Crystal structures, phase transitions and thermal expansion properties of NaZr2(PO4)3–SrZr4(PO4)6 solid solutions
Crystal structure evolution and temperature-dependent phase transition of solid solutions are much desired for the understanding of the optimization of functional properties. Herein, the NASICON-type NaZr2(PO4)3–SrZr4(PO4)6 solid solutions with the formula Na(2−2x)Srx[ ]xZr4(PO4)6 (0 ≤ x ≤ 1), where [ ] represents the vacancy, were prepared by the sol–gel method, and their crystal structures, phase transitions and thermal expansion properties were investigated in detail. In the range of x = 0.3–0.35, there is a reversible structural phase transition Rc ↔ R and the different structural models of the R phase and Rc phase were built to better understand the phase transition mechanism. We determined the phase transition boundary between the Rc and R structures and predicted the phase transition temperature of Na(2−2x)Srx[ ]xZr4(PO4)6 with any x for further investigation of controlled physical properties. The results indicated that Na0.5Sr0.75[ ]0.75Zr4(PO4)6 showed a near zero thermal expansion in the temperature range of 450–600 K, which can find potential applications.
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