Ag Interstitials Research Articles

Deviceization of high-performance and flexible Ag2Se films for electronic skin and servo rotation angle control

Ag2Se shows significant potential for near-room-temperature thermoelectric applications, but its performance and device design are still evolving. In this work, we design a novel flexible Ag2Se thin-film-based thermoelectric device with optimized electrode materials and structure, achieving a high output power density of over 65 W m−2 and a normalized power density up to 3.68 μW cm−2 K−2 at a temperature difference of 42 K. By fine-tuning vapor selenization time, we strengthen the (013) orientation and carrier mobility of Ag2Se films, reducing excessive Ag interstitials and achieving a power factor of over 29 μW cm−1 K−2 at 393 K. A protective layer boosts flexibility of the thin film, retaining 90% performance after 1000 bends at 60°. Coupled with p-type Sb2Te3 thin films and rational simulations, the device shows rapid human motion response and precise servo motor control, highlighting the potential of high-performance Ag2Se thin films in advanced applications.

A Route to High Thermoelectric Performance: Solution‐Based Control of Microstructure and Composition in Ag2Se

AbstractThermoelectric materials convert heat into electricity, with a broad range of applications near room temperature (RT). However, the library of RT high‐performance materials is limited. Traditional high‐temperature synthetic methods constrain the range of materials achievable, hindering the ability to surpass crystal structure limitations and engineer defects. Here, a solution‐based synthetic approach is introduced, enabling RT synthesis of powders and exploration of densification at lower temperatures to influence the material's microstructure. The approach is exemplified by Ag2Se, an n‐type alternative to bismuth telluride. It is demonstrated that the concentration of Ag interstitials, grain boundaries, and dislocations are directly correlated to the sintering temperature, and achieve a figure of merit of 1.1 from RT to 100 °C after optimization. Moreover, insights into and resolve Ag2Se's challenges are provided, including stoichiometry issues leading to irreproducible performances. This work highlights the potential of RT solution synthesis in expanding the repertoire of high‐performance thermoelectric materials for practical applications.

Study of the defect chemistry in Ag2Q (Q = S, Se, Te) by first-principles calculations

Ag2Q-based (Q = S, Se, Te) silver chalcogenides show great potential in thermoelectrics due to their suitable band gaps, high electron mobilities, and even remarkable ductility. Particularly, Ag2S and Ag2S/Se/Te solid solutions have been reported with both good ductility and thermoelectric performance, which are extremely suitable for the application in flexible wearables. However, the underlying mechanism of the native n-type conduction and p-type undopability for Ag2Q remains elusive. Herein, we use first-principles calculations based on density functional theory combined with GW correction to investigate the defect chemistry in Ag2Q. It is found that the site potential and Voronoi volume deviations resulting from Ag interstitials are noticeably smaller than those caused by Ag vacancies, which makes Ag interstitials with low formation energy more desirable during preparation, contributing to the native n-type conduction. The small and even negative dopability windows, on the other hand, account for the p-type undopability of Ag2Q. The calculated carrier concentrations of pristine Ag2Q are well consistent with the experimental observations, validating the reliability of our defect calculations. This work provides valuable guidance for first-principles calculation of defect chemistry in other narrow-gap semiconductors.

Dynamic doping and Cottrell atmosphere optimize the thermoelectric performance of n-type PbTe over a broad temperature interval

High thermoelectric energy conversion efficiency requires a large figure-of-merit, zT, over a broad temperature range. To achieve this, we optimize the carrier concentrations of n-type PbTe from room up to hot-end temperatures by co-doping Bi and Ag. Bi is an efficient n-type dopant in PbTe, often leading to excessive carrier concentration at room temperature. As revealed by density functional theory calculations, the formation of Bi and Ag defect complexes is exploited to optimize the room temperature carrier concentration. At elevated temperatures, we demonstrate the dynamic dissolution of Ag2Te precipitates in PbTe in situ by heating in a scanning transmission electron microscope. The release of n-type Ag interstitials with increasing temperature fulfills the requirement of higher carrier concentrations at the hot end. Moreover, as characterized by atom probe tomography, Ag atoms aggregate along parallel dislocation arrays to form Cottrell atmospheres. This results in enhanced phonon scattering and leads to a low lattice thermal conductivity. As a result of the synergy of dynamic doping and phonon scattering at decorated dislocations, an average zT of 1.0 is achieved in n-type Bi/Ag-codoped PbTe between 400 and 825 K. Introducing dopants with temperature-dependent solubility and strong interaction with dislocation cores enables simultaneous optimization of the average power factor and thermal conductivity, providing a new concept to exploit in the field of thermoelectrics.

Effect of defect interactions with interstitial Ag in the lattice of BixSb2−xTe3 alloys and their thermoelectric properties

In this study, the effect of Ag defects on the lattice and thermoelectric properties of Ag-doped BixSb2−xTe3 (BST) alloys are systematically investigated. Using density-functional calculations, we reveal that Ag impurity defects occupying interstitial sites in the BST affect the formation of intrinsic defects in the host materials. Ag interstitial defects, which are responsible for increasing the lattice parameter of the c axis, lower the formation energies of BiTe and SbTe acceptor defects more effectively in the Bi-rich BST than in the Bi-poor BST. In addition, these Ag interstitials induce the formation of AgBi and AgSb in BixSb2−xTe3. Therefore, Ag-induced defect interactions can be used to finely optimize the defects and doping density by varying the Bi content. Furthermore, the phonon thermal conductivity is reduced with the formation of nanoscale twin structures with various stacking faults. Finally, a high figure of merit of 1.4 at 423 K is achieved for p-type BST alloys.

Concurrent defects of intrinsic tellurium and extrinsic silver in an n-type Bi2Te2.88Se0.15 thermoelectric material

We suggested a defect system consisting of Te- and Ag-related defects in n-type Bi2(Te,Se)3. We prepared the Te-rich Bi2Te2.88Se0.15 compound, which is expected to have Te antisite defects, via a conventional pulverization process. We devised a one-pot chemical process in which Ag nanoparticles were synthesized and instantly deposited onto the Bi2Te2.88Se0.15, followed by spark plasma sintering; thus, Ag atoms were inserted into the lattice structure of the Bi2Te2.88Se0.15 during the sintering process. Atomic layers of the Bi2Te2.88Se0.15 were resolved by transmission electron microscopy and dark-field scanning electron microscopy imaging with energy dispersive X-ray spectroscopy; the Ag atoms were thereby proven to occupy the interstitial sites in the Bi2Te2.88Se0.15 (i.e., Ag interstitial defects). The defect system composed of the Te antisites and Ag interstitials decoupled the electrical properties of the Bi2Te2.88Se0.15 from its thermal properties. We endeavored to adjust the defect system to maximize the decoupling effect, which resulted in the preeminent average figures of merit for operation below 150 °C (ZTave = 1.22 at 25–100 °C and 1.18 at 25–150 °C) among n-type Bi2(Te,Se)3 materials.

Dual defect system of tellurium antisites and silver interstitials in off-stoichiometric Bi2(Te,Se)3+ycausing enhanced thermoelectric performance

Thermoelectric performance was significantly enhanced with off-stoichiometric Bi2(Te,Se)3+yhaving the dual defect system of Te antisites and Ag interstitials.

Ag diffusion in SiC high-energy grain boundaries: Kinetic Monte Carlo study with first-principle calculations

The diffusion of silver (Ag) impurities in high energy grain boundaries (HEGBs) of cubic (3C) silicon carbide (SiC) is studied using an ab initio based kinetic Monte Carlo (kMC) model. This study assesses the hypothesis that the HEGB diffusion is responsible for Ag release in Tristructural-Isotropic (TRISO) fuel particles, and provides a specific example to increase understanding of impurity diffusion in highly disordered grain boundaries. The HEGB environment was modeled by an amorphous SiC (a-SiC), which approximately represents the local environments of HEGBs. The structure and stability of Ag defects were calculated using ab initio methods based on Density Functional Theory (DFT). The defect energetics suggested that the fastest diffusion takes place via an interstitial mechanism in a-SiC and that is what is modeled. Interstitial sites were identified by a gridded search and transition states were computed using the climbing image nudged elastic band method. The formation energy of Ag interstitials (relative to bulk Ag) and the Kinetic Resolved Activation (EKRA) energies between them were well approximated with Gaussian distributions that were then sampled in the kMC. The diffusion of Ag was simulated with the effective medium model using kMC. Ag diffusion coefficients were estimated for the temperature range of 1200–1600°C. Ag in a HEGB is predicted to exhibit an Arrhenius type diffusion and with a diffusion prefactor and effective activation energy of (2.73±1.09)×10−10m2s−1 and 2.79±0.18eV, respectively. The comparison between HEGB results to other theoretical studies suggested not only that GB diffusion is predominant over bulk diffusion, but also that the HEGB is one of fastest grain boundary paths for Ag diffusion in SiC. The Ag diffusion coefficient in the HEGB shows a good agreement with ion-implantation measurements, but is 2–3 orders of magnitude lower than the reported diffusion coefficient values extracted from integral release measurements on in- and out-of- pile samples. The discrepancy between GB diffusion and integral release measurements suggests that other contributions are responsible for fast release of Ag in some experiments and we propose that these contributions may arise from radiation enhanced diffusion.

Diffusion of Cd vacancy and interstitials of Cd, Cu, Ag, Au and Mo in CdTe: A first principles investigation

We present a first principles study of the diffusion profiles of native Cd, adatom and vacancy, and cationic non-native interstitial adatoms Cu, Ag, Au, and Mo in bulk CdTe. The high symmetry Wyckoff position 4(b) is the global minimum energy location for Cd and Ag interstitials and the 4(d) site for Mo interstitials. Adatoms of Cu and Au show an asymmetric shape of the energy diffusion barrier with two structurally equivalent minima and two energetically distinct maxima in the pathway. The others, Mo, Ag and Cd interstitial and vacancy, show a symmetric diffusion barrier with two structurally unique minima and a maximum. Diffusion for Cu and Au interstitials proceeds along the [110] channel in the crystal in a near straight line path, avoiding both high symmetry 4(b) and 4(d) sites. Diffusion for Cd and Ag proceeds along two nearly straight line paths along [111] and [11–1]. Diffusion for Mo is along the [110] channel however it deviates slightly from the straight line paths along [111] and [11–1] avoiding the 4(b) site. The rate-limiting diffusion barriers range from a low of 0.10eV for the symmetric diffusion path of a Ag interstitial to a high of 1.83eV for the symmetric diffusion path of a Cd vacancy. The rate-limiting barriers for the others are 0.27eV for Au, 0.30eV for Mo, 0.33eV for a Cd interstitial and 0.46eV for Cu. The symmetric or asymmetric nature of the diffusion path as well as the bond length and atomic coordination at the energetic-extrema positions influence the size of the diffusion energy barrier. In addition there exists two electronic signatures in the local density of states: one for the bond breaking in the symmetric diffusion barrier paths and the other in the difference in the energy of occupied states between the global minimum and global maximum energy positions.

First-principles study of diffusion of Li, Na, K and Ag in ZnO

Based on ab initio total energy calculations, Li, Na and Ag interstitialsare found to be stable with at least a 1.56 eV energy barrier to transformto a zinc substitutional site in ZnO, whereas K interstitial has a relativelysmall energy barrier at 0.79 eV. The isolated dopant substitutional defects (LiZn,NaZn,KZn andAgZn) are found to be rather stable, with at least a 3.4 eV energy barrierto transform to an interstitial site. All of the dopant interstitials (Lii,Nai,Ki andAgi) are fast diffusers. The diffusion of Li interstitial is isotropic, whereas the diffusion of Na,K and Ag interstitials is highly anisotropic. Fundamental processes of the vacancy-assistedmechanisms are systematically investigated and specific values of the energy barriers areobtained.

Structural and electrical characterization of AgInSe2 crystals grown by hot-press method

Undoped polycrystalline AgInSe2 crystals were successfully grown at low temperature (650°C) using a hot-press method. The sizes of the samples were 2 cm in diameter. The largest grain size was approximately 90 nm. The presence of lattice defects such as Ag interstitials might lead to an enhancement in n-type electrical conductivity. The crystals had a resistivity of 2.2 Ω cm, a carrier concentration of 4.2 × 1016 cm3 and a mobility of 70 cm2V-1s-1 obtained by Hall measurement at RT.

Growth of AgGaSe 2 crystals by hot‐press method

Undoped polycrystalline AgGaSe2 crystals were successfully grown at a low temperature (700 °C) using a hot-press method. The sizes of the samples were 2 cm in diameter. The grain size was approximately 55 nm. The presence of lattice defects such as Se vacancies and/or Ag interstitials may lead to an enhancement in electrical conductivity. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The recovery of Ag and the formation of mixed dumbells in Ag alloyed with Au after thermal-neutron irradiation

The recovery spectrum of Ag and AgAu between 10K and 400K is discussed. In AgAu the recovery observed near 110K and in stage III indicates that not all the Ag interstitials form a mixed dumbbell configuration with Au. The defect concentration dependence of the 110K substage confirms that this substage is due to detrapping of self-interstitials from single Au impurities.

Time-Differential Quadrupole Interaction ofCd111Nuclei Implanted by (α,2n) Reactions into a Cubic Ag Lattice

The quadrupole interaction of $^{111}\mathrm{Cd}$ ions following the decay of $^{111}\mathrm{In}$ implanted by ($\ensuremath{\alpha},2n$) reactions into a cubic (fcc) Ag lattice has been measured with the time-differential perturbed-angular-correlation method. A nonvanishing quadrupole interaction corresponding to a distribution of electric field gradients was observed. The smeared out quadrupole interaction frequency has a centroid $\overline{\ensuremath{\omega}}$ from 2.04 to 1.50 MHz depending on the temperature and the time the irradiated Ag was allowed to heal. In addition, about 3% of the $^{111}\mathrm{In}$-$^{111}\mathrm{Cd}$ ions experience a quadrupole interaction with a sharp frequency ${\ensuremath{\omega}}_{Q}=157\ifmmode\pm\else\textpm\fi{}2$ MHz. The temperature dependence of the process was investigated. At room temperature no further occurs after 6 days once the $\overline{\ensuremath{\omega}}=1.50$ MHz was reached. Annealing for 12 hours at 600\ifmmode^\circ\else\textdegree\fi{}C causes the quadrupole interaction to vanish conpletely. Various quadrupole-perturbation and healing mechanisms are discussed. The most likely cause of the quadrupole perturbation in the cubic Ag lattice are vacancies and/or Ag interstitials.