Effect Of Ag Substitution Research Articles

An Investigation on Substitution of Ag Atoms for Al or Ti Atoms in the Ti2AlC MAX Phase Ceramic Based on First-Principles Calculations.

The present work introduced first-principles calculation to explore the substitution behavior of Ag atoms for Al or Ti atoms in the Ti2AlC MAX phase ceramic. The effect of Ag substitution on supercell parameter, bonding characteristic, and stability of the Ti2AlC was investigated. The results show that for the substitution of Ag for Al, the Al-Ti bond was replaced by a weaker Ti-Ag bond, decreasing the stability of the Ti2AlC. However, the electrical conductivity of the Ti2AlC was enhanced after the substitution because of the contribution of Ag 4d orbital electrons toward the density of states (DOS) at the Fermi level coupled with the filling of Ti d orbital electrons. For the substitution of Ag for Ti, new bonds, such as Ag-Al bond, Ag-C bond, Al-Al bond, Ti-Ti anti-bond, and C-C anti-bond were generated in the Ti2AlC. The Ti-Ti anti-bond was strengthened as well as the number of C-C anti-bond was increased with increasing the substitution ratio of Ag for Ti. Similar to the substitution of Ag for Al, the stability of the Ti2AlC also decreased because the original Al-Ti bond became weaker as well as the Ti-Ti and C-C anti-bonds were generated during the substitution of Ag for Ti. Comparing with the loss of Ti d orbital electrons, Ag 4d orbits contributed more electrons to the DOS at the Fermi level, improving the electrical conductivity of the Ti2AlC after substitution. Based on the calculation, the substitution limit of Ag for Al or Ti was determined. At last, the substitution behavior of Ag for Al or Ti was compared to discriminate that Ag atoms would tend to preferentially substitute for Ti atoms in Ti2AlC. The current work provides a new perspective to understand intrinsic structural characteristic and lattice stability of the Ti2AlC MAX phase ceramic.

The effect of Ag substitution on physicochemical and biological properties of sol-gel derived 60%SiO2–31%CaO–4%P2O5–5%Li2O (mol%) quaternary bioactive glass

In the present study, bioactive glasses (BGs) in 60SiO2-(31-x) CaO–4P2O5–5Li2O-xAg2O systems (x = 0, 1, 5, and 10 mol %) with optimum fixed amount of Li2O (5 mol %) were successfully synthesized through sol-gel technique and the effects of Ag2O addition on in-vitro investigations, biological properties, and bactericidal efficiency were evaluated. Structural and morphological evaluations by X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscopy (TEM) as well as scanning electron microscopy (SEM) revealed that BG with chemical composition of 60SiO2–30CaO–4P2O5–5Li2O–1Ag2O (mol%) had a higher rate of hydroxyapatite (HA) formation than other synthesized specimens. While, BGs containing 5 and 10 mol% of Ag had a lower bioactivity because of the reduced dissolution rate of Si and Ca. The results obtained from the 3-(4,5dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay and evaluation of alkaline phosphatase (ALP) activity exhibited that proliferation and differentiation of MC3T3-E1 osteoblast-like cells and osteoblastic activity were intensified by the presence of Ag in the BGs҆ composition. Meanwhile, BGs containing 1 mol% of Ag not only had no toxic effect on the cells, but also caused a significant enhancement in proliferation and differentiation of the cells within 7 days (**p < 0.01), as well as the highest ALP activity in this specimen (*p < 0.05). Additionally, all the synthesized specimens had significant antibacterial efficiency against E-coli bacteria. Our results showed that addition of 1 mol% of Ag to BG containing Li led to a significant antibacterial efficiency compared to the control (*p < 0.05). Afterwards, DAPI/actin and live/dead cell staining methods were applied, which well confirmed results of MTT assay. Finally, BG with chemical composition (LA01) of 60SiO2–30CaO–4P2O5–5Li2O–1Ag2O was introduced as an optimal novel co-doped BG in biomedical applications due to causing higher differentiation and proliferation of MC3T3-E1 cells and more increase in ALP activity and bactericidal efficiency.

The effect of Ag substitution on physico-chemical and biological properties of sol-gel derived 60%SiO2-31%CaO-4%P2O5-5%TiO2 (mol%) quaternary bioactive glass

This research presents an investigation on the simultaneous effect of titanium (Ti) and silver (Ag) on structural and biological behaviors of the co-substituted 58S bioactive glass. Structural and morphological characterizations were studied by means of X-ray diffraction (XRD) analysis, Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM) as well as Energy-dispersive X-ray Spectroscopy (EDS) analysis. The structural results exhibited that the hydroxyapatite)HA) layer was formed on the T/A-BGs after the 7th day of immersion in simulated body fluid)SBF(solution and increased overtime. Furthermore, the trend of cell proliferation and antibacterial activity were the same and by increasing Ag percentage up to 8 mol.% firstly, mentioned properties increased and then decreased. Hence, T/A-BG containing fixed 5 mol.% Ti and 2 mol. % Ag (TA2 (indicated higher in vitro biological performance compared to other synthesized T/A-BGs and suggested as an optimal specimen for further clinical applications.

Tetrahedral Distortion and Thermoelectric Performance of the Ag-Substituted CuInTe2 Chalcopyrite Compound

It is known that the electronic transport and heat conduction of thermoelectric materials are very sensitive to structural changes. In this article, the effect of Ag substitution on the crystal str...

Influence of Ag substitution on thermoelectric properties of the quaternary diamond-like compound Zn2Cu3In3Te8

The quaternary diamond-like compounds, A2Cu3In3Te8 (A = Cd, Zn, Mn, Mg), are a new class of thermoelectric materials recently proposed by complex structure design. Among them, the Zn2Cu3In3Te8 compound possesses reasonable electrical transport properties but relatively high lattice thermal conductivity. Herein, the effects of Ag substitution on the phase stability and thermoelectric properties of Zn2Cu3In3Te8 compound are reported. It is revealed that only the In sites show an appreciable tolerance for Ag doping. Ag substitution at the In sites introduces extra holes and thus results in improved electrical transport properties. Furthermore, the introducing of Ag lowers the sound velocities and enhances the phonon scattering of the Zn2Cu3In3Te8 compound, which leads to a substantially reduction in lattice thermal conductivity. Finally, in virtue of the optimization in both electrical and thermal transport properties, the maximal zT value of Zn2Cu3In2.8Ag0.2Te8 sample reaches 0.62 at 823 K, which is 43% higher than the pristine sample.

Effect of Ag substitution on structural, magnetic and magnetocaloric properties of Pr0.6Sr0.4–xAgxMnO3 manganites

A systematic investigation on the structural, magnetic and magnetocaloric properties of Pr0.6Sr0.4–xAgxMnO3 (x=0.05 and 0.1) manganites was reported. Rietveld refinements of the X-ray diffraction patterns confirmed that all samples were single phase and crystallized in the orthorhombic structure with Pnma space group. Magnetic measurements in a magnetic applied field of 0.01 T revealed that the ferromagnetic-paramagnetic transition temperature TC decreased from about 293 to 290 K with increasing silver content from x=0.05 to 0.1. The reported magnetocaloric entropy change and relative cooling power for both samples were considerably remarkable with a ΔSmax value of 1.9 J/(kg·K) and maximum RCP values of 100 J/kg, under a magnetic field change (Δµ0H) equal to 1.8 T. The analysis of the universal curves gave an evidence of a second order magnetic transition for the studied samples. The magnetic field influence on both the magnetic entropy change and the relative cooling power was also studied and discussed.

The influence of Ag substitution on structural and mechanical properties of (Bi, Pb)-2223 ceramics

In this work, Bi1.7Pb0.3Sr2Ca2Cu3−xAgxOy (x = 0.00, 0.03, 0.06, 0.09, 0.12) ceramics were prepared by conventional solid state reaction method. The effects of Ag substitution on the structural and mechanical properties of the samples were investigated by Vickers microhardness, X-ray powder diffraction (XRD) measurements and scanning electron microscope (SEM) analysis. The phase formation, volume fraction and lattice parameters were characterized by using XRD measurements. Surface morphology and grain connectivity of the samples were identified by using SEM. The mechanical properties were analyzed by microhardness measurements. Load dependent microhardness, elastic modulus, yield strength and fracture toughness were obtained by hardness measurements. XRD results indicated that the lattice parameter c decreases with increasing Ag addition. It was also observed that volume fraction of Bi-2223 phase decreases with increasing Ag addition from XRD measurements. SEM results showed that the surface morphology and grain connectivity improve, the grain sizes and porosity of the samples decrease with increasing Ag addition. Vickers microhardness (Hv), Young’s modulus (E), yield strength (Y) and fracture toughness (KIC) values were calculated separately for all samples. In our study, Young’s modulus, yield strength, and fracture toughness of the samples indicated dependency on applied load. It was seen that the load dependent Hv, E, Y, and KIC increase with increasing Ag and decreasing applied load. Experimental results of the microhardness measurements were analyzed using two models such as elastic–plastic deformation model and the energy dissipative model. Energy dissipative model was determined as the most successful model describing the mechanical properties of our samples.

Alternative current conduction mechanisms and effect of Ag substitution on conductivity in Na1−xAgxAlP2O7 (x = 0.4, x = 0.6 and x = 0.8) compounds

The Na1−xAgxAlP2O7 (x = 0.4, x = 0.6 and x = 0.8) samples were prepared by solid–state reaction technique at high temperature. The structural and electrical transport properties have been investigated. The x-ray powder diffraction patterns at room temperature show that all samples are formed in single phase and crystallize in the monoclinic system with P21/C space group. The electrical technique was measured in the 200 Hz–5 MHz frequency range and 573–673 K temperature intervals. The impedance plot has shown semicircle arcs at different temperatures and in order to explain the impedance results, an electrical equivalent circuit has been proposed. The maximum value of conductivity achieved for this material is 3.47 × 10−6 (Ω cm) −1 for x = 0.4, 3.12 × 10−5 (Ω cm) −1 for x = 0.6 and 1.64 × 10−5 (Ω cm) −1 for x = 0.8. The conductivity increases with increase in Ag substitution. The frequency dependence of alternative current (AC) conductivity is interpreted in terms of Jonscher's law. The AC conductivity is analyzed by different processes, which can be attributed to several models: the non-overlapping small polaron tunneling model (NSPT) for x = 0.4 and x = 0.6, the correlated barrier hopping (CBH) for x = 0.8. The conduction mechanism is studied with the help of Elliot's theory, and the Elliot's parameters are determined.

Effect of Ag substitution on the electromagnetic property and microwave absorption of LaMnO3

La1−xAgxMnO3 perovskites with different doping Ag-content were prepared by the sol–gel method. The electromagnetic characteristics and microwave loss behavior of these ion-doped rare-earth manganites were studied in the 2–18GHz frequency range. The microstructure and morphology of the samples were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The complex permittivity spectra, the complex permeability spectra and microwave reflection loss were measured by a microwave vector network analyzer system. The XRD patterns show that the crystalline perovskite main phase ABO3 is formed and impurity phases disappear when calcined at 1100°C, and Ag metal as an impurity phase appears when excessive Ag+ is doped. The SEM image indicates that many of the La0.85Ag0.15MnO3 particles are fiber-like or ellipsoidal. Magnetic loss and dielectric loss coexist and cooperate in microwave attenuation by moderate substitution of Ag+ for La3+. The microwave absorption property of the La0.85Ag0.15MnO3 sample is enhanced with the bandwidth below −10dB at about 6GHz and the peak value of reflection loss is near −25.0dB at the layer thickness of 2mm.

The Effect of Silver Substitution in Bi1.7Pb0.3Sr2Ca2−x Ag x Cu3O y

The effect of Ag substitution on the properties of high-temperature superconductor Bi1.7Pb0.3Sr2Ca2−x Ag x Cu3O y system have been investigated. The electrical and structural properties of the samples, prepared by the conventional solid-state reaction method, have been characterized by X-ray diffraction (XRD), electrical resistance and scanning electron microscopy (SEM) studies. XRD analysis reveals a multiphase structure of the samples, whereas SEM micrographs indicate some morphological changes induced by silver addition. It was found that an increase of the amount of Ag2O addition leads to an enhancement of the critical temperature and the percentage of Bi-2223 phase in the phase mixture.

The effect of Ag substitution in the mixed conductor Cu 7PSe 6

Cu 7PSe 6 is a mixed conductor that crystallizes in the simple cubic structure at room temperature. Structural transitions above and below room temperature are accompanied by step-like changes in electrical conductivity. The substitution of Ag + for Cu + in Cu 7PSe 6 stabilized the simple cubic structure over a wider range of temperatures than is observed for the pure compound. A disproportionate decrease in electrical conductivity accompanies modest levels of silver substitution. The prominent step in electrical conductivity associated with the low-temperature crystallographic phase transition disappears in (Ag x Cu 1− x ) 7PSe 6 solid solutions for a composition parameter x=0.20, replaced by two distinct changes in the slope of conductivity below room temperature.

Reply to the “Comment on papers ‘Effect of Ag substitution on the transport property and magnetoresistance of LaMnO 3’ [J. Magn. Magn. Mater. 248 (2002) 26] and ‘Possible magnetic phase separation in Ru doped La 0.67Ca 0.33’ [J. Magn. Magn. Mater. 257 (2003) 195

Reply to the “Comment on papers ‘Effect of Ag substitution on the transport property and magnetoresistance of LaMnO 3’ [J. Magn. Magn. Mater. 248 (2002) 26] and ‘Possible magnetic phase separation in Ru doped La 0.67Ca 0.33’ [J. Magn. Magn. Mater. 257 (2003) 195

Reply to the “Comment on papers ‘Effect of Ag substitution on the transport property and magnetoresistance of LaMnO 3’ [J. Magn. Magn. Mater. 248 (2002) 26] and ‘Possible magnetic phase separation in Ru doped La 0.67Ca 0.33’ [J. Magn. Magn. Mater. 257 (2003) 195

The author of the comment is too unilateral to associate double-peak behaviour (broad insulator–metal (I–M) transition below the Curie temperature ( T c)) and a sharp one near ( T c) in rare-earth manganese perovskites only with the grain boundaries (GB) effect. Moreover, it is especially confused that the grain-size effect should be necessary to relate with this electronic transport behaviour. In this reply, we provide an argument in support of the statement that inhomogeneous electronic/magnetic phase separation is one of the most important reasons for the double-peak behaviour in the ρ( T) curve.

Comment on papers “Effect of Ag substitution on the transport property and magnetoresistance of LaMnO 3” [J. Magn. Magn. Mater. 248 (2002) 26] and “Possible magnetic phase separation in Ru-doped La 0.67Ca 0.33O 3” [J. Magn. Magn. Mater. 257 (2003) 195

In recent papers Ye et al. (J. Magn. Magn. Mater. 248 (2002) 26) and Lakshmi et al. (J. Magn. Magn. Mater. 257 (2003) 195) reported the characteristic features of electrical resistivity ( ρ) versus temperature ( T) dependences of polycrystalline-doped manganites La 1− x Ag x MnO 3 and La 0.67Ca 0.33Mn 1− x Ru x O 3. Infact, two peaks on ρ( T) curve coexist: broad one at some T max below the Curie points ( T C) of these compounds and a sharp peak near T C. Authors interpreted such coexistence as an evidence of electronic/magnetic phase separation in the above-noted systems below its T C. It is shown in this comment that such an interpretation is obviously invalid for La 1− x Ag x MnO 3 system and is very questionable for La 0.67Ca 0.33Mn 1− x Ru x O 3. The simplest and natural reason for the appearance of considered features on ρ( T) dependences of polycrystalline manganites is the well-known grain-boundary effects.

Effect of Ag substitution on the transport property and magnetoresistance of LaMnO3

The structural, magnetic and electronic properties of the polycrystalline La1−xAgxMnO3 are systematically investigated as a function of Ag-doping level. The result of the Rietveld refinement of X-ray powder diffraction shows that the samples are single rhombohedral (R3̄C) structure phase for x<0.2. For x⩾0.2, the samples are composed of a R3̄C perovskite phase and a nonmagnetic metal Ag phase. The temperature dependence of resistivity shows that all samples undergo a sharp insulator–metal (I–M) transition accompanying a paramagnetic to ferromagnetic transition with the decrease of temperature. However, for x<0.2, an obvious double I–M transition with a single ferromagnetic transition is observed. In the meanwhile, a large magnetoresistance (MR) with low applied magnetic field is observed. The electronic and magnetic inhomogeneity induced by Ag doping and the nonmagnetic metal Ag phase are presented to account for the transport properties and large MR in these compounds.

Effects of silver on the phase formation of the Bi-Pb-Sr-Ca-Cu-O superconductors

The effects of Ag substitution on the formation of the superconducting phases in the BPSCCO system have been investigated by Raman spectroscopy and XRD. The silver was found either to accelerate the formation of the 2212 phase or to reduce the formation temperature of the 2212 phase. Moreover, addition of even a small amount of silver (Bi∶Pb∶Ag=8∶2∶1) poisons or inhibits the formation of the 2223 phase. However, there is no apparent effect on theT c of both the 2212 and 2223 phases. In addition, the presence of silver does not alter the mechanism for the formation of the PBSCCO superconducting phases.

TRANSPORT CRITICAL CURRENT DENSITIES IN Y–Ag–Ba–Cu–O SUPERCONDUCTORS

The influence of Ag substitution in amount of 2 mol% instead of Y, Ba and Cu in Y 1 Ba 2 Cu 3 O 7−x high temperature superconductor on magnetic field dependence of the critical current density at 77 K was studied. The samples were prepared by powder technology as well as by citrate method. An increase of transport critical current density as well as its smaller magnetic field dependence was found in case of substitution Ag → Y and Ag → Ba for samples prepared by both methods. In the magnetic field 9 T, the transport critical current density of the sample Y 0.98 Ag 0.02 Ba 2 Cu 3 O 7−x was 0.3 A/cm 2. On the other hand, substitution Ag → Cu lowers transport critical current densities in comparison with undoped samples. The effect of Ag substitution was more pronounced in samples prepared by powder technology.

Ce(Cu0.9Ag0.1)6: Highest electronic specific-heat coefficient of the heavy-fermion systems.

We have measured the static magnetic susceptibility $\ensuremath{\chi}$ of the compound $\mathrm{Ce}{({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Ag}}_{x})}_{6}$ for $x\ensuremath{\le}0.1$ from 2.4 to 300 K and the specific heat of one sample ($x=0.1$) from 0.6 to 30 K. The effect of Ag substitution is to markedly increase both $\ensuremath{\chi}$ and the Sommerfeld constant $\ensuremath{\gamma}$ at low temperatures. $\ensuremath{\gamma}$ for the $x=0.1$ sample is temperature dependent and reaches the value 2.1 J/mole ${\mathrm{K}}^{2}$ at 0.6 K, extrapolating to approximately 2.8 J/mole ${\mathrm{K}}^{2}$ at $T=0$ K. These results can be analyzed in terms of a twofold decrease in the value of the Kondo temperature ${T}_{K}$ with 10% Ag substitution.