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Our and others' results on the thermal expansion of compounds and the crystal-chemical information about their structure have been used to properly select compositions of new NASICON materials with small thermal expansion and low thermal expansion anisotropy: MM′Ti(PO) (M and M′ are alkali metals, 0 ≤ x ≤ 1), M″FeTi(PO) (M″ is an alkaline-earth metal), and CaFeTi(PO) (0 ≤ x ≤ 1). Such materials have been synthesized through salt coprecipitation from aqueous solutions and their thermal expansion has been assessed by high-temperature X-ray diffraction. We have determined their unit-cell parameters as functions of temperature and correlated their thermal expansion parameters and composition. The KRbTi(PO) and RbCsTi(PO) materials obtained combine small volumetric thermal expansion and near-zero thermal expansion anisotropy. [ABSTRACT FROM AUTHOR]