Infrared Absorption and Its Sources of CdZnTe at Cryogenic Temperature

To reveal the causes of infrared absorption in the wavelength region between electronic and lattice absorptions, we measured the temperature dependence of the absorption coefficient of p-type low-resistivity ($$\sim 10^2~ \Omega \mathrm{cm}$$ ∼ 10 2 Ω cm ) CdZnTe crystals. We measured the absorption coefficients of CdZnTe crystals in four wavelength bands ($$\lambda =6.45$$ λ = 6.45 , 10.6, 11.6, 15.1$$~\mu $$ μ m) over the temperature range of $$T=8.6$$ T = 8.6 -300 K with an originally developed system. The CdZnTe absorption coefficient was measured to be $$\alpha =0.3$$ α = 0.3 -0.5 $$\mathrm{cm}^{-1}$$ cm - 1 at $$T=300$$ T = 300 K and $$\alpha =0.4$$ α = 0.4 -0.9 $$\mathrm{cm}^{-1}$$ cm - 1 at $$T=8.6$$ T = 8.6 K in the investigated wavelength range. With an absorption model based on transitions of free holes and holes trapped at an acceptor level, we conclude that the absorption due to free holes at $$T=150$$ T = 150 -300 K and that due to trapped-holes at $$T<50$$ T < 50 K are dominant absorption causes in CdZnTe. We also discuss a method to predict the CdZnTe absorption coefficient at cryogenic temperature based on the room-temperature resistivity.

Effects of POE and Carbon Black on the PTC Performance and Flexibility of High-Density Polyethylene Composites

High-density polyethylene (HDPE)/carbon black (CB) is widely used in positive temperature coefficient (PTC) composites. In order to expand its applications to fields that need good flexibility, polyolefin elastomer (POE) was incorporated into HDPE/CB composites as a secondary thermoplastic elastomer phase to provide flexibility. The effects of POE and CB content on the PTC performance and flexibility were investigated. Micro morphology and crystallization behavior are closely related to PTC properties. SEM was conducted to reveal phase morphology and filler dispersion, and DSC was conducted to research crystallization behavior. The results show that the incorporation of 18 wt.% POE can decrease the percolation threshold of conductive carbon black from 22.5 wt.% to 16 wt.%. When the CB content is 30 wt.%, the room temperature resistivity gradually increases with the increasing content of POE because of the barrier effect of POE phase, and the PTC intensity is gradually enhanced. Meanwhile, the PTC switching temperature shifts down to a lower temperature. The incorporation of 18 wt.% POE significantly increases the elongation at break, reaching an ultrahigh value of 980 wt.%, which means great flexibility has been achieved in HDPE/POE/CB composites. This work provides a new method of fabricating PTC composites with balanced electrical and mechanical properties.

Low-temperature sintered Ni–Zn–Co–Mn–O spinel oxide ceramics for multilayer NTC thermistors

The phase formation, sintering behavior and electrical properties of Ni–Co–Zn–Mn spinel NTC thermistor ceramics of the series Ni0.5ZnzCo0.5Mn2−zO4 with 0 ≤ z ≤ 1 were studied. In contrast to NiMn2O4, which exhibits limited stability in air below 730 °C and above 970 °C, the Zn–Co-substituted nickel manganite spinels are stable at T < 730 °C and decompose at Td > 900 °C, with Td increasing with decreasing Zn Content z. The samples were sintered at 900 °C with addition of 3 wt% Bi2O3 as sintering aid and densities of above 92% were achieved. The room temperature resistivity and thermistor B-constants are almost independent of composition at 0 ≤ z ≤ 0.6 and start to increase at higher Zn concentrations. A multilayer NTC thermistor was fabricated using green tapes of a spinel of composition z = 0.75, commercial Ag paste, and cofiring at 900 °C. The firing behavior, microstructure formation and electrical properties of the multilayer thermistor are reported.

Solution Synthesis of Cubic Spinel Mn–Ni–Cu–O Thermistor Powder

Toward the development of NTCR thermistors, nanocrystalline Mn–Ni–Cu–O powder was synthesized from a mixed chloride aqueous solution by a simple co-precipitation method.The introduction of an oxidizing agent (H2O2) into the solution led to the partial oxidation of Mn2+ ions into Mn3+ ions, which enabled the collected powder to be well crystallized at 650 °C. Such a low calcining temperature resulted in fine particles with a mean size of 60 nm, which significantly promoted densification of the resulting ceramics. As a result, a dense and homogenous microstructure with a relative density up to 97.2% was achieved for pellets sintered at 1100 °C. Furthermore, these sintered ceramics exhibited a room temperature resistivity (ρ25) of 67 Ω·cmand a thermistor constant (B25/85) of 2843 K, which make them suitable for use in industrial thermistors. In addition, electrical stability was greatly improved when the ceramics were prepared by a new two-step sintering method. The results suggest that the co-precipitation route with the introduction of H2O2 is suitable for the fabrication of cubic spinel thermistor nanopowders.

Titanium Nitride as a New Prospective Material for NanoSQUIDs and Superconducting Nanobridge Electronics

Nanobridge Josephson junctions and nanometer-scale superconducting quantum interference devices (nanoSQUIDs) based on titanium nitride (TiN) thin films are described. The TiN films have a room temperature resistivity of ~15 µΩ·cm, a superconducting transition temperature Tc of up to 5.3 K and a coherence length ξ(4.2 K) of ~105 nm. They were deposited using pulsed DC magnetron sputtering from a stoichiometric TiN target onto Si (100) substrates that were heated to 800 °C. Electron beam lithography and highly selective reactive ion etching were used to fabricate nanoSQUIDs with 20-nm-wide nanobridge Josephson junctions of variable thickness. X-ray and high-resolution electron microscopy studies were performed. Non-hysteretic I(V) characteristics of the nanobridges and nanoSQUIDs, as well as peak-to-peak modulations of up to 17 µV in the V(B) characteristics of the nanoSQUIDs, were measured at 4.2 K. The technology offers prospects for superconducting electronics based on nanobridge Josephson junctions operating within the framework of the Ginzburg–Landau theory at 4.2 K.

Electrical conductivity and temperature sensitivity of Cu/Mo co-modified YFeoO ceramics

To develop a new kind of thermistor with the negative temperature coefficient (NTC) behaviour, the Cu/Mo co-doped YFeO3 based ceramics were prepared by wet-chemical synthesis and sintering at 1300?C. The orthorhombic perovskite structure was identified in all ceramics by XRD analysis. The possible valence states of Fe, Cu and Mo in the doped YFeO3 compounds were examined by X-ray photoelectron spectroscopy. By adjusting the concentration of Cu- and Mo-ions, the room temperature resistivity (?25) and temperature-sensitive constant (B25/85) can be modified from 1.13?103 to 3.09?105 ??cm and 3000 to 7000K, respectively. The complex impedances at various temperatures (from 25 to 150?C) are tested and analysed. The results show that both grain and grain boundary exhibit the NTC characteristics. The electrical conduction mechanisms composing of polaron hopping conduction and band conduction were proposed in the YFeO3 based ceramics.

TiO2 thin films: Impact of substrate temperature on structural and morphological properties

Smooth and white spherical shaped TiO2 thin films are successfully deposited by Nebulizer Spray Pyrolysis (NSP) technique. The TiO2 thin films are characterized by XRD, SEM, DRS, PL and I-V analysis. Anatase phase polycrystalline tetragonal structure with preferential orientation along (1 0 1) direction obtained form XRD. The expansion and contraction of Ti-O bonds leads to a high crystalline nature with its purity at 289 nm. The absorbance increases with substrate temperature due to the decrease of film thickness, packing density and shrinkage of spray droplets. TiO2 thin films indicate that the film is made up of small granules having slab like particles with some voids at lower temperature. The tiny particles are combined together to form white spherical shaped flower particles with pinholes at 450oC. A room temperature resistivity of the film deposited at 400oC is found to be in the order of 105 Ω/cm, which decreases to 103 Ω/cm for the films prepared at 450oC.

Effects of Manganese on Highly Donor-Doped Barium Titanate Ceramics with Resistivity of Positive Temperature Coefficient

Highly donor-doped ceramics with composition of Ba0.984Y0.016TiO3 were prepared for thermistors with positive temperature coefficient of resistivity (PTCR) via a route of solid reaction, reducing sintering and aerial oxidation. The effects of Mn additive were investigated on the ceramic characteristics of composition, morphology and electrical properties. The Mn incorporation affected little on ceramic composition but resulted in an obvious change in ceramic morphology, which illustrated the average grain size of 1.16, 1.65 and 1.01 μm for Mn addition amount of 0, 0.0005 and 0.0010, respectively. The grain growth, together with the Mn additive, influenced the electrical properties of room temperature resistivity, PTCR jump, donor and acceptor densities as well as the depletion layer width.

Structural and Electrical Properties of Ca2+ Doped LaFeO3: The Effect of A-site Cation Size Mismatch

In this study, nanosized La1-xCaxFeO3 (0.00≤x≤0.40) compounds prepared via sol-gel method followed by heat treatment at 1100oC for 24 hours are studied. Crystal structure, microstructure, surface morphology and temperature-dependent resistivity of the samples are investigated. TEM investigation reveals nanoparticles with an average size of 35nm produced from the sol-gel process. The crystal structure of the compounds belongs to an orthorhombically distorted perovskite structure with Pbnm space group. Lattice distortion and cation size mismatch increase with an increase in Ca and particle and grain growth are suppressed by Ca doping. Electrical conduction is explained via thermally activated hopping of small polarons. Unit cell volume, charge ordering temperature, and activation energy for small polarons decrease linearly with an increase in cation size mismatch. Room temperature resistivity decreases with Ca doping and gets its minimum value for 30% Ca at which the orthorhombic distortion is maximum.