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 Bi 2 Mo 1 - x W x O 6 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 Bi 2 O 3:MoO 3:WO 3 mixture indicates that mechanosynthesis of a Bi 2 Mo 0.25 W 0.75 O 6 amorphous phase takes place. The ferroelectric properties of Bi 2 Mo 0.25 W 0.75 O 6 well-densified ceramic material have been measured. The crystal structure of Bi 2 Mo 0.25 W 0.75 O 6 has been refined using X-ray and neutron powder diffraction combined with Rietveld analysis. This oxide is isostructural with both γ(L) Bi 2 MoO 6 and Bi 2 WO 6 belonging to the orthorhombic system, space group Pca 2 1, a = 5.44547(7) Å, b = 16.3731(2) Å, and c = 5.46659(7) Å, V = 487.40(1) Å 3, Z = 4, and ρ cal = 9.21 g·cm - 3 . The structure keeps the Aurivillius-type framework with alternating [Bi 2 O 2 ] and [Mo/WO 4 ] layers. The structural characteristics of Bi 2 Mo 0.25 W 0.75 O 6 can be considered intermediate between those of γ(L) Bi 2 MoO 6 and Bi 2 WO 6 .