Showing papers on "Temperature coefficient published in 2013"
TL;DR: The abrupt first-order metal-insulator phase transition in single-crystal vanadium dioxide nanowires (NWs) is engineered to be a gradual transition by axially grading the doping level of tungsten, yielding an extremely high temperature coefficient of resistivity ~10%/K and a very low resistivity down to 0.001 Ω·cm.
Abstract: The abrupt first-order metal–insulator phase transition in single-crystal vanadium dioxide nanowires (NWs) is engineered to be a gradual transition by axially grading the doping level of tungsten. We also demonstrate the potential of these NWs for thermal sensing and actuation applications. At room temperature, the graded-doped NWs show metal phase on the tips and insulator phase near the center of the NW, and the metal phase grows progressively toward the center when the temperature rises. As such, each individual NW acts as a microthermometer that can be simply read out with an optical microscope. The NW resistance decreases gradually with the temperature rise, eventually reaching 2 orders of magnitude drop, in stark contrast to the abrupt resistance change in undoped VO2 wires. This novel phase transition yields an extremely high temperature coefficient of resistivity ∼10%/K, simultaneously with a very low resistivity down to 0.001 Ω·cm, making these NWs promising infrared sensing materials for uncoole...
96 citations
TL;DR: In this article, a nano-ceramic is characterized by X-ray diffraction (XRD), dielectric study and impedance spectroscopy, which shows single phase ceramic of orthorhombic symmetry and a significant shift in impedance loss peaks toward the higher frequency side indicates conduction in the material favoring the long-range motion of mobile charge carriers.
Abstract: Nanocrystalline calcium titanate (CT) ceramic has been synthesized by a combination of solid-state reaction and high-energy ball milling. This nano-ceramic is characterized by X-ray diffraction (XRD), dielectric study and impedance spectroscopy. The XRD pattern shows single phase ceramic of orthorhombic symmetry. The frequency-dependent dielectric study shows that the dielectric constant is maximized at low frequencies and decreases with an increase in frequency. Impedance spectroscopy analyses reveal a non-Debye type relaxation phenomenon. A significant shift in impedance loss peaks toward the higher-frequency side indicates conduction in the material favoring the long-range motion of mobile charge carriers. The grain conduction effect is observed from the complex impedance spectrum by the appearance of one semicircular arc in Nyquist plot. It is also observed that the resistance decreases with an increase in temperature showing a negative temperature coefficient of resistance (NTCR). Various thermistor parameters have been calculated by fitting with Steinhart-Hart equation. The modulus plots represent the presence of temperature- dependent electrical relaxation phenomenon with the material. The frequency-dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated. The activation energy has been calculated from an Arrhenius plot of DC conductivity and relaxation frequency.
88 citations
TL;DR: In this paper, the I-V-curve of the Ge bottom cell of a triple-junction Ga0.50In0.01As was investigated under a broad range of operating conditions, namely temperatures T from 5 to 170°C and concentration ratios C from 1 to 3000.
85 citations
TL;DR: In this article, the lattice parameter c/a ratio of the MnBi compound increases with the increasing temperature and finally reaches a maximum of 1.433 around 600 k. The temperature dependence of the coercivity is related to the change of magnetocrystalline anisotropy, and shows strong dependence on the sizes of MnBi particles.
84 citations
TL;DR: It is found that both planar and out-of-plane characteristic modes in molybdenum disulfide atomic layers are highly sensitive to temperature variations, and this temperature dependency is linear and can be fully explained by the first-order temperature coefficient.
Abstract: Raman spectroscopy is utilized to quantify the temperature dependency of the vibrational modes in molybdenum disulfide (MoS2) atomic layers. These analyses are essential for understanding the structural properties and phononic behaviors of this two-dimensional (2D) material. We quantitatively analyze the temperature dependent shifts of the Raman peak positions in the temperature range from 300 to 550 K, and find that both planar and out-of-plane characteristic modes are highly sensitive to temperature variations. This temperature dependency is linear and can be fully explained by the first-order temperature coefficient. Using a semi-quantitative model, we evaluate the contributions of the material's thermal expansion and intrinsic temperature effects to this dependency. We reveal that the dominating source of shift in the peak position of planar mode E2g1 for samples of all thicknesses investigated is the four-phonon process. In addition to the four-phonon process, thermal expansion plays a significant role in the temperature dependency of the out-of-plane mode, A1g. The thickness dependency of the temperature coefficient for MoS2 and a drastic change in behaviors of samples from bi- to single-layered are also demonstrated. We further explore the role of defects in the thermal properties of MoS2 by examining the temperature dependency of Raman modes in CVD-grown samples.
81 citations
TL;DR: In this article, the phase presence, surface morphology and according energy dispersive spectrometer (EDS) analysis were determined by X-ray diffractometer (XRD) and scanning electron microscope (SEM) techniques, respectively.
80 citations
TL;DR: An inkjet printing process was developed to produce thermistor arrays for temperature sensing applications that responds quickly to small temperature changes and provides an effective tool for transient temperature measurements.
Abstract: In this study, an inkjet printing process was developed to produce thermistor arrays for temperature sensing applications. First, a formulation process was carefully performed to generate a stable nanoparticle ink for nickel oxide, a material with a large temperature coefficient of resistance. The thermistor was then fabricated by printing a square NiO thin film in between two parallel silver conductive tracks on either glass plates or polyimide films. The printed thermistor, which has an adjustable dimension with a sub-millimeter scale, can operate over a wide range from room temperature to 200 °C with great sensitivity (B values ∼4300 K) without hysteretic effects. When printed on polyimide films, the thermistors can also be bent or attached to curved surfaces to provide accurate and reliable temperature measurements. Moreover, the thermistor responds quickly to small temperature changes and provides an effective tool for transient temperature measurements. Finally, a thermistor array was fabricated to ...
78 citations
TL;DR: In this article, the phonon and thermal properties of thin films of tantalum diselenide (2H-TaSe2) obtained via the “graphene-like” mechanical exfoliation of crystals grown by chemical vapor transport were investigated.
Abstract: We report on the phonon and thermal properties of thin films of tantalum diselenide (2H-TaSe2) obtained via the “graphene-like” mechanical exfoliation of crystals grown by chemical vapor transport. The ratio of the intensities of the Raman peak from the Si substrate and the E2g peak of TaSe2 presents a convenient metric for quantifying film thickness. The temperature coefficients for two main Raman peaks, A1g and E2g, are −0.013 and −0.0097 cm−1/oC, respectively. The Raman optothermal measurements indicate that the room temperature thermal conductivity in these films decreases from its bulk value of ∼16 W/mK to ∼9 W/mK in 45-nm thick films. The measurement of electrical resistivity of the field-effect devices with TaSe2 channels shows that heat conduction is dominated by acoustic phonons in these van der Waals films. The scaling of thermal conductivity with the film thickness suggests that the phonon scattering from the film boundaries is substantial despite the sharp interfaces of the mechanically cleaved samples. These results are important for understanding the thermal properties of thin films exfoliated from TaSe2 and other metal dichalcogenides, as well as for evaluating self-heating effects in devices made from such materials.
77 citations
TL;DR: In this paper, the conductive fillers were premixed with UHMWPE by melt-mixing and then polyvinylidene fluoride (PVDF) was introduced into the blends.
Abstract: Aiming to enhance the positive temperature coefficient (PTC) effect of resistance, immiscible polymer blends [ultra-high molecular weight polyethylene (UHMWPE)/polyvinylidene fluoride (PVDF) = 4 : 1] based composites containing hybrid fillers [carbon nanotubes (CNTs) and carbon black (CB)] were explored. The conductive fillers were premixed with UHMWPE by melt-mixing and then PVDF was introduced into the blends. The preferential distribution of conductive fillers in the UHMWPE phase was desirably observed. Besides decreasing the electrical resistivity of the single UHMWPE based PTC materials, the addition of PVDF with much higher melting point could improve the temperature range of the PTC materials, which is important for their potential applications. A remarkable synergetic effect arising from the combination of CB and CNTs with different geometric structures and aspect ratios on improving the PTC behavior was demonstrated. By introducing 0.5 vol% CNTs into the 4 vol% CB filled UHMWPE0.8–PVDF0.2 composites, the initial resistivity decreased by about two orders of magnitude and the PTC intensity (PTCI) increased by about 30%. Owing to the 3-dimensional conductive networks provided by tube-shaped CNTs and spherical CB and the high viscosity of the UHMWPE matrix, favorable PTC repeatability was also achieved.
77 citations
TL;DR: In this paper, a lead-free piezoelectric perovskite ceramic (BNT-BT 0.05 ), prepared by conventional high temperature solid state reaction technique at 1160 °C/3h in air atmosphere, is investigated by impedance and modulus spectroscopy in a temperature range 35-400 °C, over a frequency range 100 Hz-1 MHz.
Abstract: Lead-free piezoelectric perovskite ceramic (Bi 0.5 Na 0.5 ) 0.95 Ba 0.05 TiO 3 (BNT-BT 0.05 ), prepared by conventional high temperature solid state reaction technique at 1160 °C/3h in air atmosphere, is investigated by impedance and modulus spectroscopy in a temperature range 35–400 °C, over a frequency range 100 Hz–1 MHz. The crystal structure, microstructure, and piezoelectric properties as well as the AC conductivity of the sample were studied. Powder X-ray diffraction pattern derived from the resulting data at the room temperature subjected to Rietveld refinements and Williamson-Hall plot analysis confirmed the formation of phase pure compound with monoclinic unit cells having a crystallite-size ~33.8 nm. Observed SEM micrograph showed a uniform distribution of grains inside the sample having an average grain size ~3 mm. Longitudinal piezoelectric charge coefficient of the sample poled under a DC electric field of ~ 2.5 kV/mm at 80 °C in a silicone oil bath was found to be equal to 95 pC/N. The frequency and temperature dependent electrical data analysed in the framework of AC conductivity, complex impedance as well as electric modulus formalisms showed negative temperature coefficient of resistance (NTCR) character of the material and the dielectric relaxation in the material to be of non-Debye type. Double power law for the frequency-dependence of AC conductivity and Jump Relaxation Model (JRM) were found to explain successfully the mechanism of charge transport in BNT-BT 0.05 .
77 citations
TL;DR: It is suggested that the temperature dependence curves produced by the Dobbins model may be used tentatively as a simple theoretical guide for streams with free surface water but not self-aerated flows encountered in whitewater rapids, cascades or weirs.
TL;DR: In this article, the forward and reverse bias currentvoltage (I-V ) characteristics in the Au/(Zn-doped) PVA/n-GaAs SBDs were investigated in the temperature range of 80 −350 k by the steps of 30 k.
Abstract: In order to obtain detailed information about the current-transport mechanisms (CTMs) in the Au/(Zn-doped) PVA/n-GaAs SBDs, the forward and reverse bias current–voltage ( I – V ) characteristics were investigated in the temperature range of 80–350 K by the steps of 30 K. The ideality factor ( n ) decreases from 12.850 to 2.805, while the zero-bias barrier height ( Φ Bo ) increases from 0.145 eV to 0.606 eV with increasing temperature from 80 K to 350 K. While the n decreases, Φ Bo increases with increasing temperature. Such positive temperature coefficient ( α ) of Φ Bo is not in agreement with the negative temperature coefficient of band gap GaAs or barrier height (BH) of ideal diode. On the other hand, the value of modified barrier height (= nΦ Bo ) decreases almost linearly with the increasing temperature as Φ B ( T ) = (1.909–5.852 × 10 −4 T ) eV. It is clear that this value of the BH is in good agreement with the negative temperature coefficient of band gap of GaAs (−5.4 × 10 −4 eV K −1 ). In addition, the semi-logarithmic ln I – V plots at low bias voltages are almost parallel for each temperature. As a result of that, its inverse slope ( E o = nkT / q = 87 meV) remained almost constant, indicating it is independent of temperature. Such behavior of BH can be explained by the field emission (FE) theory especially at low temperatures rather than thermionic emission (TE) and thermionic field emission (TFE) theories. Therefore, the non-ideal behavior of the forward-bias I – V characteristics in Au/(Zn-doped)-PVA/n-GaAs SBD was successfully explained in terms of the TE mechanism with a double GD of BHs.
TL;DR: In this article, a uniformly distributed matrix of silicon dioxide pillars is embedded inside the silicon substrate to form a homogenous composite silicon oxide platform (SilOx) with nearly perfect temperature-compensated stiffness moduli.
Abstract: This paper presents a passive temperature compensation technique that can provide full cancellation of the linear temperature coefficient of frequency (TCF1) in silicon resonators. A uniformly distributed matrix of silicon dioxide pillars is embedded inside the silicon substrate to form a homogenous composite silicon oxide platform (SilOx) with nearly perfect temperature-compensated stiffness moduli. This composite platform enables the implementation of temperature-stable microresonators operating in any desired in- and out-of-plane resonance modes. Full compensation of TCF1 is achieved for extensional and shear modes of SilOx resonators resulting in a quadratic temperature characteristic with an overall frequency drift as low as 83 ppm over the industrial temperature range ( -40°C to 80°C). Besides a 40 times reduction in temperature-induced frequency drift in this range, SilOx resonators exhibit improved temperature stability of Q compared with their single crystal silicon counterparts.
TL;DR: In this article, the influence of phases and phase boundaries of TiO2 and Ta2O5 in the dielectric and electric response of TiTaO (100 nm thick) elaborated by RF magnetron sputtering was highlighted by complex impedance spectroscopy.
Abstract: The influence of phases and phase’s boundaries of TiO2 and Ta2O5 in the dielectric and electric response of TiTaO (100 nm thick) elaborated by RF magnetron sputtering was highlighted by complex impedance spectroscopy. Dielectric and electric modulus properties were studied over a wide frequency range (0.1–10 5 Hz) and at various temperatures (−160 to 120 ◦ C). The diagram of Argand (e �� versus e � ) shows the contribution of phases, phases’ boundaries and conductivity effect on the electric response of TiTaO thin films. Moreover, the resistance of the material decreases when the temperature increases, thus the material exhibits a negative temperature coefficient of resistance. The electric modulus plot indicates the presence of two peaks of relaxation. The first relaxation process appears at low temperature with activation energy of about 0.22 eV and it is related to the first ionization energy of oxygen vacancies. The second relaxation process appears at high temperature with activation energy of about 0.44 eV. This second peak is attributed to the Maxwell–Wagner–Sillars relaxation. The plots of the complex dielectric modulus and the impedance as a function of frequency allow concluding to a localized relaxation due to the long-range conductivity in the TiTaO film. (Some figures may appear in colour only in the online journal)
TL;DR: In this paper, vanadium oxide thin films were grown onto quartz substrates using the pulsed DC reactive magnetron sputtering technique at room temperature and afterwards post annealed under vacuum conditions in the temperature range from 75 to 230°C.
Abstract: Vanadium oxide thin films were grown onto quartz substrates using the pulsed DC reactive magnetron sputtering technique at room temperature and afterwards post annealed under vacuum conditions in the temperature range from 75 to 230 °C. The electrical resistance, temperature coefficient of resistance (TCR), optical energy gap and structural properties were investigated. The films are amorphous, nanoscale grained V 2 O 5 phase and the mean grain size increases with increasing temperature. Additionally, the post-annealing at 230 °C induces formation of both V 2 O 5 and V 4 O 9 phases and pinholes on the film surface. The temperature dependent variation of the electrical resistance indicates two activation energy areas corresponding to two TCR values for the films post annealed up to 180 °C, but only one activation area was found after annealing at 230 °C. Analyses of the absorption coefficient versus photon energy revealed a direct forbidden transition. The mean grain size and TCR values increase with increasing post-annealing temperature, whereas the optical energy gap and electrical resistance do not follow this tendency. The evolution of the structure and its correlation to the optical energy gap, electrical resistance, activation energy and TCR were discussed by means of the results obtained in the present study.
TL;DR: In this article, the electric field-induced strain of Bi1/2(Na0.82K0.18) 1/2TiO3 (BNKT) was investigated as a function of composition and temperature.
TL;DR: In this paper, the complex permittivity of a SiC fiber-reinforced SiC matrix (SiCf/SiC) composite was measured in a temperature range of 25-700°C at frequencies from 82 to 18 GHz.
TL;DR: A 1.1-MHz submicrowatt current-mode relaxation oscillator with temperature compensation is presented, in this oscillator, the current-starving inverters are biased by using the current sources with positive and negative temperature coefficients to relax the temperature variations.
Abstract: A 1.1-MHz submicrowatt current-mode relaxation oscillator with temperature compensation is presented. In this oscillator, the current-starving inverters are biased by using the current sources with positive and negative temperature coefficients. It relaxes the temperature variations. This oscillator is fabricated in a 0.18- μm CMOS process, and its area is 0.075 mm2. The power consumption is 0.859 μW, with a supply voltage of 1.8 V, and the calculated figure of merit is 0.78 nW/kHz. The measured output relative frequency variation is less than 3%/V for the supply voltage of 1.2-2.4 V and ±0.5% for the temperature of -20°C-80°C. The average temperature coefficient is 64.3 ppm/°C.
TL;DR: The interaction between graphene and GO and the chemical doping effect were responsible for the tunable control of its electrical response to temperature variation and made it a promising candidate in many areas, such as high-end film electronic device and sensor applications.
Abstract: Materials with low temperature coefficient of resistivity (TCR) are of great importance in some areas, for example, highly accurate electronic measurement instruments and microelectronic integrated circuits. In this work, we demonstrated the ultrathin graphene–graphene oxide (GO) hybrid films prepared by layer-by-layer assembly with very small TCR (30–100 °C) in the air. Electrical response of the hybrid films to temperature variation was investigated along with the progressive reduction of GO sheets. The mechanism of electrical response to temperature variation of the hybrid film was discussed, which revealed that the interaction between graphene and GO and the chemical doping effect were responsible for the tunable control of its electrical response to temperature variation. The unique properties of graphene–GO hybrid film made it a promising candidate in many areas, such as high-end film electronic device and sensor applications.
TL;DR: In this article, negative thermal expansion (NTE) was achieved in a wide temperature region covering room temperature (α = −6.8 ppm/K, 150 K-400 K).
Abstract: Our recent research on the Mn-based antiperovskite functional materials AXMn3 (A: metal or semiconducting elements; X: C or N) is outlined. Antiperovskite carbides (e.g., AlCMn3) show large magnetocaloric effect comparable to those of typical magnetic refrigerant materials. Enhanced giant magnetoresistance up to 70% at 50 kOe (1 Oe = 79.5775 Am−1) over a wide temperature span was obtained in Ga1−xZnxCMn3 and GaCMn3−xNix. In Cu0.3Sn0.5NMn3.2, negative thermal expansion (NTE) was achieved in a wide temperature region covering room temperature (α = −6.8 ppm/K, 150 K–400 K). Neutron pair distribution function analysis suggests the Cu/Sn-Mn bond fluctuation is the driving force for the NTE in Cu1−xSnxNMn3. In CuN1−xCxMn3 and CuNMn3−yCoy, the temperature coefficient of resistivity (TCR) decreases monotonically from positive to negative as Co or C content increases. TCR is extremely low when the composition approaches the critical points. For example, TCR is ~ 1.29 ppm/K between 240 K and 320 K in CuN0.95C0.05Mn3, which is one twentieth of that in the typical low-TCR materials (~ 25 ppm/K). By studying the critical scaling behavior and X deficiency effect, some clues of localized-electron magnetism have been found against the background of electronic itinerant magnetism.
TL;DR: In this article, the authors investigated the microstructures, crystalline structures, dielectric and piezoelectric properties of lead-free high-temperature ceramics.
Abstract: The 0.72Bi(Fe1−xAlx)O3–0.28BaTiO3 (x = 0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFAx–BT) lead-free high-temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high-temperature stability of piezoelectric properties was carried out. The crystalline structures of BFAx–BT ceramics evolve from rhombohedral structure with x 0.03. Remarkably high-temperature stability with near-zero temperature coefficient of piezoelectric properties (TCkp), together with improved piezoelectric properties has been achieved for x = 0.01 BFAx–BT ceramics. The BFAx–BT(x = 0.01) ceramics simultaneously show the excellent piezoelectric properties of d33 = 151 pC/N, kp = 0.31 and super-high-temperature stability of Td = 420°C, TCkp = 1 × 10−4. It is considered that the observed strong piezoelectricity and remarkably high-temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCkp value and the pseudocubic phases possess a negative TCkp value. Thus, the TCkp value of BFAx–BT ceramics can be tuned by composition of x.
TL;DR: In this paper, the phase evolution and microstructures of spinel-structured ZnGa2O4 ceramics were studied by XRD and SEM, and their microwave dielectric properties were investigated.
Abstract: Spinel ZnGa2O4 ceramics were synthesized by conventional solid-state method and their microwave dielectric properties were investigated. The phase evolution and microstructures of specimens were studied by XRD and SEM. The textured surface microstructures of ZnGa2O4 ceramics formed at high sintering temperatures. The spinel-structured ZnGa2O4 ceramics sintered at 1385°C exhibited excellent microwave dielectric properties: a dielectric constant (er) of 10.4, a quality factor (Q × f) of 94.600 GHz, and a temperature coefficient of resonant frequency (τf) of −27 ppm/°C. ZnGa2O4 ceramics have a low sintering temperature, a wide temperature region, and a small negative τf value. They are promising candidate materials for millimeter-wave devices.
TL;DR: In this paper, a site ion and gathering at grain boundaries (GBs) were proposed to describe the existence of Ag substitution in LCMO:Agx ceramics, which can be used as a candidate of bolometer or infrared detector around room temperature.
TL;DR: In this article, the electrical resistivity of the as-consolidated and coarse-grained bulk gadolinium (Gd) metals was studied in the temperature range of 3-315 K.
TL;DR: In this paper, the electrical conduction mechanism of amorphous titanium oxide thin films applied for bolometers was investigated and it was shown that the resistivity and activation energy vary from −1.2% to −2.3% and from 0.09
Abstract: We report the electrical conduction mechanism of amorphous titanium oxide thin films applied for bolometers. As the O/Ti ratio varies from 1.73 to 1.97 measured by rutherford backscattering spectroscopy, the resistivity of the films increases from 0.26 cm to 10.1 cm. At the same time, the temperature coefficient of resistivity and activation energy vary from −1.2% to −2.3% and from 0.09 eV to 0.18 eV, respectively. The temperature dependence of the electrical conductivity illustrates a thermally activated conduction behavior and the carrier transport mechanism in the titanium oxide thin films is found to obey the normal Meyer-Neldel Rule in the temperature range from 293 K to 373 K.
TL;DR: In this paper, a polycrystalline sample of (Bi0.8Gd0.2)FeO3 was prepared by a high-temperature solid-state reaction technique.
Abstract: The polycrystalline sample of (Bi0.8Gd0.2)FeO3 was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the sample confirms the formation of the desired compound with rhombohedral phase. The scanning electron micrograph of the sample showed uniform distribution of the plate- and rod-shaped grains. Studies of dielectric and electrical properties of the material were investigated within a wide range of temperature (25–400 °C) and frequency (1 kHz–1 MHz) using complex impedance spectroscopic method. The observation of hysteresis loop of the material confirmed that the material has a ferroelectric property at room temperature. The ac conductivity suggests that the sample obey Jonscher’s universal power law. The dc conductivity follows Arrhenius equation. Detailed studies of ac and dc conductivity show a negative temperature coefficient of resistance (NTCR) behavior of the sample.
TL;DR: In this article, photo-pumped GaAs1−xBix laser diodes with Al0.3Ga0.7As electron blocking layer were used to achieve long-wavelength emission of up to 1204nm.
Abstract: This study demonstrates long-wavelength emission of up to 1204 nm in photo-pumped GaAs1−xBix lasers grown by molecular beam epitaxy under low temperature conditions. The characteristic temperature (T0) between 20 and 80 °C in the GaAs1−xBix lasers with Al0.3Ga0.7As electron blocking layer is approximately 100 K, which is larger than that of the typical 1.3-μm InGaAsP Fabry-Perot laser diodes (FP-LDs; T0 = 66 K). The temperature coefficient of the lasing wavelength is approximately 40% of that of InGaAsP FP-LDs.
TL;DR: In this article, complex impedance analysis of polycrystalline complex perovskite structured BaZr 0·025Ti 0·975O3 prepared by solid state reaction method was performed.
Abstract: This paper reports complex impedance analysis of polycrystalline complex perovskite structured BaZr 0·025Ti 0·975O3 prepared by solid state reaction method. XRD analysis reveals the formation of single phase perovskite structure. SEM has been used to investigate grain morphology of the material. Impedance plots have been used as a tool to analyse electrical properties of the sample as a function of frequency and temperature. Bulk resistance is observed to decrease with an increase in temperature showing a typical negative temperature coefficient of resistance (NTCR) type behaviour. Nyquist (Cole–Cole) plots show both inter and intra grain boundary effects. Relaxation time is found to decrease with increasing temperature and it obeys the Arrhenius relationship. The variation of d.c. and a.c. conductivity as a function of temperature is also reported.
TL;DR: In this paper, the authors synthesize Zn2GeO4 ceramics by solid-state method and investigate their properties with X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectrum, Raman spectrum, XPS, and high resolution transmission electron microscopy (HRTEM).
TL;DR: In this paper, the forward current transport mechanisms in Ni/Au-AlGaN/GaN Schottky diodes were studied by temperature dependent currentvoltage (T-I-V) measurements from 298 to 473 K.
Abstract: The forward current transport mechanisms in Ni/Au-AlGaN/GaN Schottky diodes are studied by temperature dependent current-voltage (T-I-V) measurements from 298 to 473 K. The zero-bias barrier height qϕBn and ideality factor values determined based on the conventional thermionic-emission (TE) model are strong functions of temperature, which cannot be explained by the standard TE theory. Various transport models are considered to analyze the experimental I-V data. The fitting results indicate that the increased current at low bias is due to the trap-assisted tunneling with an effective trap density of about 8.8 × 106 cm−2, while the high-bias current flow is dominated by the TE transport mechanism, accompanied by a significant series resistance effect. By fitting the high-forward-bias I-V characteristics, the effective qϕBn values with a small negative temperature coefficient are obtained. The temperature dependence of the saturation tunneling current and qϕBn is finally explained by considering the thermall...