Defect chemistry and transport properties of BaxCe 0 . 85 M 0 . 15 O 3 -
The site-incorporation mechanism of M dopants into ABO3 perovskites controls the overall defect chemistry and thus their transport properties. For charge-balance reasons, incorporation onto the A-site would require the creation of negatively charged point defects (such as cation vacancies), whereas incorporation onto the B-site is accompanied by the generation of positively charged defects, typically oxygen vacancies. Oxygen-vacancy content, in turn, is relevant to proton-conducting oxides in which protons are introduced via the dissolution of hydroxyl ions at vacant oxygen sites. We propose here, on the basis of x-ray powder diffraction studies, electron microscopy, chemical analysis, thermal gravimetric analysis, and alternating current impedance spectroscopy, that nominally B-site doped barium cerate can exhibit dopant partitioning as a consequence of barium evaporation at elevated temperatures. Such partitioning and the presence of significant dopant concentrations on the A-site negatively impact proton conductivity. Specific materials examined are BaxCe0.85M0.15O3(x 0.85 − 1.20; M Nd, Gd, Yb). The compositional limits for the maximum A-site incorporation are experimentally determined to be: (Ba0.919Nd0.081)(Ce0.919Nd0.081)O3, (Ba0.974Gd0.026)(Ce0.872Gd0.128)O2.875, and Ba(Ce0.85Yb0.15)O2.925. As a consequence of the greater ability of larger cations to exist on the Ba site, the H2O adsorption and proton conductivities of large-cation doped barium cerates are lower than those of small-cation doped analogs.
Investigation of structural and electrical properties of Gd3+ ions modified BaZr0.05Ti0.95O3 ceramic
Gadolinium (Gd) doped BaZr0.05Ti0.95O3 ceramic samples with general formula Ba(1−x)Gd2x/3Zr0.05Ti0.95O3 were prepared by the solid state reaction method. The effect of Gd on the structural and dielectric behaviours of BaZr0.05Ti0.95O3 have been studied in detail. X-ray diffraction studies revealed that site substitution by Gd3+ ions had a great impact on the site occupancy of the BaZr0.05Ti0.95O3 pervoskite. The lattice parameters increased up to x = 0.03 followed by a decrease at higher concentration showing both donor and acceptor behaviours of Gd in BaZr0.05Ti0.95O3 matrix. Structural changes were studied by Raman spectroscopy also, which showed the non-linear shifting of the modes with increasing doping concentration. The scanning electron microscopy images showed a drastic modification in grain size with increasing Gd concentration. The effect of substitution of Gd3+ ions in BaZr0.05Ti0.95O3 was investigated by means of dielectric studies and the dielectric behaviour was explained using self-compensation model. The diffusivity in the samples was studied by modified Curie–Weiss law.
Wood Microbiology: Decay and Its Prevention
Introductory text on the principles of decay and discoloration processes in wood, with emphasis on the major fungal damages which may develop during the growth, storage, and use of wood. The characteristics, detection, effects, and control of microbial attacks are stressed. Provides a synthesis of the current literature on wood microbiology, a rapidly expanding field of study. (Abstractor's note: This is an important resource for conservation researchers studying the decay of wood in art and architecture.) The following is a list of chapter headings: 1) Introduction to wood microbiology; 2) Wood deterioration agents; 3) Characteristics and classification of fungi and bacteria; 4) Factors affecting the growth and survival of fungi in wood (fungal ecology); 5) Fungal metabolism in relation to wood decay; 6) The decay setting: some structural, chemical, and moisture features of wood in relation to decay development; 7) General features, recognition, and anatomical aspects of wood decay; 8) Chemical changes in wood caused by decay fungi; 9) Ultrastructural features of wood decay; 10) Changes caused by decay fungi in the strength and physical properties of wood; 11) Colonization and microbial interactions in wood decay; 12) Decays originating in the stems of living trees; 13) Biodeterioration of stored wood and its control; 14) Wood stains and discolorations; 15) Decay problems associated with some major uses of wood products; 16) Detection of internal decay; 17) Paint mildew and related degradative problems; 18) Natural decay resistance (wood durability); 19) Chemical protection of wood (wood preservation); and 20) Some trends in wood microbiology research and a new emphasis (biotechnology). -- AATA