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 R3 - c. R3 and the different structural models of the R3 phase and R3 c phase were built to better understand the phase transition mechanism. We determined the phase transition boundary between the R3 ($) over bar c and R3 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.