Copper ions distribution in synthetic copper-zinc hydrosilicate

Copper ions distribution in the structure of synthetic copper-zinc hydrosilicate of zincsilite structure, obtained non-hydrothermal synthesis have been studied. Zinesilite is referred to the layered silicates of smectite group and is described by the formula Zn_x (Zn_3-x▪_x) [Si₄O₁₀](OH)₂.nH₂O, where Zn_3-x – are the ions located in the octahedral positions of layers, formed by two sheets of [Si₄O₁₀] tetrahedrons; Zn_x are zinc ions in the interlayer; ▪_x are the cation vacancies. Two types of copper ions were distinguished in accordance with the character of their interaction with hydrogen: (1) – substituting zinc ions in the octahedral positions of layers; (2) – substituting zinc ions in the interlayer. These two types of copper ions display the following properties when reacting with hydrogen: (1) – copper ions in octahedral positions start to be reduced at temperatures 553–573 K, and at 723 K reduction degree is 50% ; (2) – copper ions from interlayer start to be reduced at 503–533 K with a constant energy of activation, and their reduction may be complete at this temperature. Received: 4 April 2001 / Reviewed/Accepted: 11 April 2001     

Reliability studies of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu soldered joints with aging treatment

In this study, the interfacial reactions and joint reliabilities of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu were investigated during isothermal aging at 150 °C for aging times of up to 1,000 h. Cu₅Zn₈ IMCs layer is formed at the as-soldered Sn–9Zn/Cu interface. Adding 0.3wt.% Ag results in the adsorption of AgZn₃ on the Cu₅Zn₈ IMCs layer. The as-soldered Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu joints have sufficient pull strength. The thickness of the IMCs layer formed at the interface of Sn–9Zn/Cu and Sn–9Zn–0.3Ag/Cu both increase with increasing aging time. Correspondingly, both the pull forces of the Sn–9Zn and Sn–9Zn–0.3Ag soldered joints gradually decrease as the aging time prolonged. However, the thickness of the IMCs layer of Sn–9Zn–0.3Ag/Cu increases much slower than that of Sn–9Zn/Cu and the pull force of Sn–9Zn–0.3Ag soldered joint decreases much slower than that of Sn–9Zn soldered joint. After aging for 1,000 h, some Cu–Sn IMCs form between the Cu₅Zn₈ IMC and the Cu substrate, many voids form at the interface between the Cu₅Zn₈ layer and solder alloy, and some cracks form in the Cu₅Zn₈ IMCs layer of Sn–9Zn/Cu. The pull force Sn–9Zn soldered joint decreases by 53.1% compared to the pull force measured after as-soldered. Fracture of Sn–9Zn/Cu occurred on the IMCs layer on the whole and the fracture micrograph implies a brittle fracture. While the pull force of Sn–9Zn–0.3Ag soldered joint decreases by 51.7% after aging at 150 °C for 1,000 h. The fracture mode of Sn–9Zn–0.3Ag soldered joint is partially brittle at the IMCs layer, and partially ductile at the outer ring of the solder.     

Superconducting Properties of Zn-Doped Cu0.5Tl0.5Ba2Ca2Cu3?yZnyO10?δ Superconductors

A reproducible synthesis and characterization of Zn-doped Cu_0.5Tl_0.5Ba₂Ca₂Cu_3−y Zn _y O_12−δ (y=0, 0.5, 1.0, 1.5) superconductors at a relatively lower synthesis temperature of 840°C are studied by using X-ray diffraction, resistivity, ac-susceptibility and FTIR absorption measurements. The X-ray diffraction (XRD) studies of these samples have shown a tetragonal structure in which the c-axis length has been found to decrease with increased Zn doping. The critical temperature and magnitude of diamagnetism have not been significantly affected with the doping of Zn at this synthesis temperature. The magnitude of diamagnetism in the as-prepared undoped samples is decreased, whereas it remains stable (unchanged) in oxygen post-annealed samples. The apical oxygen phonon’s modes of type Tl–O_A–M(2) and Cu(1)–O_A–M(2) {where M=Cu/Zn} and the planar oxygen phonon modes of type M(2)–O_P–M(2) are also softened with the increase of Zn doping. We interpreted the softening of these oxygen related phonon modes linked with the decreased c-axis length, reduced John–Teller distortions and increased mass of Zn (65.38 amu) as compared to that of Cu (63.54 amu) (Kaplan et al., Phys. Rev. B 65, 214509, 2002).     

Formation of interfacial structure of Sn–3.7Ag–0.9Zn eutectic solder with different Al additions

The structural evolution of interfaces between the Sn–3.5Ag–0.9Zn–xAl (x = 0.5 and 1.0) solders and Cu substrate has been investigated by microstructural observations. The results suggest that the addition of Al in the Sn–3.5Ag–0.9Zn restrains the formation of Cu₅Zn₈ intermetallic compounds (IMCs) at the soldered interface. Moreover, the formation of Al₂Cu and Cu₉Al₄ IMCs leads to a crack failure near the interface of the Sn–3.7Ag–0.9Zn–1Al and Cu pad. It is suggested that the increase of Al content (e.g. 1 wt%) in the Sn–Ag–Zn eutectic solder would do harm to the reliability of the solder joint.     

Cu0.5Tl0.5Ba2Ca3Cu4−y Zn y O12−δ (y=0, 1.0, 2.0, 3.0, 3.5): Superconductor with Four ZnO2 Planes

A new Cu_0.5Tl_0.5Ba₂Ca₃Cu_4−y Zn _y O_12−δ (y=0, 1.0, 2.0, 3.0, 3.5) superconductor with four ZnO₂ planes is reported. The structure of the material remains tetragonal for all Zn doping concentration. The substitution of Zn at CuO₂ planar site was carried out following Cu_0.5Tl_0.5Ba₂Ca₃Cu_4−y Zn _y O_12−δ (y=0, 1.0, 2.0, 3.0, 3.5) formula. Contrary to all previous studies of Zn doping in all copper oxide high temperature superconductors, the zero resistivity critical temperature T _c(R=0), critical current density and quantity of diamagnetism increase with increased Zn concentration. The onset temperature of superconductivity in these samples was observed at 128 K and T _c(R=0) at 122 K for y=3.5. The volume of the unit cell observed through X-ray diffraction scan is found to decrease with increase Zn doping; promoting an increase in Fermi vector K _F and effective density of states which results in enhanced superconductivity parameters. The synthesis of Cu_0.5Tl_0.5Ba₂Ca₃Cu_4−y Zn _y O_12−δ material by this method is highly reproducible.      

Spinel ferrites of the quaternary system Cu-Ni-Fe-O: Synthesis and characterization

The decomposition of the freeze dried Cu(II)-Ni(II)-Fe(III) formate precursors at 1000°C in air yields complex oxides Cu_xNi_1−xFe₂O_4±δ (0 ≤ x ≤ 1) with a cubic spinel structure. For x < 0.7, single phase spinels are formed at 1000°C. However, for 0.7 ≤ x ≤ 1, Copper oxide (CuO) is identified as a second phase and the formation of a pure spinel phase requires an increase of the iron content in the mixture. For example, Cu_0.81Ni_0.1Fe_2.09O₄ is a single phase at 1000°C/air. Other single spinel phases Cu_0.5+yNi_0.5−y−zFe_2+zO_4±δ, 0 ≤ (y + z) ≤ 0.5, in the phase triangle Cu_0.5Ni_0.5Fe₂O₄–CuFe₂O₄–Cu_0.5Fe_2.5O₄ have been synthesized under special p(O₂)/T—synthesis conditions. The increase of the iron content requires an increase of the reaction temperature and/or a decrease of the p(O₂) in the reaction gas stream. The oxygen exchange between Cu_0.9Fe_2.1O_4.02 and the reducing gaseous phases shows that the non stoichiometry δ of copper ferrite is only about ±0.03. Significant changes in the oxygen content lead to the separation in different phases. The electrical and magnetic properties of copper ferrite samples depend on their chemical composition and preparation conditions.     

Ferromagnetism in Cu-doped ZnO nanoparticles at room temperature

Cu-doped ZnO nanoparticles were successfully synthesized and structurally characterized by using X-ray diffraction (XRD) and transmission electron microscope (TEM). XRD shows that Zn_1−xCu_xO (x ≤ 0.04) samples are single phase with the ZnO-like wurtzite structure, while the secondary phase Cu is observed in Zn_0.95Cu_0.05O sample. Magnetic measurements indicated that Zn_1−xCu_xO (x = 0.02, 0.03, 0.04) are ferromagnetic at room temperature and the magnetic moment per Cu atom decreased with increasing Cu concentration. XRD, TEM and X-ray photoelectron spectroscopy (XPS) analysis revealed that no ferromagnetic-related secondary phase was detected. The origin of the ferromagnetism in Zn_1−xCu_xO (x ≤ 0.04) was mainly due to Cu ions substituted into the ZnO lattice.     

Preparation of SiC–SiO<Subscript>2</Subscript>–CuO composites

SiC–SiO₂–CuO composite particles were prepared by double coating processes. SEM, DSC-TG, XRD techniques were carried out to characterize the coated composite particles and sintered compacts. It was found that a core-shell structure was constructed in the composite particles with the core of SiC and the shell of SiO₂–CuO. Cu–silicides were detected in hot-pressed compacts. SiO₂ might decompose at 1,300 °C. The decomposition product of Si would result in the transformation from Cu_6.69Si into Cu₃Si.     

Die attach properties of Zn–Al–Mg–Ga based high-temperature lead-free solder on Cu lead-frame

Several candidate alloys have been suggested as high-temperature lead-free solder for Si die attachment by different researchers. Among them, Zn–Al based alloys have proper melting range and excellent thermal/electrical properties. In this study, Zn–Al–Mg–Ga solder wire was used to attach Ti/Ni/Ag metallized Si die on Cu lead-frame in an automatic die attach machine. Die attachment was performed in a forming gas environment at temperature ranging from 370 to 400 °C. At the interface with Cu lead-frame, CuZn₄, Cu₅Zn₈ and CuZn intermetallic compound (IMC) layers were formed. At the interface with Si, Al₃Ni₂ IMC formed when 200 nm Ag layer was used at the die back and AgZn and AgZn₃ IMC layers when the Ag layer was 2,000 nm thick. Microstructure of the bulk solder consists of mainly two phases: one with a brighter contrast (about 80.9 wt% Zn) and the other one is a mixture of light (about 73.7 wt% Zn) and dark phases (about 45 wt% Al). Zn–Al–Mg–Ga solder wetted well on Cu lead-frame, covered entire die area and flowed in all directions under the Si die. Less than 10% voids were found in the die attach samples at die attach temperatures of 380 and 390 °C. Die shear strength was found within the acceptable limit (21.8–29.4 MPa) for all the die attach temperatures. Die shear strength of standard Pb–Sn solder was also measured for comparison and was found to be 29.3 MPa. In electrical test, maximum deviation of output voltage after 1,000 thermal cycles was found 12.1%.     

Growth mechanisms of interfacial intermetallic compounds in Sn/Cu–Zn solder joints during aging

The interfacial reactions of Sn/Cu–xZn (x = 15 and 30 at.%) solder joints were investigated. Before aging, [Cu₆(Sn,Zn)₅] and [Cu₆(Sn,Zn)₅/Cu–Zn–Sn] intermetallic compounds (IMCs) formed at the [Sn/Cu–15Zn] and [Sn/Cu–30Zn] interfaces, respectively. After thermal aging at 150 °C for 80 days, [Cu₆(Sn,Zn)₅/Cu₃(Sn,Zn)/Cu(Zn,Sn)/CuZn] and [Cu₆(Sn,Zn)₅/Cu(Zn,Sn)/CuZn] IMCs, respectively, formed at the [Sn/Cu–15Zn] and [Sn/Cu–30Zn] interfaces. Increasing the amount of Zn in the Cu–Zn substrates evidently suppresses the growth of Cu₃Sn and Kirkendall voids at the solder joint interfaces. Transmission electron microscopy images show the different microstructure of CuZn and Cu–Zn–Sn phases in Sn/Cu–Zn joints. These Cu–Zn phases act to inhibit the growth of Cu₆Sn₅ and Cu₃Sn IMCs. As the content of Zn increased in Cu–Zn substrates, both CuZn and Cu(Zn,Sn) grew significantly. In addition, the growth of the Cu₆(Sn,Zn)₅/Cu₃Sn IMCs approached a reaction-controlled process. The formation mechanisms of the CuZn and Cu(Zn,Sn) phases were probed and proposed with regard to the interfacial microstructure, elemental distribution, and the compositional variation at Sn/Cu–xZn interfaces.     

Cd-Doped Cu0.5Tl0.5Ba2Ca2Cu3?yCdyO10?δ (y=0,0.5,1.0,1.5,2.0) Superconductors

Superconducting properties of cadmium doped Cu_0.5Tl_0.5Ba₂Ca₂Cu_3−y Cd _y O_10−δ (y=0,0.5,1.0,1.5,2.0) samples have been studied using X-ray diffraction, resistivity, ac-susceptibility and FTIR absorption measurements. In X-ray diffraction studies these samples have shown to have tetragonal structure. The zero resistivity critical temperature and magnitude of diamagnetism are suppressed with the increased incorporation of Cd in the final compound. A change in the shape of FTIR absorption spectra, after doping, has shown the incorporation of Cd in the unit cell. A systematic hardening of the apical oxygen modes and softening of the CuO₂ planar modes of vibration with increased Cd doping have shown that it is incorporated in the unit cell of Cu_0.5Tl_0.5Ba₂Ca₂Cu_3−y Cd _y O_10−δ (y=0,0.5,1.0,1.5,2.0) superconductors. The FTIR absorption measurements of these samples have shown that hardening of the apical oxygen modes of types Cu(1)–O(2)–Tl and Cu(1)–O(2)–Cu(2)/Cd _y (y=0,0.5,1.0,1.5,2.0) increases with the increase of Cd doping in the samples. A softening of the CuO₂ planar oxygen mode Cu(2)–O–Cu(2) is also observed with the increased Cd doping in the final compound. It is most likely that hardening of the apical oxygen modes and the softening of the planar modes of vibration are associated damped harmonic oscillations produced by heavier Cd atoms in the CuO₂ planes, which suppress the phonon population from a desired level, reducing the magnitude of superconductivity in the final compound.     

Vibration fracture behavior of Sn–9Zn–<Emphasis Type="Italic">x</Emphasis>Cu lead-free solders

The effect of Cu content on the microstructure and the vibration deformation mechanisms of a potential lead-free solder, Sn–9Zn–xCu (x = 0.2, 0.5, 0.7, 1.0 wt.%), are examined in this study. Results show that Zn-rich phase and Sn–Zn eutectic decreased, while Cu–Zn intermetallic compound and proeutectic Sn-rich phase increased with increasing the Cu content. For the specimens with high Cu content (0.7Cu and 1.0Cu), hard massive Cu₅Zn₈ existed mostly amongst the proeutectic Sn-rich phase dendrites, and Zn-rich dispersed unevenly, leading to the deterioration in the tensile strength and ductility. Under a constant vibration force and constant initial-deflection testing, the high Cu specimen with a higher damping capacity was able to absorb more vibration energy and thus possessed a greater vibration fracture resistance. In addition, the lamellar-deformed structures (LDS) and Cu₅Zn₈ were able to increase the crack tortuosity, which in turn increased the crack propagation resistance.     

Classification of Lattice Defects in the Kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 Earth‐Abundant Solar Cell Absorbers

The kesterite‐structured semiconductors Cu₂ZnSnS₄ and Cu₂ZnSnSe₄ are drawing considerable attention recently as the active layers in earth‐abundant low‐cost thin‐film solar cells. The additional number of elements in these quaternary compounds, relative to binary and ternary semiconductors, results in increased flexibility in the material properties. Conversely, a large variety of intrinsic lattice defects can also be formed, which have important influence on their optical and electrical properties, and hence their photovoltaic performance. Experimental identification of these defects is currently limited due to poor sample quality. Here recent theoretical research on defect formation and ionization in kesterite materials is reviewed based on new systematic calculations, and compared with the better studied chalcopyrite materials CuGaSe₂ and CuInSe₂. Four features are revealed and highlighted: (i) the strong phase‐competition between the kesterites and the coexisting secondary compounds; (ii) the intrinsic p‐type conductivity determined by the high population of acceptor Cu_Zn antisites and Cu vacancies, and their dependence on the Cu/(Zn+Sn) and Zn/Sn ratio; (iii) the role of charge‐compensated defect clusters such as [2Cu_Zn+Sn_Zn], [V_Cu+Zn_Cu] and [Zn_Sn+2Zn_Cu] and their contribution to non‐stoichiometry; (iv) the electron‐trapping effect of the abundant [2Cu_Zn+Sn_Zn] clusters, especially in Cu₂ZnSnS₄. The calculated properties explain the experimental observation that Cu poor and Zn rich conditions (Cu/(Zn+Sn) ≈ 0.8 and Zn/Sn ≈ 1.2) result in the highest solar cell efficiency, as well as suggesting an efficiency limitation in Cu₂ZnSn(S,Se)₄ cells when the S composition is high.     

Normal and Anomalous Pseudogap of Superconducting Y0.9−x Pr x Ca0.1Ba2[Cu1−y Zn y ]3O7−δ

Electrical resistivity measurements on the superconducting oxides of the compositions Y_0.9−x Pr _x Ca_0.1Ba₂[Cu_1−y Zn _y ]₃O_7−δ (0≤x≤0.20 and 0.0≤y≤0.10) sintered in oxygen atmosphere were carried out to obtain the normal and anomalous pseudogaps in underdoped and overdoped samples. It is observed that pseudogap temperature T ^* decreases with increasing doping level p in the underdoped case. For the overdoped sample with y=0.06, T ^* shows no p dependence.      

Influence of Co Doping on the Zn Distribution in?Nd1.05Ba1.95Cu3?xZnxOz

The structural effects of Zn doping and Zn, Co co-doping in Nd_1.05Ba_1.95Cu₃O _z have been investigated by using neutron diffraction. The Zn atoms are found to occupy exclusively the planar sites in Nd_1.05Ba_1.95Cu_3−x Zn _x O _z samples with x≤0.4. An orthorhombic-to-tetragonal transition behavior was observed in the Nd_1.05Ba_1.95Cu_3−x Zn _x O _z (x=0–0.6) system, while a tetragonal-to-orthorhombic transition was observed in the Nd_1.05Ba_1.95Cu_2.8−x Zn _x Co_0.2O _z (x=0–0.6) system as the Zn doping content x increases. A comparative analysis of the structural behavior of Nd_1.05Ba_1.95Cu_3−x Zn _x O _z and Nd_1.05Ba_1.95Cu_2.8−x Zn _x Co_0.2O _z (x=0, 0.2, 0.4, 0.6) samples showed that the Co doping can induce an increase in Zn occupancy at the Cu(1) sites as the Zn doping concentration increases above x=0.4, implying that the distribution of Zn ions between the chain and planar sites can be tuned by the Co substitution for the chain Cu sites.     

Fabrication of spherical CaO–SrO–ZnO–SiO2 particles by sol–gel processing

This study was concerned with the fabrication of ceramic CaO–SrO–ZnO–SiO₂ spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol–gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO–SrO–ZnO–SiO₂ particles by sol–gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H₂O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3–5 μm homogenous spherical particles were obtained at a H₂O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO₃):Ca(NO₃)₂:Zn(NO₃)₂:Si(OC₂H₅)₄ = x:0.12:(0.40 − x):0.48 (0 ≤ x ≤ 0.8). Starting composition limitations are caused by the low solubility of strontium ions in the minimal amount of water used and the acceleration of hydrolysis as well as polycondensation at higher water content.     

Effect of Ba Substitution on the Formation of (Tl,Bi)-1234 Superconducting Phase

(Tl_1−x Bi _x )(Sr_2−y Ba _y )Ca₃Cu₄O _z ((Tl,Bi)-1234) samples (x=0.1–0.3, y=0.4–1.5) were synthesized under ambient pressure by using a two-step solid-state reaction method to investigate the effect of Ba substitution on the formation and superconducting properties of the (Tl,Bi)-1234 phase. X-ray diffraction analysis shows that nearly single-phased samples are obtained for (Tl_0.8Bi_0.2)(Sr_2−y Ba _y )Ca₃Cu₄O _z (0.8≤y≤1.2), suggesting that control of the composition ratio of Sr and Ba in the bridging layer is a key to stabilizing the 1234-type structure. The critical temperature for the nearly single-phased samples remained between 106.9 K and 109.1 K and was not significantly affected by the change in the Ba content.     

Electrical and optical properties of Hg1-x-y Zn x Mn y Te crystals

Hg_1-x-y Zn _x Mn _y Te (x ≤ 0.10,y ≤ 0.15) crystals were grown, and their electrical and optical properties were studied in the temperature range from 80 to 295 K. Heat treatment of the crystals in Hg vapor made it possible to vary the concentration of electrically active defects and preparen- andp- type materials with various carrier concentrations. The band gaps and band-gap temperature coefficients of Hg_1-x-y Zn _x Mn _y Te were determined from the 80- and 295-K optical absorption spectra.     

Study on SiN x passivated Cu/Ta/SiO2/Si multilayer structure

Silicon nitride (SiN _x ) thin film layers were deposited on Cu/Ta/SiO₂/Si multilayer structures by Plasma Enhanced Chemical Vapor Deposition at the temperature 285°C. The influence of post deposition thermal annealing treatments on the micro-structural, compositional and thermal stability study of SiN _x /Cu/Ta/SiO₂/Si multilayer structure was studied and compared with unpassivated, Cu/Ta/SiO₂/Si multilayer structure. It was found that after SiN _x passivation, the formation of Cu₂O and Ta₂O₅ was significantly reduced and the structure becomes more stable than unpassivated one. The reaction between Cu, Ta and O was not found in this SiN _x /Cu/Ta/SiO₂/Si multiplayer structure but the out diffusion of Ta to the Cu surface was unable to be suppressed. The Ta barrier was observed to fail at temperatures above 750°C due to the formation of Ta _x N _y , at the interface of SiN _x /Cu.     

Laser induced photoluminescence and morphological characterization of Cd(1?x)?yZnxMnyS nanocrystals

Doped II–VI chalcogenide semiconductor nanostructures have recently attracted a lot of attention due to the possibility of their application in various modern era devices. In the present study, Cd_(1−x)−y Zn _x Mn _y S {(0 ≤ x ≤ 0.5); (0.0001 ≤ y ≤ 0.1)} nanocrystals (NC) have been synthesized by facile wet chemical technique. Morphological and structural analyses of these synthesized quaternary NC have been done using X-ray diffraction (XRD) and transmission electron microscope (TEM) studies. Room temperature photoluminescence (PL) has been investigated using high peak power pulsed N₂-laser. Important optical parameter; excited state lifetime values have been calculated from the recorded multi-exponential decay curves. These fast and efficient nanophosphors have wide applications in opto-electronic industry as futuristic displays, lasers, nanoelectronics and nanosensors.