Shaw, Graham Andrew; (2000) Solvent mediated synthesis of metal chalcogenides. Doctoral thesis (Ph.D.), University College London.

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Abstract

This thesis is primarily concerned with the synthesis of binary and ternary transition metal and main-group metal chalcogenides (excluding oxides) at room temperature. Bulk material was sought using both elemental combination and metathetical reactions, in either liquid ammonia or n-butylamine. In addition, solid-state metathesis reactions were employed in the synthesis of a selection of low valent transition metal chalcogenides. Elemental combination reactions at room temperature afforded a simple, reproducible single- stage preparation of a range of transition and main-group metal chalcogenides in good yield (> 90%). Products were either highly crystalline (c) or X-ray amorphous (a) in nature. In most cases, annealing the X-ray amorphous powders at 200-250 °C for 2h was found to induce sufficient crystallinity for characterisation by X-ray powder diffraction. Both binary and ternary materials were afforded by the liquid ammonia reactions - MS(a) (M = Cd, Hg, Ni, Sn), ZnE(a) (E = S, Se Te), As2S3(a), Cu(2-x)E(a) (E = S, Se, Te), NiE2(a) (E = Se, Te), ME(c) (M = Pb, Tl, E = S, Se; M = Cd Hg, E = Se, Te), Ag2E(c) (E = S, Se, Te), Tl(2-x)E(c) (E = Se, Te). AgTlTe(c), Zn0.45Cd0.55S(a), MSrE2(a) (M = Mg, Ca, Ba, Yb; E = S, Se, Te), SrxBayS2(a) / CdxHgyTe2(a) (?(x,y) = 1.00; X = 0.25, 0.50, 0.75), EuYbE2(a) (E = S, Se, Te), MSxSey(a) (?(x,y) = 1.00; M = Cu, Cd), Ag3PnS3(c) (Pn = As, Sb), CuAsS(c). Similar reaction schemes and conditions were carried out in n-butylamine, resulting in a more restricted range of binary materials - ME(c) (M = Hg, Tl, Pb, E = S, Se; M = Hg, Pb, E = Te), Ag2E(c) (E = S, Se, Te), Cu(2-x)E(c) (E = Se, Te), Cu2S(a) and As2S3(a). In some cases, elemental combination was obtained by annealing the solvent treated elements, yielding highly crystalline, homogeneous products - liquid ammonia: M2E3 (M = In, Sb, Bi; E = S, Se; Ga2Se3), As2Te3, Bi2Te3, InE (E = S, Se) and PbTe; n-butylamine: NiS, M2E3 (M = As, Sb, Bi; E = Se Te). Solid state metathetical reactions of sodium chalcogenide (Na2S2 or Na2E where E = S, Se Te) and low valent transition metal halides MXn (n = 1,2) were carried out in evacuated ampoules at 300 °C for 48h. In each case, removal of the co-produced salt from the highly sintered, fused product mixture afforded crystalline binary chalcogenides (typically of a single phase) - ME2 (M = Fe, Co, E = S, Te), NiS(2+x), ME (MnS, FeSe, SnSe and SnTe), M(1-x)E (M = Fe, Co, E = S), Ni(1-x)E (E = S, Se, Te) and Ag2E (E = S, Se, Te). Analogous reactions were observed in liquid ammonia at room temperature, affording a range of amorphous (a) and crystalline (c) chalcogenide powders, with each exhibiting an aggregated structure of typically <50-100 nm. Average crystallite sizes of ca. 10-50 nm have been calculated for nanocrystalline materials. Both binary and ternary materials were obtained as single phases in high yield (> 90%) - ME(c) (M = Pb, Tl; E = S, Se), PbTe(c), Ag2E(c) (E = S, Se, Te), Tl(2-x)Te(c), MS(a) (M = Ni, Zn, Cd, Hg), HgE(a) (E = Se, Te), Cu(2-x)S(a), CuE(a) (E = S, Se, Te), M2E3(a) (M = Ga, In; E = S, Se, Te), MPn(a) (M = Fe, Co, Ni; Pn = As, Sb), M3E2(a) (M = Zn, Cd; Pn = As, Sb), ABE2(a) (A = Cu, Ag, B = Ga, In, E = S, Se; A = Cu, B = Sb, E = S, Se, Te), Cu12Sb4S13(a) and CuFeS2(a).

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