New Bi2Mo1-xWxO6 solid solution:: Mechanosynthesis, structural study, and ferroelectric properties of the x=0.75 member

To search for new ferroelectric materials exhibiting an Aurivillius structural type, the syntheses of the solid solution Bi2Mo1-xWxO6 has been undertaken. A phase with a large homogeneity range exists for 0.5 < x less than or equal to 1.0. The thermal behavior of mechanochemically assisted precursor powders has been studied, showing that the consecutive crystallization of fluorite and Aurivillius-type phases arrives before a ferro-paraelectric transition occurs. TEM studies of the representative mechanoactivated 1:0.25:0.75 Bi2O3:MoO3:WO3 mixture indicates that mechanosynthesis of a Bi2Mo0.25W0.75O6 amorphous phase takes place. The ferroelectric properties of Bi2Mo0.25W0.75O6 well-densified ceramic material have been measured. The crystal structure of Bi2Mo0.25W0.75O6 has been refined using X-ray and neutron powder diffraction combined with Rietveld analysis. This oxide is isostructural with both gamma(L) Bi2MoO6 and Bi2WO6 belonging to the orthorhombic system, space group Pca2(1), a = 5.44547(7) Angstrom, b = 16.3731(2) Angstrom, and c = 5.46659(7) Angstrom, V = 487.40(1) Angstrom(3), Z = 4, and rho(cal) = 9.21 g.cm(-3). The structure keeps the Aurivillius-type framework with alternating [Bi2O2] and [Mo/WO4] layers. The structural characteristics of Bi2Mo0.25W0.75O6 can be considered intermediate between those of gamma(L) Bi2MoO6 and Bi2WO6.