Synthesis, structure and electronic properties of the cerium and potassium thiosilicate:: KCeSiS4

The cerium and potassium thiosilicate KCeSiS4 has been synthesized at 800 degrees C from Ce, Si, K2S and S precursors weighted in the K:Ce:Si:S = 1:1:1.15:4.3 ratio. This yellow, air stable compound crystallizes in the monoclinic space group P2(1) (No. 4) with the cell parameters: a = 6.5201(3) Angstrom, b = 6.5982(3) Angstrom, c = 8.6920(5) Angstrom, beta = 107.701(3)degrees, V = 356.23(3) Angstrom(3) and Z = 2. Refinement of 36 parameters by the Rietveld method, using 974 reflections led to R-p (%) = 2.49, R-wp (%) = 3.35 and chi(2) = 2.71. KCeSiS4, isostructural to KLnMQ(4) (Ln = La, Nd, Gd, Y; M = Si, Ge; Q = S, Se), consists of two-dimensional (2)(infinity)[CeSiS4](-) anionic layers separated by K+ ions. These layers are built upon [CeS7] distorted monocapped trigonal prisms, sharing 2 edges and 2 corners with each other, and upon [SiS4] tetrahedra linked to the (2)(infinity)[CeS4](5-) skeleton by edge and face sharing. From magnetic measurements, an effective magnetic moment mu(eff)(300 K) = 2.73(2) mu(B) was calculated in good agreement with the (KCeSiS4(-II))-Ce-(I)-Si-(III)-S-(IV) charge balance. From diffuse reflectance measurements, a band gap of 2.68(1) eV correlated to the occurrence of a 4f--> 5d electronic transition was evidenced. Moreover, chromatic L/a/b coefficients, equal respectively to 88.37/-18.85/52.91, have been determined for the bright yellow colour of the compound. These parameters compare rather well with those of NiTiO3, a well known industrial pigment. The room temperature strong green luminescence at E = 2.45 eV (lambda = 506.1 nm) of KCeSiS4 has been investigated through emission and excitation spectroscopy in the UW-visible range. (C) 1999 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.