Mass Fluctuations Research Articles

Vacancy Suppression Induced Synergetic Optimization of Thermoelectric Performance in Sb-Doped GeTe Evidenced by Positron Annihilation Spectroscopy.

Synergetic optimization of the electrical and thermal transport performance of GeTe has been achieved through Sb doping in this work, resulting in a high thermoelectric figure of merit ZT of 2.2 at 723 K. Positron annihilation measurements provided clear evidence that Sb doping in GeTe can effectively suppress the Ge vacancies, and the decrease of vacancy concentration coincides well with the change of hole carrier concentration after Sb doping. The decreased scattering by hole carriers and vacancies causes notable increase in carrier mobility. Despite this, the density of states effective mass is not enhanced by Sb doping, a maximum power factor of 4562 μW m-1 K-2 at 723 K is obtained for Ge0.94Sb0.06Te with an optimized carrier concentration of ∼3.65 × 1020 cm-3. Meanwhile, the electronic thermal conductivity κe is reduced because of the decreased electrical conductivity σ with the increase of the Sb doping amount. In addition, the lattice thermal conductivity κL is also suppressed due to multiple phonon scattering mechanism, such as the large mass and strain fluctuations by the substitution of Sb for Ge atoms, and also the unique microstructure including grain boundary, nano-pore, and dislocation in the samples. In conclusion, a maximum ZT of 2.2 is gained at 723 K, which contributes to preferable TE property for GeTe-based materials.

Enhanced Thermoelectric Properties of Nb-Doped Ti(FeCoNi)Sb Pseudo-Ternary Half-Heusler Alloys Prepared Using the Microwave Method.

Pseudo-ternary half-Heusler thermoelectric materials, which are formed by filling the B sites of traditional ternary half-Heusler thermoelectric materials of ABX with equal atomic proportions of various elements, have attracted more and more attention due to their lower intrinsic lattice thermal conductivity. High-purity and relatively dense Ti1-xNbx(FeCoNi)Sb (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.1) alloys were prepared via microwave synthesis combined with rapid hot-pressing sintering, and their thermoelectric properties are investigated in this work. The Seebeck coefficient was markedly increased via Nb substitution at Ti sites, which resulted in the optimized power factor of 1.45 μWcm-1K-2 for n-type Ti0.93Nb0.07(FeCoNi)Sb at 750 K. In addition, the lattice thermal conductivity was largely decreased due to the increase in phonon scattering caused by point defects, mass fluctuation and strain fluctuation introduced by Nb-doping. At 750 K, the lattice thermal conductivity of Ti0.97Nb0.03(FeCoNi)Sb is 2.37 Wm-1K-1, which is 55% and 23% lower than that of TiCoSb and Ti(FeCoNi)Sb, respectively. Compared with TiCoSb, the ZT of the Ti1-xNbx(FeCoNi)Sb samples were significantly increased. The average ZT values of the Nb-doped pseudo-ternary half-Heusler samples were dozens of times that of the TiCoSb prepared using the same process.

Centrifugal balance for the detection of mass fluctuations in advanced propulsion concepts

Propellantless propulsion with a greater thrust-to-power ratio than photon rockets and functioning independently from the Sun or Earth-based lasers promise to revolutionize interstellar space travel. Claims of micronewtons in force for a Mach-Effect-Thruster on a torsion balance in vacuum, along with theories predicting mass fluctuations in a device with large fluctuations in internal energy, have paved the way for experimental investigations. In this experiment originally conceived by Woodward, devices are subjected to high centrifugal acceleration for direct measurement of mass fluctuations using an embedded force transducer. The test devices included a capacitor stack, a toroid and a pre-stressed, multi-layer piezoelectric stack in which electromechanical energy was varied. This paper first describes the design of a centrifugal balance: a rotating apparatus with low eccentricity and maximal angular frequency of 3600 rpm, capable of applying an acceleration above 1000 g's to the test device. The piezoelectric force transducer was characterized and calibrated under quasi-static conditions using an electrodynamic test instrument. The second harmonic response of the force transducer was then examined at different rotational rates to identify the presence of mass fluctuations. The experiment revealed a maximal resolution of 40 μg over a 100 kHz measurement bandwidth. Results with the electrostatic and inductive devices did not show mass fluctuations, orders of magnitude below the prediction. Even if the measurement resolution with the piezoelectric stack was more strongly affected by the centrifugal force, electromagnetic interaction, and nonlinear behavior, the measured noise reached one order of magnitude below the mass fluctuation prediction as well. Despite some limitations with the calibration and with the piezoelectric test device, the experiments have successfully demonstrated the feasibility of the centrifugal balance for high-frequency and high-precision mass variation measurements and have ruled out the postulated Mach-Effect mass fluctuations.

Influence of cation vacancy concentrations on ultra-low thermal conductivity in (1-x)BiVO4 – xBi2/3MoO4 scheelite solid solutions

Bismuth vanadate – bismuth molybdate solid-solution was prepared to elaborate ceramics with different amounts of cation vacancies. Dense ceramics with similar microstructures were obtained and the evolution of their melting point, specific heat, thermal diffusivity, and conductivity as a function of the amount of vacancy was evaluated. At room temperature, the thermal conductivity decreases from 1.74 W m−1 K−1 for BiVO4 (x=0) to 1.12 W m−1 K−1 for Bi0.867□0.133Mo0.4V0.6O4 (x=0.4). Moreover, we show that a very small amount of vacancy (1.7%, x=0.05) is enough to provide a large decrease in thermal conductivity by more than 15%, in agreement with a mass fluctuation scattering model. However, the temperature of the melting point also decreases with increasing amount of vacancy. Our results suggest adding only a very small amount of vacancy as the best strategy to obtain superior materials for thermal barriers and thermoelectric devices, with ultra-low thermal conductivity and high-temperature stability.

On the effects of surface waviness upon catalytic steam reforming of methane in micro-structured reactors - a computational study

The effects of wavy channels upon steam methane reforming in catalytic micro-structured reactors, using Nickle as the catalyst, are investigated numerically. Laminar, three-dimensional models of reacting flows, with heterogeneous chemistry, are developed and applied to micro-structured reactors with different wave patterns on their internal walls. It is observed that introduction of surface waves on the walls of reactor, can significantly alter production and consumption of H2 and CH4. This is shown to be due to large fluctuations in convective mass and heat transfer, induced by the surface waviness. In particular, it is shown that separation and reattachment of concentration and thermal boundary layers and the subsequent modifications in Sherwood and Nusselt number can significantly affect the catalytic processes over the walls of reactor. A major local intensification of catalytic processes is observed where Sherwood and Nusselt number are maximised. Similarly, the catalytic process becomes highly inefficient in places with minimal Sherwood (and Nusselt) number. The analyses further reveal that a strategic discrete coating of wavy walls with the catalyst can substantially improve the performance of microstructure. For example, by coating only 25% of the surface area of wavy walls, CH4 conversion rate and selectivity per coated surface area increase by 459% and 308% compared to those of an equivalent fully coated straight channel. This implies the possibility of developing highly efficient and cost-effective catalytic micro-reactors for production of hydrogen from methane.

High‐entropy rare earth titanates with low thermal conductivity designed by lattice distortion

AbstractHigh‐entropy single‐phase rare earth titanates (RE0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 (RE = Sm, Y, Lu) were designed and synthesized successfully, in which their lattice distortion was quantitatively described by mass disorder and size disorder. It is worth mentioning that (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 could obtain the low thermal conductivity (1.51 W·m−1·K−1, 1500°C), high thermal expansion coefficient (average, 11.69×10−6 K−1, RT ∼1500°C) and excellent high‐temperature stability. In addition, the relationship between the microstructure and thermal transport behaviors has been studied at the atomic scale. Due to the disorder of A‐site ions, severe lattice distortion occurred in specific crystal planes, and the large mass difference between Y3+ and other RE3+ further causes mass fluctuation and results in lower thermal conductivity. Compared with YSZ, the high‐entropy rare earth titanate (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 has lower thermal conductivity, higher thermal expansion coefficient, and excellent high‐temperature stability, which has great potential for application in the thermal protection field.

Proposition of a Simplified Protocol and New Parameter Introduction in NMRI Mice Anhedonia Induction

Abstract A broad spectrum of research involving stress and stress protocols has long proven that a point of anhedonia, social defeat and learned helplessness can be achieved and observed – with anhedonia being a clinical symptom of Anxiety, Depression and Bipolar Affective Disorder. The aim of this study is the development of a simplified protocol for anhedonia induction in NMRI male mice in order to shorten the period of mice suffering and decrease complexity of the procedure for other researchers and introduction of new parameter in order to achieve better standardization of results. 21 male NMRI mice were introduced to 2 different stress protocols (one found in literature and one simplified) where cognitive- behavioral status was tested using the Sucrose Preference Test, Open Field Test, Grooming Pattern and histological examination of adrenal glands, and to propose a new protocol for fellow researchers. Results observed include the successful induction of anhedonia proven by Sucrose Preference Tests, Barbering effect and microhemorrhage of the adrenal glands. Simplified protocol showed superiority compared to the one found in literature. Simplified protocol showed higher efficiency and reduced amount of work during testing phase. Introduction of NMI as a new parameter during behavioral evaluation resulted in better standardization of measured SPT values that incorporates common knowledge of mammal physiology. A big developmental step was the introduction of the Normalised Mass Index to even out mass fluctuations and differences in basal metabolism, which we recommend to other researchers and institutions.

Quantum origins of scalar gravitational waves: Exploring the conformal factor in scalar–tensor theory of gravity

Delving into the realm of scalar–tensor theory of gravity, this paper uncovers the intricate details of the conformal factor and its correspondence to quantum mechanical mass fluctuations. Shedding light on the theory’s key findings, we explore the quantum mechanical nature of the wave equation associated with mass fluctuations, predicting the creation of scalar gravitational waves. The association of conformal fluctuations with the quantum potential presents a remarkable feature of this theory, which predicts a scalar component of gravitational waves. With the potential to generate such waves in a laboratory set-up, this theory invites exciting possibilities for empirical testing, highlighting the quantum mechanical origin of scalar gravitational waves.

Abstract 476: Negligible Impacts Of Anesthesia On The Morphodynamics Of Individual Red Blood Cells What Is Good News For Vessels: A Study Exploiting Holotomography

Rationale: The shape and membrane dynamics of individual red blood cells (RBCs) are known to play a significant role in their functionality. The morphodynamics of RBCs optimizes their flow properties in vessels and capillaries, which is important for the balance and optimal distribution of blood and nutrients to the tissues. It is also crucial in pathological contexts because changes can influence vascular and microvascular hemodynamics. It can dysregulate vascular function through the modulation of oxygen delivery and the scavenging and generation of nitric oxide. Therefore, the ideal conditions of RBCs are essential for healthy vascular function. Anesthetics, sedatives, analgesics, and fluids used during anesthesia can impact RBCs. The same applies to pneumoperitoneum performed in laparoscopic procedures. Objectives: Taking above we aimed to prospectively evaluate the influence of anesthesia on RBC volume (CV, fL), surface area (SA, μm2), sphericity (SI), dry mass (CH, pg), Hb concentration (CHC, g/dL) and membrane fluctuation (nm). Methods: We exanimated RBCs (n=760) from 5 female dogs undergoing laparoscopic-assisted ovariohysterectomy (OVH). The blood was collected 15 min after premedication with medetomidine and 1h after full anesthesia (isoflurane, fentanyl). Measurements of RBC parameters we performed using the non-invasive, label-free method of imaging with holotomography. Statistical significance was determined using Mann-Whitney test. Results: Morphodynamics parameter values during anesthesia were stable. We observe statistically no significant changes for RBC parameters after premedication vs. one hour of full anesthesia: CH 24.20 vs. 24,19, p=0.57; CV 59.17 vs. 59.04, p=0.89; CHC 42.33 vs. 41.53, p=0.60; SA 117.38 vs. 119.56, p=0.13; SI 0.63 vs. 0.62, p=0.31; fluctuation 68.18 vs. 65.18, p=0.95. Conclusions: Procedures related to OVH are not reflected in the parameters of RBCs and their well-being. This provides new insight into the impact and safety of the anesthetic protocol used in this study on blood cell function, which translates into the lack of risk of vascular damage.

Polarity switching via defect engineering in Cu doped SnSe0.75S0.25 solid solution for mid-temperature thermoelectric applications

Solid solution SnSe0.75S0.25 has potential to improve thermoelectric performance via ultra-low thermal conductivity as compared to the pristine SnSe which originates from phonon scattering due to disordered atoms of selenium (Se) and sulfur (S). SnSe0.75S0.25 and Cu-doped SnSe0.75S0.25 compounds were prepared via high energy ball milling and pelletized by a spark plasma sintering (SPS) process. Dislocation and point defects were successfully introduced by SnSe0.75S0.25. The existence of S in the Se site induced mass fluctuation which favors high-frequency phonon scattering. This leads to an impressively ultra-low thermal conductivity (κT) value of 0.258 W mK−1 at 753 K for SnSe0.75S0.25. Next, the Cu dopant was selected to enhance the electrical conductivity, which improved from 514.44 S m−1 (SnSe0.75S0.25) to 725.08 S m−1 for Sn0.98Cu0.02Se0.75S0.25 at 738 K. Interestingly, the Cu dopant induced nanoprecipitates of Cu2Se inside the grains, which further strengthens the phonon scattering. The Cu2Se nanoprecipitates and various defects at the grain boundaries contributed to a lower κT of 0.295 W mK−1 at 753 K for a Sn0.94Cu0.06Se0.75S0.25 sample. Moreover, the maximum figure of merit of (ZT) ∼0.19 at 738 K was attained for the Sn0.98Cu0.02Se0.75S0.25 sample.

Ultralow Lattice Thermal Conductivity and High Thermoelectric Performance in Ge1–x–yBixCayTe with Ultrafine Ferroelectric Domain Structure

GeTe and its derivatives emerging as a promising lead-free thermoelectric candidate have received extensive attention. Here, a new route was proposed that the minimization of κL in GeTe through considerable enhancement of acoustic phonon scattering by introducing ultrafine ferroelectric domain structure. We found that Bi and Ca dopants induce strong atomic strain disturbance in the GeTe matrix because of large differences in atom radius with host elements, leading to the formation of ultrafine ferroelectric domain structure. Furthermore, large strain field and mass fluctuation induced by Bi and Ca codoping result in further reduced κL by effectively shortening the phonon relaxation time. The co-existence of ultrafine ferroelectric domain structure, large strain field, and mass fluctuation contribute to an ultralow lattice thermal conductivity of 0.48 W m-1 K-1 at 823 K. Bi and Ca codoping significantly enhances the Seebeck coefficient and power factor through reducing the energy offset between light and heavy valence bands of GeTe. The modified band structure boosts the power factor up to 47 μW cm-1 K-2 in Ge0.85Bi0.09Ca0.06Te. Ultimately, a high ZT of ∼2.2 can be attained. This work demonstrates a new design paradigm for developing high-performance thermoelectric materials.

Fluctuations of Dry and Total Mass of Cells Exposed to Different Molecular Weights of Polyethylene Glycol

Polyethylene glycol (PEG) is used in many applications, and in the clinical field, it is one of the main components of the latest Covid vaccines. Its wide use is justified by a relatively safe profile and few known side effects. However, little is known about the biophysical effects of PEG on cells such as, cell stiffness, dry mass, and total mass. Herein, exploiting a digital holographic microscope, an inertial picobalance, and a nanoindenter, these properties are characterized in rat embryonic fibroblast exposed to different molecular weights of PEG. Immediately after the first minutes of PEG exposure to the cells, a reduction in cell dry mass can be observed as well as a rapid fluctuation in total cell weight. Cell stiffness decreases significantly after 48 h, while no important morphological changes are observed. Here, it is revealed how dry mass and total mass are rapidly and finely regulated, highlighting how the maintenance of cell density is of primary importance in cellular activities.

Spatio-Temporal Analysis of a Self-Pulsating Gas-Centered Swirl Coaxial Injector with Forced Gas Jet

The objective of the present work is to examine the effects of the acoustically forced gas jet on self-pulsating sprays generated from a gas-centered swirl coaxial injector. We conduct the experiments on self-pulsating spray by forcing the gas jet over a range of forcing frequencies and amplitudes. Various image processing techniques, including proper orthogonal decomposition (POD), have been employed to characterize the spray response. Our spatial mapping of dominant frequencies from time-resolved spray width reveals that although both natural and forcing frequencies prevail in the primary breakup region, a modulation frequency (corresponding to the double of the beat frequency) outcompetes the others. The spatial influence of the forcing is also evaluated by measuring liquid mass fluctuations and drop size statistics at various downstream locations. The experiments were extended to investigate the role of various geometrical parameters, such as swirl number, recess, and length of the gas line on the spray response. The influence of the forcing was observed to prevail even in the liquid mass shedding zone with the appearance of all dominant frequencies. This may have important consequences on the thermoacoustic stability of the combustor. In any case, far downstream of the nozzle, the influence of acoustic forcing is not significant to alter the droplet statistics.

Ultralight dark matter searches at the sub-Hz frontier with atom multigradiometry

Single-photon atom gradiometry is a powerful experimental technique that can be employed to search for the oscillation of atomic transition energies induced by ultralight scalar dark matter (ULDM). In the sub-Hz regime the background is expected to be dominated by gravity gradient noise (GGN), which arises as a result of mass fluctuations around the experiment. In this work we model the GGN as surface Rayleigh waves, and we construct a likelihood-based analysis that consistently folds GGN into the sensitivity estimates of vertical atom gradiometers in the frequency window between 1 mHz and 1 Hz. We show that in certain geological settings GGN can be significantly mitigated when operating a multigradiometer configuration, which consists of three or more atom interferometers in the same baseline. Multigradiometer experiments, such as future versions of AION and MAGIS-100, have the potential to probe regions of scalar ULDM parameter space in the sub-Hz regime that have not been excluded by existing experiments.

Inhibiting the bipolar effect via band gap engineering to improve the thermoelectric performance in n-type Bi2-Sb Te3 for solid-state refrigeration

• Se replacement can enlarge the E g and thus effectively mitigate the bipolar effect. • The manipulation of donor-like effect retains the optimized carrier concentration. • The large strain field and mass fluctuation reduce lattice thermal conductivity. • A state-of-the-art zT = 1.0 at 300 K is attained for n -type Bi 1.5 Sb 0.5 Te 2.8 Se 0.2 . • n -type Bi 2- x Sb x Te 3 becomes a promising candidate for solid-state cooling field. To date, the benchmark Bi 2 Te 3 -based alloys are still the only commercial material system used for thermoelectric solid-state refrigeration. Nonetheless, the conspicuous performance imbalance between the p -type Bi 2- x Sb x Te 3 and n -type Bi 2 Te 3- x Se x legs has become a major obstacle for the improvement of cooling devices to achieve higher efficiency. In our previous study, novel n -type Bi 2- x Sb x Te 3 alloy has been proposed via manipulating donor-like effect as an alternative to mainstream n -type Bi 2 Te 3- x Se x . However, the narrow bandgap of Bi 2- x Sb x Te 3 provoked severe bipolar effect that constrained the further improvement of zT near room temperature. Herein, we have implemented band gap engineering in n -type Bi 1.5 Sb 0.5 Te 3 by employing isovalent Se substitution to inhibit the undesired intrinsic excitation and achieve the distinguished room-temperature zT . First, the preferential occupancy of Se at Te 2 site appropriately enlarges the band gap, thereby concurrently improving the Seebeck coefficient and depressing the bipolar thermal conductivity. In addition, the Se alloying mildly suppresses the compensation mechanism and essentially preserves the already optimized carrier concentration, which maintains the peak zT near room temperature. Moreover, the large strain field and mass fluctuation generated by Se alloying leads to the remarkable reduction of lattice thermal conductivity. Accordingly, the zT value of Bi 1.5 Sb 0.5 Te 2.8 Se 0.2 reaches 1.0 at 300 K and peaks 1.1 at 360 K, which surpasses that of most well-known room-temperature n -type thermoelectric materials. These results pave the way for n -type Bi 2- x Sb x Te 3 alloys to become a new and promising top candidate for large-scale solid-state cooling applications.

Coupling of electronic transport and defect engineering substantially enhances the thermoelectric performance of p-type TiCoSb HH alloy

Further advancements in thermoelectric technology rely on the capacity to control both electrical and thermal transport properties simultaneously. Although TiCoSb-based half-Heusler compounds are promising for mid-range-temperature thermoelectric applications owing to their high Seebeck coefficient and good electrical conductivity, their high thermal conductivity has been so far the main issue to overcome. Here, we show that a combined approach of tuning the electronic properties and defect engineering enhances the thermoelectric performance of p-type TiCoSb-based compounds. By alloying on the Co and Ti sites with Fe and Zr, respectively, an overall increase in the peak ZT value of up to ∼90% at 823 K is achieved in Ti0.8Zr0.2Co0.85Fe0.15Sb. This enhancement is directly tied to the more pronounced metallic nature of transport upon Fe alloying combined with a significant reduction in thermal conductivity due to mass and strain field fluctuations driven by the substitution of Zr for Ti, as evidenced by the Debye-Callaway model. Further adjusting the hole concentration with aliovalent Sn doping leads to an additional increase in ZT, eventually leading to a peak value of ∼0.54 at 823 K in Ti0.8Zr0.2Co0.85Fe0.15Sb0.96Sn0.04, which is 224% higher than in TiCo0.85Fe0.15Sb, and the highest value reported so far in Hf-free p-type TiCoSb based HH alloys.

Cosmological constraints from the power spectrum of eBOSS quasars

We present the effective-field theory (EFT)-based cosmological full-shape analysis of the anisotropic power spectrum of eBOSS quasars at the effective redshift $z_{\rm eff}=1.48$. We perform extensive tests of our pipeline on simulations, paying a particular attention to the modeling of observational systematics, such as redshift smearing, fiber collisions, and the radial integral constraint. Assuming the minimal $\Lambda$CDM model, and fixing the primordial power spectrum tilt and the physical baryon density, we find the Hubble constant $H_0=(66.7\pm 3.2)~$km~s$^{-1}$Mpc$^{-1}$, the matter density fraction $\Omega_m=0.32\pm 0.03$, and the late-time mass fluctuation amplitude $\sigma_8=0.95\pm 0.08$. These measurements are fully consistent with the Planck cosmic microwave background results. Our eBOSS quasar $S_8$ posterior, $0.98\pm0.11$, does not exhibit the so-called $S_8$ tension. Our work paves the way for systematic full-shape analyses of quasar samples from future surveys like DESI.

Снижение колебаний массы бумаги в бумагоделательной машине

The subject of the research is a paper for sanitary-hygienic purposes. The objects of the study are a pulper infeed system and a round grid perforated forming device. The purposes of the work are to identify sources and reduce fluctuations of 1 m2 of pulp for sanitaryhygienic paper, which decrease the structural irregularities of the paper web in longitudinal and transverse directions. The methodology of the study is to investigate the flow pulsation of the pulp, the fluctuations of the pulp web at the Yankee cylinder (without crepe), to verify the tensile strength of the paper web in longitudinal and transverse directions for identification of a correlation between the pulsation, the vibration of the pulp and the strength of the paper web. The trials were made during the production of sanitary-hygienic paper with the mass 17–18 g/m2 at a steady working speed of the machine 5 m/s. Pulsations of paper pulp in the low-frequency spectrum of 0.14–1.35 Hz prevail in the mass-intake device. The rectangular paper samples 432×230 mm2 were created for examination of structural irregularities of the paper web. The length 432 mm was taken in the longitudinal direction of paper movement in the machine. It was equal to 0.125 mm in the circumference of the round grid screen cylinder. The width of the paper web in the commodity bobbin was 230 mm. The samples were made from a single sheet of paper sequentially without intermediate cuts at 5 m/s speed of the machine. It was determined that the frequencies of fluctuations of the masses of sanitary paper samples coincide by 86 % with the pulsation frequencies of the pulp and depend on other factors by 14 %. The major frequency was 1.45 Hz. The amplitude of the deviation of the mass at this frequency from the arithmetic mean was 0.026 g. The tensile strength of the paper web in the machine direction was 5.6 times greater than in the transverse direction. It was caused by unregulated rotation frequency of the holey roll and clogging of its holes. The significant change of speed of the pulp flow on the short cylindrical part of the vacuum chambers initiated synchronically low frequency pulsation of the pulp and fluctuations of masses of the paper samples, therefor, the paper web in the machine. The irregularities of the structure of the paper web create the frequent paper breaks and reduced quality of the commodity products.

A simple Pb-doping to achieve bonding evolution, VSn and resonant level shifting for regulating thermoelectric transport behavior of SnTe

The intensification of energy crises and environmental pollution inspire researchers' attention to environment-friendly SnTe thermoelectric materials. In this work, we achieved a lower lattice thermal conductivity and optimized the power factor via the synergistic optimization of bonding characteristic, VSn, and resonant level for the SnTe system, respectively. Pb-introduction produces weak bonding strength, mass fluctuation, and stress distortion, which result in lower thermal conductivity. The lowest lattice thermal conductivity achieves 0.66 W m–1 K–1 at 773 K. Further introduced VSn relieves loss of electrical conductivity caused by Pb-introduction, and it also makes the bigger g(E) and up-shift of resonance level. The VSn, enhanced g(E), and resonant level make electrical conductivity and Seebeck coefficient enhance simultaneously. Finally, the further optimization of thermal and electronic transport performance contributes to a higher ZT value of ∼0.86 at 773 K in the Sn0.685Pb0.285In0.015Te0.7Se0.3 sample. The strategy of bonding characteristic, VSn, and resonant level synergistic engineering will be widely applicable to various TE systems for achieving better thermoelectric performance.

Dynamic correlations in the conserved Manna sandpile.

We study dynamic correlations for current and mass, as well as the associated power spectra, in the one-dimensional conserved Manna sandpile. We show that, in the thermodynamic limit, the variance of cumulative bond current up to time T grows subdiffusively as T^{1/2-μ} with the exponent μ≥0 depending on the density regimes considered and, likewise, the power spectra of current and mass at low frequency f varies as f^{1/2+μ} and f^{-3/2+μ}, respectively. Our theory predicts that, far from criticality, μ=0 and, near criticality, μ=(β+1)/2ν_{⊥}z>0 with β,ν_{⊥}, and z being the order parameter, correlation length, and dynamic exponents, respectively. The anomalous suppression of fluctuations near criticality signifies a "dynamic hyperuniformity," characterized by a set of fluctuation relations, in which current, mass, and tagged-particle displacement fluctuations are shown to have a precise quantitative relationship with the density-dependent activity (or its derivative). In particular, the relation, D_{s}(ρ[over ¯])=a(ρ[over ¯])/ρ[over ¯], between the self-diffusion coefficient D_{s}(ρ[over ¯]), activity a(ρ[over ¯]) and density ρ[over ¯] explains a previous simulation observation [Eur. Phys. J. B 72, 441 (2009)10.1140/epjb/e2009-00367-0] that, near criticality, the self-diffusion coefficient in the Manna sandpile has the same scaling behavior as the activity.