Soil Chemical Analysis

A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 °C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm2, 4.0 μC/cm2, and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials.

Room-temperature saturated ferroelectric polarization in BiFeO3 ceramics synthesized by rapid liquid phase sintering

Novel gas sensors with high sensing properties, simultaneously operating at room temperature are considerably more attractive owing to their low power consumption, high security and long-term stability. Till date, zinc oxide (ZnO) as semiconducting metal oxide is considered as the promising resistive-type gas sensing material, but elevated operating temperature becomes the bottleneck of its extensive applications in the field of real-time gas monitoring, especially in flammable and explosive gas atmosphere. In this respect, worldwide efforts have been devoted to reducing the operating temperature by means of multiple methods In this communication, room-temperature gas sensing properties of ZnO based gas sensors are comprehensively reviewed. Much more attention is particularly paid to the effective strategies that create room-temperature gas sensing of ZnO based gas sensors, mainly including surface modification, additive doping and light activation. Finally, some perspectives for future investigation on room-temperature gas-sensing materials are discussed as well.

Room-temperature gas sensing of ZnO-based gas sensor: A review

Advances in gas sensors and electronic nose technologies for agricultural cycle applications

InN/GaN heterostructure based Schottky diodes were fabricated by plasma-assisted molecular beam epitaxy. The temperature dependent electrical transport properties were carried out for InN/GaN heterostructure. The barrier height and the ideality factor of the Schottky diodes were found to be temperature dependent. The temperature dependence of the barrier height indicates that the Schottky barrier height is inhomogeneous in nature at the heterostructure interface. The higher value of the ideality factor and its temperature dependence suggest that the current transport is primarily dominated by thermionic field emission (TFE) other than thermionic emission (TE). The room temperature barrier height obtained by using TE and TFE models were 1.08 and 1.43 eV, respectively.

Temperature dependent electrical transport behavior of InN/GaN heterostructure based Schottky diodes

The present work explores the electrical transport and infrared (IR) photoresponse properties of InN nanorods (NRs)/n-Si heterojunction grown by plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN NRs is verified by the X-ray diffraction and transmission electron microscopy. Raman measurements show that these wurtzite InN NRs have sharp peaks E
2(high) at 490.2 cm-1 and A
1(LO) at 591 cm-1. The current transport mechanism of the NRs is limited by three types of mechanisms depending on applied bias voltages. The electrical transport properties of the device were studied in the range of 80 to 450 K. The faster rise and decay time indicate that the InN NRs/n-Si heterojunction is highly sensitive to IR light.

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Transport and infrared photoresponse properties of InN nanorods/Si heterojunction.

2D materials are a promising new class of materials for next generation optoelectronic devices owing to their appealing optical and electrical properties. Pristine molybdenum disulfide (MoS2) is widely used in next generation photovoltaic and optoelectronic devices, but its low photo-dark current ratio prevents its use in highly efficient photo detection applications. Here, we decorated crumpled reduced graphene oxide (rGO) particles on a large-area vertically aligned MoS2 flake network to enhance the performance of the MoS2-based photodetector by forming multiple nanoscale p–n heterojunctions. The rGO/MoS2 device exhibited a significantly improved photoresponsivity of ~2.10 A W−1 along with a good detectivity of ~5 × 1011 Jones (Jones = cm Hz1/2/W) compared to that of the pristine MoS2 photodetector in ambient atmosphere. Moreover, the rGO/MoS2 photodetector showed a fast response of ~18 ms with excellent stability and reproducibility in ambient air even after three months. The high performance of the photodetector is attributed to enhanced photoexcited carrier density and suppressed photo generated electron–hole recombination due to the strong local built-in electric field developed at the rGO/MoS2 interface. Our results showed that integration of rGO with MoS2 provides an efficient platform for photo detection applications.

https://iopscience.iop.org/article/10.1088/1361-6528/aad2f6/pdf

High-performance photodetector based on hybrid of MoS2 and reduced graphene oxide.

The present report investigates hydrogen gas sensing properties on PAN/(PAN-b-PMMA) derived electrospun nanoporous carbon nanofibers loaded on ZnO nanostructures. Polymer blend of PAN and PAN-b-PMMA is used to obtain the high surface area porous CNF which improve further sensing performance. Moreover, a facile technique such as drop cast method is used to load the CNF (0.1–0.5 wt%) on Au pattern interdigitated electrodes over ZnO nanostructures. Loading of CNF was optimized to ensure proper connection between the electrodes over ZnO surface, which was measured using I–V characteristics. Initially, current decreased for less amount of CNF (0.1–0.2 wt%), which later increased for high concentration of CNF (0.3–0.5 wt%). It was further observed that 0.2 wt% CNF/ZnO nanostructures based sensor exhibited maximum sensing response (73.54%) as compared to CNF (3.29%) and ZnO (44.51%) for 100 ppm hydrogen at 150 °C. This enhanced sensing response may be attributed to diffusion of hydrogen molecules through the nanoporous CNF, thus enabling the formation of p - n heterojunction at the interface of CNF and ZnO. The presence of oxygen functional groups on CNF surface also contributes to the enhancement of the sensing performance.

Mahesh Kumar

Papers

Advances in gas sensors and electronic nose technologies for agricultural cycle applications

Temperature dependent electrical transport behavior of InN/GaN heterostructure based Schottky diodes

Transport and infrared photoresponse properties of InN nanorods/Si heterojunction.

High-performance photodetector based on hybrid of MoS2 and reduced graphene oxide.

PAN/(PAN-b-PMMA) derived nanoporous carbon nanofibers loaded on ZnO nanostructures for hydrogen detection