New inorganic pigments in the Ca-Nd-S system: Stabilization of γ phase

The structure-microstructure and colour properties of the Ca(3/2)yNd2−y□0.25−(1/2)yS3 (0 ≤ y ≤ 0.5) system are studied in this work. The sample with y = 0 (Nd2S3) presents the α-type structure of the light lanthanide sesquisulphides while the samples containing Ca2+ (y > 0) present the γ-Th3P4 type structure. The introduction of Ca2+ cations in the system, according to the relation 3Ca2+ → 2Nd3+ + □ (□: cation vacancy), induces the stabilization of the γ-phase at 1173 K, even at very low Ca2+ concentration. The samples colour characteristics were studied from reflectance spectra in the visible region. When y > 0, the samples present good quality green colour. This system has possible applications as inorganic pigments for plastics and paints.