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Samples were synthesised by solid-state reaction at high temperatures and characterised by X-ray diffraction analysis, colouristic analysis and particle size analysis. Possible MoO evaporation at high temperatures was studied by method of thermal analysis. The most interesting sample is SrO-0.65SnO-0.05MoO-0.075TbO which was prepared by calcination at 1500 °C. This powder is single phase, with cubic structure. Colour of the sample is dark green ( L* = 46.37, b* = −9.630 and b* = 10.60). [ABSTRACT FROM AUTHOR]

All the known chromium(III) NASICON-related phosphates are considered to be solid solutions. In these compounds chromium atoms share their position in the basic framework of the crystal lattice with other structure forming elements such as zirconium. In our study, we have hypothesised a completely new way of structural organisation of the chromium(III) zirconium(IV) NASICON framework, consisting in the distribution of chromium over the charge-compensating atom sites with tetrahedral oxygen coordination. The possibility of formation of the corresponding phosphate, Cr1/3Zr2P3O12, was studied using a classical ceramic route and a sol-gel method. Structural affiliation of the obtained pure phase product was studied using XRD analysis. The results confirmed that the Cr1/3Zr2P3O12 phosphate belongs to monoclinic SW-subtype of the NASICON family. In this structure, chromium atoms occupy charge-compensating sites with a strongly distorted tetrahedral oxygen environment. To the best of our knowledge, it is the first example of tetrahedral coordination of chromium(III) in phosphates. Along with the unusual crystallographic characteristics of chromium, special attention in this paper is devoted to the thermal stability of this phosphate and to its performance as an inorganic pigment. The sample was characterised by heating microscopy and DTA study, particle size distribution analysis, and IR- and VIS-spectroscopy. The stability of the obtained powder in a glaze environment, its colouring performance and lightfastness are discussed as well. [ABSTRACT FROM AUTHOR]

Due to the outstanding stability and resistivity to dissolution agents of the compounds related to NaZr2(PO4)3 (NZP family), our attention has been focussed on CoZr4(PO4)6 and its performance as an inorganic pigment for coloration of ceramic glazes. Mixed cobalt zirconium phosphate has been prepared by a solid state reaction and a sol–gel method and was characterised (through thermal analysis, XRD, heating microscopy, SEM, VIS-spectrophotometry and lightfastness measurement) for the first time as a ceramic pigment. In order to reduce the cobalt content in the samples the series of Co1−x Mg x Zr4(PO4)6 (x = 0.25; 0.5) have also been prepared using a solid state reaction and were investigated with the same techniques. It was shown that a solid state reaction provides the formation of CoZr4(PO4)6 through a three component system stage (ZrP2O7, ZrO2 and CoP2O6/Co2P2O7), when employment of the sol–gel method leads to the direct formation of a CoZr4(PO4)6 phase at lower temperatures. During further thermal treatment, with an increase of the calcination temperature up to 1200–1300 °C, an additional phase of Zr2O(PO4)2 appears in the composition. A solid state reaction can be suggested as a preferable method for achieving enhanced thermal stability of this phosphate and the substitution of Co by Mg not only helps to reduce the content of Co in the sample compositions, but also to improve their thermal characteristics. Thus, the obtained results indicate that employment of the more complicated sol–gel method does not provide any advantages at high calcination temperatures with respect to the phase composition, thermal stability, homogeneity and particle size distribution of the obtained samples and the conventional ceramic route does not deteriorate on the basis of these parameters. An irregular change of the colour parameters was observed for the samples during the calcination and the temperature of 1300 °C and 6–12 h of soaking time were chosen for pigment synthesis. Colouring ability of the obtained samples has been analysed with two types of ceramic glazes. The mixed phosphates exhibit saturated purple-blue colour, which becomes lighter only with an increase of Mg content to x = 0.5. Enamelled samples showed excellent lightfastness and the investigated compounds can be considered as high performance inorganic pigments for coloration of ceramic glazes. [ABSTRACT FROM AUTHOR]