Reduced Temperature Coefficient Research Articles

Enhanced stress relaxation resistance and strength-electrical conductivity combination of graphene reinforced Cu-0.5La composite wire for high temperature applications

The temperature-rise effect caused by the boom of high-power equipment for communications and transportation brings new challenges to the stress relaxation resistance and tensile properties of Cu wires at elevated temperatures. In order to meet higher property requirements, herein we introduced a graphene reinforced Cu-0.5La alloy (Gr/Cu-0.5La) composite wire prepared by in-situ synthesis and powder metallurgy methods. Thanks to the distribution of in-situ formed graphene and Gr-La2O3 hybrid reinforcements at the grain boundaries, the mechanical properties of the composite wire were improved. The uniformly dispersed graphene at grain boundaries created a strong pinning force, which limited the mobility of the grain boundaries and ultimately improved their thermal stability. Notably, the composite wire exhibits significantly enhanced stress relaxation resistivity, demonstrating advantages over element doping strategy. Meanwhile, the electrical conductivity of the Gr/Cu-0.5La composite wire reaches 89.3 % IACS, accompanied by a reduced temperature coefficient of resistance. Cyclic stress relaxation tests revealed that the excellent high-temperature mechanical properties mainly come from the dislocation-controlled strengthening and deformation mechanisms. The excellent comprehensive performance achieved proposes the good application prospects of Gr/Cu-0.5La composite wire in a wide temperature range.

Enhancing temperature stability of Ce: RIG films Faraday rotation through magnetic sublattice control

Cerium doped rare-earth iron garnet (Ce: RIG) film is a promising candidate for magneto-optical devices in laser systems with giant Faraday effect; nevertheless, devices fail nonreciprocally with increasing temperature due to a negative Faraday rotation angle temperature coefficient. To mitigate this effect, the relationship between the magnetic moments of three distinct magnetic sublattices and the temperature coefficients of the Faraday rotation angle was investigated. Cerium doped holmium iron garnet (Ce: HoIG) film, where magnetic Ho3+ occupied the dodecahedrons, exhibited an enhanced Faraday rotation angle retention at a temperature of 400 K. However, the nonmagnetic ion doping in tetrahedral and octahedral sites yielded a negligible effect. The mechanism behind this occurrence is attributed to the magnetic compensation effect, which results in a small magnetic moment temperature coefficient within the range of 300–400 K. The study not only offers strategies for designing Ce: RIG components with reduced temperature coefficient, but also presents the development of a Ce: HoIG film exhibiting promising stability in Faraday rotation angle as a function of temperature.

Effect of raw material pretreatment and ionic radius on the preparation and microwave dielectric properties of Re2TiO5 ceramics

The present study focuses on the synthesis and characterization of rare-earth titanates, specifically Re2TiO5 (ReLa, Nd, Sm), with a particular emphasis on their microwave dielectric properties. The factors influencing the synthesis of La2TiO5 compound through the traditional solid-state method were thoroughly investigated, with a significant finding being the notable impact of moisture absorption in La2O3. The impact of variations in rare-earth cation radii on the structure and dielectric properties was systematically analyzed. Re2TiO5 (ReLa, Nd, Sm) ceramics crystallized into an orthorhombic structure with space group Pnam, which was confirmed through Rietveld refinement. The resulting materials demonstrated exceptional microwave dielectric properties characterized by a low permittivity range of 13.72–17.39, high-quality factors ranging from 8331 to 17,795 GHz, and a significantly reduced temperature coefficient of resonance frequency (−33.2∼-12.6 ppm/°C). The correlation between microwave dielectric properties and structural characteristics (including ionic polarizability, packing fraction, and bond valence) was investigated. The exceptional potential of these rare-earth titanates lies in their ability to meet the stringent requirements for low signal transmission delay in wireless communication systems, owing to their advantageous low permittivity within the microwave frequency spectrum.

Surface-Acoustic-Wave Devices Based on Lithium Niobate and Amorphous Silicon Thin Films on a Silicon Substrate

This work presents an acoustic platform using solidly mounted thin-oriented lithium niobate (LiNbO3) film on silicon (Si). A thin layer of amorphous Si eliminates a conductive layer generated in the thin-film bonding processes and contributes to acoustic energy confinement and thermal frequency stability. The gigahertz operating frequency is achieved by resorting to the guided acoustic wave shear-horizontal wave (SH0) in a 400-nm-thick X-cut LiNbO3 thin film. Due to the elimination of the parasitic surface conduction (PSC) effect, the electromechanical coupling of the guide acoustic wave is maximized in the Si-based heterogeneous wafer. Due to the minimized acoustic impedance mismatch between surface material and substrate, longitudinal and higher order spurious modes are suppressed. Due to the stiff substrate with a small temperature expansion coefficient (TEC), the solidly mounted structure features a reduced temperature coefficient of frequency (TCF) and improved power handling. The fabricated resonator shows an extracted electromechanical coupling coefficient of 22.8%, a high loaded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 1208 at 1.6 GHz, and a TCF of −36 p/min/K. The compressed filter is demonstrated with a minimum insertion loss (IL) of 0.6 dB, a fractional bandwidth (FBW) of 8%, an out-of-band rejection of 30 dB, a TCF of −38.5 p/min/K at roll-off, and a miniaturized footprint of 0.4 mm2. The performance has shown the strong potential of the LiNbO3–Si platform for front-end applications in 5G.

Temperature Coefficient of Conductivity Dependent Electric Field Distribution in GFRP Based SFCL Bushing

In order to solve the problem of DC electric field distortion of superconducting fault current limiter (SFCL) bushing under the huge temperature range of 77 K-300 K, the glass fiber-reinforced epoxy resin (GFRP) insulation with reduced temperature coefficient of conductivity is used to improve the DC electric field distribution. For the DC 160 kV/1 kA SFCL bushing, the electric field distribution of condenser core has been figured out to analyze the effectiveness of reduced temperature coefficient of conductivity. The results show that, compared to traditional insulation, the modified GFRP material can significantly reduce the electric field distortion.

Experimental and Theoretical Analysis of Energy Efficiency in a Flat Plate Solar Collector Using Monolayer Graphene Nanofluids

Flat-plate solar collectors are one of the cleanest and most efficient heating systems available. Studies on the presence of covalently functionalized graphene (Gr) suspended in distilled water as operating fluids inside an indoor flat-plate solar collector (FPSC) were experimentally and theoretically performed. These examinations were conducted under different testing conditions namely 0.025 wt.%, 0.05 wt.%, 0.075 wt.%, and 0.1 wt.%, 0.5, 1, and 1.5 kg/min, 30, 40, and 50 °C, and 500, 750, and 1000 W/m2. Various techniques were used to characterize the functionalized nanofluids’ stability and morphological properties namely UV/Vis spectrophotometry, EDX analysis with a Scanning Electron Microscope (SEM), zeta potential, and nanoparticle size. The results showed that the collected heat improved as the percentage of GrNPs and the fluid mass flow rates increased, although it decreased as the reduced temperature coefficient increased, whereas the maximum increase in collector efficiency at higher concentration was 13% and 12.5% compared with distilled water at 0.025 kg/s. Finally, a new correlation was developed for the base fluid and nanofluids’ thermal efficiency as a function of dropped temperature parameter and weight concentration with 2.758% and 4.232% maximum deviations.

X-Cut Lithium Niobate-Based Shear Horizontal Resonators for Radio Frequency Applications

This article reports Lithium Niobate (LN) based shear horizontal (SH0) resonators utilizing suspended and solidly mounted structures for radio frequency (RF) applications. The solidly mounted SH0 structure (also termed guided SH0 structure) is advantageous in obtaining reduced temperature coefficient of frequency (TCF), reduced high frequency overtone spurious responses, and improved power handling. The demonstrated solidly mounted guided SH0 resonators exhibit a mechanical Q as high as 1316 around 950 MHz, and electromechanical coupling factor (k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) of around 21.8 % - resulting in a figure of merit (FoM = k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> · Q) of 288.

Temperature-stable dielectric and energy storage properties of (0.94Bi0.47Na0.47Ba0.06TiO3-0.06BiAlO3)–NaNbO3 ceramics

The lead-free ceramics (1-x)(0.94Bi0.47Na0.47Ba0.06TiO3-0.06BiAlO3)-xNaNbO3 were prepared by means of a traditional solid-state sintering method. All ceramics have pure perovskite structure and average grain sizes around 1 μm. Their dielectric and energy storage behavior were studied. The NaNbO3-doped ceramics display drastically reduced temperature coefficient of capacitance (TCC) compared to the ceramics without doping. The samples with x = 0.02 exhibit high permittivity and excellent temperature stability between 67 °C and 380 °C, meeting the requirement of TCC ≤ ±15%. The energy storage density was greatly improved to 1.71 J/cm3 as x = 0.03, showing excellent frequency stability from 0.5 Hz to 100 Hz, great temperature stability from 25 °C to 130 °C, and excellent fatigue resistance within 105 fatigue cycles.

Improved Electric Field Distribution Within Bushing Insulation by EP/GO Nanocomposites With Reduced Temperature Coefficient of Conductivity

Field grading within the dry-type bushing insulation presents a major challenge for DC applications due to the highly temperature-dependent conductivity of the epoxy resin insulation. An electric field regulation method based on the epoxy/graphene oxide (EP/GO) nanocomposites with the reduced temperature coefficient of conductivity is proposed and investigated in this paper. DC conductivity of EP/GO nanocomposites with different loadings of 0, 0.05, 0.1 and 0.5 wt% at various temperature are investigated. Trap level distributions are characterized by the isothermal discharge current (IDC) method to clarify the conduction mechanism. Obtained results show that more shallower traps are introduced and the thermal activation energies of the nanocomposites are reduced by the GO nanoparticles, indicating that the temperature coefficient of conductivity of the nanocomposites is reduced. The improvement of electric field distribution within the bushing insulation under operating voltage is verified when the EP/GO nanocomposite with an appropriate content is employed, based on an established ±800 kV valve-side bushing for a converter transformer. However, more defects will be introduced by the GO fillers with excessive content (0.5 wt%), resulting in an obvious reduction of the DC breakdown strength.

Investigation of the Amide Proton Solvent Exchange Properties of Glycosaminoglycan Oligosaccharides.

One-dimensional 1H NMR experiments were conducted for aqueous solutions of glycosaminoglycan oligosaccharides to measure the amide proton temperature coefficients and activation energy barriers for solvent exchange and evaluate the effect of pH on the solvent exchange properties. A library of mono- and oligosaccharides was prepared by enzymatic depolymerization of amide-containing polysaccharides and by chemical modification of heparin and heparan sulfate saccharides including members that contain a 3- O-sulfated glucosamine residue. The systematic evaluation of this saccharide library facilitated assessment of the effects of structural characteristics, such as size, sulfation number and site, and glycosidic linkage, on amide proton solvent exchange rates. Charge repulsion by neighboring negatively charged sulfate and carboxylate groups was found to have a significant impact on the catalysis of amide proton solvent exchange by hydroxide. This observation leads to the conclusion that solvent exchange rates must be interpreted within the context of a given chemical environment. On their own, slow exchange rates do not conclusively establish the involvement of a labile proton in a hydrogen bond, and additional supporting experimental evidence such as reduced temperature coefficients is required.

Structure and Properties of R – (Fe, Co) – B (R = Nd, Dy, Ho) Permanent Magnets with Low Temperature Coefficient of Induction

Two groups of sintered permanent magnets with reduced temperature coefficient of induction (TCI) are considered, i.e., (A ) (Nd0.64Dy0.36)16(Fe1 – xCox)77.5Cu0.1Ga0.3B6.1(x = 0.22 – 0.36) and (B) Nd0.64 – zDy0.36Hoz)16(Fe0.64Co0.36)77.5Cu0.1Ga0.3B6.1 ( z = 0.08 – 0.26). It is shown that substitution of 36% Fe by Co raises the Curie temperature of the magnets to 576°C and lowers the TCI to ∣ − 0.02 ∣ % /K in the range of 27 – 120°C. Substitution of Nd by Ho lowers the TCI additionally to zero at z = 0.17 and changes it to ∣ + 0.009 ∣ % /K at z = 0.26. The results of the study of the phase composition and of the microstructure of the magnets make it possible to explain the observed lowering of the coercivity under the alloying.

Giant Enhancement of Polarization and Strong Improvement of Retention in Epitaxial Ba0.6Sr0.4TiO3‐Based Nanocomposites

In Ba0.6Sr0.4TiO3 (BSTO)‐based epitaxial nanocomposite films increased P r values are demonstrated by up to a factor of 3 compared to standard BSTO films. A strongly reduced temperature coefficient of polarization retention is also obtained, i.e., 0.07% °C−1 compared to 0.24% °C−1. Piezopoling with only marginal leakage current is also achieved up to 200 °C, the highest temperature studied. The origin of the improved performance is the incorporation of Sm2O3 nanopillars in the films which acted as stiff vertical nanoscaffolds, inducing a strong tetragonal distortion in the BSTO (up to 1.033(7) in terms of the out‐of‐plane/in‐plane lattice dimensions). The films have comparable performance to industry‐standard Pb(Zr,Ti)O3 films, at the same time as being Pb‐free.

Phase Transformation, Vibrational and Electronic Properties of K2Ce(PO4)2: A Combined Experimental and Theoretical Study.

Herein we report the high-temperature crystal chemistry of K2Ce(PO4)2 as observed from a joint in situ variable-temperature X-ray diffraction (XRD) and Raman spectroscopy as well as ab initio density functional theory (DFT) calculations. These studies revealed that the ambient-temperature monoclinic (P21/n) phase reversibly transforms to a tetragonal (I41/amd) structure at higher temperature. Also, from the experimental and theoretical calculations, a possible existence of an orthorhombic (Imma) structure with almost zero orthorhombicity is predicted which is closely related to tetragonal K2Ce(PO4)2. The high-temperature tetragonal phase reverts back to ambient monoclinic phase at much lower temperature in the cooling cycle compared to that observed at the heating cycle. XRD studies revealed the transition is accompanied by volume expansion of about 14.4%. The lower packing density of the high-temperature phase is reflected in its significantly lower thermal expansion coefficient (αV = 3.83 × 10-6 K-1) compared to that in ambient monoclinic phase (αV = 41.30 × 10-6 K-1). The coexistences of low- and high-temperature phases, large volume discontinuity in transition, and large hysteresis of transition temperature in heating and cooling cycles, as well as drastically different structural arrangement are in accordance with the first-order reconstructive nature of the transition. Temperature-dependent Raman spectra indicate significant changes around 783 K attributable to the phase transition. In situ low-temperature XRD, neutron diffraction, and Raman spectroscopic studies revealed no structural transition below ambient temperature. Raman mode frequencies, temperature coefficients, and reduced temperature coefficients for both monoclinic and tetragonal phases of K2Ce(PO4)2 have been obtained. Several lattice and external modes of rigid PO4 units are found to be strongly anharmonic. The observed phase transition and structures as well as vibrational properties of both ambient- and high-temperature phases were complimented by DFT calculations. The optical absorption studies on monoclinic phase indicated a band gap of about 2.46 eV. The electronic structure calculations on ambient-temperature monoclinic and high-temperature phases were also carried out.

A Curvature-Compensated, High Power Supply Rejection CMOS Bandgap Reference for MEMS Micro-Accelerometer

The reference is an important part in the accelerometer system. With the development of science and technology, the request of the performance of accelerometers is increasingly higher and the precision of reference directly affects the performance of accelerometers. Therefore, a reference voltage applicable to accelerometers is presented based on the analysis of basic principles of conventional bandgap reference (BGR) in this paper. A high-order curvature compensation technique, which uses a temperature dependent resistor ratio generated by a high poly resistor and a nwell resistor, effectively serves to reduce temperature coefficient of proposed reference voltage circuit and to a large extent improve its performance. To achieve a high power supply rejection ratio (PSRR) over a broad frequency range, a pre-regulator is introduced to remain the supply voltage of the core circuit of BGR relatively independent of the global supply voltage. The proposed circuitry is designed in standard 2.0μm CMOS process. The simulated result shows that the average temperature coefficient is less than 2ppm/°C in the temperature range from -40 to 120°C. The improvement on temperature coefficient (TC) is about 10 times reduction compared to the conventional approach. And the PSR at DC frequency and 1kHz achieves -107 and -71dB respectively at 9.0V supply voltage.

Experimental Characterization of Optical Fiber Long Period Grating with Reduced Temperature Sensitivity

Abs tract—In this paper we show the experimental characterization of optical fiber long period grating for the reduced temperature sensitivity by optimizing the refractiveindex profile of the host fiber. In Long Period Fiber grating the fundamental guided mode light couple with the into copropagating cladding modes at various wavelengths. The two layer Geometry later on the three layer geometry which is useful for refractive index sensing sensing application. The sensitivity of LPFGs to environmental parameters is influenced by the period of the LPFG by the order of the cladding mode to which coupling takes place and by the composition of the optical fiber. A novel method to compensate the temperature sensitivity using a boron co-doped germanosilicate core fiber is used as a host fiber. The Theoretical Characteristic Results matches with the experimental results which demonstrate that such gratings with reduced temperature coefficient retain their capability to detect strain and ambient index variations.

Reduced Temperature Coefficient of Capacitance (TCC) of Embedded Capacitor Films (ECFs) for Organic Substrates using SrTiO3 and Multifunctional Epoxy

Epoxy/ceramic composites have attracted great interest as embedded capacitor materials, mainly due to the process compatibility of epoxy with printed circuit boards (PCBs). However, one of the potential problems of epoxy/ceramic composites is the temperature dependence of their dielectric properties. This study focuses mainly on reducing the temperature coefficient of capacitance (TCC) of epoxy/ceramic composites using multifunctional epoxy and SrTiO3 powder. The TCC of an epoxy/ceramic composite mainly depends on the properties of its epoxy and ceramic powder. Using multifunctional epoxy, the epoxy resin showed two glass-transition temperatures, resulting in a lower dimensional change after the first glass-transition temperature. Additionally, the TCC of epoxy/SrTiO3 ECFs can be decreased by increasing the SrTiO3 powder content. As a result, reduced TCC of epoxy/ceramic composite capacitors using a multifunctional epoxy and SrTiO3 powder was successfully demonstrated for embedded capacitors in organic substrates.

Oxygenated Protocrystalline Silicon Thin Films for Wide Bandgap Solar Cells

AbstractProtocrystalline silicon, which is a material that has enhanced medium range order (MRO), can be prepared by using high hydrogen dilution in PECVD, or, alternatively, using high atomic H production from pure silane in HWCVD. We show that this material can accommodate percentage-level concentrations of oxygen without deleterious effects. The advantage of protocrystalline SiO:H for application in multijunction solar cells is not only that it has an increased band gap, providing a better match with the solar spectrum, but also that the solar cells incorporating this material have a reduced temperature coefficient. Further, protocrystalline materials have a reduced susceptibility to light-induced defect creation. We present the unique result in the PV field that these oxygenated protocrystalline silicon solar cells have an efficiency temperature coefficient (TCE) that is virtually zero (TCE is between -0.08%/°C and 0.0/°C). It is thus beneficial to make this cell the current limiting cell in multibandgap cells, which will lead to improved annual energy yield.

Study of polydiethylsiloxane-based ferrofluid with excellent frost resistance property

The polydiethylsiloxane-based ferrofluid was prepared by dispersing finely divided magnetic Fe 3O 4 particles which are modified with oleoyl sarcosine and lauroyl sarcosine. The optimized experiment parameters including molar ratio of surfactant to Fe 3O 4 (1:5), temperature (80 °C), stirring rate (300 RPM), the surfactant content of lauroyl sarcosine (0 to 33 mol%) and the modification time (25 min) were obtained by the orthogonal test. The magnetic liquid was characterized by a transmission electron microscope (TEM), infrared (IR) spectrometer, X-ray diffractometer (XRD), thermogravimetry (TG), vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC). It is indicated that the surfactant is mainly bonded to the surface of Fe 3O 4 nanoparticles through covalent bond between carboxylate (COO −) and Fe atom. The modified magnetic particles are equally dispersed into the carrier and remain stable below −12 °C over 4 months. The ferrofluids exhibit excellent frost resistance property and distinctly reduced temperature coefficient of viscosity compared with polydimethylsiloxane-based ferrofluids and hydrocarbon-based ferrofluids, respectively. The saturation magnetization could reach up to 27.7 emu/g.

Sinterability studies and microwave dielectric properties of sol–gel synthesized Ba(Zn 1/3Ta 2/3)O 3 nanoparticles

Nanosized phase pure powder of Ba(Zn 1/3Ta 2/3)O 3 (BZT) was prepared by sol–gel method and subsequent pyrolysis of the dried gel. The powders were pyrolyzed at different elevated temperatures and the effect of pyrolysis temperature on particle size was investigated. The sinterability of BZT ceramics made from nanopowders was found to be very high. Hence the sintered microstructure shows very large grains. However sintered density and microwave dielectric properties of sintered nanopowders were found to be poor. Reason for the poor densification was found to be the formation of large amounts of intergranular porosity and drastic grain growth during sintering. The samples were sintered by muffling with calcined BZT powder. Different sintering additives were added to calcined nanosized powders and then sintered. Most of the dopants are found to promote grain growth of sintered microstructure. Some of the dopants are found to reduce temperature coefficient of resonant frequency to zero when the average ionic radius was about 0.615 Å.

Investigation on SAW properties of LGS and optimal cuts for high-temperature applications

A promising perspective for surface acoustic wave (SAW) device applications at high temperature has been opened by langasite (LGS). The SAW properties of LGS in singly and doubly rotated cuts at 250 degrees C are investigated. Three noticeable regions for SAW-cut orientations and propagation directions at high temperature are put forward and are defined by Euler angles [0 degrees, 20 degrees --> 50 degrees, 35 degrees --> 45 degrees], [0 degrees, 85 degrees --> 110 degrees, 0 degrees --> 5 degrees], and [0 degrees, 138 degrees --> 145 degrees, 20 degrees --> 23 degrees], respectively. The first region includes zero or comparatively reduced temperature coefficient of delay (TCD) (<2 ppm) and smaller electromechanical coupling factor (K2) (0.2%-0.35%); the second one exhibits higher K2 (0.35%-0.45%) and moderate TCD (<5 ppm); and the highest K2 (>0.45%) and larger TCD (25-30 ppm) characterize the last region. For some typical orientations within the above-mentioned three regions, the temperature dependency of SAW characteristics (up to 1000 degrees C) is discussed. The second region [0 degrees, 85 degrees --> 110 degrees, 0 degrees --> 5 degrees], especially the orientation [0 degrees, 90 degrees, 0 degrees], has better comprehensive characteristics of SAW and is more suitable for high-temperature applications. Therefore, we should give a top priority to the orientation [0 degrees, 90 degrees, 0 degrees] in the design of SAW devices operating at high temperature. Comparison between published experimental results and numerical predictions based on LGS constants and their temperature coefficients available in the literature reveals that the theoretical results of TCD under 250 degrees C are in agreement with the experimental ones (the relative error of TCD is within 10%).