Potassium-zinc monophosphate: An original polymorphic tridymite derivate

The previously reported low-temperature (LT) alpha-KZnPO4 crystallizes in t he hexagonal space group P6(3). It undergoes two phase transitions at 691 a nd 783 degrees C. The medium-temperature (MT) beta-KZnPO4 structure is orth orhombic (space group Pna2(1), a = 8.7305(7), b = 9.1651(5) Angstrom, c = 5 .3539(3) Angstrom, Z = 4. The high-temperature (HT) gamma-KZnPO4 structure is orthorhombic (space group Pnma, a = 8.7695(5), b = 5.3490(3), c = 9.1817 (5) Angstrom, Z = 4). All of these structures belong to the stuffed tridymi te family with a tetrahedra skeleton. The alpha-beta transition is a new re constructive phenomenon that proceeds by tetrahedra reversal; the beta-gamm a transition is displacive with ferroelectric character. The effects of str uctural changes on relative permittivity and ionic conductivity are reporte d. (C) 1999 Elsevier Science Ltd.