Showing papers on "Atmospheric temperature range published in 2018"

Deep defect level engineering: a strategy of optimizing the carrier concentration for high thermoelectric performance

Abstract: Thermoelectric properties are heavily dependent on the carrier concentration, and therefore the optimization of carrier concentration plays a central role in achieving high thermoelectric performance. The optimized carrier concentration is highly temperature-dependent and could even possibly vary within one order of magnitude in the temperature range of several hundreds of Kelvin. Practically, however, the traditional doping strategy will only lead to a constant carrier concentration, and thus the thermoelectric performance is only optimized within a limited temperature range. Here, we demonstrate that a temperature-dependent carrier concentration can be realized by simultaneously introducing shallow and deep defect levels. In this work, iodine (I) and indium (In) are co-doped in PbTe, where iodine acts as the shallow donor level that supplies sufficient electrons and indium builds up the localized half-filled deep defect state in the band gap. The indium deep defect state traps electrons at a lower temperature and the trapped electrons will be thermally activated back to the conduction band when the temperature rises. In this way, the carrier concentration can be engineered as temperature-dependent, which matches the theoretically predicted optimized carrier concentration over the whole temperature range. As a result, a room temperature ZT of ∼0.4 and a peak ZT of ∼1.4 at 773 K were obtained in the n-type In/I co-doped PbTe, leading to a record-high average ZT of ∼1.04 in the temperature range of 300 to 773 K. Importantly, since deep defect levels also exist in other materials, the strategy of deep defect level engineering should be widely applicable to a variety of materials for enhancing the thermoelectric performance across a broad temperature range.

Lightweight and High-Performance Microwave Absorbing Heteroatom-Doped Carbon Derived from Chicken Feather Fibers

Abstract: Doped material is an innovation in developing the lightweight microwave absorbing material. Herein, heteroatom-doped carbon is synthesized by pyrolysis of chicken feather fibers (CFFs) in the temperature range of 400–1400 °C. The synthesis method exhibits that poultry waste is more nature-friendly as no external hazardous dopants are used during pyrolysis, and it has a much lower cost. The morphology and structural characteristics have been studied via SEM, AFM, TEM, XRD, Raman, and XPS. The density of surface chemical states, defects, roughness, and structural property are found to vary significantly with pyrolysis temperature. The electromagnetic properties of CFF/epoxy composites have been studied in the frequency range of 8.2–12.4 GHz (X band). In addition, the correlations between pyrolysis temperature and absorption properties are established. High absorption properties at temperature ≥800 °C are attributed to the large fraction of heteroatoms, defects, surface roughness, and high porosity. In addit...

Boosting the thermoelectric performance of PbSe through dynamic doping and hierarchical phonon scattering

Abstract: Here we find the peculiar behavior of Cu ions in the PbSe–Cu system increases its thermoelectric performance. For the electrical transport, a dynamic doping effect is achieved because more Cu ions enter into the PbSe lattice and provide extra charge carriers as the temperature increases, which guarantees an optimized carrier concentration over a wide temperature range. For the thermal transport, the presence of Cu2Se nanoprecipitates and dislocations at a low temperature range as well as the vibration of Cu atoms around the interstitial sites of PbSe at high temperatures result in hierarchical phonon scattering and a significantly reduced lattice thermal conductivity over the whole temperature range. As a result, a peak thermoelectric material figure of merit zT of up to 1.45 and a thermoelectric device figure of merit ZT close to unity are obtained for the sample with 0.375 at% Cu. Furthermore, enhanced thermoelectric properties are also realized for the Cu-intercalated PbS, implying that the temperature-driven dynamic behavior of Cu ions in a rigid lattice can serve as a general strategy to optimize the thermoelectric performance of IV–VI compounds.

Thermal Transport and Phonon Hydrodynamics in Strontium Titanate.

Abstract: We present a study of thermal conductivity, κ, in undoped and doped strontium titanate in a wide temperature range (2-400 K) and detecting different regimes of heat flow In undoped SrTiO_{3}, κ evolves faster than cubic with temperature below its peak and in a narrow temperature window Such behavior, previously observed in a handful of solids, has been attributed to a Poiseuille flow of phonons, expected to arise when momentum-conserving scattering events outweigh momentum-degrading ones The effect disappears in the presence of dopants In SrTi_{1-x}Nb_{x}O_{3}, a significant reduction in lattice thermal conductivity starts below the temperature at which the average inter-dopant distance and the thermal wavelength of acoustic phonons become comparable In the high-temperature regime, thermal diffusivity becomes proportional to the inverse of temperature, with a prefactor set by sound velocity and Planckian time (τ_{p}=(ℏ/k_{B}T))

Oxidation mechanism of thin Cu films: A gateway towards the formation of single oxide phase

Abstract: Controlled thermal oxidations of thin copper films at relatively lower temperatures (up to 500°C) leading towards the formation of a single phase of copper oxide are investigated where the oxidation temperature, duration, oxygen partial pressure, film thickness and the crystallographic orientations play very crucial roles to significantly control the final phase of the copper oxide. Thin Cu films of thicknesses 100-1000 nm were deposited on glass and silicon substrates using the vacuum assisted thermal evaporation technique. Oxidations of those Cu films were performed at different temperatures for variable durations in air ambient as well as oxygen ambient conditions. Four probe resistivity measurement, x-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM) and x-ray photoemission spectroscopy (XPS) techniques have been used to characterize the oxide films. At a thermodynamic equilibrium, it has been observed that the oxide phase is solely determined by the oxidation temperature, however, the oxygen partial pressure can significantly alter this temperature range. In case of thermal oxidation in air, the initial oxidation of the copper films starts at about 150 °C, but a well ordered crystalline phase of the cuprous oxide (Cu2O) is observed only above 200 °C. However, the cupric oxide (CuO) phase starts to appear only above 320 °C. The details of the oxidation mechanism of the Cu film are explained with a probable schematic model in terms of thermal diffusion as well as the chemical reactivity.

Thermal conductivity of metal powders for powder bed additive manufacturing

Abstract: The thermal conductivities of five metal powders for powder bed additive manufacturing (Inconel 718, 17-4 stainless steel, Inconel 625, Ti-6Al-4V, and 316L stainless steel) were measured using the transient hot wire method. These measurements were conducted with three infiltrating gases (argon, nitrogen, and helium) within a temperature range of 295–470 K and a gas pressure range of 1.4–101 kPa. The measurements of thermal conductivity indicate that the pressure and the composition of the gas have a significant influence on the effective thermal conductivity of the powder, but that the metal powder properties and temperature do not. Our measurements improve the accuracy upon which laser parameters can be optimized in order to improve thermal control of powder beds in selective laser melting processes, especially in overhanging and cellular geometries where heat dissipation by the powder is critical.

Enhanced thermoelectric performance of Bi-Sb-Te/Sb2O3 nanocomposites by energy filtering effect

Abstract: Engineering of thermoelectric materials through hybridization with nanoparticles has been proved effective to boost their thermoelectric efficiency by providing the means to decouple thermal and electrical transport phenomena. Here, we report the synthesis of p-type Bi0.5Sb1.5Te3/X wt% Sb2O3 (X = 0, 1, 2, 4, 6) nanocomposites, in which the Sb2O3 nanoparticles are dispersed mainly at the grain boundaries of the Bi0.5Sb1.5Te3 matrix. It is shown that incorporation of up to 4 wt% Sb2O3 into the matrix results in simultaneous enhancement of the Seebeck coefficient (by filtering of low energy charge carriers) and decline of thermal conductivity (mainly by charge carrier scattering at the interfaces), both of which contribute to improving the thermoelectric figure of merit to a maximum of 1.51 at 350 K. Moreover, the nanocomposites with 2, 4, and 6 wt% Sb2O3 demonstrate ZT > 1.0 up to 450 K, making them commercially appealing for thermoelectric applications in a wide temperature range. Furthermore, it is shown that Bi0.5Sb1.5Te3/4 wt% Sb2O3 samples exhibit excellent thermal and chemical stability in ambient atmosphere and 300–475 K temperature range over a 24 month period.

Phase Behavior and Polymorphism of Formamidinium Lead Iodide

Abstract: A greater understanding of the structure–property relationships of hybrid perovskites for solar cells is crucial for enhancing their performance. The low-temperature phases of formamidinium lead iodide (FAPbI3) have been investigated using rapid neutron powder diffraction. On cooling, the metastable α-polymorph descends in symmetry from the cubic unit cell phase present at room temperature through two successive phase transitions. Between 285 and 140 K a tetragonal phase, adopting the space group P4/mbm, is confirmed and the orientation of the disordered FA cation over this temperature range determined. The cation dynamics have also been investigated, over the same temperature range, at the atomic scale by using ab initio molecular dynamics simulations, which indicate contrasting FA motion in the cubic and tetragonal structures. Below 140 K the neutron powder diffraction data display weak Bragg scattering intensities not immediately indexable to a related unit cell. Data collected at 100 K from N-deuterat...

Monolayer and bilayer polyaniline C3N: two-dimensional semiconductors with high thermal conductivity

Abstract: Polyaniline (PANI) has been extensively studied in the past few decades owing to its broad applications in electronic devices. However, two dimensional PANI was not realized until very recently. In this work, the thermal transport properties of one of the newly synthesized 2D PANI structures, C3N, are systematically investigated using classical molecular dynamics simulations. The in-plane thermal conductivity (κ) of monolayer and bilayer C3N structures is computed, and the κ values for infinite-length systems are found to be as high as 820 and 805 W m−1 K−1, respectively. Both the values are markedly higher than those of many prevailing 2D semiconducting materials such as phosphorene, hexagonal boron nitride, MoS2 and MoSe2. The effects of different modulators, such as system dimension, temperature, interlayer coupling strength and tensile strain, on the calculated thermal conductivity are evaluated. Monotonic decreasing trends of thermal conductivity with temperature and tensile strain are found, while a positive correlation between the thermal conductivity and system dimension is revealed. Interlayer coupling strength is found to have negligible effects on the in-plane thermal conductivity of bilayer C3N. The cross-plane interfacial thermal resistance (R) between two adjacent C3N layers is evaluated in the temperature range from 100 to 500 K and at different coupling strengths. The predicted R at temperature 300 K equals 3.4 × 10−8 K m−2 W−1. The maximum reductions of R can amount to 59% and 68% with respect to temperature and coupling strength, respectively. Our results provide theoretical guidance to future applications of C3N-based low-dimensional materials in electronic devices.

The influence of manganese concentration on the sensitivity of bandshape and lifetime luminescent thermometers based on Y3Al5O12:Mn3+,Mn4+,Nd3+ nanocrystals.

Abstract: Luminescent thermometers based on transition metal and lanthanide ion codoped nanocrystals have become a group of non-contact thermometers which are gaining importance due to their high sensitivity upon temperature changes. Here we present two types of luminescent thermometers, namely, bandshape and lifetime temperature sensors based on Y3Al5O12:Mn3+,Mn4+,Nd3+ nanocrystals. Their ability for temperature sensing was investigated as a function of Mn concentration. It was found that both sensitivity and usable temperature range depend on the Mn concentration. The highest sensitivity (S = 2.69%/K) was found for the lifetime luminescent thermometer with 0.01%Mn concentration and its value is gradually reduced with Mn content. Similarly, in the case of the bandshape luminescent thermometer, the sensitivity decreases from 1.69%/K for 0.01%Mn to 0.54%/K for 1%Mn. On the other hand the usable temperature range extends with dopant concentration. The concentration effect on the temperature dependent optical parameters is discussed in terms of interionic interactions facilitated for shorter Mn–Mn distances.

Thermal-stability of electric field-induced strain and energy storage density in Nb-doped BNKT-ST piezoceramics

Abstract: In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi0.5Na0.84K0.16TiO3)–0.04SrTiO3 (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x = 0.0175, a large-signal piezoelectric coefficient (Smax/Emax = d33*) of 735 pm V−1 at 6 kV mm−1 was observed at room temperature. Interestingly, at a higher temperature of 110 °C, the sample still showed a large d33* of 570 pm V−1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285 m4 C−2 over the temperature range of 25–170 °C. Moreover, the energy density for x = 0.030 sample was ∼1.0 J cm−3 with an energy storage efficiency of ˃70% in the temperature range of 25–135 °C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications.

Reduced Graphene Oxide based Temperature Sensor: Extraordinary performance governed by lattice dynamics assisted carrier transport

Abstract: In this article, we report the sensing performance of reduced graphene oxide (rGO) based resistive type temperature sensor fabricated by spin coating. A detailed analysis is presented for understanding the combined effect of lattice vibrational properties and temperature dependent electrical conductivity while considering charge carrier scattering with phonons, impurities, defects, and edge boundaries of rGO flakes. The purpose of this analysis is to find out how together they influence the temperature coefficient of resistance (TCR) and thermal hysteresis (HTh) of rGO based films. TCR and Hth are the core factors for efficient operation of a temperature sensor as these govern important sensing characteristics such as sensitivity, resolution, drift, response- and recovery-time. Experimental results show that the proposed sensor exhibits TCR ∼ −0.801%/K (in 303K–373K) and negligible thermal hysteresis (∼0.7%) resulting in high resolution (∼0.1 K), response- and recovery-time of ∼52 s and ∼285 s respectively. Besides, TCR and Hth are also found to depend on rGO concentration and working temperature range of sensors. By lowering the sensing temperature range to 303K–77K region, TCR was found to increase abruptly from −0.801%/K to −32.04%/K. All this optimized data were obtained for the sensor with 3 wt.% of rGO. Dynamic plot shows its sensitivity to respond to even ∼0.1 K change in temperature. Cyclic testing demonstrates good stability in 77K–573K temperature range with negligible drift. These studies are significant towards the fabrication of simple, highly sensitive, and cost effective temperature sensor with high reproducibility. There is still enough room to improve TCR of rGO based sensors through synthesis, advanced sensor design and development; higher TCR will definitely lead to far better temperature sensing performance as theory predicts.

High-Temperature Raman Spectroscopy of Nano-Crystalline Carbon in Silicon Oxycarbide.

Abstract: The microstructure of segregated carbon in silicon oxycarbide (SiOC), hot-pressed at T = 1600 °C and p = 50 MPa, has been investigated by VIS Raman spectroscopy (λ = 514 nm) within the temperature range 25–1000 °C in air. The occurrence of the G, D’ and D bands at 1590, 1620 and 1350 cm−1, together with a lateral crystal size La < 10 nm and an average distance between lattice defects LD ≈ 8 nm, provides evidence that carbon exists as nano-crystalline phase in SiOC containing 11 and 17 vol % carbon. Both samples show a linear red shift of the G band up to the highest temperature applied, which is in agreement with the description of the anharmonic contribution to the lattice potential by the modified Tersoff potential. The temperature coefficient χG = −0.024 ± 0.001 cm−1/°C is close to that of disordered carbon, e.g., carbon nanowalls or commercial activated graphite. The line width of the G band is independent of temperature with FWHM-values of 35 cm−1 (C-11) and 45 cm−1 (C-17), suggesting that scattering with defects and impurities outweighs the phonon-phonon and phonon-electron interactions. Analysis of the Raman line intensities indicates vacancies as dominating defects.

Critical Comparison of FAPbX3 and MAPbX3 (X = Br and Cl): How Do They Differ?

Abstract: Dielectric measurements on formamidinium lead halide perovskites, FAPbCl3 and FAPbBr3, compared to those of MAPbCl3 and previously reported MAPbBr3, reveal the strongly suppressed temperature dependence of dielectric constants in FA compounds in the temperature range of approximately 140–300 K. Although the behavior of dielectric constants of FA compounds for temperatures <140 K resembles that of the MAPbX3 system, the absence of any strong temperature dependence in sharp contrast to MA analogues in the higher temperature range up to room temperature suggests that the formamidinium (FA) dipoles are in a deep-frozen glassy state unlike the MA dipoles that rotate nearly freely in the temperature range relevant for any photovoltaic application. This observation is further supported by the temperature-dependent single-crystal X-ray diffraction (XRD) results.

Broadening the Valid Temperature Range of Optical Thermometry Through Dual-mode Design

Abstract: In this study, a double-perovskite Pr3+:Gd2ZnTiO6 thermometric phosphor is designed and successfully synthesized for the first time via a high-temperature solid-state method. By taking advantage of the intervalence charge transfer state (IVCT) interfered Pr3+ luminescence, the synthesized phosphor exhibits excellent optical thermometric performance in terms of both the fluorescence intensity ratio and luminescence lifetime. Specifically, by using the fluorescence intensity ratio between Pr3+: 3P0 → 3H4 and 1D2 → 3H4 transitions as a temperature detecting signal in the range of 293–433 K, the maximum absolute and relative sensitivities reach as high as 0.63 K−1 and 1.67% K−1, respectively; taking the fluorescence lifetime of the 1D2 state as a detecting signal in the range of 433–593 K, the corresponding sensitivities are 0.096 μs K−1 and 1.48% K−1. The results demonstrate that a thermal reading with high sensitivity over a wide range of temperature can be realized by this novel dual-mode design.

Non-Boltzmann Luminescence in Na Y F 4 : Eu 3 + : Implications for Luminescence Thermometry

Abstract: Luminescence (nano)thermometry is an important technique for remote temperature sensing. The recent development of lanthanide-doped nanoparticles with temperature-dependent emission has expanded the field of applications, especially for ratiometric methods relying on the temperature variation of relative emission intensities from thermally coupled energy levels. Analysis and calibration of the temperature dependence is based on a Boltzmann equilibrium for the coupled levels. To investigate the validity of this assumption, we analyze and model thermal equilibration for Eu3+ D15 and D05 emission in NaYF4. The results show that for low Eu3+ concentrations, temperature-dependent multiphonon relaxation can accurately explain both the intensity ratio and emission decay dynamics. The analysis also reveals that a Boltzmann equilibrium is not realized in the temperature regime investigated (300-900 K). By increasing the Eu3+ concentration, cross relaxation between neighboring Eu3+ ions enhances D15-D05 relaxation rates and extends the temperature range in which emission intensity ratios can be used for temperature sensing (500-900+ K). The results obtained are important for recognizing, understanding, and controlling deviations from Boltzmann behavior in luminescence (nano)thermometry. By varying the dopant concentration, the range for accurate temperature sensing can be adjusted. These insights are crucial in the development and understanding of reliable temperature sensors.

On the conduction mechanisms of Au/(Cu 2 O–CuO–PVA)/n-Si (MPS) Schottky barrier diodes (SBDs) using current–voltage–temperature (I–V–T) characteristics

Abstract: The temperature effect on the conduction mechanism of Au/Cu2O–CuO–PVA/n-Si (MPS) type Schottky barrier diodes (SBDs) have been investigated in detail in the wide temperature range of 100–380 K by using the forward bias current–voltage (I–V) measurements. It is observed that the semi logarithmic forward bias I–V plots have two distinct linear regions with different slopes for each temperature. These regions are called low bias region (LBR) and moderate bias region (MBR), respectively. The LBR and MBR correspond to (0.6–1.04 V) and (1.10–1.65 V) bias voltages, respectively. Main diode parameters such as reverse saturation current (I0), ideality factor (n) and zero-bias barrier height (Φb0) were calculated for these two regions. It is observed that the values of Φb0 increased as the values of n decreased with the increasing temperature and such behavior of Φb0 and n with temperature was attributed to the barrier inhomogeneities by assuming Gaussian distribution (GD) at the M/S interface. The Φb0 versus n and q/2kT plots were drawn to get an evidence of the GD. These two plots also have two linear regions at LBR and MBR. These regions are called the low temperature region (LTR) and high temperature region (HTR). Thus the mean values of barrier height (BH) and standard deviation (σs) were obtained by using the intercept and slope of these plots. After that, the conventional Richardson plot was drawn [(Ln(I0/T2) − q2σs 2/2k2T2) vs. q/kT] and it also has two linear regions. The main values of BH and effective Richardson constant (A*) were obtained from the slope and intercept of these plots. These values are found as 0.82 eV and 110.7 A/cm2 K2 for LTR and 1.53 eV and 115.5 A/cm2 K2 for HTR in the LBR and 0.77 eV and 111.9 A/cm2 K2 for LTR and 1.26 eV and 133.9 A/cm2 K2 for HTR in the MBR, respectively. The obtained values of A* are in good agreement with their theoretic values (112 A/cm2 K2) especially for HTR. Thus, the I–V–T characteristics of MPS type SBDs are successfully explained by the double GD model. Besides, the interface state density (Nss) of the MPS diode was calculated from forward-bias I–V measurements.

Investigating the Luminescence Behaviors and Temperature Sensing Properties of Rare-Earth-Doped Ba2In2O5 Phosphors.

Abstract: We present a strategy for selecting an optimal material in a particular temperature range by investigating the relationship between the absolute sensitivity ( Sa) and energy gap (Δ E), as well as the relationship between Sa and temperature on the basis of Yb3+/Ln3+ (Ln = Er3+, Ho3+)-codoped Ba2In2O5 phosphors. Through an investigation of optical performance, the phosphors exhibit near-infrared (NIR) downshifting and visible upconversion (UC) emissions under 980 nm excitation. The NIR spectral range from 700 to 1800 nm is referred to as the "biological window". The NIR emission peaks of Er3+ and Ho3+ are located at 1550 nm of the third biological window and 1192 nm of the second biological window, respectively. The temperature sensing behaviors based on the UC luminescence in Yb3+/Ln3+-codoped Ba2In2O5 phosphors are recorded by the fluorescence intensity ratio (FIR) technique in the temperature range from 303 to 573 K. The Ba2In2O5:Er3+/Yb3+ sample is usable at temperatures above 350 K, and the Ho3+/Yb3+-codoped Ba2In2O5 phosphor is suitable at temperatures below 350 K in our experimental region. The above results show that the Ba2In2O5:Ln3+/Yb3+ phosphors could be promising candidates for optical temperature sensors and applications in the biological imaging field.

Recrystallization behavior of hot-rolled pure tungsten and its alloy plates during high-temperature annealing

Abstract: We aimed to clarify the behavior of change in the grain structure and hardness of hot-rolled pure W and its alloys plates developed for various properties by holding at high temperature for long and short durations in the absence of irradiation. The isothermal annealing was performed at 1100 °C for 10–3115 h. The isochronous annealing was performed for 1 h in a temperature range of 1100 to 2300 °C. After heat treatment, the grain structure was observed using electron backscatter diffraction (EBSD) and the Vickers hardness was measured in the observed plane. Pure W did not recrystallize by the heat treatment for a short duration of 1 h at 1100 °C, while the recrystallization of pure W progressed during the heat treatment for long duration of 3115 h at 1100 °C. The temperature and duration at which the recrystallization occurs increase because of the dispersion of K bubbles and solid solution of Re. Considering the actual operation period of fusion reactors, a temperature of 1100 °C can result in recrystallization. It is necessary to decrease the maximum operating temperature or to use materials having a high recrystallization temperature by alloying.

Optimizing the defect chemistry of Na1/2Bi1/2TiO3-based materials: paving the way for excellent high temperature capacitors

Abstract: For applications in automotive, aviation and renewable energy industries temperature and power requirements have been significantly increased for electronic components. In particular, capacitors have been identified as the most critical materials considering the fulfillment of these requirements. Ceramics are the most promising materials for high temperature capacitors but no ceramic has been able to meet the necessary electrical properties so far. In this work, Na1/2Bi1/2TiO3 (NBT) solid solutions are investigated to optimize the respective electrical properties. A reduction of bismuth vacancy and oxygen vacancy concentration by increasing the initial Bi content leads to a significant decrease in dielectric loss. Additionally, energy efficiencies of up to 97% can be achieved for the composition Na1/2Bi1/2O3–BaTiO3–CaZrO3 (NBT–BT–CZ) and the temperature range of stable high permittivity together with low dielectric loss (tan δ ≤ 0.02) extends from −67 °C to 362 °C. Hence, optimization of the defect chemistry of NBT-materials results in highly stable electrical properties over a large temperature and electric field range, which leads to the fulfillment of industrial requirements.

Role of Hydrogen in High-Yield Growth of Boron Nitride Nanotubes at Atmospheric Pressure by Induction Thermal Plasma

Abstract: We recently demonstrated scalable manufacturing of boron nitride nanotubes (BNNTs) directly from hexagonal BN (hBN) powder by using induction thermal plasma, with a high-yield rate approaching 20 g/h. The main finding was that the presence of hydrogen is crucial for the high-yield growth of BNNTs. Here we investigate the detailed role of hydrogen by numerical modeling and in situ optical emission spectroscopy (OES) and reveal that both the thermofluidic fields and chemical pathways are significantly altered by hydrogen in favor of rapid growth of BNNTs. The numerical simulation indicated improved particle heating and quenching rates (∼105 K/s) due to the high thermal conductivity of hydrogen over the temperature range of 3500–4000 K. These are crucial for the complete vaporization of the hBN feedstock and rapid formation of nanosized B droplets for the subsequent BNNT growth. Hydrogen is also found to extend the active BNNT growth zone toward the reactor downstream, maintaining the gas temperature above t...