THE STRUCTURE OF ONE OF THE HIGH-TEMPERATURE MODIFICATIONS OF NA2ZNSIO4

The structure of one of the high-temperature polymorphs of Na2ZnSiO4 h as been determined from powder diffractometer data, recorded at 750 de grees C with CuK alpha radiation. Differential scanning calorimetry sh owed that the reversible phase transition from the low-temperature mod ification occurs at ca. 600 degrees C, with an enthalpy of 1.45 kJ/mol . The high-temperature modification crystallises in space group Pna2(1 ) with a = 10.759(2), b = 5.313(1), c = 7.211(1) Angstrom and V = 412. 2 Angstrom(3). The structure was refined by the Rietveld method to R(F ) = 5.7%, using 285 reflections in the 2 theta range 15-110 degrees. T he structural relationship between the low- and high-temperature modif ications is discussed.