Hydrothermal synthesis of new rare earth silicate fluorides: A novel class of polar materials

Polar crystals provide an interesting avenue for materials research both in the structures they form and the properties they possess. This work describes the hydrothermal synthesis and structural characterization of three novel silicate fluorides. Compound (1), LiY3(SiO4)2F2 crystallizes in space group C2/c, with a=17.651(4) Å, b=4.8868(10) Å, c=11.625(2) Å and β=131.13(3)°. BaY2(Si2O7)F2 (2) crystallizes in space group P−1, with a=5.1576(10) Å, b=6.8389(14) Å, c=11.786(2) Å, α=93.02(3)°, β=102.05(3)° and γ=111.55(3)°. Finally, the structure of Ba2Y3(SiO4)2F5 (3) was determined in the polar orthorhombic space group Pba2, having unit cell parameters a=8.8864(18) Å, b=12.764(3) Å and c=5.0843(10) Å. The structures are compared based on their building blocks and long range polarities. Aligned silicate tetrahedra segregated into a single layer in (3) impart the observed polarity.

The polar structure of Ba2Y3(SiO4)2F5.Figure optionsDownload as PowerPoint slideHighlights
► Natural yttrium silicate fluoride minerals are briefly reviewed.
► The synthesis and structures of LiY3(SiO4)2F2, BaY2(Si2O7)F2 and Ba2Y3(SiO4)2F5 are discussed.
► Ba2Y3(SiO4)2F5 crystallizes in the polar space group Pba2.
► Polarity occurs primarily through aligned silicate tetrahedra in a segregated layer.