Thermal conductivity of ordered-disordered material: a case study of superionic Ag2Te

Synthesis, Properties and Bioimaging Applications of Silver-Based Quantum Dots

Ag-based quantum dots (QDs) are semiconductor nanomaterials with exclusive electrooptical properties ideally adaptable for various biotechnological, chemical, and medical applications. Silver-based semiconductor nanocrystals have developed rapidly over the past decades. They have become a promising luminescent functional material for in vivo and in vitro fluorescent studies due to their ability to emit at the near-infrared (NIR) wavelength. In this review, we discuss the basic features of Ag-based QDs, the current status of classic (chemical) and novel methods ("green" synthesis) used to produce these QDs. Additionally, the advantages of using such organisms as bacteria, actinomycetes, fungi, algae, and plants for silver-based QDs biosynthesis have been discussed. The application of silver-based QDs as fluorophores for bioimaging application due to their fluorescence intensity, high quantum yield, fluorescent stability, and resistance to photobleaching has also been reviewed.

Simple synthesis of crooked Ag2Te nanotubes and their photoelectrical properties

Crooked Ag₂Te nanotubes were prepared through homogeneous precipitation and the photoelectric properties of the film-based photodetector were investigated.

Computational and training requirements for interatomic potential based on artificial neural network for estimating low thermal conductivity of silver chalcogenides

We examined the estimation of thermal conductivity through molecular dynamics simulations for a superionic conductor, α-Ag₂Se, using the interatomic potential based on an artificial neural network (ANN potential). The training data were created using the existing empirical potential of Ag₂Se to help find suitable computational and training requirements for the ANN potential, with the intent to apply them to first-principles calculations. The thermal conductivities calculated using different definitions of heat flux were compared, and the effect of explicit long-range Coulomb interaction on the conductivities was investigated. We clarified that using a rigorous heat flux formula for the ANN potential, even for highly ionic α-Ag₂Se, the resulting thermal conductivity was reasonably consistent with the reference value without explicitly considering Coulomb interaction. It was found that ANN training including the virial term played an important role in reducing the dependency of thermal conductivity on the initial values of the weight parameters of the ANN.

Realizing High Thermoelectric Performance in Sb-Doped Ag2Te Compounds with a Low-Temperature Monoclinic Structure

To recover the low-grade waste heat (300-500 K), it is of urgent importance to develop and improve the thermoelectric performance at a low-temperature region. Herein, we have realized a record high ZT value of 1.4 at 410 K and a record high average ZT value of 0.6 in the temperature interval from 300 to 400 K for Sb-doped Ag₂Sb_xTe_1-x (x = 0-0.03) compounds, which show an improvement of 180 and 120% compared to pristine Ag₂Te, respectively. Sb doping increases the carrier concentration and electrical conductivity, leading to a remarkable improvement of electrical transport properties. The Ag₂Sb_0.015Te_0.985 sample obtains the maximal power factor of 1.07 × 10^-3 W m^-1 K^-2 at 410 K, which is increased by 80% in comparison to that of pristine Ag₂Te. Moreover, as a result of the intensified alloying phonon scattering by Sb doping, Ag₂Sb_0.01Te_0.99 possesses the minimum lattice thermal conductivity of 0.35 W m^-1 K^-1 at 300 K, which demonstrates a decline of 57% compared to that of pristine Ag₂Te. All of these produce a great enhancement on the thermoelectric performance of Ag₂Te materials, which shows great potential in the application of recycling the low-grade waste heat at a low-temperature region.

Thermal transport crossover from crystalline to partial-crystalline partial-liquid state

Phase-change materials (crystalline at low temperatures and partial-crystalline partial-liquid state at high temperatures) are widely used as thermoelectric converters and battery electrodes. Here, we report the underlying mechanisms driving the thermal transport of the liquid component, and the thermal conductivity contributions from phonons, vibrations with extremely short mean free path, liquid and lattice-liquid interactions in phase-changed Li₂S. In the crystalline state (T ≤ 1000 K), the temperature dependent thermal conductivity manifests two different behaviors, i.e., a typical trend of 1/T below 800 K and an even faster decrease between 800 and 1000 K. For the partial-crystalline partial-liquid Li₂S when T ≥ 1100 K, the contributions of liquid and lattice-liquid interactions increase significantly due to the fluidization of Li ions, and the vibrations with extremely short mean free path, presumably assimilated to diffusons, can contribute up to 46% of the total thermal conductivity at T = 1300 K.

Phase-change materials are applied as thermoelectric converters and battery electrodes, but underlying mechanisms are not fully understood. Here, the authors comprehensively describe thermal transport mechanisms of lithium sulfide based on molecular dynamics and first-principles simulations.

Concerted Rattling in CsAg5 Te3 Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance

Thermoelectric (TE) materials convert heat energy directly into electricity, and introducing new materials with high conversion efficiency is a great challenge because of the rare combination of interdependent electrical and thermal transport properties required to be present in a single material. The TE efficiency is defined by the figure of merit ZT=(S(2) σ) T/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the total thermal conductivity, and T is the absolute temperature. A new p-type thermoelectric material, CsAg5 Te3 , is presented that exhibits ultralow lattice thermal conductivity (ca. 0.18 Wm(-1)  K(-1) ) and a high figure of merit of about 1.5 at 727 K. The lattice thermal conductivity is the lowest among state-of-the-art thermoelectrics; it is attributed to a previously unrecognized phonon scattering mechanism that involves the concerted rattling of a group of Ag ions that strongly raises the Grüneisen parameters of the material.