Ab initioinvestigation of the lattice dynamics and thermophysical properties of BCC vanadium and niobium.

In the present work, we have performed the phonon dispersion calculations of body-centered cubic vanadium (V) and niobium (Nb) with the supercell approach using different supercell size. Using DFT method, the calculated phonon spectra of V and Nb are found to be in a good agreement with the available experimental data. Our calculated results show a 'dip'-like feature in the longitudinal acoustic phonon mode along the Γ-H high symmetric path for both transition metals in the case of supercell size4×4×4. However, in supercell size2×2×2and3×3×3, the 'dip'-like feature is not clearly visible. In addition to this, thermodynamical properties are also computed, which compare well with the experimental data. Apart from this, the phonon lifetime due to electron-phonon interactions (τephph) and phonon-phonon interactions (PPIs) (τphph) are calculated. The effect of PPIs is studied by computing the average phonon lifetime for all acoustic branches. The value ofτephphof V (Nb) is found to be 23.16 (24.70)×10-15s at 100 K, which gets decreased to 1.51 (1.85)×10-15s at 1000 K. Theτphphof V (Nb) is found to be 8.59 (18.09)×10-12and 0.83 (1.76)×10-12s at 100 and 1000 K, respectively. Nextly, the lattice thermal conductivity is computed using linearized phonon Boltzmann equation. The present work suggests that studying the variation of phonon dispersion with supercell size is crucial for understanding the phonon properties of solids accurately.

Evidence of charge susceptibility and multiplef-chybridization configurations with the La doping in CeGe: a DFT + DMFT study.

Kondo coupling has been extensively investigated in several Ce-based systems. However, the search for materials showing the interplay between the Kondo effect, spin-orbit interaction, and crystal-field effect along with the presence of local charge susceptibility; remains a challenge for the condensed matter community. Actually, in Ce-based systems, the strong coupling of the conduction electrons to the local magnetic moments usually hides these properties. Here, we present a detailed investigation of Ce0.6La0.4Ge through a combined density functional theory and dynamic mean-field theory study. Our investigations give evidence of the significant charge susceptibility and the multiple differentf-chybridization configurations. The weakening of the magnetization owing to the dilution of the Ce-site is the main cause for the appearance of such properties, which is believed to occur due to the presence of the relevant local moment andf-chybridization over the competition with the on-site Coulomb interaction.

Possible realization of three-dimensional quantum spin liquid behavior in HoVO4.

The study of geometrically frustrated magnetic systems with unusual crystal field ground states offers a possibility of realizing the new aspects of physics of disordered systems. In this study, we report our results of structural, magnetic susceptibility, heat capacity measurements, along with density functional theory (DFT) calculations on HoVO4; a compound in which the presence of a distorted kind of HoO8polyhedral leads to multiple magnetic interaction paths. The observed broad maximum below 10 K in the temperature response of DC susceptibility curves implies the presence of short-range correlations. AC susceptibility rules out the possibility of any kind of spin freezing. Temperature dependent heat capacity measurement at zero field indicate towards the absence of long-range ordering, along with the presence of a broad maximum centered around 14 K. The residual heat capacity exhibits a characteristic power-law (Tα) behavior with the exponentαnearly equal to 2, which is analogous to that observed for other three-dimensional (3D) quantum spin liquid (QSL) systems. The DFT calculations signify the presence of dominant second and third nearest neighbor interactions, which in turn lead to magnetic frustration in our system. Our investigations suggest that HoVO4can be a candidate for realizing a 3D QSL state.

Evidence of phase stability, topological phonon and temperature-induced topological phase transition in rocksalt SnS and SnSe.

Both SnS and SnSe have been experimentally and theoretically confirmed as topological crystalline insulators in native rocksalt structure. Here, phononic structure, thermodynamic properties and temperature dependent electron-phonon interaction (EPI) have investigated for both the materials in rocksalt phase. Previously performed theoretical studies have predicted the phase instability of SnS in this crystal structure at ambient condition. But, after a detailed study performing on the phonon calculation of SnS, we have predicted the phase stability of SnS with considering the Sn 4porbitals as valence states inab-initiocalculation. The importance of long range Coulomb forces along with the themodynamical properties are also described in detailed for both materials. The computed value of Debye temperature (ΘD) for SnS (SnSe) is ∼315.0 K (∼201.7 K). The preliminary evidence of topological phonon is found alongX-Wdirection, where the linear band touching is observed as compared to type II Weyl phononic material ZnSe (Liuet al2021Phys. Rev.B103094306). The topological phase transition is seen for these materials due to EPI, where non-linear temperature dependent bandgap is estimated. The predicted value of transition temperature for SnS (SnSe) is found to be ∼700 K, where after this temperature the non-trivial to trivial topological phase is seen. The strength of EPI shows more stronger impact on the electronic structure of SnS than SnSe material. The reason of non-linear behaviour of bandgap with rise in temperature is discussed with the help of temperature dependent linewidths and lineshifts of conduction band and valence band due to EPI. The present study reveals the phase stability of SnS along with the comparative study of thermal effect on EPI of SnS and SnSe. Further, the possibility of temperature induced topological phase transition provides one of important behaviour to apply these two materials for device making application.

Instrument for simultaneous measurement of Seebeck coefficient and thermal conductivity in the temperature range 300-800 K with Python interfacing.

Fabrication and characterization of an instrument for the high-temperature simultaneous measurement of the Seebeck coefficient (S) and thermal conductivity (κ) have been carried out with Python automation. The steady-state-based Fourier's law of thermal conduction is employed for κ measurement. The parallel thermal conductance technique is implemented for heat loss measurement. Introducing a thin heater and insulating heater base minimizes the heat loss and makes it easier to arrive at high temperatures. Measurement of S is carried out using the differential method. The same thermocouples are used to measure the temperature as well as voltage for S measurement. Care of temperature dependent S of the thermocouple has also been taken. Simple design, small size, and lightweight make this instrument more robust. All the components for making a sample holder are easily available in the market and can be replaced as per the user's demand. This instrument can measure samples with various dimensions and shapes in the temperature range 300-800 K. The instrument is validated using different classes of samples, such as nickel, gadolinium, Fe2VAl, and LaCoO3. A wide range of S values from ∼-20 to ∼600 µV/K and κ values from ∼1.1 to ∼23.5 W/m K are studied. The measured values of S and κ are in good agreement with the reported data.

Experimental and computational approaches to study the high temperature thermoelectric properties of novel topological semimetal CoSi.

Here, we study the thermoelectric properties of topological semimetal CoSi in the temperature range 300-800 K by using combined experimental and density functional theory (DFT) based methods. CoSi is synthesized using arc melting technique and the Rietveld refinement gives the lattice parameters ofa=b=c= 4.445 Å. The measured values of Seebeck coefficient (S) shows the non-monotonic behaviour in the studied temperature range with the value of ∼-81µV K-1at room temperature. The |S| first increases till 560 K (∼-93µV K-1) and then decreases up to 800 K (∼-84µV K-1) indicating the dominating n-type behaviour in the full temperature range. The electrical conductivity,σ(thermal conductivity,κ) shows the monotonic decreasing (increasing) behaviour with the values of∼5.2×105(12.1 W m-1 K-1) and∼3.6×105(14.2 W m-1 K-1) Ω-1 m-1at 300 K and 800 K, respectively. Theκexhibits the temperature dependency as,κ∝T0.16. The DFT based Boltzmann transport theory is used to understand these behaviour. The multi-band electron and hole pockets appear to be mainly responsible for deciding the temperature dependent transport behaviour. Specifically, the decrease in the |S| above 560 K and change in the slope ofσaround 450 K are due to the contribution of thermally generated charge carriers from the hole pockets. The temperature dependent relaxation time (τ) is computed by comparing the experimentalσwith calculatedσ/τand it shows temperature dependency of 1/T0.35. Further this value ofτis used to calculate the temperature dependent electronic part of thermal conductivity (κe) and it gives a fairly good match with the experiment. Present study suggests that electronic band-structure obtained from DFT provides a reasonably good estimate of the transport coefficients of CoSi in the high temperature region of 300-800 K.

Exploring temperature dependent electron-electron interaction of rocksalt SnS and SnSe within Matsubara-time domain.

Both experimental and theoretical studies show non-trivial topological behaviour in native rocksalt phase for SnS and SnSe and categorize these materials in topological crystalline insulators. Here, the detailed electronic structures studies of SnS and SnSe in the rocksalt phase are carried out using many-bodyGWbased theory and density functional theory both for ground states and temperature dependent excited states. The estimated values of fundamental direct bandgaps aroundL-point usingG0W0(mBJ) are ∼0.27 (∼0.13) eV and ∼0.37 (∼0.17) eV for SnS and SnSe, respectively. The strength of hybridization between Sn 5pand S 3p(Se 4p) orbitals for SnS (SnSe) shows strongk-dependence. The behaviour ofW¯(ω), which is the averaged value of diagonal matrix elements of fully screened Coulomb interaction, suggests to use full-GWmethod for exploring the excited states because the correlation effects within these two materials are relatively weak. The temperature dependent electronic structure calculations for SnS and SnSe provide linearly decreasing behaviour of bandgaps with rise in temperatures. The existence of collective excitation of quasiparticles in form of plasmon is predicted for these compounds, where the estimated values of plasmon frequency are ∼9.5 eV and ∼9.3 eV for SnS and SnSe, respectively. The imaginary part of self-energy and mass renormalization factor (Zk(ω)) due to electron-electron interaction (EEI) are also calculated alongW-L-Γ direction for both the materials, where the estimated ranges ofZk(ω) are 0.70 to 0.79 and 0.71 to 0.78 for SnS and SnSe, respectively, along thisk-direction. The present comparative study reveals that the behaviour of temperature dependent EEI for SnS and SnSe are the almost same and EEI is important for high temperature transport properties.

Understanding the Seebeck coefficient of LaNiO3compound in the temperature range 300-620 K.

Transition metal oxides have been attracted much attention in thermoelectric community from the last few decades. In the present work, we have synthesized LaNiO3by a simple solution combustion process. To analyse the crystal structure and structural parameters we have used Rietveld refinement method wherein FullProf software is employed. The room temperature x-ray diffraction indicates the rhombohedral structure with space groupR3¯c(No. 167). The refined values of lattice parameters area=b=c= 5.4071 Å. Temperature dependent Seebeck coefficient (S) of this compound has been investigated by using experimental and computational tools. The measurement ofSis conducted in the temperature range 300-620 K. The measured values ofSin the entire temperature range have negative sign that indicates n-type character of the compound. The value ofSis found to be ∼-8µV/K at 300 K and at 620 K this value is ∼-12µV/K. The electronic structure calculation is carried out using DFT +Umethod due to having strong correlation in LaNiO3. The calculation predicts the metallic ground state of the compound. Temperature dependentSis calculated using BoltzTraP package and compared with experiment. The best matching between experimental and calculated values ofSis observed when self-interaction correction is employed as double counting correction in spin-polarized DFT +U(=1 eV) calculation. Based on the computational results maximum power factors are also calculated for p-type and n-type doping of this compound.

Anab initiostudy of topological and transport properties of YAuPb.

In the last few decades, the study of topological materials has been carried out on an extensive scale. Half-Heusler alloys are well known for their topological behaviours. In this work, we present a detailed study of topological properties of a ternary half-Heusler alloy, YAuPb, using the tight-binding approach. We have calculated some important topological properties which includes-finding nodes and their chiralities, Berry curvature (Ω) and the surface-states. Five pairs of characteristic nodes with equal and opposite chiralities are obtained. Based on the study of these properties, we categorise the material as non-trivial topological semimetal. Besides the topological behaviours, we present a comparative study of temperature dependent transport properties corresponding to the chemical potential (µ) of the Fermi level and the node points. The temperature range chosen for the study is 50-300 K. The results obtained from the calculations of electrical conductivity per unit relaxation time (σ/τ) and the electronic part of thermal conductivity per unit relaxation time (κ0) indicates the conducting nature of the material to both the heat and electricity. At the Fermi level, the value of Seebeck coefficient (S) is found to be ∼-9.07(-35.95) µV K-1at 50(300) K. The negative value ofSindicates the n-type behaviour of the compound. The calculated value of electronic specific heat (Pauli magnetic susceptibility) corresponding to Fermi level is ∼0.03(0.18) × 10-2 J mol-1 K-1(∼1.21(1.14) × 10-10 m3 mol-1) at 50(300) K. This work suggests that YAuPb is a promising candidate of non-trivial topological semimetals which can be employed in transmission of heat and electricity, and as n-type material within the temperature range of 50-300 K.

Studying the lifetime of charge and heat carriers due to intrinsic scattering mechanisms in FeVSb half-Heusler thermoelectric.

This work, presents a study of lifetime of carriers due to intrinsic scattering mechanisms viz. electron-electron interaction (EEI), electron-phonon interaction (EPI) and phonon-phonon interaction (PPI) in a promising half-Heusler thermoelectric FeVSb. Using the full-GWmethod, the effect of EEI and temperature on the valence and conduction band extrema and band gap are studied. The lifetime of carriers with temperature are estimated at these band extrema. At 300 K, estimated value of lifetime at VBM (CBM) is ∼1.91 × 10-14 s (∼2.05 × 10-14 s). The estimated ground state band gap considering EEI is ∼378 meV. Next, the effect of EPI on the lifetime of electrons and phonons with temperature are discussed. The comparison of two electron lifetimes suggests that EEI should be considered in transport calculations along with EPI. The average acoustic, optical and overall phonon lifetimes due to EPI are studied with temperature. Further, the effect of PPI is studied by computing average phonon lifetime for acoustic and optical phonon branches. The lifetime of the acoustic phonons are higher compared to optical phonons which indicates acoustic phonons contribute more to lattice thermal conductivity (κph). The comparison of phonon lifetime due to EPI and PPI suggests that, above 500 K EPI is the dominant phonon scattering mechanism and cannot be ignored inκphcalculations. Lastly, a prediction of the power factor and figure of merit of n-type and p-type FeVSb is made by considering the temperature dependent carrier lifetime for the electronic transport terms. This study shows the importance of considering EEI in electronic transport calculations and EPI in phonon transport calculations in FeVSb. Our study is expected to provide results to further explore the thermoelectric transport in this material.

Investigating the effect of temperature dependent many-body interactions on electronic structures of SnTe in the Matsubara-time domain.

Recently, SnTe has gained attention due to its non-trivial topological nature and eco-friendly thermoelectric applications. We report a detailed temperature dependent electronic structure of this compound using DFT andGWmethods. The calculated values of bandgaps by using PBEsol andG0W0methods are found to be in good agreement with the experiment, whereas mBJ underestimates the bandgap. The averaged value of diagonal matrix elements of fully screened Coulomb interaction (W̄) atω= 0 eV for Sn (Te) 5porbitals is ∼1.39 (∼1.70) eV. The nature of frequency dependentW̄(ω)reveals that the correlation strength of this compound is relatively weaker and hence the excited electronic state can be properly studied by full-GWmany-body technique. The plasmon excitation is found to be important in understanding this frequency dependentW̄(ω). The temperature dependent electron-electron interactions (EEI) reduces the bandgaps with increasing temperature. The value of bandgap at 300 K is obtained to be ∼161 meV. The temperature dependent lifetimes of electronic state alongW-L-Γ direction are also estimated. This work suggests that EEI is important to explain the high temperature transport behaviour of SnTe.

First-principles electronic structure, phonon properties, lattice thermal conductivity and prediction of figure of merit of FeVSb half-Heusler.

In this work, we have studied the electronic structure of a promising thermoelectric half-Heusler FeVSb using FP-LAPW method and SCAN meta-GGA including spin-orbit coupling. Using the obtained electronic structure and transport calculations we try to address the experimental Seebeck coefficient S of FeVSb samples. The good agreement between the experimental and calculated S suggests the band gap could be ∼0.7 eV. This is supported by the obtained mBJ band gap of ∼0.7 eV. Further, we study and report the phonon dispersion, density of states and thermodynamic properties. The effect of long range Coulomb interactions on phonon frequencies are also included by nonanalytical term correction. Under quasi-harmonic approximation, the thermal expansion behaviour up to 1200 K is calculated. Using the first-principles anharmonic phonon calculations, the lattice thermal conductivity κ ph of FeVSb is obtained under single-mode relaxation time approximation considering the phonon-phonon interaction. At 300 K, the calculated κ ph is ∼18.6 W m-1 K-1 which is higher compared to experimental value. But, above 500 K the calculated κ ph is in good agreement with experiment. A prediction of figure of merit ZT and efficiency for p-type and n-type FeVSb is made by finding out optimal carrier concentration. At 1200 K, a maximum ZT of ∼0.66 and ∼0.44 is expected for p-type and n-type FeVSb, respectively. For p-type and n-type materials, maximum efficiency of ∼12.2% and ∼6.0% are estimated for hot and cold temperature of 1200 K and 300 K, respectively. A possibility of achieving n-type and p-type FeVSb by elemental doping/vacancy is also discussed. Our study is expected to help in further exploring the thermoelectric material FeVSb.

Thermoelectric properties, efficiency and thermal expansion of ZrNiSn half-Heusler by first-principles calculations.

In this work, we try to understand the experimental thermoelectric (TE) properties of a ZrNiSn sample with DFT and semiclassical transport calculations using SCAN functional. SCAN and mBJ provide the same band gap E g of ∼0.54 eV. This E g is found to be inadequate to explain the experimental data. The better explanation of experimental Seebeck coefficient S is done by considering E g of 0.18 eV which suggests the non-stoichiometry and/or disorder in the sample. In the calculation of S and other TE properties temperature dependence on chemical potential is included. In order to look for the possible enhanced TE properties obtainable in ZrNiSn with E g of ∼0.54 eV, power factor and optimal carrier concentrations are calculated. The optimal electron and hole concentrations required to attain highest power factors are ∼7.6 × 1019 cm-3 and ∼1.5 × 1021 cm-3, respectively. The maximum figure of merit ZT calculated at 1200 K for n-type and p-type ZrNiSn are ∼0.5 and ∼0.6, respectively. The % efficiency obtained for n-type ZrNiSn is ∼4.2% while for p-type ZrNiSn is ∼5.1%. The ZT are expected to be further enhanced to ∼1.1 (n-type) and ∼1.2 (p-type) at 1200 K by doping with heavy elements for thermal conductivity reduction. The phonon properties are also studied by calculating dispersion, total and partial density of states. The calculated Debye temperature of 382 K is in good agreement with experimental value of 398 K. The thermal expansion behaviour in ZrNiSn is studied under quasi-harmonic approximation. The average linear thermal expansion coefficient α ave(T) of ∼7.8 × 10-6 K-1 calculated in our work is quite close to the experimental values. The calculated linear thermal expansion coefficient will be useful in designing the thermoelectric generators for high temperature applications.

Two functionals approach in DFT for the prediction of thermoelectric properties of Fe2ScX (X = P, As, Sb) full-Heusler compounds.

In the quest for new thermoelectric materials with high power factors, full-Heusler compounds having flat band are found to be promising candidates. In this direction, Fe2ScX (X = P,As,Sb) compounds are investigated using mBJ for the band gap and SCAN to describe the electronic bands and phonon properties for thermoelectric applications. The band gaps obtained from mBJ are 0.81 eV, 0.69 eV and 0.60 eV for Fe2ScX compounds. The phonon dispersion, phonon density of states (DOS) and partial DOS are calculated. The phonon contributions to specific heat are obtained as a function of temperature under harmonic approximation. The electronic band structutre calculated from mBJ and SCAN functionals are qualitatively compared. The effective mass values are calculated at the band extrema from SCAN functional. The thermoelectric parameters are calculated for both hole and electron dopings under semiclassical theory. We use a simple, but reasonable method to estimate the phonon relaxation time ([Formula: see text]). Using the specific heat, estimated [Formula: see text] and slopes (phase velocity) of acoustic branches in the linear region, lattice thermal conductivity ([Formula: see text]) at 300 K is calculated for three compounds. The obtained values of [Formula: see text] with constant [Formula: see text] are 18.2, 13.6 and 10.3 Wm-1 K-1, respectively. Finally, the temperature dependent figure of merit ZT values are calculated for optimal carrier concentrations in the doping range considered, to evaluate the materials for thermoelectric application. The ZT values for n-type Fe2ScX, in 900-1200 K, are 0.34-0.43, 0.40-0.48 and 0.45-0.52, respectively. While, the p-type Fe2ScX have ZT values of 0.25-0.34, 0.20-0.28 and 0.18-0.26, respectively in the same temperature range. The ZT values suggest that, Fe2ScX compounds can be promising materials in high temperature power generation application on successful synthesis and further [Formula: see text] reduction by methods like nanostructuring.

Effects of correlations and temperature on the electronic structures and related physical properties of FeSi and CoSi: a comprehensive study.

Here, we report detailed investigations of the temperature dependent (100-800 K) electronic structures of FeSi and CoSi by using a DFT+DMFT method where self-consistently calculated values of U and J are used. The calculated spectral functions are found to provide fairly good representation for the experimentally observed photoemission spectra for both the compounds. For FeSi, the density of states (DOS) closer to the Fermi level are found to increase with the increase in temperature up to 450 K and then they decrease, whereas, for CoSi DOS continuously decrease with an increase in temperature. The electronic states of FeSi are greatly influenced by electronic correlations while they are moderately influenced in CoSi. From momentum resolved spectral functions, the excitations have shown enhanced broadening with temperature rise in FeSi whereas an opposite behavior is observed in CoSi. In FeSi, the maximum effect of temperature on the lifetime of [Formula: see text] quasiparticles states is observed where it first decreases to 400 K and then increases, and finally becomes almost infinite at 800 K. The temperature dependent behavior of DOS and quasiparticle lifetime help us in understanding the experimentally observed electrical resistivity and Seebeck coefficient for these compounds. The calculated effective magnetic moment [Formula: see text] for Fe (∼2.5 [Formula: see text], which is closer to the experimental value) is temperature independent. The electronic structures of these compounds are showing the existence of mixed configurations with [Formula: see text] and [Formula: see text] for FeSi and CoSi, respectively. Average electrons in the d orbitals are found as ∼6.5 and ∼7.7 for FeSi and CoSi, respectively, with charge fluctuations [Formula: see text] 0.9 are obtained for both materials. This suggests that both the compounds are lying in the intermediate coupling regime of electronic correlations.

An important role of temperature dependent scattering time in understanding the high temperature thermoelectric behavior of strongly correlated system: La0.75Ba0.25CoO3.

In the present work, we report the temperature dependent thermopower (α) behavior of La0.75Ba0.25CoO3 compound in the temperature range 300-600 K. Using the Heikes formula, the estimated value of α corresponding to high-spin configuration of Co3+ and Co4+ ions is found to be ∼16 [Formula: see text], which is close to the experimental value, ∼13 [Formula: see text], observed at ∼600 K. The temperature dependent TE behavior of the compound is studied by combining the WIEN2K and BoltzTrap code. The self consistency field calculations show that the compound have ferromagnetic ground state structure. The electronic structure calculations give half metallic characteristic with a small gap of ∼50 meV for down spin channel. The large and positive value for down spin channel is obtained due to the unique band structure shown by this spin channel. The temperature dependent relaxation time for both the spin-channel charge carriers is considered to study the thermopower data in temperature range 300-600 K. For evaluation of α, almost linear values of [Formula: see text] and a non-linear values of [Formula: see text] are taken into account. By taking the temperature dependent values of relaxation time for both the spin channels, the calculated values of α using two current model are found to be in good agreement with experimental values in the temperature range 300-600 K. At 300 K, the calculated value of electrical conductivity by using the same value of relaxation time, i.e. 0.1 [Formula: see text] 10-14 seconds for spin-up and [Formula: see text] seconds for spin-dn channel, is found to be equal to the experimentally reported value.

Fabrication of setup for high temperature thermal conductivity measurement.

In this work, we report the fabrication of an experimental setup for high temperature thermal conductivity (κ) measurement. It can characterize samples with various dimensions and shapes. Steady state based axial heat flow technique is used for κ measurement. Heat loss is measured using parallel thermal conductance technique. Simple design, lightweight, and small size sample holder is developed by using a thin heater and limited components. Low heat loss value is achieved by using very low thermal conductive insulator block with small cross-sectional area. Power delivered to the heater is measured accurately by using 4-wire technique and for this, the heater is developed with 4 wires. This setup is validated by using Bi0.36Sb1.45Te3, polycrystalline bismuth, gadolinium, and alumina samples. The data obtained for these samples are found to be in good agreement with the reported data. The maximum deviation of 6% in the value κ is observed. This maximum deviation is observed with the gadolinium sample. We also report the thermal conductivity of polycrystalline tellurium from 320 K to 550 K and the nonmonotonous behavior of κ with temperature is observed.

Electronic structure of Mo1-x Re x alloys studied through resonant photoemission spectroscopy.

We studied the electronic structure of Mo-rich Mo1-x Re x alloys ([Formula: see text]) using valence band photoemission spectroscopy in the photon energy range 23-70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to -6 eV, whereas s states lie in the binding energy range -4 to -10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p-5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p-4d transition (threshold: 42 eV) and the Re 5p-5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE = 0) to -5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x > 0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1-x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s-d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x.

Emissions of amides (N,N-dimethylformamide and formamide) and other obnoxious volatile organic compounds from different mattress textile products.

The emission rates of N,N-dimethylformamide (DMF), formamide (FAd), and certain hazardous volatile organic compounds (VOCs) were measured from seventeen mattress textile samples with four different raw material types: polyurethane (PU: n=3), polyester/polyethylene (PE: n=7), ethylene vinyl acetate (EV: n=3), and polyvinyl chloride (PC: n=4). To simulate the emissions in a heated room during winter season, measurements were made under temperature-controlled conditions, i.e., 50°C by using a mini-chamber system made of a midget impinger. Comparison of the data indicates that the patterns were greatly distinguished between DMF and FAd. PU products yielded the highest mean emission rates of DMF (2940 µg m(-2)h(-1): n=3) followed by PE (325 µg m(-2)h(-1): n=7), although its emission was not seen from other materials (EV and PC). In contrast, the pattern of FAd emission was moderately reversed from that of DMF: EV>PC>PE>PU. The results of our analysis confirm that most materials used for mattress production have the strong potential to emit either DMF or FAd in relatively large quantities while in use in children׳s care facilities, especially in winter months. Moreover, it was also observed that an increase in temperature (25°C to 50°C) had a significant impact on the emission rate of FAd and other hazardous VOCs. In addition to the aforementioned amides, the study revealed significant emissions of a number of hazardous VOCs, such as aromatic and carbonyl compounds.