Superior Temperature Stability Research Articles

Electroluminescence enhancement in mid-infrared InAsSb resonant cavity light emitting diodes for CO2 detection

In this work, we demonstrated a mid-infrared resonant cavity light emitting diode (RCLED) operating near 4.2 μm at room temperature, grown lattice-matched on a GaSb substrate by molecular beam epitaxy, suitable for CO2 gas detection. The device consists of a 1λ-thick microcavity containing an InAs0.90Sb0.1 active region sandwiched between two high contrast, lattice–matched AlAs0.08Sb0.92/GaSb distributed Bragg reflector (DBR) mirrors. The electroluminescence emission spectra of the RCLED were recorded over the temperature range from 20 to 300 K and compared with a reference LED without DBR mirrors. The RCLED exhibits a strong emission enhancement due to resonant cavity effects. At room temperature, the peak emission and the integrated peak emission were found to be increased by a factor of ∼70 and ∼11, respectively, while the total integrated emission enhancement was ∼×33. This is the highest resonant cavity enhancement ever reported for a mid-infrared LED operating at this wavelength. Furthermore, the RCLED also exhibits a superior temperature stability of ∼0.35 nm/K and a significantly narrower (10×) spectral linewidth. High spectral brightness and temperature stable emission entirely within the fundamental absorption band are attractive characteristics for the development of next generation CO2 gas sensor instrumentation.

Simultaneous realization of broad temperature stability range and outstanding dielectric performance in (Ag+, Ta5+) co–doped TiO2 ceramics

Effects of sintering condition on dielectric properties and microstructure were systematically investigated in (Ag1/4Ta3/4)0.005Ti0.995O2 ceramics. A giant dielectric constant of ∼9831 (1 kHz) and a relatively low dielectric loss of ∼0.041 (1 kHz) were realized at the optimal sintering condition of 1330 °C with a holding time for 10 h. Notably, stable temperature coefficient (within −6.8% to 8.8%) of the dielectric constant at 10 kHz was achieved in a broader temperature range (-200–200 °C), which shows superior temperature stability of our sample than the application requirements (−55–200 °C and Δεr/ε25 °C < ±15%) of commercial X9R capacitor.

High-Quality-Factor AlGaAs-on-Sapphire Microring Resonators

We realize an AlGaAs-on-sapphire platform through Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -assisted direct wafer bonding and substrate removal processes. The direct wafer bonding process is optimized concerning the intermediate layer deposition and annealing temperature to obtain a high bonding strength between the AlGaAs and sapphire wafers. High quality-factor (Q) microring resonators are fabricated using electron-beam lithography in which the charging effect is mitigated by applying a thin aluminum layer, and a smooth pattern sidewall definition is obtained using a multi-pass (exposure) process. We achieve an intrinsic Q of up to ~460,000 which is the highest Q for AlGaAs microring resonators. Taking advantage of such high Q resonators, we demonstrate an ultra-efficient nonlinear four-wave mixing process in this platform and obtain a conversion efficiency of -19.8 dB with continuous-wave pumping at a power level of 380 μW. We also investigate the thermal resonance shift of microring resonators with different substrate layouts and observe superior temperature stability for devices in the AlGaAs-on-sapphire platform. The realization of the AlGaAson-sapphire platform also opens new prospects for AlGaAs devices in nonlinear applications in the mid-infrared wavelength range.

Enhancing temperature stability in potassium-sodium niobate ceramics through phase boundary and composition design

Phase boundaries and composition design were explored to achieve both high piezoelectricity and favorable temperature stability in potassium-sodium niobate ceramics, using (1-x)(K,Na)(Nb,Sb)O3-xBi(Na,K)(Zr,Sn,Hf)O3 ceramics. A rhombohedral-tetragonal (R-T) phase boundary was constructed at x=0.035–0.04 by co-doping with Sb5+ and Bi(Na,K)(Zr,Sn,Hf)O3. More importantly, a superior temperature stability was observed in the ceramics with x=0.035, accompanying with a stable unipolar strain at room temperature to 100 °C. The ceramics with x=0.035 also exhibited improved piezoelectric properties (e.g., piezoelectric coefficient d33∼465 pC/N and electromechanical coupling factor kp=0.47) and Curie temperature (Tc∼240 °C). The Rietveld refinement and in-situ temperature-dependent piezoresponse force microscopy (PFM) results indicated that the enhancement of the piezoelectric properties was caused by the easy domain switching, high tetragonal fraction, and tetragonality, while the improved temperature stability mainly originated from the stable domain structures.

High-Performance 0-3 Type Niobate-Based Lead-Free Piezoelectric Composite Ceramics with ZnO Inclusions.

Because of their high toxicity, lead-based materials in electronic devices must be replaced by lead-free piezoelectric materials. However, some issues remain that hinder the industrial applications of these alternative ceramics. Here, we report the construction of a 0-3-type ceramic composite (KNNS-BNKZ: xZnO), where the Sb-doped ZnO submicronic particles were randomly distributed throughout the potassium-sodium niobate-based ceramic matrix. In this (K,Na)NbO3 (KNN)-based ceramic composite, superior temperature stability, excellent piezoelectric properties, and a high Curie temperature were simultaneously achieved. The unipolar strain varied from +20 to -16% when the temperature was increased from 23 to 200 °C in KNNS-BNKZ: xZnO with x = 0.75. By increasing the ZnO content from x = 0 to x = 5.0, the Curie temperature was increased from 227 to 294 °C. More importantly, the piezoelectric coefficient remained high ( d33 = 480-510 pC/N) for a wide range of compositions, x = 0.25-1.0. Transmission electron microscopy (TEM) experiments showed that the compensatory electric fields generated by the Sb-doped ZnO submicronic particles were responsible for the improved temperature stability. The high piezoelectricity was due to the existence of nanodomains, which were clearly observed in the TEM experiments. The results presented in this work clarify some of the physical mechanisms in this KNN-based ceramic composite, thus advancing the development of lead-free ceramics.

Cloning and characterisation of four catA genes located on the chromosome and large plasmid of Pseudomonas putida ND6

Although the functional redundancy of catechol 1,2-dioxygenase (C12O) genes has been reported in several microorganisms, limited enzymes were characterised, let alone the advantage of the coexistence of the multiple copies of C12O genes. In this study, four novel C12O genes, designated catA, catAI, catAII and catAIII, in the naphthalene-degrading strain Pseudomonas putida ND6, were cloned and characterised. Phylogenetic analysis of their deduced amino acid sequences revealed that the four C12O isozymes each formed independent subtrees, together with homologues from other organisms. All four enzymes exhibited maximum activity at pH 7.4 and higher activity in alkaline than in acidic conditions. Furthermore, CatA, CatAI and CatAIII were maximally active at a temperature of 45°C, whereas a higher optimum temperature was observed for CatAII at a temperature of 50°C. CatAI exhibited superior temperature stability compared with the other three C12O isozymes, and kinetic analysis indicated similar enzyme activities for CatA, CatAI and CatAII, whereas that of CatAIII was lower. Significantly, among metal ions tested, only Cu2 + substantially inhibited the activity of these C12O isozymes, thus indicating that they have potential to facilitate bioremediation in environments polluted with aromatics in the presence of metals. Moreover, gene expression analysis at the mRNA level and determination of enzyme activity clearly indicated that the redundancy of the catA genes has increased the levels of C12O. The results clearly imply that the redundancy of catA genes increases the available amount of C12O in P. putida ND6, which would be beneficial for survival in challenging environments. How to cite: Li S, Qin K, Li H, et al. Cloning and characterisation of four catA genes located on the chromosome and large plasmid of Pseudomonas putida ND6. Electron J Biotechnol 2018;34.

All-solution processed, scalable superhydrophobic coatings on stainless steel surfaces based on functionalized discrete titania nanotubes

Stainless steel structures are used in reactor vessels, pipelines, boilers and industrial tubing in the oil and gas industries and they regularly experience corrosion, erosion and fouling that necessitate frequent replacement and repairs. We demonstrate a new method to robustly protect the stainless steel surface and render it superhydrophobic. Our method utilizes self-assembled monolayers (SAMs) of octadecylphosphonic acid (ODPA) grown on discrete TiO2 nanotube (d-TNT)-coated stainless steel surfaces for complete passivation. While the formation of superhydrophobic coatings based on anodically formed titania nanotube arrays has been previously reported by several research groups including us, the key techno-economic obstacle has been the need to use vacuum deposition to grow adherent and uniform precursor Ti films on non-native substrates such as stainless steel prior to electrochemical anodization. Vacuum deposition of the precursor Ti films is simply neither scalable nor economically feasible for the large and complex stainless steel structures used in pipelines, boilers and industrial tubing and solution processing, preferably a spray-coatable solution, is an absolute must. Our innovation here consists of formulating a spray-coatable suspension of functionalized discrete TiO2 nanotubes that forms a superhydrophobic surface on stainless steel substrates. Vacuum deposition is completely eliminated from our process sequence and as such, we expect our coatings to inhabit the same niche as current commercial formulations while possessing the superior temperature stability and wear resistance of TiO2.

Enhanced energy-storage performance and dielectric temperature stability of (1-x)(0.65Bi0.5Na0.5TiO3-0.35Bi0.1Sr0.85TiO3)-xKNbO3 ceramics

Leed-free ferroelectric (1-x)(0.65Bi0.5Na0.5TiO3−0.35Bi0.1Sr0.85TiO3)-xKNbO3 (BNBST-xKN) ceramics were prepared by the conventional solid state sintering method. The dielectric, ferroelectric and energy-storage properties were systematically investigated. Temperature dependent permittivity curves showed the relaxation properties of BNBST ceramics enhanced with the increase of KNbO3. BNBST-15KN exhibited a high permittivity of 3484 and low dielectric loss of 0.003 at 150 °C. Furthermore, Δε/ε150 °C varied no more than 10% within the tmperature range of 30–297 °C, indicating an excellent dielectric temperature stability. The introduction of KNbO3 gave rise to a large Pm while P-E loops kept slim in shape. Therefore, the optimum energy-storage performance was realized in BNBST-15KN with an energy-storage density Wrec of 1.32 J/cm3 and energy-storage efficiency η of 82.5% at 95 kV/cm, accompanied with superior temperature stability and fatigue performance. The results demonstrated that BNBST-xKN system was a promising lead-free candidate for energy-storage applications.

Reinforcing cycling stability and rate capability of LiNi0.5Mn1.5O4 cathode by dual-modification of coating and doping of a fast-ion conductor

A simple solid state method was utilized to synthesize excellent spinel Li2SiO3-modified LiNi0.5Mn1.5O4 cathodes. Dual-modification of coating and doping of fast-ion conductor Li2SiO3 leads to stable crystal structure and additional three-dimensional (3-D) channels for Li+-ion diffusion, and protects the electrode surface from electrolyte attack. The Li2SiO3-modified material possesses coexistence of ordered P4332 and disordered Fd-3m phases. As a result of improved structure, morphology and conductivity, the Li2SiO3-modified LiNi0.5Mn1.5O4 shows more superior cyclic performance, rate capability and high temperature stability than the pristine: capacity retention of 95.17% at 0.1 C after 100 cycles vs. that of 79.23%; rate capability of 130–89.1 mAh g−1 at 0.1–10 C vs. that of 120–57.6 mAh g−1; and high temperature capacity retention of 99.42% at 0.1 C vs. that of 79.59%. Our study provides a facile approach to stabilize crystal structure, optimize morphology and conductivity, and thus enhance electrochemical performance of LiNi0.5Mn1.5O4-based materials.

Practical high strain with superior temperature stability in lead-free piezoceramics through domain engineering

New domain engineering by utilizing phase boundary design, chemical modification, and electric-field driving achieves high and stable strain in lead-free piezoceramics.

High electrocaloric effect in hot‐pressed Pb0.85La0.1(Zr0.65Ti0.35)O3 ceramics with a wide operating temperature range

AbstractThe temperature stability of the electrocaloric effect (ECE) in relaxor ferroelectric Pb0.85La0.1(Zr0.65Ti0.35)O3 (PLZT) prepared by the hot‐press sintering method has been investigated. Compared to the PLZTs prepared via the conventional sintering process, the hot‐pressed PLZTs exhibit larger ECE and superior temperature stability. The hot‐pressed sample with an appropriate content of excess PbO presents a high ΔT of 2.4°C and ΔS of 2.3 J kg−1·K−1, both of which are 30% greater than those of the conventionally sintered samples measured at 100 kV·cm−1. More importantly, the hot‐pressed specimens display great stable electrical properties, including the dielectric breakdown strength and electrical resistivity in the temperature range from 0°C to 100°C, whose ECE instability, especially, is only one‐half that of the samples prepared by the conventional solid‐state method. In addition, the ECE and its stability of the hot‐pressed sample can be further enhanced by increasing the operating electric field to a relatively high level of 200 kV·cm−1. This work demonstrates hot‐press sintering is an effective method to fabricate ferroelectric ceramics with high ECE as well as desirable temperature stability.

A Two-Parameter Calibration Technique Tracking Temperature Variations for Current Source Mismatch

This brief presents a foreground calibration technique for current source mismatch that is insensitive to temperature variations. Two calibration digital-to-analog converters (CAL DACs) provide correction currents to compensate two current source mismatch components caused by the threshold voltage mismatch and the current factor mismatch. Each CAL DAC has the same temperature dependence as its corresponding mismatch component. The sum current of the two CAL DACs automatically tracks the temperature variations of the current source mismatch with no need for temperature information. To obtain the CAL DAC input codes, two different bias current settings are used instead of calibrating at two separate temperatures. This scheme significantly reduces the calibration time and cost. A 16-bit DAC with this calibration technique is fabricated in a 65-nm CMOS process. The measurement results show that the matching of the most significant bit currents is improved from intrinsic 12 to 16 bits across the temperature range from −40 °C to 85 °C. The proposed calibration technique achieves superior temperature stability compared to the previously published schemes.

High-frequency current sensor based on lead-free multiferroic BiFeO 3 -BaTiO 3 -based ceramics

Abstract This paper presents the study of a high-frequency current sensor fabricated using BiFeO3-BaTiO3-based multiferroic ceramics. The frequency response of the sensor is ranged from 1 kHz to 1 MHz. The sensitivity of the current sensor is 4.5 mV/A in a flat response zone from 1 kHz to 20 kHz with an error of 5%. Besides, the sensor exhibits superior temperature stability with a wide operational temperature range (room temperature to ∼353 K). The sensor is also assembled with a high magnetic permeability material that is capable of shielding the DC biased magnetic field up to 2026 Oe. The environmental friendly sensing material and stable output characteristics make the proposed current sensor preferable for the high-frequency current measurement. Besides the performance evaluation, the non-linear frequency response of the current senor is also investigated quantitatively from the aspects of impedance and conductivity.

Understanding the superior temperature stability of iridium light-emitting electrochemical cells

The temperature dependence of iridium and ruthenium devices are studied, and fundamental assumptions governing their emission are challenged.

Grain-orientated lead-free BNT-based piezoceramics with giant electrostrictive effect

In this study, we propose an effective approach to gain prominent electrostrictive behavior by taking advantage of texture construction in lead-free (Bi0.5Na0.5)TiO3(BNT)-based piezoceramics for actuator applications. The electrostrictive effect was explored systematically in <00l> textured 0.90(0.83Bi0.5Na0.5TiO3-0.17Bi0.5K0.5TiO3)-0.10NaNbO3(BNT-BKT-NN) ceramics with respect to grain orientation, temperature and electric fields. It was found that the electrostrctive coefficient Q33 and recoverable strain increase monotonously with the grain orientation increasing. At the optimized microstructure (F00l=92%), a giant Q33 with nearly purely electrostrictive characteristics was detected to be around ~0.0354m4C−2, which was far larger than the reported values of Pb(Mg1/3Nb2/3)O3 (PMN) and the existing BNT-based electrostrictive materials. Meanwhile, the acquired Q33 was found to exhibit excellent stability for the highly textured sample under different temperature or electric field conditions. Our achievement demonstrates that the giant electrostrictive properties with superior temperature and electric field stability for <00l> textured BNT-BKT-NN ceramic are of great significance in replacing traditional PMN ceramics for actuator applications.

Nano-scale, planar and multi-tiered current pathways from a carbon nanotube-copper composite with high conductivity, ampacity and stability.

New lithographically processable materials with high ampacity are in demand to meet the increasing requirement for high operational current density at high temperatures existing in current pathways within electronic devices. To meet this demand, we report an approach to fabricate a high ampacity (∼100 times higher than Cu) carbon nanotube-copper (CNT-Cu) composite into a variety of complex nano-scale, planar and multi-tiered current pathways. The approach involved the use of a two-stage electrodeposition of copper into a pre-patterned template of porous, thin CNT sheets acting as the electrode. The versatility of this approach enabled the realization of completely suspended multi-tier, dielectric-less 'air-gap' CNT-Cu circuits that could be electrically isolated from each other and are challenging to fabricate with pure Cu or any metal. Importantly, all such complex structures, ranging from 500 nm to 20 μm in width, exhibited ∼100-times higher ampacity than any known metal, with comparable electrical conductivity as Cu. In addition, CNT-Cu structures also exhibited a superior temperature stability compared to the ∼10-times wider Cu counterparts. We believe that the combination of our approach and the properties demonstrated here are vital achievements for the future development of efficient and powerful electrical devices.

Phase transition behavior and enhanced electromechanical properties in (Ba0.85Ca0.15)(ZrxTi1−x)O3 lead-free piezoceramics

Lead-free (Ba0.85Ca0.15)(ZrxTi1−x)O3 (BCZT,0.03≤x≤0.25) ceramics were synthesized in a wide compositional range to investigate the relationship between its phase diagram and electromechanical properties. The effects of Zr content on microstructure, phase transition behavior, ferroelectric, dielectric, piezoelectric and strain properties of BCZT ceramics were systemically studied. The morphotropic phase boundary (MPB) of BCZT ceramics was closely connected with the presence of orthorhombic phase between rhombohedral and tetragonal phases at a narrow region, which could meet in a region that is termed the diffuse ferroelectric phase transition region (DPTR) in this work. As a result, the composition x=0.08 located at near MPB region close to tetragonal phase side exhibited the outstanding electrical behavior at room temperature: d33=349pC/N, kp=43%, S=0.185% and Smax/Emax=463pm/V. Furthermore, pure electrostrictive effect with large electrostrictive coefficient Q11 of 0.036m4C−2 had also been observed in the composition x=0.20, and large Q11 of MPB composition showed superior temperature stability in the investigated temperature range.

Low dielectric loss and good thermal stability of Eu and Ti co-doped K0.5Na0.5NbO3 ceramics

In order to develop dielectric ceramics with temperature-stable permittivity characteristics, Eu and Ti co-doped K0.5Na0.5NbO3 [(1 − x)K0.5Na0.5NbO3-xEuTiO3] ceramics were prepared by a conventional solid state route. The effect of EuTiO3 on the phase structure and dielectric performance of KNN ceramics were investigated. The temperature dependence of the relative permittivity illustrated that the small amount of EuTiO3 depressed the dielectric peak of ferroelectric-paraelectric transition. Therefore, the temperature stability and relative permittivity of ceramics were effectively improved. As x = 0.03, the ceramic showed superior dielectric temperature stability (±10 %), very low dielectric loss (0.008 at 250 °C) and a relatively high permittivity (>1500 at 250 °C) over the temperature range from ~100 to 350 °C. It suggests that this ceramic is a promising candidate for high-temperature capacitor application.

New magnetic nanocomposites: Polyurethane/ Fe3O4-synthetic talc

New Fe3O4-synthetic talc was used as filler in the synthesis of PU/Fe3O4-synthetic talc nanocomposites obtained by physical mixture. The Fe3O4-synthetic talc-nanofillers were exfoliated/well dispersed into the polyurethane matrix even at high filler content of 10wt.% as supported by XRD and TEM analyses. The SEM micrographs corroborated the good distribution of the fillers and evidenced an important morphology change with the increase of the filler content. These morphological changes caused by the balance between the hydrogen bonding among polymer/polymer, polymer/filler and filler/filler were also confirmed by topological changes as well as in the roughness values evaluated by AFM. The magnetic behavior of the nanocomposites was confirmed by means of Mossbauer transmission and magnetic measurements. The use of Fe3O4-synthetic talc for obtaining magnetic nanocomposites resulted in improved materials with superior crystallization temperature and thermal stability proving to be a simple way of avoiding dipolar attraction of magnetite and consequently the filler aggregation.

GaAsSb/InAlAs/InGaAs Tunnel Diodes for Millimeter Wave Detection in 220–330-GHz Band

We report on high-frequency performance and temperature stability of zero-bias GaAsSb/InAlAs/InGaAs tunnel diodes for millimeter-wave detection in 220-330-GHz band. The average voltage sensitivity of 1400 V/W has been achieved in 0.8 × 0.8μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> mesa devices at room temperature. Measured current-voltage characteristics revealed a superior temperature stability of the devices compared with Schottky barrier diodes. The expected sensitivity variations over a temperature range from T=17-300 K are 1.7 dB.