Improved Temperature Stability Research Articles

Highly tunable compositionally graded (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 multilayer with low temperature capacitance coefficients

Compositionally graded (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 {BCZT} thin films were deposited on LaNiO3 coated Si via the pulsed laser deposition technique to investigate permittivity temperature stability improvement. The results showed that the internal stress produced by the gradient of composition and different phase transition temperatures of constituent layers could be a dominant factor to influence the dielectric properties and temperature stability in different temperature regions. Graded film in the vicinity of morphotropic phase boundary displayed the highest tunability and the lowest temperature capacitance coefficient values. The maximum tunability of 63% and minimum temperature capacitance coefficient of 1.21×10−4°C had been observed in the graded multilayered films compared to the single-layer BCZT film prepared in the identical conditions.

Phase transition behavior and temperature-stable piezoelectric properties of new quaternary (K, Na)NbO3 based ceramics

(K, Na)NbO3-based lead free materials have been found to exhibit good piezoelectric properties due to the orthorhombic–tetragonal polymorphic phase transition (PPT) temperature compositionally shifted downward to near room temperature. However, this transition correspondingly results in a strong temperature dependence of the dielectric and piezoelectric properties. In this work, new quaternary (1−x) (K0.4425Na0.52Li0.0375)(Nb0.8925Sb0.07Ta0.0375)O3 (KNLNST)–xSrTiO3 (ST) lead-free piezoelectric ceramics were fabricated by a conventional ceramic technique and their structure and piezoelectric properties were also studied. The results of X-ray diffraction reveal that SrTiO3 diffuses into the KNLNST lattices to form a new solid solution with a perovskite structure. After the addition of SrTiO3, tetragonal–orthorhombic phase transition shifts to lower temperatures. The good piezoelectric properties of 0.995 KNLNST–0.005 ST material were found to be d33∼295pC/N, kp∼42%, and εr∼1902, with greatly improved temperature stability over the temperature range of 0–100°C, demonstrating practical potential for actuator and ultrasonic transducer applications.

Nurses’ Commitment to Best Practice Infant Care and Family Bonding Founded on Evidence-Based Research: A Journey of Infant Bathing

The Professional Practice Committee hypothesized that we could improve postpartum wellborn baby care by switching from sponge bathing to immersion bathing. A research review revealed evidence supporting the theory that immersion bathing improved temperature stability, bonding, breastfeeding, and parental education. The current practice in the Providence Alaska Medical Center Maternity Center is to perform sponge bathing under a radiant warmer on newborns within 2 hours of birth in the absence of birth stress or trauma. Parental involvement is minimal because of decreased mobility from anesthesia, exhaustion, and environmental or social distractions during the immediate postpartum period. Nurses also reported that breastfeeding and skin-to-skin bonding time often was interrupted to complete baths in the allotted 2-hour recovery time.

Temperature Effects on the Propagation Characteristics of Love Waves along Multi-Guide Layers of Sio2/Su-8 on St-90°X Quartz

Theoretical calculations have been performed on the temperature effects on the propagation characteristics of Love waves in layered structures by solving the coupled electromechanical field equations, and the optimal design parameters were extracted for temperature stability improvement. Based on the theoretical analysis, excellent temperature coefficient of frequency (Tcf) of the fabricated Love wave devices with guide layers of SU-8/SiO2 on ST-90°X quartz substrate is evaluated experimentally as only 2.16 ppm.

Vaccine process technology

The evolution of vaccines (e.g., live attenuated, recombinant) and vaccine production methods (e.g., in ovo, cell culture) are intimately tied to each other. As vaccine technology has advanced, the methods to produce the vaccine have advanced and new vaccine opportunities have been created. These technologies will continue to evolve as we strive for safer and more immunogenic vaccines and as our understanding of biology improves. The evolution of vaccine process technology has occurred in parallel to the remarkable growth in the development of therapeutic proteins as products; therefore, recent vaccine innovations can leverage the progress made in the broader biotechnology industry. Numerous important legacy vaccines are still in use today despite their traditional manufacturing processes, with further development focusing on improving stability (e.g., novel excipients) and updating formulation (e.g., combination vaccines) and delivery methods (e.g., skin patches). Modern vaccine development is currently exploiting a wide array of novel technologies to create safer and more efficacious vaccines including: viral vectors produced in animal cells, virus-like particles produced in yeast or insect cells, polysaccharide conjugation to carrier proteins, DNA plasmids produced in E. coli, and therapeutic cancer vaccines created by in vitro activation of patient leukocytes. Purification advances (e.g., membrane adsorption, precipitation) are increasing efficiency, while innovative analytical methods (e.g., microsphere-based multiplex assays, RNA microarrays) are improving process understanding. Novel adjuvants such as monophosphoryl lipid A, which acts on antigen presenting cell toll-like receptors, are expanding the previously conservative list of widely accepted vaccine adjuvants. As in other areas of biotechnology, process characterization by sophisticated analysis is critical not only to improve yields, but also to determine the final product quality. From a regulatory perspective, Quality by Design (QbD) and Process Analytical Technology (PAT) are important initiatives that can be applied effectively to many types of vaccine processes. Universal demand for vaccines requires that a manufacturer plan to supply tens and sometimes hundreds of millions of doses per year at low cost. To enable broader use, there is intense interest in improving temperature stability to allow for excursions from a rigid cold chain supply, especially at the point of vaccination. Finally, there is progress in novel routes of delivery to move away from the traditional intramuscular injection by syringe approach.

Improvement of temperature-stability in a quantum well laser with asymmetric barrier layers

We fabricated and tested a quantum well laser with asymmetric barrier layers. Such a laser has been proposed earlier to suppress bipolar carrier population in the optical confinement layer and thus to improve temperature-stability of the threshold current. As compared to the conventional reference laser structure, our laser with asymmetric barrier layers demonstrates reduced internal optical loss, lower threshold current density at elevated temperatures, and higher characteristic temperature (143 vs. 99 K at 20 °C).

Structure and Electrical Properties of (1-x)[(K0.5Na0.5)0.95Li0.05](Nb0.95Sb0.05)O3-xSrTiO3 Lead-Free Piezoelectric Ceramics with Improved Temperature Stability

Lead-free piezoelectric ceramics (1-x)[(K0.5Na0.5)0.95Li0.05](Nb0.95Sb0.05)O3-xSrTiO3 (abbreviated as KNLNS-xST) were sintered by the conventional method. The effects of SrTiO3 content on the structure, the electrical properties and the temperature stability of ceramics were investigated. The X-ray diffraction patterns revealed that all the ceramics have a perovskite structure, and the SEM micrographs revealed that the grain size of the ceramics was decreased with the increase of SrTiO3 content. The partial substitution of SrTiO3 decreased the Curie temperature (Tc) and shifted the orthorhombic–tetragonal phase transition temperature (TO–T) to below room temperature. It was found that the ceramics with x = 0.008 possess optimum piezoelectric properties (d33 = 250 pC/N, kp = 51.7%, ϵr ∼1143 and tanδ ∼ 4.45%), and the ceramics with x = 0.015 exhibit improved temperature stability, due to the shift of TO-T to below room temperature. These results indicate that these materials are promising candidates for lead-free piezoelectric ceramics for practical applications.

Improved Temperature Stability of Atomic Layer Deposition Coated Cellulose Nanocrystal Aerogels

ABSTRACTAtomic layer deposition (ALD) was used to coat cellulose nanocrystal (CNC) aerogel scaffolds with a thin conformal layer of Al2O3. Electron probe microanalysis indicates that the penetration of Al2O3 into the aerogel was greater than 50 μm. Thermogravimetric analysis (TGA) shows that Al2O3 coated CNC aerogel composites have improved temperature and oxidation resistance.

Nanoemulsions with enhanced temperature stability using thermo-sensitive association of nonionic surfactant and amphiphilic polyelectrolytes

Aqueous mixtures containing a non-ionic surfactant (tetraethylene glycol monododecylether, C12E4), an amphiphilic polymer (poly(sodium acrylate) hydrophobically modified with azobenzene groups randomly attached along the chains, HMPA) and 0.3M NaNO3 were studied regarding the associations between macromolecules and surfactant assemblies (micelles or lamellar phases) at various temperatures (4–37°C). The effects of the thermo-induced transition of surfactant assemblies from micelles to lamellar phase on phase separation behavior were systematically investigated as a function of surfactant and polymer concentration, polymer structure (amount of grafted hydrophobic groups) and temperature. Rheological properties of polymer-rich coacervates revealed thermo-thickening behavior, in accordance with phase separation behavior. Finally, bulk phenomena were applied to design nanoemulsions with improved temperature stability taking the opportunity of strengthening interfacial layers through thermo-thickening properties.

Improvement in temperature stability and modified polymorphic phase transition of La-doped (Na0.52K0.44Li0.04) Nb0.8Ta0.2O3 lead-free piezoelectric ceramics

Lead-free ceramics (Na0.52K0.44Li0.04)1-3xLaxNb0.8Ta0.2O3 (KNLNT-Lax, x=0.00–1.25mol%) were prepared by traditional method. The piezoelectric proprieties and the polymorphic phase transition behaviors around the room temperature were investigated. The results show that high density (ρ~95%) and outstanding piezoelectric performance (d33≥200pC/N, kp≥40%) were obtained with 0.5–0.75mol% La doping. By the research of temperature dependent εr, Δfr/fr20°C, and kp, we acquired the extended and mild polymorphic phase transition region, and obvious improvement of temperature stability in −50–80°C with the maximum derivation d(Δfr/fr20°C)max less than 2%, as the La doping content exceeds 0.5mol%. The possible mechanism of enhanced properties and temperature stability was analyzed. Both excellent piezoelectric and temperature stability characteristics make the La-doped KNLNT ceramics feasible for practical applications.

Effects of BiAlO3 on structure and electrical properties of K0.5Na0.5NbO3–LiSbO3 lead-free piezoceramics

Abstract (1−x)(0.948 K0.5Na0.5NbO3–0.052LiSbO3)–xBiAlO3 (KNNLS–xBA) lead-free piezoceramics were synthesized by conventional solid state reaction method. The compositional dependence of phase structure and electrical properties of the ceramics was systemically studied. XRD patterns revealed that all the ceramic samples possessed pure perovskite structure. In addition, polymorphic phase transition (PPT) for the ceramics with BA doping could not be observed in the measuring range from room temperature to 500 °C. Within the studied range of BA addition, the ceramics with x = 0.002 represented a relatively desirable balance between the degradation of the piezoelectric properties, improvement in temperature stability and mechanical quality factor. It was found that the KNNLS–0.002BA ceramics exhibited optimum overall properties (d33 = 233 pC/N, kp = 35%, tanδ = 0.047, Pr = 27.3 μC/cm2, Qm = 56 and Tc = 349 °C), suggesting that this material should be a promising lead-free piezoelectric candidate for piezoelectric applications.

Phase diagram and structure-property relationships in the lead-free piezoelectric system: Na0.5K0.5NbO3-LiTaO3

A phase-diagram for the Na(0.5)K(0.5)NbO(3)-LiTaO(3) solid solution series (NKN-LT) is presented for compositions ≤ 10 mol% LT, based on the combined results of temperaturevariable X-ray powder diffraction and dielectric measurements. In addition to the reported orthorhombic and tetragonal polymorphs of NKN-LT, a monoclinic phase is revealed. Changes to electrical properties as a function of LT substitution are correlated to phase content. Increasing the LT content from 5 to 7 mol% LT led to improved temperature stability of piezoelectric properties because of the avoidance of the monoclinic-tetragonal polymorphic phase transition during thermal cycling (at >25°C). For 7 mol% LT samples: d(33) = 200 pC/N; T(c) = 440°C; ε(r) = 550 and tan δ = 0.02 (at 20°C). Modification of this composition by solid solution with BiScO(3) led to a decrease in d(33) values. Transmission electron microscopy of a sample of 0.95[0.93 NKN-0.07LT]-0.05BiScO(3) indicated a core-shell grain structure which led to temperature-stable dielectric properties.

Temperature Stability in Dy‐Doped (Ba0.99Ca0.01)(Ti0.98Zr0.02)O3 Lead‐Free Ceramics with High Piezoelectric Coefficient

We report on excellent temperature stability of the Dy‐doped (Ba0.99Ca0.01)(Ti0.98Zr0.02)O3 (BCZT‐D) ceramics with high piezoelectric coefficient of d33 = 366 pC/N and planar electromechanical coupling factor of kp = 43.0%. Meanwhile, Curie temperature of the BCZT‐D ceramics is found to be 125°C. Greatly improved temperature stability of the electromechanical coupling coefficients is found over a common usage temperature range between 20°C and 100°C, in which the BCZT‐D ceramics exhibit pure tetragonal phase. The results indicate that the BCZT‐D ceramics are promising lead‐free materials for practical applications.

Lightly Al-doped Ta 2O 5: Electrical properties and mechanisms of conductivity

Lightly Al-doped Ta 2O 5 films (10;15 nm) obtained by rf sputtering have been studied with respect to their dielectric and electrical properties. The formed metal–high- k dielectric–semiconductor capacitors have been characterized by capacitance–voltage and temperature-dependent current–voltage characteristics. It was established that the introduction of small amount (5 at.%) Al into the matrix of Ta 2O 5 improves dielectric constant, introduces negative oxide charge, suppresses deep oxygen-vacancy centers in Ta 2O 5 but creates shallow traps and changes the dominant conduction mechanism in the stacks. The doping produces more leaky films at room temperature and lower current at high temperature as compared to the case of pure Ta 2O 5. It is concluded that the strong contribution of tunneling processes through shallow traps in the conductivity of doped films could explain the observed current degradation at room temperature and its improved temperature stability at high temperatures. The energy levels of the traps responsible for the current transport are estimated.

1100 nm InGaAs/(Al)GaAs quantum dot lasers for high-power applications

InGaAs/(Al)GaAs quantum dot lasers emitting at 1100 nm are developed with a relatively low In content of 28% used for dot formation and an appropriate laser design to allow for high power emission. In comparison with an InGaAs QD laser with a similar design but a higher In content of 60% the newly developed lasers exhibit an improved temperature stability of the threshold current and internal quantum efficiency.

Structural, Dielectric and Ferroelectric Properties of Mn Doped Ba0.80Pb0.20Ti0.90Zr0.10O3 Ceramics

In the present work, we are reporting the effect of Mn doping on the structural, dielectric and ferroelectric properties of Ba0.80Pb0.20Ti0.90Zr0.10O3. Samples were prepared by solid state reaction route. X-ray diffraction analysis confirmed the compositions to be single phase. Dielectric properties were studied as a function of temperature and phase transition temperature (Tc) was determined. Ferroelectric behaviour was studied in detail as a function of temperature. Mn doping was found to improve temperature stability of the material.

Stable temperature characteristics of InGaN blue light emitting diodes using AlGaN/GaN/InGaN superlattices as electron blocking layer

P-type AlGaN/GaN/InGaN superlattices were incorporated in a InGaN based blue light emitting diode as electron blocking layer to minimize the temperature dependence on optical output power. For the characteristic temperatures in range of 10 to 100 °C and at operation current of 350 mA, the external quantum efficiency varied by less than 0.5%. For the presented device, the negative characteristic temperature was shown to occur below temperature of 50 °C. The improved temperature stability in optical output power is thought to be attributed to (1) the efficiency of hole carrier transport in AlGaN/GaN/InGaN superlattices and (2) the enhanced blocking of electron overflow between multiple quantum wells and AlGaN/GaN/InGaN superlattices.

Towards a solution for viscous heating in ultra-high pressure liquid chromatography using intermediate cooling

A generic solution is proposed for the deleterious viscous heating effects in adiabatic or near-adiabatic systems that can be expected when trying to push the column operating pressures above the currently available range of ultra-high pressures (i.e., 1200 bar). A set of proof-of-principle experiments, mainly using existing commercial equipment, is presented. The solution is based on splitting up a column with given length L into n segments with length L/ n, and providing an active cooling to the capillaries connecting the segments. In this way, the viscous heat is removed at a location where the radial heat removal does not lead to an efficiency loss (i.e., in the thin connection capillaries), while the column segments can be operated under near-adiabatic conditions without suffering from an unacceptable rise of the mobile phase temperature. Experimental results indicate that the column segmentation does not lead to a significant efficiency loss (comparing the performance of a 10 cm column with a 2 cm × 5 cm column system), whereas, as expected, the system displays a much improved temperature stability, both in time (because of the shortened temperature transient times) and in space (reduction of the average axial temperature rise by a factor n). The method also prevents a large backflow of heat along the column wall that would lead to large efficiency losses if one would attempt to operate columns at pressures of 1500 bar or more. A real-world pharmaceutical example is given where this improved temperature robustness could help in moderating the changes in selectivity during method transfer from a low to a high pressure operation, although the complex non-linear behavior of the viscous heating and high pressure effects result in lower than expected improvement.

A Holistic Approach to the Application of Model Predictive Control to Batch Reactors

An advanced process control (APC) system using G2 and AspenTech's DMCplus controller was implemented on Anglo Platinum's Precious metals refinery. The APC was implemented on a batch reactor where an exothermic reaction occurred. The APC controller was able to counter the effects of an integrating process model and long time delay to improve overall stability of the reactor. The APC controller resulted in improved temperature stability, reduction in total batch time and reduction in a regent consumption.

Temperature Dependence of Current Gain, Ideality Factor, and Offset Voltage of AlGaAs/GaAs and InGaP/GaAs HBTs

This paper elucidates the stabilities of the dc current gain, ideality factor, and offset voltage against variations in temperature and currents for GaAs-based heterojunction bipolar transistors (HBTs). The InGaP/GaAs HBT markedly reduces the offset voltage and improves the temperature stability of the dc current gain relative to those of AlGaAs/GaAs benchmark devices. The relative insensitivity of the offset voltage in the InGaP/GaAs HBT to the temperature is established by comparison with AlGaAs/GaAs counterparts. One of the more intriguing aspects of these two HBTs is the replacement of the AlGaAs emitter with the InGaP emitter to improve the temperature stability of the offset voltage. Specifically, the effect of the base current on the offset voltage is abnormal in these devices. In this paper, the conventional Ebers-Moll model cannot account completely for our observed phenomena. Accordingly, the results herein (improved temperature stability of the offset voltage in the InGaP emitter HBT and the uncommon base current effect in these two devices) are interpreted in terms of a physics-based analytical model. A strong consistency existed between the experimental data and the theory. Additionally, some reasonable predictions (not obtained from the measured data) of the specific physically based model are presented. The large-signal model provides a description of device performance that will be of use to device engineers and designers.