Electrical properties of A′Ca2Nb3O10 (A′=K, Rb, Cs) layered perovskite ceramics

The electrical conductivity properties of Dion-Jacobson type layered perovskites A′Ca₂Nb₃O₁₀ (A′=K, Rb, Cs) was investigated under different gas atmospheres. An increase in the electrical conductivity by about 2–5 orders in magnitude in both ammonia and hydrogen atmospheres is observed compared to air. Among the members of the series, the compound with the smallest size of the alkali ion, i.e. KCa₂Nb₃O₁₀, exhibits the highest conductivity. In air and hydrogen, a single activation energy value in the range 0.25 – 0.80 eV is observed, while in ammonia a sharp increase in the electrical conductivity is found at about 500 °C. The activation energy at low-temperatures (300–500 °C) is attributed to ionic motion and at higher temperatures (500–700 °C) to both defect formation and ionic motion. The unusual electrical conductivity behavior in ammonia is explained on the basis of the model developed for alkali halides. EMF measurements reveal that the layered perovskites are ionic (proton) conductors. The electrical conductivity changes as a function of the ammonia gas concentration; accordingly, layered perovskites appear to be useful solid electrolytes in galvanic cells for practical applications, e.g. for gas sensors. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Characteristics of counter-rotating vortex rings formed ahead of a compressible vortex ring

Characteristics of high Mach number compressible vortex ring generated at the open end of a short driver section shock tube is studied experimentally using high-speed laser sheet-based flow visualization. The formation mechanism and the evolution of counter rotating vortex ring (CRVR) formed ahead of the primary vortex ring are studied in details for shock Mach number (M) 1.7, with different driver section lengths. It has been observed that the strength of the embedded shock, which appears at high M, increases with time due to the flow expansion in the generating jet. Strength of the embedded shock also varies with radius; it is strong at smaller radii and weak at larger radii; hence, it creates a velocity gradient ahead of the embedded shock. At critical Mach number (M _c ≥ 1.6), this shear layer rolls up and forms a counter rotating vortex ring due to Biot-Savart induction of the vortex sheet. For larger driver section lengths, the embedded shock and the resultant shear layer persists for a longer time, resulting in the formation of multiple CRVRs due to Kelvin–Helmholtz type instability of the vortex sheet. CRVRs roll over the periphery of the primary vortex ring; they move upstream due to their self-induced velocity and induced velocity imparted by primary ring, and interact with the trailing jet. Formation of these vortices depends strongly upon the embedded shock strength and the length of the generating jet. Primary ring diameter increases rapidly during the formation and the evolution of CRVR due to induced velocity imparted on the primary ring by CRVR. Induced velocity of CRVR also affects the translational velocity of the primary ring considerably.     

The Human Genome Project: the role of analytical chemists.

The Human Genome Project (HGP) is the most ambitious and important effort in the history of biology. It has provided a complete genetic blueprint for human life, and will provide important insights into human health and development. HGP involves a huge amount of data that is stored on computers all over the world. More than just vast amounts of DNA sequences, the project is about developing sets of integrated maps that involve genetic, physical, and sequence data. The data can be sorted, annotated and organized in many different ways using different types of database software, different analysis algorithms and different forms of interfaces. The genomic sequences of the human and the substantial portions of the mouse genome are expected to be finished by 2005. Analytical chemists took the opportunity, addressing the problem of achieving a high throughput with good sensitivity. This paper discusses how analytical chemists saved the Human Genome Project or at least gave it a helping hand.     

Research status in preparation of FePO4: a review

The cathode is the most important component of a lithium-ion battery. The olivine structure lithium iron phosphate (LiFePO₄) with its numerous appealing features, such as high theoretical capacity, acceptable operating voltage, increased safety, environmental benignity, and low cost, has attracted extensive interest as a potential cathode material for Li-ion batteries. As a precursor, FePO₄ can be used to produce LiFePO₄ on a large scale with high bulk density, discharge rate, and capacity. This can be realized by controlling the crystal size and morphology of FePO₄. The characteristics, structure, and synthesis methods of FePO₄ are discussed in this review. The relative merits of these synthetic methods, as well as some suggestions on how to improve them, are also presented.     

A fluorescent ammonia sensor based on a porphyrin cobalt(II)-dansyl complex

Detecting and measuring the concentration of ammonia is of interest in many scientific and technological areas. A porphyrin based cobalt(II) complex with a dansyl fluorophore has been synthesized and investigated as a ‘turn-on’ fluorescent ammonia sensor. Over sixfold increase in fluorescence emission occurs upon the treatment of NH₃ to [Co(TPP)(Ds-pip)] sensor solution, resulting from NH₃-induced displacement of the axially coordinated fluorophore.     

Cruising in ceramics—discovering new structures for all-solid-state batteries—fundamentals,materials, and performances

Energy storage research has drawn much attention recently due to increasing demand for carbon neutral electrical energy from renewable energy sources such as solar, wind, and hydrothermal. Various electrochemical energy storage and conversion technologies are being considered for their integration into smart grid systems, of which batteries seem to play a vital role due to their wide range of energy densities. In this review, we provide the current status and recent advances in solid-state (ceramic) electrolytes based on inorganic compounds for all-solid-state batteries. This paper is specifically focused on the fundamentals, materials, and performances of solid electrolytes in batteries. A wide spectrum of inorganic solid-state electrolytes is presented in terms of their chemical composition, crystal structure, and ion conduction mechanism. Furthermore, the advantages and main issues associated with different types of inorganic solid electrolytes, including β-alumina, NASICON and LISICON-type, perovskites, and garnet-type for all-solid-state batteries are presented. Among these solid electrolytes, Zr and Ta-based Li-stuffed garnets exhibit high Li-ion conductivity, electrochemical stability window (up to 6  V/Li at room temperature), and chemical stability against reaction with molten elemental Li. However, their stability under humidity and carbon dioxide should be improved to decrease the fabrication and operational costs.