Framework Structure, Phase Transition, and Transport Properties in MIIZr4(PO4)6 Compounds (MII = Mg, Ca, Sr, Ba, Mn, Co, Ni, Zn, Cd, and Pb)

The crystal structure, phase transition, electrical conduction behavior of various kinds of MIIZr4(PO4)6 (MIIZP) compounds (MII = Mg, Ca, Sr, Ba, Mn, Co, Ni, Zn, Cd, and Pb) have been investigated. The Mg, Co, Ni, and Zn compounds are of the β-Fe2(SO4)3-type structure and show an order-disorder transition between 600 and 720 °C; the Ca, Sr, Ba, Cd, and Pb compounds, however, are of the NASICON-type structure and do not show any phase transition between r.t. and 1000 °C. The Mn compound sintered at 900 °C shows the former characteristics (the phase transition temperature is around 560 °C), and that sintered above 900 °C the latter. The ZnZP and MnZP show the highest conductivity, ca. 2 × 10−3 and ca. 8 × 10−4 S cm−1 at 800 °C, in the β-Fe2(SO4)3- and the NASICON-type structure, respectively. The ionic size of the mobile cation is the predominant factor regarding ionic conduction in the zirconium phosphate framework.