Soft-chemistry forms of Sn2P2S6 and CuInP2S6

We present our attempts to prepare lamellar SnP2S6 and CuInP2S6 by metathes is reactions in aqueous media, Use of a SnCl4 precursor unexpectedly led to the formation of the three-dimensional compound (Sn2P2S6)-P-II rather than (SnP2S6)-P-IV. The crystallites thus obtained were about 65 nm in size, i. e., much larger than those previously synthesized from SnCl2. We correlate this with the smaller Sn/P ratio (< 1), which implies fewer nucleation site s and probably enhanced particle growth in the present case. The product te sted positive for second-harmonic generation (SHG) at room temperature (RT) . Initial P-31 NMR-MAS spectroscopy data indicate that this material is in an intermediate state between the ferroelectric and paraelectric phases of crystalline Sn2P2S6. An analogous solution method readily yielded CuInP2S6, the first quaternary thiophosphate prepared ria this soft-chemistry route, A rather small coherence length approximate to 27 Angstrom, equivalent to four layers, is found for this product; band broadening is also observed in the Raman spectrum. SHG measurements likewise revealed a signal for this m aterial at RT; a non polar macroscopic state may, however, not be precluded , given the known order-disorder nature of the ferroelectric-paraelectric t ransition in crystalline CuInP2S6. (C) 1998 Academic Press.