Electrical and mechanical properties of ZrO2(2Y)/TiN composites and laminates made from these materials

High density composites with the compositions of ZrO₂(2Y):TiN=40:60 and 70:30 mol% have been fabricated by hot isostatic pressing for 2 h at 1500°C and 196 MPa. The electrical resistivities (ρ) of the two composites are very different; showing metallic behaviour in the first case and insulating behaviour in the latter case. These properties are highly dependent on the sample texture. Laminated materials with compositions of ZrO₂(2Y)/TiN=(40:60)/(70:30)/(40:60) mol% have been prepared by hot isostatic pressing. The electrical resistivities in the perpendicular and parallel to the interface directions have been determined to be ρ⊥≈1×109 and ρ∥≈ 1×10^-6 Ωm, respectively. A residual stress of as much as ≈ 150 MPa is induced in the interfaces. The fracture toughness is greatly affected by the residual stress. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of Mg doping on the properties of combustion synthesized LiCoO<Subscript>2</Subscript> powders

The LiCo_1-xMg_xO₂ (x = 0–0.1) cathode materials for rechargeable lithium ion batteries were synthesized by starch assisted combustion route method. The structural characterization was carried out by X-ray powder diffraction and Laser Raman Spectroscopy. The sample exhibited a well-defined rhombohedral structure and the lattice parameters varied with the increasing magnesium contents. Surface morphology of the synthesized materials was determined by Scanning electron microscope. The cathode materials consist of highly-ordered single crystalline particles with spherical shape. The electrical resistivities of the samples were studied by Hall Effect. Electrical resistivities decrease with increase in magnesium content. Electrochemical properties were characterized by the assembled test cells using Galvanostatic discharge studies that were carried out at a current rate of 0.1 C. Magnesium doped LiCo_0.95Mg_0.05O₂ show improved structural stability, high reversible capacity and excellent electrochemical performance.     

In2O3 : (Sn) and SnO2 : (F) films - application to solar energy conversion part II — Electrical and optical properties

Highly conductive and transparent thin films of SnO₂ : F and In₂O₃ : Sn have been prepared using the simple pyrolitic (spray) method. The electrical properties of these layers are studied in relation to their dopant concentrations and their stoichiometric deviation. Typically we obtained for In₂O₃ : Sn and SnO₂ : F layers having the best overall properties (higher transparency and lower sheet resistance), resistivities ranging between 4 and 6.10^?4 Ω cm with transparency exceding 85% over the visible and near infra-red range of the spectrum. Emphasis is put on the possible applications of these films in solar energy conversion systems (solar cell and flat plate collectors technology).     

Influence of doping concentration on the properties of ZnO:Mn thin films by sol-gel method

Thin films of Mn-doped ZnO with different doping concentration (0.8, 1, 3, 5 at%) were prepared on Pt/Ti/SiO₂/Si substrates by using sol-gel method. The effects of the doping concentration on the structural properties, electrical characteristics and element binding energy in films were investigated. X-ray diffraction (XRD) results showed that the c-axis orientation of ZnO films was affected by Mn²⁺ content. Current-voltage (I-V) measurements indicated that resistivities of ZnO films were observably enhanced by dopant of Mn²⁺ and the resistivities value increased with a doping level up to 5 at% Mn. X-ray photoelectron spectroscopy (XPS) patterns suggested that the binding energies of O1s and ZnL₃M₄₅M₄₅ were affected by the content of Mn²⁺.     

F-doped SnO2 thin films grown on flexible substrates at low temperatures by pulsed laser deposition

Fluorine-doped tin oxide (SnO₂:F) films were deposited on polyethersulfone plastic substrates by pulsed laser deposition. The electrical and optical properties of the SnO₂:F films were investigated as a function of deposition conditions such as substrate temperature and oxygen partial pressure during deposition. High quality SnO₂:F films were achieved under an optimum oxygen pressure range (7.4-8 Pa) at relatively low growth temperatures (25-150 °C). As-deposited films exhibited low electrical resistivities of 1-7 mΩ-cm, high optical transmittance of 80-90% in the visible range, and optical band-gap energies of 3.87-3.96 eV. Atomic force microscopy measurements revealed a reduced root mean square surface roughness of the SnO₂:F films compared to that of the bare substrates indicating planarization of the underlying substrate.     

Optical and electrical properties of carbon nitride films deposited by cathode electrodeposition

Carbon nitride (CN _x ) films were prepared on silicon (100) wafers and ITO conductive glasses by cathode electrodeposition, using dicyandiamide (C₂H₄N₄) in acetone as precursors. The composition ratios (N/C) were approximated to or larger than 1 from XPS. The optical properties and electrical resistivities of the films were investigated. Intense PL with two bands in the range 2.5–3.5 eV was observed on the CN _x films. The band gaps (E _opt) deduced from measurements of the optical absorption coefficients in the UV-VIS spectra were found to be in the range of 1.1–1.6 eV. From the PL and UV-VIS spectra, the nitrogen content has a large effect on the PL band gap and E _opt. The electrical resistivities of the films on Si wafers are in the 10⁹–10¹⁰ · cm range.     

Novel transparent conducting sol-gel oxide coatings

This work focuses on the preparation of novel ternary transparent conducting oxide coatings on glass by the sol-gel method. The coatings were deposited by spin-coating from solutions of appropriate metal precursors and heat-treated at different heat-treatment procedures. An increase in electrical conductivity was achieved by a final forming gas treatment. Best electrical and optical properties have been obtained for coatings of crystalline Zn₂SnO₄, Zn₃In₂O₆ and Zn₅In₂O₈ and X-ray amorphous ZnSnO₃ with resistivities in the order of 10^− 2-10^− 1 Ω cm, an average transmission in the visible of 85% and an average surface roughness of ∼ 1 nm. ZnGa₂O₄ and GaSbO₄ coatings showed no electrical conductivity. For Zn₂SnO₄ coatings, a restricted crystallite growth was observed probably due to phase segregation effects. Electrical properties of coatings in the system ZnO-In₂O₃ were interpreted on the basis of the percolation theory.     

The preparation and characterization of crystals of the superconducting polymer, (SN)x

A technique is described for growing (SN)_x crystals which have superior electrical properties to those reported previously. The room temperature electrical conductivity has increased, so has the ratio of the room temperature and 4°K resistivities. There is no conductivity maximum in the region 20–30°K and the superconducting transition temperature is higher.     

Preparation and electrical conductivity of Cr2V2WO10 and Cr2Nb2WO10 with the rutile structure

Polycrystalline samples of Cr₂V₂WO₁₀ and Cr₂Nb₂WO₁₀ isostructural with the rutile type FeNbO₄ have been prepared. The compounds are nonstoichiometric with respect to all the constituent metal ions. Their crystallographic parameters and electrical resistivities have been characterized. The stabilization of rutile structure in these compounds is attributed to electronic effects.     

Electrical resistivity of thin bismuth films

For quantitative and reproducible observation of the quantum size effect (QSE) 78 samples of thin bismuth films were deposited at one time onto three muscovite substrates in ultrahigh vacuum. The electrical resistivity of these films, either in step-up series or a fixed thickness, was measured between 4.2 and 320 K. The experiments covered a thickness range from 300 to 3350 Å. The measured resistivities had a large scatter among simultaneously deposited samples of a fixed thickness. This scatter became more pronounced with decreasing temperature and it was due to the variation of the TCR above liquid nitrogen temperature. The thickness dependence of the ratio of resistivities at 4.2 K and 77 K (?_4.2/?₇₇), which had a relatively small scatter, did not show the oscillatory behavior predicted by Sandomirskii.     

Effect of heat treatment on precipitation behaviour in a Cu-Ni-Si-P alloy

The effects of applying different solution and ageing conditions on the electrical resistivity and precipitation behaviour of a Cu-1.3Ni-0.3Si-0.03P (wt%) alloy were studied. The electrical resistivity of solution-treated material is greatly reduced, by about 50%, by the ageing processes. The reduction in resistivity is due to depletion of solute atoms from the copper matrix by the formation of precipitates. Double ageing peaks appeared during isothermal ageing due to the formation of Ni₃P and Ni₂Si precipitates. The first maximum, due to the precipitation of Ni₃P, appeared at about 1 h of ageing time, while the second peak, due to Ni₂Si, appeared at around 10 h of ageing time when aged at 450°C. The precipitate Ni₃P forms early and the alloy starts to over-age before Ni₂Si precipitates and the alloy reaches maximum hardness. The maximum hardness produced by the precipitations of Ni₃P and Ni₂Si decreased with increasing ageing temperature from 450 to 550°C. The time to reach the maximum hardness due to Ni₃P precipitation became shorter, while that of Ni₂Si became longer, as the solution treatment temperature increased from 780 to 1020° C. The apparent activation energy for Ni₂Si precipitation was found to be about 80 kJ mol^–1 while that for Ni₃P precipitation was about 25 kJ mol^–1.     

Thermoelectric Power of Deoxygenated Bi1.6Pb0.4Sr2Ca2Cu3O10 + δ Sintered Superconducting Pellets

The thermal variation of the electrical resistivity and thermoelectric power of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_{10 + δ} pellets subjected to various degrees of deoxygenation is reported. The temperature dependence of the electrical resistivities of deoxygenated samples displays gradual transformation from metallic-like to semiconductor-like features in the normal state. All the samples however, show superconducting transition, but increasing deoxygenation depresses T _C0 from 102 to 45 K. Gross features of the temperature variation of thermoelectric power observed in properly oxygenated (Bi, Pb)-2223 cuprates are retained in all the deoxygenated samples. Our results on electrical resistivity and thermoelectric power in the normal state have been found to be consistent with a two-band model.     

The development of microstructural and electrical characteristics in some thick-film resistors during firing

The development of microstructural and electrical characteristics (sheet resistivities, TCRs, and noise indices) in some thick-film resistors during the firing process has been evaluated. Three 1 kohm/sq. resistor pastes (Du Pont), based on RuO₂, ruthenate or a mixture of both conductive phases, were fired at temperatures from 500°C to 950°C. The cell parameters of the RuO₂ in the 8031 and the 2031 resistors, the bismuth ruthenate in the 8029 resistors and the lead ruthenate in the 2031 resistors, were calculated from X-ray data. Microstructures were analyzed by SEM and EDS microanalysis. The absolute values of the cold and hot TCRs first decreased to a minimum at 850°C and then increased again with increasing firing temperature. The noise indices of the resistors generally decrease with increasing firing temperature.     

Growth of polysilicon and silicide films for MOS-VLSI application

Doped and undoped polycrystalline silicon films were grown byapcvd and thermal evaporation techniques. The effect of growth and annealing conditions on the crystalline nature of the films and their properties were studied by electrical, optical, x-ray diffraction andsem techniques. Metal silicides such as TiSi₂ and PtSi₂ were prepared by co-evaporation technique over polysilicon layers to study their suitability in microelectronic applications. Some of the properties of polysilicon and silicides are discussed.     

Growth and vacuum post-annealing effect on the properties of the new absorber CuSbS2 thin films

Post-growth treatments in vacuum atmosphere were performed on CuSbS₂ films prepared by the single-source thermal evaporation method on glass substrates. The films were annealed in vacuum atmosphere for 2 h in temperature range 130-200 °C. The effect of this thermal treatment on the structural, optical and electrical properties of the films was studied. X-ray diffraction (XRD) patterns indicated that the films exhibited an amorphous structure for annealing temperature below 200 °C and a polycrystalline structure with CuSbS₂ principal phase. For the films annealed at temperatures below 200 °C one direct optical transition in range 1.8-2 eV was found. For the films annealed at 200 °C, two optical direct transitions emerged at 1.3 and 1.79 eV corresponding to the CuSbS₂ and Sb₂S₃ values respectively. The electrical measurements showed a conversion from low resistivities (3.10^− 2-9.10^− 2) Ω cm for the samples annealed at temperatures below 200 °C to relatively high resistivities (2 Ω cm) for the samples annealed at 200 °C. In all cases the samples exhibited p-Ztype conductivity.     

Characterization of negative temperature coefficient of resistivity in (Sn1−x Ti x )0.95Sb0.05O2 (x ≤ 0.1) ceramics

Sb-doped SnO₂-based ceramics substituted by a trace of titanium, (Sn_1?x Ti _x )_0.95Sb_0.05O₂ (x ≤ 0.1), were prepared through a wet chemical process polymerized with polyvinyl alcohol. The phase component and related electrical properties of the ceramics were investigated. The results show that all the ceramics have the tetragonal rutile-type SnO₂ crystalline lattice and show typical effect of negative temperature coefficient (NTC) of resistivity. The room-temperature resistivities and NTC material constants can be adjusted widely by changing the Ti content in the ceramics. The investigations by analyzing the electrochemical impedance spectra at various temperatures show that both grain effect and grain-boundary effect contribute to the NTC feature of the ceramics. The conduction mechanisms combining the electron-hopping model and band conduction are proposed for the NTC effect in the ceramics.     

The electrical properties of ferromagnetic SrCoO3−δ (0 <δ <0.5)

The electrical resistivity of ferromagnetic SrCoO_3?δ (0 <δ <0.5) was measured in the temperature range from 77 to 300 K. All samples were good conductors and showed metallic behavior. The magnetic transition was independent of the electrical conductivity in SrCoO_3?δ. The logarithm specific electrical resistivities (logρ) at 80 K and 300 K monotonously decreased with increasing the oxygen deficiency, and this result was explained by the itinerant-electron model.     

Methods for the evaluation of biocompatibility of soluble synthetic polymers which have potential for biomedical use: 1 — Use of the tetrazolium-based colorimetric assay (MTT) as a preliminary screen for evaluation ofin vitro cytotoxicity

A tetrazolium-based colorimetric assay (MTT) was first introduced by Mossman in 1983 to assess the potential of novel antitumour agents, and it has been used here to evaluate the cytotoxicity of several soluble synthetic polymers proposed as drug carriers. Polymers including poly-l-lysine (molecular weight 57 000) were incubated (up to 1 mg ml^–1) with two human cell lines, hepatocellular carcinoma (HepG₂) and lymphoblastoid leukaemia (CCRF), adherent and suspension cells, respectively. Tests were carried out in the presence and absence of serum proteins. The assay was first modified to optimize the colorimetric profiles produced by the cell lines following incubation with MTT, to increase both the test sensitivity and the reproducibility of the method. Polymer toxicity observed using the MTT test was compared with data obtained using other methods; [³H]thymidine or [³H]leucine incorporation and counting cell numbers. Poly-l-lysine was very toxic to both cell lines with approximate IC₅₀-values of 60 and 30 µg ml^–1 for HepG₂ and CCRF, respectively, the values obtained being similar for each of the three different viability methods used. In the absence of serum proteins the toxicity of poly-l-lysine increased, the IC₅₀-values falling to 25.5 µg ml^–1 for the adherent and 0.8 µg ml^–1 for the suspension cell line. Other polymers such as poly-l-proline, polyethylene glycol, dextran, polyvinylpyrrolidone and poly-l-glutamic acid were not cytotoxic (MTT assay), either in the presence or in the absence of serum proteins. The MTT assay is a useful technique for the primary and rapid evaluation of the cytotoxicity of soluble polymers.     

Magnetic properties of RRh3B2(R=La,Ce, Nd,Gd) compounds

The¹¹Bnmr results on RRh₃B₂(R=La, Ce, Nd and Gd) are reported. For CeRh₃B₂, specific heat and electrical resistivity are reported. From a comparative study of the¹¹Bnmr Knight shifts and the spin lattice relaxation times of these compounds it is shown that in CeRh₃B₂, there is strong hybridization of 4f states with the conduction electrons. A local moment on Ce with admixture of 4f and 5d–6s orbitals is suggested.     

Properties of stannic oxide thin films produced from the SnCl4-H2O and SnCl4-H2O2 reaction systems

Transparent and conductive stannic oxide films were produced at the relatively low temperature of 250°C from the SnCl₄-H₂O and SnCl₄-H₂O₂ reaction systems by a chemical vapour deposition method. The films were not doped with impurities. Films formed from the first system are superior to those formed from the second with respect to electrical properties although they have a lower deposition rate at the same deposition temperature. The former system gives rise to films with resistivities in the range 10–10^-3 Ω cm between 250 and 400°C. The latter system produces films with resistivities in the range 10²–10^-2 Ω cm between 250 and 450°C. The electrical properties depend on the absorption of hydrogen peroxide as well as on the grain size, which depends on the deposition temperature and the reaction system. The spectral transmissivity for films 0.36–1.1 μm thick varies over the range 80–95% in the regions between 400 and 650 nm for both systems. Different reaction mechanisms take place in different temperature regions for both systems since there are two activation energies in the plot of deposition rate as a function of temperature.