Phosphates ZnxMg0.5 + xE2 – x(PO4)3 (E = Ti, Zr) have been synthesized by the sol-gel method with further thermal treatment and studied by X-ray diffraction, electron microprobe analysis, and IR spectroscopy. It has been established that the ZnxMg0.5 + xTi2 – x(PO4)3 solid solution (0 ≤ х ≤ 0.5, space group R $$\bar {3}$$ ) crystallizes in the NaZr2(PO4)3 structural type and is stable up to 1050°C. The structure of Zn0.2Mg0.7Ti1.8(PO4)3 has been refined. It is based on the framework of PO4 tetrahedra with shared apices and (Mg,Ti)O6 octahedra. The framework cavities accommodate Mg2+ and Zn2+ cations with octahedral oxygen coordination. The ZnxMg0.5 + xZr2 – x(PO4)3 solid solution (0 ≤ х ≤ 0.5, space group P21/n) crystallizing in the Sc2(WO4)3 structural type is thermally unstable above 1000°C. The number of bands for the stretching and bending vibrations of the $${\text{PO}}_{4}^{{3 - }}$$ ion in the IR spectra of these orthophosphates agrees with the group factor analysis for space groups R $$\bar {3}$$ and P21/n. The thermal expansion of the ZnxMg0.5 + xE2 – x(PO4)3 solid solutions has been studied within a temperature range of 25–800°C. The control over the composition of these moderately and highly expansive materials provides the possibility to change the thermal expansion characteristics in the desired direction.