MS16-P24 Crystallographic studies of NaZr2(PO4)3 phosphates at high temperaturesCrystal-chemical principles have been used in this paper for modeling of the compositions of NaZr2(PO4)3 compounds and solid solutions with adjustable thermal expansion characteristics. Knowledge about materials on their base helps to solve many engineering problems associated with the combination of materials in different designs, including the required resistance to thermal stress.
NaZr2(PO4)3 (NZP) is a convenient structure for these aims as it offers an opportunity to include a big variety of cations in different combinations with oxidation states from +1 to +5, with different size and electronegativity into the composition of isostructural phases.
Well-known NZP materials have high melting temperatures, high hardness, thermomechanical, radiation, and chemical stability, ion conductivity, optical and magnetic properties, catalytic activity.
Although many of the possible formula compositions calculated in  are well studied, but those that have their thermal expansion characteristics determined are quite few.
In this paper new phosphates Na1+2xZr2-xCox(PO4)3 and Ca0,5+xZr2-xCox(PO4)3 (0≤x≤0,5) in various concentration combinations of zirconium and cobalt in the structure framework and with respectively changing population density of interframe positions are obtained and characterized, their behavior during heating through high-temperature XRD is studied for T=25–700°С.
Synthesis of powder samples was carried out using solid-phase processes (Tfinal = 700 °C). The forming of phases of a planed composition and structure were established by XRD and SEM methods. Lattice parameters of the obtained materials were determined and their dependencies on the composition and temperature were analyzed.
It was found that with the temperature rising, a and b parameters were decreased, while с parameter was increased, which is typical for NZP structure. With cobalt growing in the phase composition, absolute values of thermal expansion linear coefficients were decreased: αa from -4,65·10-6 to -3,06·10-6 °C-1, αс from 21,85·10-6 to 19,49·10-6 °C-1 for Na-containing series, αa from -1,82·10-6 to -1,14·10-6 °C-1, αс from 9,20·10-6 to 9,10·10-6 °C-1 for Ca-containing series and anisotropy: Δα from 26,50·10-6 to 21,55·10-6 °C-1 for Na-containing series, from 11,02·10-6 to 10,24·10-6 °C-1 for Ca-containing series.
Analysis of the obtained results shows that the phosphates studied belong to the class of medium-expanders ones.
The studied objects have blue color. This property is useful for heat-resistant inorganic dyes applied as a cover on the material, as well as for imparting a functional color to the material itself.
The study has been performed with the financial support of the Russian Science Foundation Grant No. 16-13-10464.References:
 Orlova A. I. (2002). Radiochemistry. 44, 423-445.Keywords: NZP, thermal expansion