STRUCTURE, DIELECTRIC-PROPERTIES, AND THERMAL-EXPANSION OF THE NEW PHASE HF0.75SN0.25O2

A new phase with the alpha-PbO2 structure has been discovered with the composition Hf0.75Sn0.25O2. Single crystals were prepared in a potass ium berate flux. The structure was refined from single crystal X-ray d iffraction data, leading to R = 0.026. The space group is Pbcn with a = 4.86(1), b = 5.699(1), and c = 5.204(1) Angstrom. Over the temperatu re range hem 30 to 800 degrees C, a rather low thermal expansion (simi lar to 4 x 10(-6)/degrees C) is observed. The dielectric constant of a Hf0.75Sn0.25O2 Sample measured from 10(3) to 10(7) Hz and from room t emperature to 300 degrees C was found to be 13; the dielectric loss is very low. (C) 1996 Academic Press, Inc