Design of energy band alignment at the Zn(1-x)Mg(x)O/Cu(In,Ga)Se2 interface for Cd-free Cu(In,Ga)Se2 solar cells

The electronic band structure at the Zn(1-x)Mg(x)O/Cu(In(0.7)Ga(0.3))Se(2) interface was investigated for its potential application in Cd-free Cu(In,Ga)Se(2) thin film solar cells. Zn(1-x)Mg(x)O thin films with various Mg contents were grown by atomic layer deposition on Cu(In(0.7)Ga(0.3))Se(2) absorbers, which were deposited by the co-evaporation of Cu, In, Ga, and Se elemental sources. The electron emissions from the valence band and core levels were measured by a depth profile technique using X-ray and ultraviolet photoelectron spectroscopy. The valence band maximum positions are around 3.17 eV for both Zn(0.9)Mg(0.1)O and Zn(0.8)Mg(0.2)O films, while the valence band maximum value for CIGS is 0.48 eV. As a result, the valence band offset value between the bulk Zn(1-x)Mg(x)O (x = 0.1 and x = 0.2) region and the bulk CIGS region was 2.69 eV. The valence band offset value at the Zn(1-x)Mg(x)O/CIGS interface was found to be 2.55 eV after considering a small band bending in the interface region. The bandgap energy of Zn(1-x)Mg(x)O films increased from 3.25 to 3.76 eV as the Mg content increased from 0% to 25%. The combination of the valence band offset values and the bandgap energy of Zn(1-x)Mg(x)O films results in the flat (0 eV) and cliff (-0.23 eV) conduction band alignments at the Zn(0.8)Mg(0.2)O/Cu(In(0.7)Ga(0.3))Se(2) and Zn(0.9)Mg(0.1)O/Cu(In(0.7)Ga(0.3))Se(2) interfaces, respectively. The experimental results suggest that the bandgap energy of Zn(1-x)Mg(x)O films is the main factor that determines the conduction band offset at the Zn(1-x)Mg(x)O/Cu(In(0.7)Ga(0.3))Se(2) interface. Based on these results, we conclude that a Zn(1-x)Mg(x)O film with a relatively high bandgap energy is necessary to create a suitable conduction band offset at the Zn(1-x)Mg(x)O/CIGS interface to obtain a robust heterojunction. Also, ALD Zn(1-x)Mg(x)O films can be considered as a promising alternative buffer material to replace the toxic CdS for environmental safety.     

New barium copper chalcogenides synthesized using two different chalcogen atoms: Ba2Cu(6-x)STe4 and Ba2Cu(6-x)Se(y)Te(5-y)

Ba(2)Cu(6-x)STe(4) and Ba(2)Cu(6-x)Se(y)Te(5-y) were prepared from the elements in stoichiometric ratios at 1123 K, followed by slow cooling. These chalcogenides are isostructural, adopting the space group Pbam (Z = 2), with lattice dimensions of a = 9.6560(6) ?, b = 14.0533(9) ?, c = 4.3524(3) ?, and V = 590.61(7) ?(3) in the case of Ba(2)Cu(5.53(3))STe(4). A significant phase width was observed in the case of Ba(2)Cu(6-x)Se(y)Te(5-y) with at least 0.17(3) ≤ x ≤ 0.57(4) and 0.48(1) ≤ y ≤ 1.92(4). The presence of either S or Se in addition to Te appears to be required for the formation of these materials. In the structure of Ba(2)Cu(6-x)STe(4), Cu-Te chains running along the c axis are interconnected via bridging S atoms to infinite layers parallel to the a,c plane. These layers alternate with the Ba atoms along the b axis. All Cu sites exhibit deficiencies of up to 26%. Depending on y in Ba(2)Cu(6-x)Se(y)Te(5-y), the bridging atom is either a Se atom or a Se/Te mixture when y ≤ 1, and the Te atoms of the Cu-Te chains are partially replaced by Se when y > 1. All atoms are in their most common oxidation states: Ba(2+), Cu(+), S(2-), Se(2-), and Te(2-). Without Cu deficiencies, these chalcogenides were computed to be small gap semiconductors; the Cu deficiencies lead to p-doped semiconducting properties, as experimentally observed on selected samples.     

Soluble precursors for CuInSe2, CuIn(1-x)Ga(x)Se2, and Cu2ZnSn(S,Se)4 based on colloidal nanocrystals and molecular metal chalcogenide surface ligands

We report a new platform for design of soluble precursors for CuInSe(2) (CIS), Cu(In(1-x)Ga(x))Se(2) (CIGS), and Cu(2)ZnSn(S,Se)(4) (CZTS) phases for thin-film potovoltaics. To form these complex phases, we used colloidal nanocrystals (NCs) with metal chalcogenide complexes (MCCs) as surface ligands. The MCC ligands both provided colloidal stability and represented essential components of target phase. To obtain soluble precursors for CuInSe(2), we used Cu(2-x)Se NCs capped with In(2)Se(4)(2-) MCC surface ligands or CuInSe(2) NCs capped with {In(2)Cu(2)Se(4)S(3)}(3-) MCCs. A mixture of Cu(2-x)Se and ZnS NCs, both capped with Sn(2)S(6)(4-) or Sn(2)Se(6)(4-) ligands was used for solution deposition of CZTS films. Upon thermal annealing, the inorganic ligands reacted with NC cores forming well-crystallized pure ternary and quaternary phases. Solution-processed CIS and CZTS films featured large grain size and high phase purity, confirming the prospects of this approach for practical applications.     

Electrosynthesis of Cu-Se films on copper electrodes in alkaline media: a voltammetric, electrochemical quartz crystal microbalance and I/t transient study

The electroformation of Cu-Se phases, obtained by selenizing a thin film of copper deposited on the quartz/gold electrode system, was studied with an electrochemical quartz crystal microbalance (EQCM) and by cyclic voltammetry (CV) in an alkaline solution (0.05 M Na(2)B(4)O(7)) containing selenide ion. Potentiodynamic parameters showed that the formation of the initial Cu-Se phases (Cu(2-x)Se/Cu(3)Se(2)) is ruled by an irreversible diffusion controlled mechanism, where a first electron transfer is the rate-determining step. A CV study was also performed with a bulk copper electrode in 1 M NaOH solution containing selenide ion. The deconvolution of the anodic and cathodic I/E profiles corresponding to the electroformation and electroreduction of the Cu-Se film formed allowed us to establish that, depending on the anodic potential limit of the potentiodynamic scan, the Cu-Se phases formed were either a mixture of Cu(2)(-x)Se/Cu(3)Se(2) or Cu(2-x)Se/Cu(3)Se(2)/CuSe. An EQCM study showed that, during the initial stage of Cu-Se phase electroformation, water molecules were released from the electrode. In advanced stages of the process, when the electrode was completely covered by Cu-Se compounds, selenide anions were adsorbed on the formed phase. When the anodic potential limit was extended to -0.2 V, copper oxide compounds were formed. The analysis of the cathodic charge related to Cu-Se phase electroreduction and Energy Dispersive X-ray Spectroscopy (EDXS) analysis confirmed that when the anodic limit was -0.8 V, a mixture of different Cu-Se phases was formed. A I/t transient study performed with a bulk copper electrode in alkaline solution containing selenide established that the nucleation and growth mechanism (NGM) of the Cu-Se phases takes place through an initial bidimensional-instantaneous nucleation (IN2D), followed by four bidimensional-progressive nucleations (PN2D). These results and atomic force microscopy (AFM) experiences supported that the growth of the Cu-Se films occurs through a layer-by-layer mechanism.     

Structure and thermoelectric properties of the new quaternary bismuth selenides A(1-x)M(4-x)Bi(11+x)Se21 (A = K and Rb and Cs; M = Sn and Pb)--members of the grand homologous series Km(M6Se8)m(M(5+n)Se(9+n))

Several members of the new family A(1-x)M(4-x)Bi(11+x)Se21 (A = K, Rb, Cs; M = Sn, Pb) were prepared by direct combination of A2Se, Bi2Se3, Sn (or Pb), and Se at 800 degrees C. The single-crystal structures of K(0.54)Sn(3.54)Bi(11.46)Se21, K(1.46)Pb(3.08)Bi(11.46)Se21, Rb(0.69)Pb(3.69)Bi(11.31)Se21, and Cs(0.65)Pb(3.65)Bi(11.35)Se21 were determined. The compounds A(1-x)M(4-x)Bi(11+x) Se21 crystallize in a new structure type with the monoclinic space group C2/m, in which building units of the Bi2Te3 and NaCl structure type join to give rise to a novel kind of three-dimensional anionic framework with alkali-ion-filled tunnels. The building units are assembled from distorted, edge-sharing (Bi,Sn)Se6 octahedra. Bi and Sn/Pb atoms are disordered over the metal sites of the chalcogenide network, while the alkali site is not fully occupied. A grand homologous series Km(M6Se8)m(M(5+n)Se(9+n)) has been identified of which the compounds A(1-x)M(4-x)Bi(11+x)Se21 are members. We discuss here the crystal structure, charge-transport properties, and very low thermal conductivity of A(1-x)M(4-x)Bi(11+x)Se21.     

Large scale synthesis of stable tricolor Zn(1-x)Cd(x)Se core/multishell nanocrystals via a facile phosphine-free colloidal method

Here we report a new "green" method to synthesize Zn(1-x)Cd(x)Se (x = 0-1) and stable red-green-blue tricolor Zn(1-x)Cd(x)Se core/shell nanocrystals using only low cost, phosphine-free and environmentally friendly reagents. The first excitonic absorption peak and photoluminescence (PL) position of the Zn(1-x)Cd(x)Se nanocrystals (the value of x is in the range 0.005-0.2) can be fixed to any position in the range 456-540 nm. There is no red or blue shift in the entire reaction process. Three similar sizes of alloyed Zn(1-x)Cd(x)Se nanocrystals with blue, green, and yellow emissions were successfully selected as cores to synthesize high quality blue, green, and red core/shell nanocrystal emitters. For the synthesis of core/shell nanocrystals with a high quantum yield (QY) and stability, the selection of shell materials has been proven to be very important. Therefore, alternative protocols have been used to optimize thick shell growth. ZnSe/ZnSe(x)S(1-x) and CdS/Zn(1-x)Cd(x)S have been found as an excellent middle multishell to overcoat between the alloyed Zn(1-x)Cd(x)Se core and ZnS outshell. The QYs of the as-synthesized core/shell alloyed Zn(1-x)Cd(x)Se nanocrystals can reach 40-75%. The Cd content is reduced to less than 0.1% for Zn(1 -x)Cd(x)Se core/shell nanocrystals with emissions in the range 456-540 nm. More than 15 g of high quality Zn(1-x)Cd(x)Se core/shell nanocrystals were prepared successfully in a large scale, one-pot reaction. Importantly, the emissions of such thick multishell nanocrystals are not susceptible to ligand loss and stability in various physiological conditions.     

Unusual physical and chemical properties of Cu in Ce(1-x)Cu(x)O(2) oxides

The structural and electronic properties of Ce(1-x)Cu(x)O(2) nano systems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Cu atoms embedded in ceria had an oxidation state higher than those of the cations in Cu(2)O or CuO. The lattice of the Ce(1)(-x)Cu(x)O(2) systems still adopted a fluorite-type structure, but it was highly distorted with multiple cation-oxygen distances with respect to the single cation-oxygen bond distance seen in pure ceria. The doping of CeO(2) with copper introduced a large strain into the oxide lattice and favored the formation of O vacancies, leading to a Ce(1-x)Cu(x)O(2-y) stoichiometry for our materials. Cu approached the planar geometry characteristic of Cu(II) oxides, but with a strongly perturbed local order. The chemical activities of the Ce(1-x)Cu(x)O(2) nanoparticles were tested using the reactions with H(2) and O(2) as probes. During the reduction in hydrogen, an induction time was observed and became shorter after raising the reaction temperature. The fraction of copper that could be reduced in the Ce(1-x)Cu(x)O(2) oxides also depended strongly on the reaction temperature. A comparison with data for the reduction of pure copper oxides indicated that the copper embedded in ceria was much more difficult to reduce. The reduction of the Ce(1-x)Cu(x)O(2) nanoparticles was rather reversible, without the generation of a significant amount of CuO or Cu(2)O phases during reoxidation. This reversible process demonstrates the unusual structural and chemical properties of the Cu-doped ceria materials.     

Overall water splitting on (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution photocatalyst: relationship between physical properties and photocatalytic activity

The physical and photocatalytic properties of a novel solid solution between GaN and ZnO, (Ga(1-x)Zn(x))(N(1-x)O(x)), are investigated. Nitridation of a mixture of Ga(2)O(3) and ZnO at 1123 K for 5-30 h under NH(3) flow results in the formation of a (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution with x = 0.05-0.22. With increasing nitridation time, the zinc and oxygen concentrations decrease due to reduction of ZnO and volatilization of zinc, and the crystallinity and band gap energy of the product increase. The highest activity for overall water splitting is obtained for (Ga(1-x)Zn(x))(N(1-x)O(x)) with x = 0.12 after nitridation for 15 h. The crystallinity of the catalyst is also found to increase with increasing the ratio of ZnO to Ga(2)O(3) in the starting material, resulting in an increase in activity.     

Efficient overall water splitting under visible-light irradiation on (Ga(1-x)Zn(x))(N(1-x)O(x)) dispersed with Rh-Cr mixed-oxide nanoparticles: Effect of reaction conditions on photocatalytic activity

The photocatalytic activity of (Ga(1-x)Zn(x))(N(1-x)O(x)) loaded with Rh-Cr mixed-oxide (Rh(2-y)Cr(y)O3) nanoparticles for overall water splitting under visible-light irradiation (lambda > 400 nm) is investigated with respect to reaction pH and gas pressure. The photocatalytic performance of the catalyst is found to be strongly dependent on the pH of the reactant solution but largely independent of gas pressure. The present photocatalyst exhibits stable and high photocatalytic activity in an aqueous solution of pH 4.5 for 72 h. The photocatalytic performance is much lower at pH 3.0 and pH 6.2, attributable to corrosion of the cocatalyst and hydrolysis of the catalyst. The dispersion of Rh(2-y)Cr(y)O3 as a cocatalyst on the (Ga(1-x)Zn(x))(N(1-x)O(x)) surface promotes hydrogen evolution, which is considered to be the rate-determining step for overall water splitting on this catalyst.     

Growth kinetic on the optical properties of the Pb(1-x)Mn(x)Se nanocrystals embedded in a glass matrix: thermal annealing and Mn2+ concentration

Semimagnetic Pb(1-x)Mn(x)Se nanocrystals were synthesized by a fusion method in a glass matrix and characterized by optical absorption (OA), atomic/magnetic force microscopy (AFM/MFM), and photoluminescence techniques. MFM images strongly indicated the formation of Pb(1-x)Mn(x)Se magnetic phases in the glass system. Quantum dot size was manipulated by tuning annealing time. It was shown that Mn(2+) impurity affects nucleation, where Mn(2+)-doped samples present a redshift of the OA peak after a short annealing time and a blueshift after long annealing time compared to undoped PbSe NCs. This behavior was linked to the dependence of band-gap energy and the absorption selection rule on Mn(2+) concentration. Photoluminescence in the Pb(1-x)Mn(x)Se nanocrystals increases as the temperature rises up to a point and then decreases at higher temperatures. Anomalous increases in emission efficiency were analyzed by considering temperature induced carrier-transfer in semimagnetic Pb(1-x)Mn(x)Se quantum dots nanocrystals of different sizes.     

Solid state NMR characterization of individual compounds and solid solutions formed in Sc(2)O(3)--V(2)O(5)--Nb(2)O(5)--Ta(2)O(5) system

In this study, (51)V, (45)Sc and (93)Nb MAS NMR combined with satellite transition spectroscopy analysis were used to characterize the complex solid mixtures: VNb(9(1-x))Ta(9x)O(25), ScNb((1-x))Ta(x)O(4) and ScNb(2(1-x))Ta(2x)VO(9) (x = 0, 0.3, 0.5, 0.7, 1.0). This led us to describe the structures of Sc and V sites. The conclusions were based on accurate values for (51)V quadrupole coupling and chemical shift tensors obtained with (51)V MAS NMR/SATRAS for VNb(9)O(25), VTa(9)O(25) and ScVO(4). The (45)Sc NMR parameters have been obtained for Sc(2)O(3), ScVO(4), ScNbO(4) and ScTaO(4). On the basis of (45)Sc NMR and data available from literature, the ranges of the (45)Sc chemical shift have been established for ScO(6) and ScO(8). The gradual change of the (45)Sc and (51)V NMR parameters with x confirms the formation of solid solutions in the process of synthesis of VNb(9(1-x))Ta(9x)O(25) and ScNb((1-x))Ta(x)O(4), in contrast to ScNb(2(1-x))Ta(2x)VO(9). The cation sublattice of ScNb((1-x))Ta(x)O(4) is found to be in octahedral coordination. The V sites in VNb(9(1-x))Ta(9x)O(25) are present in the form of slightly distorted tetrahedra. The (93)Nb NMR parameters have been obtained for VNb(9)O(25).     

Composition-tunable Zn(x)Cd(1-x)Se nanocrystals with high luminescence and stability

High-quality Zn(x)Cd(1-x)Se nanocrystals have been successfully prepared at high temperature by incorporating stoichiometric amounts of Zn and Se into pre-prepared CdSe nanocrystals. With increasing Zn content, a composition-tunable emission across most of the visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength. The photoluminescence (PL) properties for the obtained Zn(x)Cd(1-x)Se nanocrystals (PL efficiency of 70-85%, fwhm = 22-30 nm) are comparable to those for the best reported CdSe-based QDs. In particular, they also have good PL properties in the blue spectral range. Moreover, the alloy nanocrystals can retain their high luminescence (PL efficiency of over 40%) when dispersed in aqueous solutions and maintain a symmetric peak shape and spectral position under rigorous experimental conditions. A rapid alloying process was observed at a temperature higher than "alloying point". The mechanism of the high luminescence efficiency and stability of Zn(x)Cd(1-x)Se nanocrystals is explored.     

Spectral analysis of Cu(2+): B(2)O(3)--ZnO--PbO glasses

A new series of heavy metal oxide (PbO) based zinc borate glasses in the chemical composition of (95-x)B(2)O(3)-5ZnO-xPbO (x=10, 15, 20, 25, 30, 35, 40, 45 and 50 mol%) have been prepared to verify their UV filtering performance. Both direct and indirect optical band gaps (E(opt)) have been evaluated for these glasses. For a reference glass of 45B(2)O(3)-5ZnO-50PbO, refractive indices at different wavelengths are measured and found the results satisfactorily correlated with the theoretical data upon the computation of Cauchy's constants of A=1.766029949, B=159531.024 nm(2) and C=-1.078 x 10(10) nm(4). Measurements concerning X-ray diffraction (XRD), FT-IR, differential scanning colorimeter (DSC) profiles have been carried out for this glass. The FT-IR profile has revealed that the glass has both BO(3) and BO(4) units. From DSC thermogram, glass transition temperature (T(g)), crystallization temperature (T(c)) and melting temperature (T(m)) have been located and from them, other related parameters of the glass have also been calculated. Visible absorption spectra of 45B(2)O(3)-5ZnO-(50-x)PbO-xCuO (x=0. 1, 0.2, 0.5 and 1.0 mol%) have revealed two absorption bands at around 400 nm ((2)B(1g)-->(2)E(g)) and 780 nm ((2)B(1g)-->(2)B(2g)) of Cu(2+) ions, respectively. Emission bands at 422 and 512 nm are found for the 1 mol % CuO doped glass with excitations at 306 and 332 nm.     

Crystal structure of novel compounds in the systems Zr-Cu-Al, Mo-Pd-Al and partial phase equilibria in the Mo-Pd-Al system

The crystal structures of three Al-rich compounds have been solved from X-ray single crystal diffractometry: τ(1)-MoPd(2-x)Al(8+x) (x = 0.067); τ(7)-Zr(Cu(1-x)Al(x))(12) (x = 0.514) and τ(9)-ZrCu(1-x)Al(4) (x = 0.144). τ(1)-MoPd(2-x)Al(8+x) adopts a unique structure type (space group Pbcm; lattice parameters a = 0.78153(2), b = 1.02643(3) and c = 0.86098(2) nm), which can be conceived as a superstructure of the Mo(Cu(x)Al(1-x))(6)Al(4) type. Whereas Mo-atoms occupy the 4d site, Pd(2) occupies the 4c site, Al and Pd(1) atoms randomly share the 4d position and the rest of the positions are fully occupied by Al. A B?rnighausen tree documents the crystallographic group-subgroup relation between the structure types of Mo(Cu(x)Al(1-x))(6)Al(4) and τ(1). τ(7)-Zr(Cu(1-x)Al(x))(12) (x = 0.514) has been confirmed to crystallize with the ThMn(12) type (space group I4/mmm; lattice parameters a = 0.85243(2) and c = 0.50862(3) nm). In total, 4 crystallographic sites were defined, out of which, Zr occupies site 2a, the 8f site is fully occupied by Cu, the 8i site is entirely occupied by Al, but the 8j site turned out to comprise a random mixture of Cu and Al atoms. The compound τ(9)-ZrCu(1-x)Al(4) (x = 0.144) crystallizes in a unique structure type (space group P4/nmm; lattice parameters a = 0.40275(3) and c = 1.17688(4) nm) which exhibits full atom order but a vacancy (14.4%) on the 2c site, shared with Cu atoms. τ(9)-ZrCu(1-x)Al(4) is a superstructure of Cu with an arrangement of three unit cells of Cu in the direction of the c-axis. A B?rnighausen tree documents this relationship. The ZrCu(1-x)Al(4) type (n = 3) is part of a series of structures which follow this building principle: Cu (n = 1), TiAl(3) (n = 2), τ(5)-TiNi(2-x)Al(5) (n = 4), HfGa(2) (n = 6) and Cu(3)Pd (n = 7). A partial isothermal section for the Al-rich part of the Mo-Pd-Al system at 860 °C has been established with two ternary compounds τ(1)-MoPd(2-x)Al(8+x) and τ(2) (unknown structure). The Vickers hardness (H(v)) for τ(1) was found to be 842 ± 40 MPa.     

One-pot noninjection synthesis of Cu-doped Zn(x)Cd(1-x)S nanocrystals with emission color tunable over entire visible spectrum

Unlike Mn doped quantum dots (d-dots), the emission color of Cu dopant in Cu d-dots is dependent on the nature, size, and composition of host nanocrystals (NCs). The tunable Cu dopant emission has been achieved via tuning the particle size of host NCs in previous reports. In this paper, for the first time we doped Cu impurity in Zn(x)Cd(1-x)S alloyed NCs and tuned the dopant emission in the whole visible spectrum via variation of the stoichiometric ratio of Zn/Cd precursors in the host Zn(x)Cd(1-x)S alloyed NCs. A facile noninjection and low cost approach for the synthesis of Cu:Zn(x)Cd(1-x)S d-dots was reported. The optical properties and structure of the obtained Cu:Zn(x)Cd(1-x)S d-dots have been characterized by UV-vis spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The influences of various experimental variables, including Zn/Cd ratio, reaction temperature, and Cu dopant concentration, on the optical properties of Cu dopant emission have been systematically investigated. The as-prepared Cu:Zn(x)Cd(1-x)S d-dots did show PL emission but with quite low quantum yield (QY) (typically below 6%). With the deposition of ZnS shell around the Cu:Zn(x)Cd(1-x)S core NCs, the PL QY increased substantially with a maximum value of 65%. More importantly, the high PL QY can be preserved when the initial oil-soluble d-dots were transferred into aqueous media via ligand replacement by mercaptoundeconic acid. In addition, these d-dots have thermal stability up to 250 °C.     

Compositionally tunable Cu2ZnSn(S(1-x)Se(x))4 nanocrystals: probing the effect of Se-inclusion in mixed chalcogenide thin films

Nanocrystals of multicomponent chalcogenides, such as Cu(2)ZnSnS(4) (CZTS), are potential building blocks for low-cost thin-film photovoltaics (PVs). CZTS PV devices with modest efficiencies have been realized through postdeposition annealing at high temperatures in Se vapor. However, little is known about the precise role of Se in the CZTS system. We report the direct solution-phase synthesis and characterization of Cu(2)ZnSn(S(1-x)Se(x))(4) nanocrystals (0 ≤ x ≤ 1) with the aim of probing the role of Se incorporation into CZTS. Our results indicate that increasing the amount of Se increases the lattice parameters, slightly decreases the band gap, and most importantly increases the electrical conductivity of the nanocrystals without a need for annealing.     

(1-x)La_(0.67)Ca_(0.33)MnO_3/xCuO复合体系与La_(0.67)Ca_(0.33)Mn_(1-x)Cu_xO_3电输运行为比较

用不同实验方法制备了名义组分为(1-x)La_(0.67)Ca_(0.33)MnO_3/xCuO(LCMO/CuO)和La_(0.67)Ca_(0.33)Mn_(1-x)Cu_xO_3(LCMCO)两组样品,在宽的温度范围内研究了样品的电输运行为随Cu含量x的变化关系,发现这两组样品表现出不同的行为.对于LCMCO,随x的增加,金属-绝缘体转变温度T_p迅速降低,当x=5.5%,样品表现出绝缘体导电行为;而LCMO/CuO复合样品,当x≤6%时,随x增加,Tp逐渐下降,x≥6%时,T_p不再继续降低,所有样品几乎表现出相同的电输运行为.另外,这两组样品均表现出较好的低场磁电阻效应(LFMR),在0.3 T下样品的最大磁电阻分别达到了～76%和88%.基于样品结构以及制备过程的分析,我们认为LFMR效应的增强主要是因为颗粒边界上形成的Cu相关自旋无序层引起的.     

Pyrazolate-based copper(II) and nickel(II) [2 x 2] grid complexes: protonation-dependent self-assembly, structures and properties

The pyrazole-based diamide ligand N,N'-bis(2-pyridylmethyl)pyrazole-3,5-dicarboxamide (H(3)L) has been structurally characterised and successfully employed in the preparation of [2 x 2] grid-type complexes. Thus, the reaction of H(3)L with Cu(ClO(4))2.6H(2)O or Ni(ClO(4))2.6H(2)O in the presence of added base (NaOH) affords the tetranuclear complexes [M(4)(HL(4))].8H(2)O (1: M = Cu, 2: M = Ni). Employment of a mixture of the two metal salts under otherwise identical reaction conditions leads to the formation of the mixed-metal species [Cu(x)Ni(4-x)(HL)(4)].8H(2)O (x相似文献   

Controlled hydrothermal synthesis and structural characterization of a nickel selenide series

A series of nickel selenides (NiSe2 microcrystals, Ni(1-x)Se and Ni3Se2 microspheres) has been successfully synthesized through a convenient, low-temperature hydrothermal method. A good nucleation and growth environment has been created by forming a uniform and transparent solution reaction system. The compositions (including the x value of Ni(1-x)Se), phase structures, as well as the morphologies of nickel selenides, can be controlled by adjusting the Ni/Se ratio of the raw materials, the pH, the reaction temperatures and times, and so forth. The newly produced Se microspheres in the system have been used as both reactant and in situ template to the Ni(1-x)Se microspheres. It is found that Ni(1-x)Se microspheres act as the intermediate precursor during the formation of Ni3Se2 microspheres. Under certain conditions, hexagonal NiSe microspheres can be converted into rhombohedral NiSe nanowires in solution. The formation mechanisms of a series of nickel selenides has been investigated in detail by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. This work has provided a general, simple, and effective method to control the composition, phase structure, and morphology of metal selenides in aqueous solution, which will be important for inorganic synthesis methodology and further applications of selenides.     

Crystal structure and physical properties of the new chalcogenides Ba3Cu(17-x)(S,Te)11 and Ba3Cu(17-x)(S,Te)11.5 with two different Cu clusters

The sulfide-tellurides Ba(3)Cu(17-x)(S,Te)(11) and Ba(3)Cu(17-x)(S,Te)(11.5) were synthesized from the elements in stoichiometric ratios heated to 1073 K, followed by slow cooling to 873 K over 100 h. Ba(3)Cu(17-x)(S,Te)(11) is isostructural to Ba(3)Cu(17-x)(Se,Te)(11) when [S] > [Te], space group R ?3m, with lattice dimensions of a = 12.009(1) ?, c = 27.764(2) ?, V = 3467.6(5) ?(3), for Ba(3)Cu(15.7(4))S(7.051(5))Te(3.949) (Z = 6). The structure is composed of Cu atoms forming paired hexagonal antiprisms, capped on the two outer hexagonal faces, where each Cu atom is tetrahedrally coordinated by four Q (= S, Te) atoms. The new variant is formed when [Te] > [S]; then Ba(3)Cu(17-x)(S,Te)(11.5) adopts space group Fm3?m with a = 17.2095(8) ?, V = 5096.9(4) ?(3), for Ba(3)Cu(15.6(2))S(5.33(4))Te(6.17) (Z = 8). This structure consists of eight Te-centered Cu(16) icosioctahedra per cell interconnected by cubic Cu(8) units centered by Q atoms. Electronic structure calculations and property measurements illustrate that these compounds behave as extrinsic p-type semiconductors-toward metallic behavior for the latter compound. With standard oxidation states Ba(2+), Cu(+), and Q(2-), the electron precise formulas are Ba(3)Cu(16)Q(11) and Ba(3)Cu(17)Q(11.5).