Thermal expansion of phosphates with the NaZr2(PO4)3 structure containing lanthanides and zirconium: R0.33Zr2(PO4)3 (R = Nd, Eu, Er) and Er0.33(1–x) Zr0.25xZr2(PO4)3

Phosphates R0.33Zr2(PO4)3 (R = Nd, Eu, or Er) and Er0.33(1–х)Zr0.25Zr2(PO4)3 (х = 0, 0.25, 0.5, 0.75, 1.0) of the NaZr2(PO4)3 family have been synthesized and investigated by high-temperature X-ray diffraction. The crystallochemical approach is used to obtain compounds with expected small and controllable thermal-expansion parameters. Phosphates with close-to-zero thermal-expansion parameters, including those with low thermal-expansion anisotropy, have been obtained: Nd0.33Zr2(PO4)3 with αa =–2.21 × 10−6 °С−1, αc = 0.81 × 10−6 °С−1, and Δα = 3.02 × 10−6 °С–1 and Er0.08Zr0.19Zr2(PO4)3 with αa =–1.86 × 10−6 °С−1, αc = 1.73 × 10−6 °С−1, and Δα = 3.58 × 10−6 °С−1.