New Bi₂Mo₁_-<i>_x</i>W<i>_x</i>O₆ Solid Solution: Mechanosynthesis, Structural Study, and Ferroelectric Properties of the <i>x</i> = 0.75 Member

Abstract

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 ≤ 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 γ(L) Bi2MoO6 and Bi2WO6 belonging to the orthorhombic system, space group Pca21, a = 5.44547(7) Å, b = 16.3731(2) Å, and c = 5.46659(7) Å, V = 487.40(1) Å3, Z = 4, and ρcal = 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 γ(L) Bi2MoO6 and Bi2WO6.