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Microscopic motions of Li+ ions in the fast ionic conductor Li3xLa2/3−xTiO3 (x = 0.09) are studied by dielectric spectroscopy in the frequency range from 103 to 4 × 109 Hz and in the temperature range from 200 to 400 K. Several dielectric relaxations are evidenced by this technique and can be ascribed to different motions of the Li+ ions in the oxide. These motions are related to the Li+ motions observed by means of 7Li NMR and dc conductivity and already reported in previous papers. From these two complementary techniques, three motions of Li+ ions are evidenced in the perovskite structure ABO3: a slow motion that corresponds to the hopping of the Li+ ions from one A-cage to the next vacant one through bottlenecks made of four oxygen ions and two fast motions that correspond to local motions of the mobile ions between their off-centred positions in the A-cage of the perovskite structure. A change in the mechanism of conduction is observed around 200 K. This change is attributed to a change in the dimensionality of the Li+ ion motion from 2D to 3D as temperature is increased. At low temperatures (T<200 K) both the local and the long range Li+ ion motions happen in the (a,b) planes of the crystallographic structure (2D motion). As temperature increases, Li+ ions experience the entire volume of the A-cage finally moving in three directions above 400 K (3D motion). This change is corroborated by the ratio of the activation energies in the two domains, i.e. 1.5, observed in T1 versus 103/T plots as well as in the dc conductivity plot and in the dielectric relaxations versus 103/T plot. These results confirm the fact that, in Li3xLa2/3−xTiO3, the long range motion of Li+ ions is evidenced by T1ρ and σdc and their local motions in the A-site of the perovskite structure are evidenced by T1 and by dielectric spectroscopy at frequencies higher than 1 MHz, in the temperature range investigated. Therefore, T1ρ and σdc can be compared since they are related to the same ionic motion. Finally, we found that the constant loss behaviour, observed by previous authors, is in fact the contribution of two quasi-Debye dielectric relaxations.
Microscopic motions of Li+ ions in the fast ionic conductor Li3xLa2/3−xTiO3 (x = 0.09) are studied by dielectric spectroscopy in the frequency range from 103 to 4 × 109 Hz and in the temperature range from 200 to 400 K. Several dielectric relaxations are evidenced by this technique and can be ascribed to different motions of the Li+ ions in the oxide. These motions are related to the Li+ motions observed by means of 7Li NMR and dc conductivity and already reported in previous papers. From these two complementary techniques, three motions of Li+ ions are evidenced in the perovskite structure ABO3: a slow motion that corresponds to the hopping of the Li+ ions from one A-cage to the next vacant one through bottlenecks made of four oxygen ions and two fast motions that correspond to local motions of the mobile ions between their off-centred positions in the A-cage of the perovskite structure. A change in the mechanism of conduction is observed around 200 K. This change is attributed to a change in the dimensionality of the Li+ ion motion from 2D to 3D as temperature is increased. At low temperatures (T<200 K) both the local and the long range Li+ ion motions happen in the (a,b) planes of the crystallographic structure (2D motion). As temperature increases, Li+ ions experience the entire volume of the A-cage finally moving in three directions above 400 K (3D motion). This change is corroborated by the ratio of the activation energies in the two domains, i.e. 1.5, observed in T1 versus 103/T plots as well as in the dc conductivity plot and in the dielectric relaxations versus 103/T plot. These results confirm the fact that, in Li3xLa2/3−xTiO3, the long range motion of Li+ ions is evidenced by T1ρ and σdc and their local motions in the A-site of the perovskite structure are evidenced by T1 and by dielectric spectroscopy at frequencies higher than 1 MHz, in the temperature range investigated. Therefore, T1ρ and σdc can be compared since they are related to the same ionic motion. Finally, we found that the constant loss behaviour, observed by previous authors, is in fact the contribution of two quasi-Debye dielectric relaxations.
A survey is offered of applications to fundamental physical research, in the years immediately following World War II, of the instrumentalities developed for radar during that war. Attention is given to radar astronomy and radio astronomy, linear and cyclical accelerators, microwave spectroscopy, molecular beams, nuclear magnetic resonance, electron paramagnetic and ferromagnetic resonance, measurements of resistivity at high frequencies in metals and of second sound in helium II, and to the concepts of information and signal-to-noise ratio as basic to the design and analysis of experiments. In conjunction with this survey, consideration is given to the autonomy of physics as a knowledge-producing enterprise, framed as a question of continuity in research directions. As that question implies a baseline, the survey of postwar applications is preceded by a survey of those prewar directions of physical research requiring the highest available radio frequencies. Some 500 references are given.
The 1930s marked a significant transformation in the content and direction of industrial research at the Westinghouse Electric and Manufacturing Company. Westinghouse was widely respected for its engineering expertise, but it was not as well known for the type of advanced scientific research that was already underway at General Electric, AT&T, and other large companies. In a deliberate attempt to improve its image within the scientific community and match the intellectual strength of its industrial rivals, Westinghouse established a new academic-style research program in 1935. Edward Condon, a respected theoretical physicist at Princeton University, was hired to lead this effort. By 1942, Westinghouse's long-standing reputation for engineering excellence was complemented by growing recognition for its accomplishments in nuclear physics, mass spectrometry, and microwave electronics. Unlike its competitors, however, Westinghouse never conceived a coherent strategy to link Condon's research in these fields to new products and markets. Consequently, the company derived few commercial benefits from its investment in fundamental research.
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