Structure of polymer intercalated MnPS 3 and CdPS 3
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Layered MnPS3 and CdPS3 powders were used to prepare M1−xK2xPS3/poly(ethylene glycol) (PEG) and M1−xK2xPS3/poly(vinyl pyrrolidone) (PVP) (M ⳱ Cd, Mn) intercalation nanocomposites. The structure of these compounds was studied by x-ray diffraction. The host layers in Cd0.8K0.4PS3(PEG)2.0 and Mn0.8K0.4PS3(PEG)2.0 nanocomposites were 3-dimensional crystals with a monoclinic unit cell. The in-plane spacings were slightly expanded from original monoclinic MPS3 (0.2% for CdPS3 and 0.5% for MnPS3), while the inter-layer spacing was expanded by 8.87 Å for Cd0.8K0.4PS3(PEG)2.0 and 8.86 Å for Mn0.8K0.4PS3(PEG)2.0. The Cd0.8K0.4PS3(PVP)1.1 and Mn0.8K0.4PS3(PVP)1.1 nanocomposites, on the other hand, had an expanded interlayer spacing of about 30 Å and the diffraction patterns contained only (00l) and (hk0) peaks, and no mixed (hkl) peaks were observed. The (hk0) peaks were 2-dimensional, with strongly asymmetric line shapes, and there was excellent agreement with pattern calculations for single molecular layers. This demonstrated that the host layers in Cd0.8K0.4PS3(PVP)1.1 and Mn0.8K0.4PS3(PVP)1.1 nanocomposites were tubostratically stacked layered systems.
I. INTRODUCTION
Recently, there has been considerable interest in the synthesis and characterization of inorganicpolymer nanocomposites in which polymers are intercalated in layered compounds such as transition metal dichalcogenides, 1,2 layered metal oxides, 3,4 clays, 5 and layered transition metal phosphorus trisulfides (MPS3).6 –10 Transition metal phosphorous trisulfides11 share the general formula MPS3, where M represents a transition metal Mn, Cd, Fe, Co, Ni, Zn, or V. These compounds have a layered structure similar to that of the transition metal dichalcogenides. Using the formula M2/3(P2)1/3S2, they can be considered as layered metal disulfides in which a third of the metal M sites are substituted by phosphorous atom pairs P2, as shown in Fig. 1. The MPS3 structure is built from a closed-packed stacking of sulfur atoms in the ABC sequence (CdCl2 type). In the undistorted case, the unit cell of MPS3 can be viewed as a hexagonal or a monoclinic cell (Fig. 1). The hexagonal cell extends over three MPS3 layers and contains three M2P2S6 units. The monoclinic cell extends over only one MPS3 layer and contains two M2P2S6 units with b ⳱ √3 a and cos ⳱ a/(3c). The monoclinic cell is the primitive cell. The sturcture of many MPS3 compounds is not exactly hexagonal due to a slight distortion, but remains monoclinic. For example for CdPS3, a ⳱ 6.218 Å, 2408
http://journals.cambridge.org
J. Mater. Res., Vol. 15, No. 11, Nov 2000 Downloaded: 16 Mar 2015
b ⳱ 10.763 Å, c ⳱ 6.867 Å, and  ⳱ 107.58°; and for MnPS3, a ⳱ 6.076 Å, b ⳱ 10.524 Å, c ⳱ 6.796 Å, and  ⳱ 107.35°, where  is the angle between a and c. Intercalation of various polymers into the van der Waals S-S gap of MPS3 compounds has been reported. These polymers include poly(ethylene glycol) (PEG),6 poly(ethylene oxide) (PEO),6,8,10 poly(ethylenimine) (PEI),10 and poly(propylene glycol) (PPG).9 Expanded interlayer
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