DFT based study on structural stability and transport properties of Sr3AsN: A potential thermoelectric material

Antiperovskite materials are well known for their high thermoelectric performance and gained huge research interest. Here, we report the structural stability and transport properties of Sr$_3$AsN from a precise first-principles study. The calculated equilibrium lattice parameters are in a good agreement with the available data. We find that Sr$_3$AsN is a mechanically, energetically and dynamically stable at ambient condition. Our calculated electronic structure indicates that it is a direct bandgap semiconductor, with a value ~1.2 eV. Sr-4d and N-2p orbitals mainly formulate the direct bandgap. This antiperovskite possesses a high Seebeck coefficient. Although its lattice thermal conductivity is comparatively low, electronic thermal conductivity is very high. The calculated maximum TE figure of merit is 0.75 at 700 K, indicating that it is a potential material for thermoelectric applications.Comment: 22 pages, 11 figure

High Seebeck coefficient and ultra-low lattice thermal conductivity in Cs2InAgCl6

The elastic, electronic and thermoelectric properties of indium-based double-perovskite halide, Cs2InAgCl6 have been studied by first principles study. The Cs2InAgCl6 is found to be elastically stable, ductile, anisotropic and relatively low hard material. The calculated direct bandgap 3.67 eV by TB-mBJ functional fairly agrees with the experimentally measured value 3.3 eV but PBE functional underestimates the bandgap by 1.483 eV. The relaxation time and lattice thermal conductivity have been calculated by using relaxation time approximation (RTA) within the supercell approach. The lattice thermal conductivity (\k{appa}l) is quite low (0.2 Wm-1K-1). The quite low phonon group velocity in the large weighted phase space, and high anharmonicity (large phonon scattering) are responsible for small \k{appa}l. The room temperature Seebeck coefficient is 199 {\mu}VK-1. Such high Seebeck coefficient arises from the combination of the flat conduction band and large bandgap. We obtain power factors at 300K by using PBE and TB-mBJ potentials are ~29 and ~31 mWm-1K-2, respectively and the corresponding thermoelectric figure of merit of Cs2BiAgCl6 are 0.71 and 0.72. However, the maximum ZT value obtained at 700K is ~0.74 by TB-mBJ potential. The obtained results implies that Cs2InAgCl6 is a promising material for thermoelectric device applications.Comment: 19 pages. arXiv admin note: text overlap with arXiv:1801.0370

First-principles prediction of phonon-mediated superconductivity in XBC (X= Mg, Ca, Sr, Ba)

From first-principles calculations, we predict four new intercalated hexagonal $X$BC ($X$=Mg, Ca, Sr, Ba) compounds to be dynamically stable and phonon-mediated superconductors. These compounds form a LiBC like structure but are metallic. The calculated superconducting critical temperature, $T{_c}$, of MgBC is 51 K. The strong attractive interaction between $\sigma$-bonding electrons and the B${_{1g}}$ phonon mode gives rise to a larger electron-phonon coupling constant (1.135) and hence high $T_c$; notably, higher than that of MgB$_2$. The other compounds have a low superconducting critical temperature (4-17 K) due to the interaction between $\sigma$-bonding electrons and low energy phonons (E${_{2u}}$ modes). Due to their energetic and dynamic stability, we envisage that these compounds can be synthesized experimentally.Comment: 7 pages, 6 figure

First-principles prediction of extraordinary thermoelectric efficiency in superionic Li2SnX3(X=S,Se)

Thermoelectric materials create an electric potential when subject to a temperature gradient and vice versa hence they can be used to harvest waste heat into electricity and in thermal management applications. However, finding highly efficient thermoelectrics with high figures of merit, zT$\geq$1, is very challenging because the combination of high power factor and low thermal conductivity is rare in materials. Here, we use first-principles methods to analyze the thermoelectric properties of Li$_2$Sn$X_3$ ($X$=S,Se), a recently synthesized class of lithium fast-ion conductors presenting high thermal stability. In p-type Li$_2$Sn$X_3$, we estimate highly flat electronic valence bands that render high Seebeck coefficients exceeding 400 ${\mu}$VK$^{-1}$ at 700K. In n-type Li$_2$Sn$X_3$, the electronic conduction bands are slightly dispersive however the accompanying weak electron-acoustic phonon scattering induces high electrical conductivity. The combination of high Seebeck coefficient and electrical conductivity gives rise to high power factors, reaching a maximum of 4 mWm$^{-1}$K$^{-2}$ in p-type Li$_2$SnS$_3$ and 8 mWm$^{-1}$K$^{-2}$ in n-type Li$_2$SnSe$_3$ at 300 K. Likewise, the thermal conductivity in Li$_2$Sn$X_3$ is low as compared to conventional thermoelectric materials, 2-5 Wm$^{-1}$K$^{-1}$ at room temperature. As a result, we estimate a maximum zT = 1.05 in p-type Li$_2$SnS$_3$ at 700 K and an extraordinary 3.07 (1.5) in n-type Li$_2$SnSe$_3$ at the same temperature (300 K). Our findings of huge zT in Li$_2$Sn$X_3$ suggest that lithium fast-ion conductors, typically employed as electrolytes in solid-state batteries, hold exceptional promise as thermoelectric materials.Comment: 21 Page

PCR Based Detection of White Spot Syndrome Virus (WSSV) in Shrimp Post Larvae (PL) of Bangladesh

Shrimp aquaculture is a very promising and rapidly growing industry that contributes about 5% to national GDP in Bangladesh. Shrimp aquaculture is the second highest foreign currency earning source and 97% of the produced shrimp being exported. However, shrimp aquaculture suffered from different diseases particularly viral disease. White Spot Disease (WSD) alone losses tens of billion dollars in every year worldwide as well as in Asia, the industry suggests annual damages is about 4 billion USD. In Bangladesh, White Spot Syndrome Virus (WSSV) infection in shrimp aquaculture alone destroys hundreds of million dollars per year. The detection of WSSV before releasing post larvae (PL) in aqua-farm is immensely important to mitigate this disease from the shrimp aquaculture industry of Bangladesh. In this investigation, a total of 65 PL of shrimp samples were collected from Cox’s Bazar (n=40 PL) and Satkhira (n=25 PL) of Bangladesh between 2015 and 2018. Samples were analyzed by conventional PCR using VP664 and VP28 genes specific primers. Among the 65 PL samples, 11 PL samples were found to be positive where six samples in Cox’s Bazar and five samples in Satkhira areas were found WSSV positive. The overall prevalence rate was 16.93% in the collected PL samples in Bangladesh. Though the infection rate of WSSV in shrimp PL was 16.93%, it will play a deleterious influence in shrimp aquaculture of Bangladesh. The present work suggests that the segregation of WSSV infected shrimp PL before releasing to the culture ponds/ghers is of immensely important to minimize or prevent the WSD infection in shrimp aquaculture

Comparative study of sodium and potassium based fly ash geopolymer at elevated temperatures

This paper presents the effects of sodium and potassium based activators on compressive strengths and physical changes of class F fly ash geopolymer exposed to elevated temperatures. Samples were heated at 2000 C, 4000 C, 6000 C and 8000 C to evaluate the residual compressive strength after 28 days of curing. The fly ash geopolymer were synthesized with combined sodium silicate and sodium hydroxide solutions and potassium silicate and potassium hydroxide solutions by varying mass ratios of Na2SiO3/NaOH and K2SiO3/KOH of 2, 2.5 and 3. Results show that in the cases of Na2SiO3/NaOH ratios of 2 and 2.5, the compressive strengths of geopolymers are decreased at 400, 600 and 800o C, with exception at 200o C. The reduction is significantly high from 32-61% at 800o C compared to ambient temperature strength. However, significant improvement is noticed in the case of Na2SiO3/NaOH ratio of 3, where the residual compressive strengths are increased upto 600o C. Better results on the geopolymer synthesized with potassium based activators are obtained where the residual compressive strength up to 600o C are much higher than their sodium based counterparts. The geopolymer containing K2SiO3/KOH ratio of 3 even gained about 5% strength at 800o C. It is also found that the fly ash geopolymer synthesized with potassium based activators is more stable at elevated temperatures than its sodium based counterparts in terms of higher residual compressive strengths, lower mass loss, lower volumetric shrinkage and lower cracking damage