Ag Substitution Research Articles

Excellent thermoelectric performance achieved over broad temperature plateau in indium-doped SnTe-AgSbTe2 alloys

SnTe is deemed as a natural candidate to replace the state-of-the-art thermoelectric material PbTe, due to its low-cost, low-toxicity, and mechanical stability. Nevertheless, both the peak and average figure of merits of SnTe currently are way too inferior as compared to PbTe. In this work, we report that a peak figure of merit as high as ∼1.3 can be achieved at 873 K in p-type SnTe when it is simultaneously doped with Indium and alloyed with AgSbTe2. Moreover, the average figure of merit can be lifted astonishingly from 0.244 up to 0.84, by a factor of 344%, which is the record high value ever reported. The enhanced thermoelectric performance comes from a synergetic improvement of the power factor and reduction of lattice thermal conductivity. The former can be ascribed to the introduction of resonant states by Indium and probable regulation of the valence band structure by AgSbTe2 alloying, while the latter is believed to originate from the vast substitutional point defects at the Sn site by Ag and Sb substitution.

Substitution defect enhancing thermoelectric properties in CuInTe2

Solid solution is an effective way to optimize thermoelectric performance because of the enhanced phonon scattering from point defect. In this article we describe the synthesis and discuss thermoelectric properties of Cu1-xAgxInTe2 solid solutions (x = 0, 0.05, 0.15, 0.30, 0.50). The effect of the substitution of Ag for Cu site on the microstructure and thermoelectric performance in CuInTe2 is investigated. The enlarged Seebeck coefficient coupled with reduced electrical conductivity is observed due to the diminished carrier concentration upon Ag substitution. Meanwhile, the lattice thermal conductivity is significantly depressed in solid solutions due to the strong phonon scattering. As a result, a zT value of 1.07 is achieved at 823 K with x = 0.05, which is a 90% improvement as compared with that of the pristine CuInTe2. These results demonstrate a valid approach to improve the thermoelectric properties of the compounds in the same family.

Influence of Cu substitution on the structural ordering, photocatalytic activity and photoluminescence emission of Ag3-2xCuxPO4 powders

Materials presenting high photocatalytic performance and interesting photoluminescence emissions are promising candidates for photodegradation of organic pollutants discharged into natural waters as well as for development of new electro-optical devices, respectively. In this study, Ag3-2xCuxPO4 (x = 0.00, 0.01, 0.02, 0.04 and 0.08) powders were synthesized by the precipitation method. The long- and short-range structural ordering was affected when the copper (Cu) content was increased in the lattice, as identified by X-ray diffraction patterns, Fourier transform infrared spectroscopy and Raman spectroscopy, respectively. The field emission scanning electron microscope and transmission electron microscope revealed a particle system composed of irregular spherical-like microcrystals. The presence of Cu as well as its real amount in the samples were confirmed by means of X-ray photoelectron spectroscopy and inductively coupled plasma-atomic emission spectrometry, respectively. On increasing Cu level, a slight variation was noted on the photocatalytic activity of Ag3-2xCuxPO4 powders for degradation of rhodamine B under visible light irradiation. A photodegradation mechanism was proposed in details. The photoluminescence emissions were explained by electronic transitions involving intermediary energy levels in the band gap. The origin these energy levels was related to defects caused by the substitution of Ag by Cu in the crystalline structure.

Impact of Coinage Metal Insertion on the Thermoelectric Properties of GeTe Solid-State Solutions

A comprehensive study on the thermoelectric effect of Ag substitution in GeTe solid solutions, a congenital base for highly efficient TAGS-m [(GeTe)m(AgSbTe2)100–m] thermoelectric materials, was performed. First-principles calculations were carried out to probe the changes arising from doping on the electronic band structure of GeTe, which exhibits a rhombohedral (r) structure at temperatures lower than 700 K. Aliovalent Ag substitution in GeTe increases the hole concentration and decreases the thermoelectric figure of merit (zT) due to the reduction of the Seebeck coefficient, which is ascribed mainly to the lowering of the Fermi level together with the loss of band degeneracy. The band structure and effective mass calculations of these doped materials also point to a soaring contribution from several hole pockets in the valence band. First-principles calculations carried out with two other group 11 transition metals (Cu, Au) reveal that silver substitution has the lowest impact on the thermopower of r-GeTe. A mean zT of ∼0.85 at 773 K is achieved for Ge1–xAgxTe (x ≤ 0.04) solid solutions. The study highlights the limits in doping just a coinage metal to GeTe and recapitulates the need for pair substitution to enhance the thermoelectric properties of GeTe-based solid-state solutions.

Écrinsite, AgTl3Pb4As11Sb9S36, a new thallium-rich homeotype of baumhauerite from the Jas Roux sulphosalt deposit, Parc national des Écrins, Hautes-Alpes, France

Ecrinsite, ideally AgTl 3 Pb 4 As 11 Sb 9 S 36 , is a new thallium sulphosalt species found in the Jas Roux As–Sb–Pb–Tl–Hg–Ag deposit, Parc National des Ecrins, Departement des Hautes-Alpes, France. Associated minerals in four different samples are jasrouxite, stibnite, smithite, guettardite, chabourneite, pierrotite and As-bearing zinkenite. Ecrinsite is opaque with metallic lustre. It is brittle without any discernible cleavage and with conchoidal fracture. In reflected light ecrinsite is white, pleochroism is not discernible. Internal reflections are absent. In crossed polarisers, anisotropism is distinct, with rotation tints in shades of grey. The reflectance data (%, air) are: 37.3, 38.6 at 470 nm, 35.2, 36.7 at 546 nm, 34.0, 35.5 at 589 nm and 32.0, 33.3 at 650 nm. Mohs hardness is 3–3½, microhardness VHN 25 is in the range 175–201, with a mean value of 189 kg mm −2 . Average results of 20 electron-microprobe analyses for the structurally investigated grain are (in wt%): Ag 2.03(10), Cu 0.02(1), Tl 14.57(20), Pb 16.23(32), Sb 23.97(25), As 17.87(17), S 25.20(15), total 99.88 (15), corresponding to Ag 0.87 Cu 0.02 Tl 3.28 Pb 3.61 Sb 9.06 As10.98S36.19 (on the basis of 28 Me + 36S = 64 apfu ). The simplified formula, AgTl 3 Pb 4 Sb 9 As 11 S 36 , is in accordance with the results of the crystal-structure analysis and may be derived from the ideal baumhauerite formula, Pb 12 As 16 S 36 , by substitution of Sb for As and [(Tl,Ag) + + (As,Sb) 3+ ] ↔ 2Pb 2+ . The density, 4.96 g cm −3 , was calculated using the ideal formula. Ecrinsite has a triclinic cell, space group P 1 ¯ , with a = 8.080(2), b = 8.533(2), c = 22.613(4) A, α = 90.23(3)°, β = 97.17 (3)°, γ = 90.83(3)°, V = 1546.7(6) A 3 , and Z = 1. The strongest five lines in the (calculated) powder-diffraction pattern are [ d in A( I )( h k l )]: 4:14(68) ( 10 5 ¯ ) , 3.72(92)(105), 3:56(100) ( 10 6 ¯ ) , 3:53(80) ( 1 2 ¯ 2 ) and 3.48(72)(122). Ecrinsite is a new member of the sartorite homologous series with N 1,2 = 3, 4, i.e. , N = 3.5. Four other members share the same N value as ecrinsite: baumhauerite, argentobaumhauerite, boscardinite and bernarlottiite. By comparison to the closely related boscardinite (ideally Tl 2 Pb 8 Sb 14 As 4 S 36 ), ecrinsite is characterised by both an excess of As over Sb and a distinctly higher substitution of [(Tl,Ag) + +(As,Sb) 3+ ] ↔ 2Pb 2+ . Baumhauerite and bernarlottiite are basically unsubstituted members, whereas argentobaumhauerite has a Ag substitution, without Tl.

Study of structural phase transitions in quinary TiNi(MoFeAg)-based alloys

The structural phase transitions of quinary Ti50Ni49.5−XMo0.3Fe0.2AgX (X = 0, 0.1, 0.2, 0.5, 1.0, and 1.5 at%) alloys prepared by vacuum-induction melting were studied by means of the four-point-probe, x-ray diffraction (XRD), and optical microscopy methods after thermal cycling. The two-stage B2 ↔ R ↔ B19′ reversible martensitic transformation (MT) took place in all the investigated samples. It is found that the substitution of Ag for Ni in the studied alloy when CAg = 0–0.5 at%, reduces the TR, Ms, and Mf characteristic points by 20–30 K, whereas they increase by 15–35 K when the Ag content was varied from 1.0 to 1.5 at% and the B2 ↔ R ↔ B19′ MT was realized in the high-temperature area. XRD patterns of the studied alloys recorded at the ambient temperature detected the pure Ag phase as well as Ti2Ni precipitate with a small volume fraction (up to 5%) alongside with structural lines of B2, R, and B19′ phases.

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.

Effect of dopant loading on the structural features of silver-doped hydroxyapatite obtained by mechanochemical method

Abstract Silver-doped hydroxyapatite (Ag-doped HA) nanopowders were synthesized using calcium hydroxide (Ca(OH) 2 ), phosphorus pentoxide (P 2 O 5 ) and silver nitrate (AgNO 3 ) precursors, through a one-pot mechanochemical process. The influence of dopant content on the phase formation, structural properties and morphological features was examined. The results showed that the as-prepared powders were single-phase hexagonal HA in the absence of the dopant. With the addition of the dopant, a similar phase structure was achieved, however some changes were observed with regards to the peak position and broadening. With the increase of Ag substitution, some alterations in the structural features of the milled powders were observed, where the crystallite size, lattice strain and crystallinity degree were between 25 ± 18 and 33 ± 14 nm, between 0.486 ± 0.0.161 and 0.824 ± 0.477, and between ~ 83 and 93%, respectively. From the Fourier transformed infrared (FTIR) spectroscopy spectra, the location of the CO 3 -derived bands revealed that the replacement of PO 4 3− by CO 3 2− (B-type) was dominant in the Ag-doped HA nanopowders. This facile solid-state method is an alternative process for the preparation of bioceramic nanopowders.

Elemental Precursor Solution Processed (Cu1–xAgx)2ZnSn(S,Se)4 Photovoltaic Devices with over 10% Efficiency

The partial substitution of Cu+ with Ag+ into the host lattice of Cu2ZnSn(S,Se)4 thin films can reduce the open-circuit voltage deficit (Voc,deficit) of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this paper, elemental Cu, Ag, Zn, Sn, S, and Se powders were dissolved in solvent mixture of 1,2-ethanedithiol (edtH2) and 1,2-ethylenediamine (en) and used for the formation of (Cu1-xAgx)2ZnSn(S,Se)4 (CAZTSSe) thin films with different Ag/(Ag + Cu) ratios. The key feature of this approach is that the impurity atoms can be absolutely excluded. Further results indicate that the variations of grain size, band gap, and depletion width of the CAZTSSe layer are generally determined by Ag substitution content. Benefiting from the Voc enhancement (∼50 mV), the power conversion efficiency is successfully increased from 7.39% (x = 0) to 10.36% (x = 3%), which is the highest efficiency of Ag substituted devices so far.

Molten Ag2 SO4 -based Ion-Exchange Preparation of Ag0.5 La0.5 TiO3 for Photocatalytic O2 Evolution.

Ag0.5 La0.5 TiO3 with an ABO3 perovskite structure was synthesized by a newly developed ion-exchange method. Molten Ag2 SO4 instead of traditional molten AgNO3 was used as Ag+ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag+ for Na+ in Na0.5 La0.5 TiO3 with a stable ABO3 perovskite structure at a high ion-exchange temperature (700 °C). Under full-arc irradiation, the O2 -evolution activity of Ag0.5 La0.5 TiO3 was about 1.6 times that of Na0.5 La0.5 TiO3 due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag+ for Na+ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light-response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag+ for Na+ induced a lattice distortion of the ABO3 perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible-light irradiation, Ag0.5 La0.5 TiO3 displayed notable O2 evolution whereas Na0.5 La0.5 TiO3 showed little O2 evolution, thus demonstrating that the substitution of Ag+ for Na+ enabled the use of visible light to evolve O2 photocatalytically. This work presents an effective route to explore novel Ag-based photocatalysts.

The effect of Zirconia/Yttria/Silver substitutions on mechanostructure and cell viability of the synthesized bioceramic bone grafts

Hydroxyapatite (HA) based biografts were synthesized by substitution of Zirconia (Zr), Yttria (Y2O3) and Silver (Ag) using the sol-gel method. Fabricated bone grafts (H40ZrYt and H50Yt10) were compared with a control biograft. The effects of Zr and Y2O3 and Ag additions on the morphological, mechanical and cell viability of the synthesized biografts were analyzed. The biografts were characterized by X-ray Diffractometer (XRD) and Scanning Electron Microscope (SEM). All biografts were then embedded into the drilled holes (D=3.2mm) in rabbit femurs. The rabbits were then sacrificed after twelve weeks. Three-point bending (3-PB) tests were conducted on defected and grafted regions. Flexural strength values were found to be 347, 149 and 180MPa, for the H40ZrYt, H50Yt10 and the control/commercial graft, respectively. Cell viability results indicated that the percentage viability ratios slightly increased after the substitution of Ag into the H50Yt10 biograft at 0.1 and 0.3µg/ml concentrations and into the H40ZrYt biograft at a 0.1µg/ml concentration. Although the cell viability was a bit lower in the H50Yt10 graft, the H40ZrYt graft achieved better results compared to the counterpart grafts. Furthermore, the hardness of both of the novel fabricated grafts were found to be higher than the control/commercial graft, however, as the flexture strength of H40ZrYt was higher but H50Yt10 was lower than the control/commercial graft.

Experimental and theoretical study of AC electrical conduction mechanisms by NSPT model of LiNa3-xAgxP2O7 (x = 0.2 and 0.6) ceramic compounds

New pyrophosphate of ceramic compounds LiNa3-xAgxP2O7 (x = 0.2 and 0.6) is synthesized by a solid-state method. All the compounds crystallize in the orthorhombic lattice with space group C2221. The infrared spectra of these compounds show characteristic bands due to a P2O7 group. The two semicircles observed in the complex impedance identify the presence of the grain interior and grain boundary contributions to the electrical response in these materials. The frequency independent conductivity of these compounds shows Arrhenius-type behavior. The activation energies have been calculated at the levels of impedance, electric modulus studies, and DC conductivity which suggest that the conductions are ionic in nature. The conductivity increases with an increase in Ag substitution. In order to determine the conduction mechanism, the AC conductivity and its frequency exponent have been analyzed in this work by a theoretical model based on quantum mechanical tunneling: the non-overlapping small polaron tunneling model (NSPT) is confirmed for x = 0.2 and x = 0.6. The conduction mechanism is studied with the help of Elliot’s theory, and the Elliot’s parameters are determined.

Ba6Li2CdSn4S16: lithium substitution simultaneously enhances band gap and SHG intensity

Ba6Li2CdSn4S16vs. Ba6Ag2CdSn4S16: the Li substitution as compared to Ag substitution simultaneously enhances the band gap and the SHG intensity.

Effects of Ag addition on the structural and electrical properties of La0.67Sr0.33MnO3 ceramics

ABSTRACTLa0.67Sr0.33MnO3:mol-%Agx (LSMO:Agx, x = 0, 0.1, 0.2, 0.3 and 0.4) polycrystalline ceramics were prepared by chemical co-precipitation methods. All of the LSMO:Agx samples showed rhombohedral perovskite structure with a space group of . The diffraction peaks of metallic Ag did not appear in the XRD graph, due to the Ag substitution at A sites (La3+ or Sr2+ ions) and the evaporation loss of the element Ag in the process of high-temperature sintering, or the residual amount of Ag beyond the sensitivity of the XRD. With the increase of Ag addition, unit cell volume (V), metal−insulator transition temperature (Tp) and conductivity at Tp (ρTp) of the LSMO:Agx samples increased significantly. At the same time, the temperature coefficient of resistance (TCR%), temperature peak of the TCR% (Tk) and the figure of merit (Z) reached the optimal values of 3.3% K−1, 367 K and 0.049 at x = 0.3. Ag substitution at A sites (La3+ or Sr2+ ions) and gathering at grain boundaries (GBs) were proposed to explain the existence of Ag addition. All results suggested that the enhancement of electrical properties was due to silver-doping and it increased the bond angles of Mn−O−Mn (θMn−O−Mn) and the bond distance of Mn−O (dMn−O), improving Mn4+ concentration, grain sizes and GBs connectivity in LSMO:Agx ceramics.

A theoretical study on the reactivity of the Mo/Cu-containing carbon monoxide dehydrogenase with dihydrogen.

The Mo/Cu-dependent CO dehydrogenase from Oligotropha carboxidovorans is an enzyme that is able to catalyze CO oxidation to CO2; moreover, it can also oxidize H2, thus eliciting a characteristic EPR signal. Interestingly, the Ag-substituted enzyme form proved unable to catalyze H2 oxidation. In the present contribution, we characterized the reactivity of the enzyme with H2 by quantum-chemical calculations. It was found that dihydrogen binding to the wild-type enzyme requires significant structural rearrangements of the active site Theoretical EPR spectra for plausible H2-bound models of the partially reduced, paramagnetic active site are also presented and compared with the experimental counterpart. Finally, density functional theory modeling shows that Ag substitution impairs H2 binding at the active site.

Physical properties of chalcopyrite-type Cu1−xAgxGaTe2 by first-principles study

[Formula: see text] is a promising thermoelectric (TE) material for high temperature TE applications. This work systematically investigated the structural, elastic and thermodynamic properties of [Formula: see text] ([Formula: see text] = 0, 0.25, 0.5, 0.75 and 1) by density functional theory. The calculated lattice volume is expanded with the increase of Ag content, but this expansion is anisotropic. The lattice parameter along [Formula: see text]-axis is linear expansion, and along [Formula: see text]-axis is parabolic expansion, which is in good agreement with available experimental data. The phase stability of [Formula: see text] alloy is studied by analyzing the formation energy, cohesive energy and elastic constants. Shear modulus, Young’s modulus, sound velocities, Debye temperature and the minimum thermal conductivity are obtained from the calculated elastic constants. The results show that Ag substitution could reduce the lattice thermal conductivity, which is helpful for improving the TE properties of [Formula: see text].

Magnetic and Electrical Properties Induced by the Substitution of Divalent by Monovalent in the La0.6Ca0.4MnO3 Compound

The La0.6Ca0.4−x Ag x MnO3 samples with x = 0 and 0.10 were prepared by sol–gel methods. Structural and electrical measurements were performed to examine the effect of the silver substitution in the calcium sites on the physical properties. Magnetization versus temperature studies have shown that all samples exhibit a magnetic transition from ferromagnetic to paramagnetic phase when temperature is increased. The second transition in the resistivity in the La0.6Ca0.4MnO3 compound can be attributed to an abnormality characteristic of charge ordering (CO) effect. The electrical resistivity was described by a phenomenological percolation model. Ten percent of Ag substitution in the Ca site exhibits a magnetoresistance value about 75 % near room temperature at the applied magnetic field of 8 T.

Synthesis and characterization of Ag doped TiO2 heterojunction films and their photocatalytic performances

In this study, undoped and silver (Ag) doped titanium dioxide (TiO2) films were successfully synthesized by sol-gel spin coating technique on the Si substrates. Photocatalytic activities of the TiO2 films with different Ag content were investigated for the degradation of methylene blue (MB) under UV light irradiation. The crystal phase structure, surface morphology, chemical and optical properties of Ag-doped TiO2 films were characterized using an X-ray diffractometer (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectrophotometer, and FTIR spectrophotometer. The results showed that the Ag-doped TiO2 films calcined at 500°C had the crystalline anatase phases and the surface morphologies with some cracks. Ag substitution into TiO2 matrix enhanced the photocatalytic activity of TiO2 films under UV light irradiation as compared to the undoped TiO2 film. Furthermore, the results indicated that the 0.7% Ag doped TiO2 film exhibited a superior photocatalytic activity than that of undoped and other Ag-doped TiO2 films. This study demonstrated the potential of an application of Ag doped films to efficiently treat dissolved organic contaminants in water.

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.

Improved thermoelectric performance of BiCuSeO by Ag substitution at Cu site

BiCuSeO oxyselenide-based thermoelectric materials are attracting much attention due to their ultra-low intrinsic thermal conductivity (ĸ) and moderate Seebeck coefficient (S). However, the low conversion efficiency limits their application in energy conversion systems. This paper investigated the effect of monovalent Ag-doping in BiCuSeO at Cu site in the presence of polyvinyl alcohol (PVA). The results show that Ag is effectively doped at Cu site. The heavy atom substitution in BiCu1−xAgxSeO at Cu site can enhance S and reduce its total thermal conductivity (k) by phonon scattering. Further, the incorporation of heavy atom (Ag) with different ionic radii results in the improved ZT of 0.64 for BiCu1−xAgxSeO, which is 16% more than that for pure BiCuSeO (ZT = 0.55) at 923 K. It is believed that the Cu site should be an efficient dopant site to improve the efficiency of oxyselenide-based thermoelectric materials.