Dielectric constants of diaspore and B-, Be-, and P-containing minerals, the polarizabilities of B_2O_3 and P_2O_5, and the oxide additivity rule

The 1-MHz dielectric constants and loss factors of the minerals diaspore, euclase, hamberyite, sinhalite, danburite, datolite, beryllonite, and montebrasite and of the synthetic oxides La_(2)Be_(2)O_5, AlP_(3)O_9, and NdP_(5)O_14, were determined. The dielectric polarizabilities of B_(2)O_3, and P_(2)O_5, derived from the dielectric constants of these compounds are 6.15 and 12.44 Å^3, respectively. The dielectric constants of the above minerals and oxides, along with the dielectric polarizabilities of Li_(2)O, Na_(2)O, BeO, MgO, CaO, Al_(2)O_3, Nd_(2_O_3, La_(2)O_3, SiO_2, diaspore, and the derived values of the polarizabilities of B_(2)O_3, and P_(2)O_5, were used to calculate dielectric polarizabilities from the Clausius-Mosotti equation and to test the oxide additivity rule. The oxide additivity rule is valid to ±0.5% for all except beryllonite. These compounds with deviations from additivity of 0.5-1.5%, along with previously studied aluminate and gallate garnets, chrysoberyl, spinel, phenacite, zircon, and olivinetype silicates, form a class of well-behaved oxides that can be used as a basis for comparison of compounds that show larger deviations (>5%) caused by ionic or electronic conductivity, the presence of H_(2)O or CO_2, or structural peculiarities

Generalized synthesis of periodic surfactant/inorganic composite materials

THE recent synthesis of silica-based mesoporous materials by the cooperative assembly of periodic inorganic and surfactant-based structures has attracted great interest because it extends the range of molecular-sieve materials into the very-large-pore regime. If the synthetic approach can be generalized to transition-metal oxide mesostructures, the resulting nanocomposite materials might find applications in electrochromic or solid-electrolyte devices, as high-surface-area redox catalysts and as substrates for biochemical separations. We have proposed recentIy that the matching of charge density at the surfactant/inorganic interfaces governs the assembly process; such co-organization of organic and inorganic phases is thought to be a key aspect of biomineralization. Here we report a generalized approach to the synthesis of periodic mesophases of metal oxides and cationic or anionic surfactants under a range of pH conditions. We suggest that the assembly process is controlled by electrostatic complementarity between the inorganic ions in solution, the charged surfactant head groups and - when these charges both have the same sign - inorganic counterions. We identify a number of different general strategies for obtaining a variety of ordered composite materials