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Reversible Structural Transformation between Polar Polymorphs of Li 2 GeTeO 6 .

Authors :: Zhao MH
Wang W
Han Y
Xu X
Sheng Z
Wang Y
Wu M
Grams CP
Hemberger J
Walker D
Greenblatt M
Li MR
Source :: Inorganic chemistry [Inorg Chem] 2019 Jan 22; Vol. 58 (2), pp. 1599-1606. Date of Electronic Publication: 2019 Jan 04.
Publication Year :: 2019
Abstract: Li <subscript>2</subscript> GeTeO <subscript>6</subscript> prepared at ambient pressure adopts the corundum derivative ordered ilmenite structure (rhombohedral R3). When heated at 1073 K and 3-5 GPa, the as-made Li <subscript>2</subscript> GeTeO <subscript>6</subscript> can convert into a LiSbO <subscript>3</subscript> -derived Li <subscript>2</subscript> TiTeO <subscript>6</subscript> -type phase (orthorhombic Pnn2), which is the third LiSbO <subscript>3</subscript> -derived double A <subscript>2</subscript> BB'O <subscript>6</subscript> phase in addition to Li <subscript>2</subscript> TiTeO <subscript>6</subscript> and Li <subscript>2</subscript> SnTeO <subscript>6</subscript> . This Pnn2 Li <subscript>2</subscript> GeTeO <subscript>6</subscript> phase spontaneously reverts to the R3 phase if annealed up to 1023 K at ambient pressure. Although the crystal structural analyses and second harmonic generation measurements clearly demonstrate the polar nature of both the R3 and Pnn2 phases, P( E) and dielectric measurements do not show any convincing ferroelectric response. Given the large estimated spontaneous polarization (17 and 80 μC/cm <superscript>2</superscript> ), the absence of ferroelectric behavior could be attributed to the random domain distribution and leakage due to Li-ion migration.