.0481 and wR2 = 0.0877 for 1556 unique reflections. From these data the tetrahedra volumes of the end members and of Cu2Mn0.68Co0.32GeS4 are calculated. In Cu2CoGeS4 tetrahedra [MS4] are similar in size. In contrast, the differences of the volumes of the polyhedra [MS4] in the orthorhombic wurtzite superstructure type compounds Cu2MnGeS4 and Cu2Mn0.68Co0.32GeS4 are significant (M = Cu, Mn, (Mn0.68Co0.32), Co, Ge). From x = 0 to x = 0.5 the tetragonal structure type dominates while from x = 0.7 to the Cu2MnGeS4 end member the products crystallize in the orthorhombic structure type. Melting points of the mixed crystals decrease linearly with increasing manganese content.

Phase Relations in the Quasi‐Binary Cu2GeS3—ZnS and Quasi‐Ternary Cu2S—Zn(Cd)S—GeS2 Systems and Crystal Structure of Cu2ZnGeS4.

AbstractFor Abstract see ChemInform Abstract in Full Text.