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Reduction in a niobium tungsten bronze, 2Nb2O5.7WO3, studied by 1 MV HRTEM (1982)

Horiuchi, S.

Copenhagen : International Union of Crystallography (IUCr)

Applied crystallography online 15 (1982), S. 323-329

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ISSN: 1600-5767

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Geosciences , Physics

Notes: 1 MV high-resolution transmission electron microscopy (HRTEM) reveals that the reduction in a niobium tungsten bronze, 2Nb2O5.7WO3, is initiated by the release of a small amount of oxygen from the –M–O–M–O– strings in the pentagonal tunnels. Its content can be measured from the weight change. At the second stage of reduction the ordered structure of 2Nb2O5.7WO3 is destroyed, i.e. the ReO3-type structure at the center of the unit cell disappears. As a result an apparently disordered matrix appears, in which isolated unit cells of 2Nb2O5.7WO3 and 4Nb2O5.9WO3 are irregularly formed. At the third stage the microdomains of 4Nb2O5.9WO3 appear and grow. The presence of oxygen vacancies in the strings at each stage is revealed by the technique utilizing the knock-on of atoms by the impact of electrons. The number of knocked-on atoms is analyzed with the help of computer simulation on image contrast. Circular diffuse scattering is excited from the disordered matrix and its origin is related to the clusters composed of nine tunnel sites.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0021889882012059

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Phase relationships in the system Si3N4-SiO2-La2O3 (1982)

Mitomo, M. ; Izumi, F. ; Horiuchi, S. ; [et al.]

Springer

Journal of materials science 17 (1982), S. 2359-2364

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ISSN: 1573-4803

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract Phase relationships in the system Si3N4-SiO2-La2O3 have been investigated after cooling from 1700° C. Two phases, 2Si3N4·La2O3 (monoclinic) and La5 (SiO4)3N (hexagonal), were identified; the other two phases in the system, LaSiO2N (monoclinic) and La4Si2O7N2 (monoclinic), were found to dissociate to La5 (SiO4)3N and a glass after cooling from temperatures above 1650° C. The unit cells of 2Si3N4·La2O3, LaSiO2N and La4Si2O7N2 have been determined and compared with those of preceding works. The results are discussed in relation to the intergranular phases observed when Si3N4 is sintered with La2O3 additions.