Showing papers on "Atmospheric temperature range published in 2015"
TL;DR: In this article, the photoluminescence, transmittance, charge-carrier recombination dynamics, mobility, and diffusion length of CH3NH3PbI3 were investigated in the temperature range from 8 to 370 K.
Abstract: The photoluminescence, transmittance, charge-carrier recombination dynamics, mobility, and diffusion length of CH3NH3PbI3 are investigated in the temperature range from 8 to 370 K. Profound changes in the optoelectronic properties of this prototypical photovoltaic material are observed across the two structural phase transitions occurring at 160 and 310 K. Drude-like terahertz photoconductivity spectra at all temperatures above 80 K suggest that charge localization effects are absent in this range. The monomolecular charge-carrier recombination rate generally increases with rising temperature, indicating a mechanism dominated by ionized impurity mediated recombination. Deduced activation energies Ea associated with ionization are found to increase markedly from the room-temperature tetragonal (Ea ≈ 20 meV) to the higher-temperature cubic (Ea ≈ 200 meV) phase adopted above 310 K. Conversely, the bimolecular rate constant decreases with rising temperature as charge-carrier mobility declines, while the Auger rate constant is highly phase specific, suggesting a strong dependence on electronic band structure. The charge-carrier diffusion length gradually decreases with rising temperature from about 3 μm at -93 °C to 1.2 μm at 67 °C but remains well above the optical absorption depth in the visible spectrum. These results demonstrate that there are no fundamental obstacles to the operation of cells based on CH3NH3PbI3 under typical field conditions. The photoconductivity in CH3NH3PbI3 thin films is investigated from 8 to 370 K across three structural phases. Analysis of the charge-carrier recombination dynamics reveals a variety of starkly differing recombination mechanisms. Evidence of charge-carrier localization is observed only at low temperature. High charge mobility and diffusion length are maintained at high temperature beyond the tetragonal-to-cubic phase transition at ≈310 K.
778 citations
TL;DR: The results show that employing a mixture of MAI and FAI in films deposited via a two-step approach, where the MAI content is <20%, results in the exchange of FA molecules with MA without any significant lattice shrinkage, and with temperature-dependent X-ray diffraction that the trigonal phase exhibits no phase changes in the temperature range studied.
Abstract: Formamidinium lead iodide (FAPbI3) has the potential to achieve higher performance than established perovskite solar cells like methylammonium lead iodide (MAPbI3), while maintaining a higher stability. The major drawback for the latter material is that it can crystallize at room temperature in a wide bandgap hexagonal symmetry (P63mc) instead of the desired trigonal (P3m1) black phase formed at a higher temperature (130 °C). Our results show that employing a mixture of MAI and FAI in films deposited via a two-step approach, where the MAI content is <20%, results in the exchange of FA molecules with MA without any significant lattice shrinkage. Additionally, we show with temperature-dependent X-ray diffraction that the trigonal phase exhibits no phase changes in the temperature range studied (25 to 250 °C). We attribute the stabilization of the structure to stronger interactions between the MA cation and the inorganic cage. Finally, we show that the inclusion of this small amount of MA also has a positive...
456 citations
TL;DR: In this paper, the thermal conductivities of β-Ga2O3 single crystals along four different crystal directions were measured in the temperature range of 80 −495 K using the time domain thermoreflectance method.
Abstract: The thermal conductivities of β-Ga2O3 single crystals along four different crystal directions were measured in the temperature range of 80–495 K using the time domain thermoreflectance method. A large anisotropy was found. At room temperature, the [010] direction has the highest thermal conductivity of 27.0 ± 2.0 W/mK, while that along the [100] direction has the lowest value of 10.9 ± 1.0 W/mK. At high temperatures, the thermal conductivity follows a ∼1/T relationship characteristic of Umklapp phonon scattering, indicating phonon-dominated heat transport in the β-Ga2O3 crystal. The measured experimental thermal conductivity is supported by first-principles calculations, which suggest that the anisotropy in thermal conductivity is due to the differences of the speed of sound along different crystal directions.
350 citations
TL;DR: The formation and modification of the surface films on the electrodes as well as structural/phase changes of the LCO electrode are found to be the main contributors to the increasing degradation rate of the maximum charge storage of LiB with temperature for the specific operating temperature range.
Abstract: Temperature is known to have a significant impact on the performance, safety and cycle lifetime of lithium-ion batteries (LiB). However, the comprehensive effects of temperature on the cyclic aging rate of LiB have yet to be found. We use an electrochemistry-based model (ECBE) here to measure the effects on the aging behavior of cycled LiB operating within the temperature range of 25 °C to 55 °C. The increasing degradation rate of the maximum charge storage of LiB during cycling at elevated temperature is found to relate mainly to the degradations at the electrodes and that the degradation of LCO cathode is larger than graphite anode at elevated temperature. In particular, the formation and modification of the surface films on the electrodes as well as structural/phase changes of the LCO electrode, as reported in the literatures, are found to be the main contributors to the increasing degradation rate of the maximum charge storage of LiB with temperature for the specific operating temperature range. Larger increases in the Warburg elements and cell impedance are also found with cycling at higher temperature, but they do not seriously affect the state of health (SoH) of LiB as shown in this work.
325 citations
TL;DR: In this paper, the authors measured the temperature dependencies of elastic moduli and thermal expansion coefficient of the CoCrFeMnNi alloy over a large temperature range (200 −1270 K).
316 citations
TL;DR: In this article, X-ray fluorescence analysis and dielectric properties analysis indicate that rhombohedral polar phase and tetragonal weakly polar phase coexist in BNTBT-xNN ceramics at room temperature.
Abstract: (1 − x)BNTBT-xNN ceramics were prepared by conventional solid state reaction method. X-ray fluorescence analysis shows that the volatilization of Na element occurs during sintering process, the resulted concentration variation of V ′ Na − V O − V ′ Na defect dipoles facilitate the grain growth. XRD analysis and dielectric properties analysis indicate that rhombohedral polar phase and tetragonal weakly polar phase coexist in BNTBT ceramics at room temperature. By increasing the NN amount, the rhombohedral polar phase content sharply decreases, leading to a smaller remnant polarization. The dielectric anomaly corresponding to the depolarization temperature disappears from the temperature range investigated. According to the XRD results, the amount of tetragonal weakly polar phase decreases with increasing NN content and the structure evolves toward a pseudocubic symmetry. The phase structure change results in more slim P–E loops. The optimum energy storage properties was obtained for the composition of x = 0.10, with energy storage density of 0.71 J/cm3 at 7 kV/mm and a good temperature stability around 25–150 °C.
257 citations
TL;DR: In this paper, the thermal conductivity and thermal diffusivity of the solid/liquid phase change linear n-alkanes were measured simultaneously by the transient multi-current hot wire technique at atmospheric pressure in the range 258-348 K. The same set-up was used to measure the liquid and the solid states at different electrical currents.
224 citations
TL;DR: This work shows imidazole loaded tetrahedral polyimides with mesopores and good stability exhibiting a high anhydrous proton conductivity over a wide temperature range from -40 to 90 °C.
Abstract: On-board fuel cell technology requires proton conducting materials with high conductivity not only at intermediate temperatures for work but also at room temperature and even at subzero temperature for startup when exposed to the colder climate. To develop such materials is still challenging because many promising candidates for the proton transport on the basis of extended microstructures of water molecules suffer from significant damage by heat at temperatures above 80 °C or by freeze below -5 °C. Here we show imidazole loaded tetrahedral polyimides with mesopores and good stability (Im@Td-PNDI 1 and Im@Td-PPI 2) exhibiting a high anhydrous proton conductivity over a wide temperature range from -40 to 90 °C. Among all anhydrous proton conductors, the conductivity of 2 is the highest at temperatures below 40 °C and comparable with the best materials, His@[Al(OH)(1,4-ndc)]n and [Zn3(H2PO4)6(H2O)3](Hbim), above 40 °C.
215 citations
TL;DR: In this paper, the dielectric properties and electrical hysteresis behaviors of Pb0.97La0.02(Zr0.58Sn0.335Ti0.085)O3 antiferroelectric (AFE) ceramics were investigated with an emphasis on energy storage properties.
Abstract: The dielectric properties and electrical hysteresis behaviors of Pb0.97La0.02(Zr0.58Sn0.335Ti0.085)O3 antiferroelectric (AFE) ceramics were investigated in this work with an emphasis on energy storage properties. Three phase transition points can be detected as temperature increases. AFE and paraelectric phases are found to coexist from 100 °C to 170 °C. The room temperature recoverable energy density is 1.37 J/cm3 at 8.6 kV/mm. With increasing temperature (from 20 °C to 100 °C) and frequency (from 0.01 to 100 Hz) under 8.6 kV/mm, the variation of recoverable energy density was less than 15%, all higher than 1.2 J/cm3. All the corresponding energy efficiencies were no less than 75%. The high energy density, high energy efficiency, and their weak dependence on temperature and frequency during a wide scope indicate that these antiferroelectric ceramics are quite promising to be used for pulse power capacitors applications.
208 citations
TL;DR: In this article, the temperature dependence of permittivity in 0.88BaTiO 3 −0.12BMT (0.88BT-0. 12BMT) ceramics was investigated and the maximum energy storage density of 1.81 J/cm 2 was obtained at room temperature.
202 citations
TL;DR: In this paper, the authors investigated the variation of the photoconductive response with temperature in solution-processed films of methylammonium lead iodide perovskite.
Abstract: The nature of the photoconductivity in solution-processed films of methylammonium lead iodide perovskite is investigated by determining the variation of the photoconductive response with temperature. Ultrabroadband terahertz (THz) photoconductivity spectra in the 0.3–10 THz range can be reproduced well by a simple Drude-like response at room temperature, where free charge carrier motion is characterized by an average scattering time. The scattering time determined from Drude fits in the 0.3–2THz region increases from ∼4 fs at 300 K (tetragonal phase; mobility of ∼27 cm2 V–1 s–1) to almost ∼25 fs at 77 K (orthorhombic phase, mobility of ∼150 cm2 V–1 s–1). For the tetragonal phase (temperature range 150 < T < 300 K) the scattering time shows a ∼T–3/2 dependence, approaching the theoretical limit for pure acoustic phonon (deformation potential) scattering. Hence, electron–phonon, rather than impurity scattering, sets the upper limit on free charge transport for this perovskite.
TL;DR: In this paper, the temperature sensitivity of Er3+/Yb3+:CaMoO4 upconversion phosphor is investigated, and its temperature dependent luminescent performance is investigated.
TL;DR: The high energy storage performance was endowed by a large dielectric breakdown strength, great relaxor dispersion, highly textured orientation, and the coexistence of FE and AFE phases.
Abstract: A highly textured (111)-oriented Pb0.8Ba0.2ZrO3 (PBZ) relaxor thin film with the coexistence of antiferroelectric (AFE) and ferroelectric (FE) phases was prepared on a Pt/TiOx/SiO2/Si(100) substrate by using a sol-gel method. A large recoverable energy storage density of 40.18 J/cm(3) along with an efficiency of 64.1% was achieved at room temperature. Over a wide temperature range of 250 K (from room temperature to 523 K), the variation of the energy density is within 5%, indicating a high thermal stability. The high energy storage performance was endowed by a large dielectric breakdown strength, great relaxor dispersion, highly textured orientation, and the coexistence of FE and AFE phases. The PBZ thin film is believed to be an attractive material for applications in energy storage systems over a wide temperature range.
TL;DR: In this paper, a Si-compatible material for monolithic devices for pyroelectric energy harvesting, electrocaloric cooling, electrostatic energy storage, and infrared sensing was presented.
TL;DR: From the temperature dependence of the average normalized change (ANC), it is deduce the temperature at which the available density of trapped charge states vanishes and the presence of electrical relaxation in materials is indicated.
Abstract: This study presents the electrical properties, complex impedance analysis and dielectrical behavior of La05Ca05−xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 02) Transport measurements indicate that all the samples have a semiconductor-like behavior The metal-semiconductor transition is not observed across the whole temperature range explored [80 K–700 K] At a specific temperature, a saturation region was marked in the σ (T) curves We obtained a maximum σdc value at ambient temperature with the introduction of 20% Ag content Two hopping models were applied to study the conduction mechanism We found that activation energy (Ea) related to ac-conductivity is lower than the Ea implicated in dc-conductivity Complex impedance analysis confirms the contribution of grain boundary to conductivity and permits the attribution of grain boundary capacitance evolution to the temperature dependence of the barrier layer width From the temperature dependence of the average normalized change (ANC), we deduce the temperature at which the available density of trapped charge states vanishes Such a temperature is close to the temperature at which the saturation region appears in σ(T) curves Moreover, complex impedance analysis (CIA) indicates the presence of electrical relaxation in materials It is noteworthy that relaxation species such as defects may be responsible for electrical conduction The dielectric behavior of La05Ca05−xAgxMnO3 manganites has a Debye-like relaxation with a sharp decrease in the real part of permittivity at a frequency where the imaginary part of permittivity (e′′) and tg δ plots versus frequency demonstrate a relaxation peak The Debye-like relaxation is explained by Maxwell–Wagner (MW) polarization Experimental results are found to be in good agreement with the Smit and Wijn theory
TL;DR: A ratiometric thermometer based on a mixed-metal Ln(III) metal-organic framework is reported that has good sensitivity in a wide temperature range from 4 to 290 K and a quantum yield of 22% at room temperature.
Abstract: A ratiometric thermometer based on a mixed-metal Ln(III) metal-organic framework is reported that has good sensitivity in a wide temperature range from 4 to 290 K and a quantum yield of 22% at room temperature. The sensing mechanism in the europium-doped compound Tb0.95Eu0.05HL (H4L = 5-hydroxy-1,2,4-benzenetricarboxylic acid) is based not only on phonon-assisted energy transfer from Tb(III) to Eu(III) centers, but also on phonon-assisted energy migration between neighboring Tb(III) ions. It shows good performance in a wide temperature range, especially in the range 4-50 K, reaching a sensitivity up to 31% K(-1) at 4 K.
TL;DR: In this paper, a combined in situ high-resolution neutron powder diffraction and electrochemical study on Li-ion cells of the 18650 type over a temperature range from 230k to 320k is reported with a focus on the graphite anode and the low temperature performance of the cell.
TL;DR: In this paper, a review of recent developments in the search for dielectric ceramics which can operate at temperatures >200°C, well above the limit of existing high volumetric efficiency capacitor materials.
Abstract: Recent developments are reviewed in the search for dielectric ceramics which can operate at temperatures >200 °C, well above the limit of existing high volumetric efficiency capacitor materials. Compositional systems based on lead-free relaxor dielectrics with mixed cation site occupancy on the perovskite lattice are summarised, and properties compared. As a consequence of increased dielectric peak broadening and shifts to peak temperatures, properties can be engineered such that a plateau in relative permittivity–temperature response (er–T) is obtained, giving a ±15 %, or better, consistency in er over a wide temperature range. Materials with extended upper temperature limits of 300, 400 and indeed 500 °C are grouped in this article according to the parent component of the solid solution, for example BaTiO3 and Na0.5Bi0.5TiO3. Challenges are highlighted in achieving a lower working temperature of −55 °C, whilst also extending the upper temperature limit of stable er to ≥300 °C, and achieving high-permittivity and low values of dielectric loss tangent, tan δ. Summary tables and diagrams are used to help compare values of er, tan δ, and temperature ranges of stability for different materials.
TL;DR: It is revealed that SnSe1-xTex solid solutions are formed when x ranges from 0 to 0.2, and an energy barrier scattering mechanism is suitable for understanding the electrical conducting behaviour observed in the present SnSe polycrystalline materials, which may be associated with abundant defects at grain boundaries.
Abstract: SnSe, a "simple" and "old" binary compound composed of earth-abundant elements, has been reported to exhibit a high thermoelectric performance in single crystals, which stimulated recent interest in its polycrystalline counterparts. This work investigated the electrical and thermal transport properties of pristine and Na-doped SnSe1-xTex polycrystals prepared by mechanical alloying and spark plasma sintering. It is revealed that SnSe1-xTex solid solutions are formed when x ranges from 0 to 0.2. An energy barrier scattering mechanism is suitable for understanding the electrical conducting behaviour observed in the present SnSe polycrystalline materials, which may be associated with abundant defects at grain boundaries. The thermal conductivity was greatly reduced upon Te substitution due to alloy scattering of phonons as well explained by the Debye model. Due to the increased carrier concentration by Na-doping, thermoelectric figure of merit (ZT) was enhanced in the whole temperature range with a maximum value of 0.72 obtained at a relatively low temperature (773 K) for Sn0.99Na0.01Se0.84Te0.16.
TL;DR: The elastocaloric effect of Ni 50 Fe 19 Ga 27 Co 4 (at.%) single crystals exhibiting first-order martensitic transformations has been studied at temperatures of 298-448 K under different compressive stresses.
TL;DR: The potential of bulk black-phosphorus, a layered semiconducting material with a direct band gap of ∼0.3 eV, for thermoelectric applications has been experimentally studied in this paper.
Abstract: The potential of bulk black-phosphorus, a layered semiconducting material with a direct band gap of ∼0.3 eV, for thermoelectric applications has been experimentally studied. The Seebeck Coefficient (S) has been measured in the temperature range from 300 K to 385 K, finding a value of S = +335 ± 10 μV/K at room temperature (indicating a naturally occurring p-type conductivity). S increases with temperature, as expected for p-type semiconductors, which can be attributed to an increase of the charge carrier density. The electrical resistance drops up to a 40% while heating in the studied temperature range. As a consequence, the power factor at 385 K is 2.7 times higher than that at room temperature. This work indicates the prospective use of black-phosphorus in thermoelectric applications such as thermal energy scavenging, which typically require devices with high performance at temperatures near room temperature.
TL;DR: A new X-ray absorption fine-structure (XAFS) spectroscopy beamline for fundamental and applied catalysis research, called XAFCA, has been built by the Institute of Chemical and Engineering Sciences, and the Singapore Synchrotron Light Source.
Abstract: A new X-ray absorption fine-structure (XAFS) spectroscopy beamline for fundamental and applied catalysis research, called XAFCA, has been built by the Institute of Chemical and Engineering Sciences, and the Singapore Synchrotron Light Source. XAFCA covers the photon energy range from 1.2 to 12.8 keV, making use of two sets of monochromator crystals, an Si (111) crystal for the range from 2.1 to 12.8 keV and a KTiOPO4 crystal [KTP (011)] for the range between 1.2 and 2.8 keV. Experiments can be carried out in the temperature range from 4.2 to 1000 K and pressures up to 30 bar for catalysis research. A safety system has been incorporated, allowing the use of flammable and toxic gases such as H2 and CO.
TL;DR: In this paper, a high-quality MOF nanofilm, HKUST-1, on flexible gold-coated polyethylene terephthalate substrates is fabricated using liquid phase epitaxy approach.
Abstract: Metal-organic frameworks (MOFs), which are formed by association of metal cations or clusters of cations (“nodes”) with soft organic bridging ligands (“linkers”), are a fascinating class of flexible crystalline hybrid materials offering potential strategy for the construction of flexible electronics. In this study, a high-quality MOF nanofilm, HKUST-1, on flexible gold-coated polyethylene terephthalate substrates is fabricated using liquid phase epitaxy approach. Uniform and reproducible resistive switching effect, which can be sustained under the strain of as high as 2.8%, and over the wide temperature range of –70 to +70 °C, is observed for the first time in the all solid-state Au/HKUST-1/Au/thin film structures. Through conductive atomic force microscopic and depth-profiling X-ray photoelectron spectroscopicanalysis, it is proposed that the electric field-induced migration of the Cu2+ ions, which may lead to subsequent pyrolysis of the trimesic acid linkers and thus the formation of highly conducting filaments, could be the possible origin for the observed uniform resistance switching in HKUST-1 nanofilms.
TL;DR: In this paper, the upconversion emission intensities of Ho/Yb-codoped Ba0.77Ca0.23TiO3 ferroelectric ceramics were investigated under the excitation of 980-nm.
TL;DR: Alkyl substituents at ortho positions of peripheral phenyl groups were found to have little effect on the electronic excited states and suggest that efficient emission from 1-5 was thermally activated delayed fluorescence (TADF).
Abstract: A series of three-coordinate copper(I) complexes (LMe)CuX [X = Cl (1), Br (2), I (3)], (LEt)CuBr (4), and (LiPr)CuBr (5) [LMe = 1,2-bis[bis(2-methylphenyl)phosphino]benzene, LEt = 1,2-bis[bis(2-ethylphenyl)phosphino]benzene, and LiPr = 1,2-bis[bis(2-isopropylphenyl)phosphino]benzene] exhibit efficient blue-green emission in the solid state at ambient temperature with peak wavelengths between 473 and 517 nm. The emission quantum yields were 0.38–0.95. The emission lifetimes were measured in the temperature range of 77–295 K using a nanosecond laser technique. The temperature dependence of the emission lifetimes was explained using a model with two excited states: a singlet and a triplet state. The small energy gaps (<830 cm−1) between the two states suggest that efficient emission from 1–5 was thermally activated delayed fluorescence (TADF). Alkyl substituents at ortho positions of peripheral phenyl groups were found to have little effect on the electronic excited states. Because the origin of the emission of complexes 2, 4, and 5 was thought to be a (σ + Br)→π* transition, photoluminescence characteristics of these complexes were dominated by the diphosphine ligands. Complexes 2, 4, and 5 had similar emission properties. Complexes 1–5 had efficient green TADF in amorphous films at 293 K with maximum emission wavelengths of 508–520 nm and quantum yields of 0.61–0.71. Organic light-emitting devices that contained complexes 1–5 and exhibited TADF exhibit bright green luminescence with current efficiencies of 55.6–69.4 cd A−1 and maximum external quantum efficiencies of 18.6–22.5%.
TL;DR: Novel flower-like α-NaYb(Mn)F4:Er(3+)/Tm(3+)@NaYF4 upconversion nanoparticles (UCNPs) as luminescent nanothermometers with high sensitivity could be excellent candidates for temperature sensors.
Abstract: Novel flower-like α-NaYb(Mn)F4:Er3+/Tm3+@NaYF4 upconversion nanoparticles (UCNPs) as luminescent nanothermometers have been developed by combining liquid–solid solution hydrothermal strategy with thermal decomposition strategy. Under 980 nm excitation, they exhibit intense upconversion luminescence and temperature-dependent upconversion luminescence over a wide temperature range. The influence of temperature on “band-shape” upconversion luminescence (UCL) spectra and the intensity of emission bands are analyzed and discussed in detail. We further successfully test and verify that intensity ratios REr of 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 and RTm of 1G4 → 3H5 and 3H4 → 3H6 are sensitive to temperature, and the population of active ions follows Boltzmann-type population distribution very well. These luminescent nanothermometers could be applied over a wide temperature range from 123 to 423 K with high sensitivity, which enable them to be excellent candidates for temperature sensors.
TL;DR: In this paper, a series of experiments have been carried out to determine the thermal conductivity and viscosity of a novel nanofluid, i.e., Mg(OH)2/ethylene glycol (EG).
Abstract: A series of experiments have been carried out to determine the thermal conductivity and viscosity of a novel nanofluid, i.e., Mg(OH)2/ethylene glycol (EG). The thermal conductivity and viscosity of nanofluids with volume fractions by 2 % in the temperature range of 25–55 °C are measured. The results unfold that in the temperature of 35 °C, called critical temperature, the ratio of nanofluid viscosity to water viscosity is minimized. This critical temperature reveals that it is more advantageous to use Mg(OH)2/EG nanofluids instead of water at temperatures higher than 35 °C from the pressure drop and pumping power viewpoint.
TL;DR: Rietveld powder XRD pattern and electron probe microanalysis revealed that all the Mn substituted samples showed a single tetrahedrite phase, and the electrical resistivity increased with increasing Mn due to substitution of Mn(2+) at the Cu(1+) site, while the thermal conductivity decreased as a function of increasing Mn.
Abstract: Tetrahedrite compounds Cu12-xMnxSb4S13 (0 <= x <= 1.8) were prepared by solid state synthesis. A detailed crystal structure analysis of Cu10.6Mn1.4Sb4S13 was performed by single crystal X-ray diffraction (XRD) at 100, 200 and 300 K confirming the noncentrosymmetric structure (space group I (4) over bar 3m) of a tetrahedrite. The large atomic displacement parameter of the Cu2 atoms was described by splitting the 12e site into a partially and randomly occupied 24g site (Cu22) in addition to the regular 12e site (Cu21), suggesting a mix of dynamic and static off-plane Cu2 atom disorder. Rietveld powder XRD pattern and electron probe microanalysis revealed that all the Mn substituted samples showed a single tetrahedrite phase. The electrical resistivity increased with increasing Mn due to substitution of Mn2+ at the Cu1+ site. The positive Seebeck coefficient for all samples indicates that the dominant carriers are holes. Even though the thermal conductivity decreased as a function of increasing Mn, the thermoelectric figure of merit ZT decreased, because the decrease of the power factor is stronger than the decrease of the thermal conductivity. The maximum ZT = 0.76 at 623 K is obtained for Cu12Sb4S13. The coefficient of thermal expansion 13.5 +/- 0.1 x 10(-6) K-1 is obtained in the temperature range from 460 K to 670 K for Cu10.2Mn1.8Sb4S13. The Debye temperature, Theta(D) = 244 K for Cu10.2Mn1.8Sb4S13, was estimated from an evaluation of the elastic properties. The effective paramagnetic moment 7.45 mu(B)/f.u. for Cu10.2Mn1.8Sb4S13 is fairly consistent with a high spin 3d(5) ground state of Mn.
TL;DR: In this paper, a blackbody radiator was fabricated via EBM and was used as a tool to determine the emissivity of Ti-6Al-4V (determined to be 0.26 in the temperature range of the current study).
Abstract: Additive manufacturing (AM) has several possible advantages over traditional manufacturing including increased design freedom, reduced material usage, and shorter lead-times. A noteworthy capability of AM is the ability to monitor the process during material deposition and interrupt the process during fabrication if necessary. Recently, such monitoring, feedback, and control have been made possible by implementing in situ infrared (IR) thermography in powder bed fusion AM technologies. The purpose of the current research was to investigate the acquisition of absolute surface temperatures using in situ IR imaging of the melted or solid surfaces layer-by-layer during fabrication within an electron beam melting (EBM) system. The thermal camera was synchronized with the system's signal voltages of three synchronized events (pre-heating, melting, and raking) to automatically capture images. To acquire absolute temperature values from the IR images, a calibration procedure was established to determine the solid material's emissivity and reflected temperature or mean radiant temperature of the build chamber, which are necessary input parameters for the IR camera. A blackbody radiator was fabricated via EBM and was used as a tool to determine the emissivity of Ti–6Al–4V (determined to be 0.26 in the temperature range of the current study). Furthermore, a mathematical model was developed to determine the view factors associated with the system's interior (e.g. heat shielding) that were used in calculating the mean radiant temperature of the manufacturing environment (∼342 °C). Experimental validation of the model was performed using a thermocouple embedded during fabrication that showed a 3.77% difference in temperature. A temperature difference of ∼366 °C (1038 °C vs . 672 °C) was observed when comparing uncorrected IR temperature data with corrected temperature data. Upon validation of the IR parameters for a melted area, experimentation was conducted to also determine powder emissivity (found to be 0.50). The thermal model presented here can be modified and implemented in other AM technologies for consideration of radiation energy to acquire absolute temperatures of layered surfaces, leading to improved thermal monitoring and control of the fabrication process.
TL;DR: A new potential model is introduced that is able to describe the thermal expansion and elastic properties of ceria to give excellent agreement with experimental data on the activation energy of oxygen migration in the temperature range 900–1900 K for both unstrained and rare-earth doped ceria systems under tensile strain.
Abstract: Doped ceria is an important electrolyte for solid oxide fuel cell applications. Molecular dynamics simulations have been used to investigate the impact of uniaxial strain along the directions and rare-earth doping (Yb, Er, Ho, Dy, Gd, Sm, Nd and La) on oxygen diffusion. We introduce a new potential model that is able to describe the thermal expansion and elastic properties of ceria to give excellent agreement with experimental data. We calculate the activation energy of oxygen migration in the temperature range 900–1900 K for both unstrained and rare-earth doped ceria systems under tensile strain. Uniaxial strain has a considerable effect in lowering the activation energies of oxygen migration. A more pronounced increase in oxygen diffusivities is predicted at the lower end of the temperature range for all the dopants considered.