The quaternary alkali-metal gallium selenostannates, Na 2-xGa2-xSn1+xSe6 and AGaSnSe 4 (A=K, Rb, and Cs), were synthesized by reacting alkali-metal selenide, Ga, Sn, and Se with a flame melting-rapid cooling method. Na 2-xGa2-xSn1+xSe6 crystallizes in the non-centrosymmetric space group C2 with cell constants a=13.308(3)Å, b=7.594(2)Å, c=13.842(3)Å, β=118.730(4)°, V=1226.7(5)Å3. α-KGaSnSe4 crystallizes in the tetragonal space group I4/mcm with a=8.186(5)Å and c=6.403(5)Å, V=429.1(5)Å3. β-KGaSnSe4 crystallizes in the space group P21/c with cell constants a=7.490(2)Å, b=12.578(3)Å, c=18.306(5)Å, β=98.653(5)°, V=1705.0(8)Å3. The unit cell of isostructural RbGaSnSe 4 is a=7.567(2)Å, b=12.656(3)Å, c=18.277(4)Å, β=95.924(4)°, V=1741.1(7)Å3. CsGaSnSe4 crystallizes in the orthorhombic space group Pmcn with a=7.679(2)Å, b=12.655(3)Å, c=18.278(5)Å, V=1776.1(8)Å3. The structure of Na2-xGa2-xSn1+xSe6 consists of a polar three-dimensional network of trimeric (Sn,Ga) 3Se9 units with Na atoms located in tunnels. The AGaSnSe4 possess layered structures. The compounds show nearly the same Raman spectral features, except for Na2-xGa2-xSn 1+xSe6. Optical band gaps, determined from UV-Vis spectroscopy, range from 1.50eV in Na2-xGa2-xSn 1+xSe6 to 1.97eV in CsGaSnSe4. Cooling of the melts of KGaSnSe4 and RbGaSnSe4 produces only kinetically stable products. The thermodynamically stable product is accessible under extended annealing, which leads to the so-called γ-form (BaGa 2S4-type) of these compounds.
Bibliographical noteFunding Information:
Financial support from the National Science Foundation (DMR-0127644) is gratefully acknowledged. This work was supported in part by Korea Research Foundation Grant (KRF-2003-042-C00065).
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry