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 beta-Fe2(SO4)3-type structure and show an order disorder transition between 600 and 720-degrees-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-degrees-C. The Mn compound sintered at 900-degrees-C shows the former characteristics (the phase transition temperature is around 560-degrees-C), and that sintered above 900-degrees-C the latter. The ZnZP and MnZP show the highest conductivity, ca. 2X10(-3) and ca. 8X10(-4) S cm-1 at 800-degrees-C, in the beta-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.